Merge branch 'rxrpc-afs-add-afs-gssapi-security-class-to-af_rxrpc-and-kafs'

David Howells says:

====================
rxrpc, afs: Add AFS GSSAPI security class to AF_RXRPC and kafs

Here's a set of patches to add basic support for the AFS GSSAPI security
class to AF_RXRPC and kafs.  It provides transport security for keys that
match the security index 6 (YFS) for connections to the AFS fileserver and
VL server.

Note that security index 4 (OpenAFS) can also be supported using this, but
it needs more work as it's slightly different.

The patches also provide the ability to secure the callback channel -
connections from the fileserver back to the client that are used to pass
file change notifications, amongst other things.  When challenged by the
fileserver, kafs will generate a token specific to that server and include
it in the RESPONSE packet as the appdata.  The server then extracts this
and uses it to send callback RPC calls back to the client.

It can also be used to provide transport security on the callback channel,
but a further set of patches is required to provide the token and key to
set that up when the client responds to the fileserver's challenge.

This makes use of the previously added crypto-krb5 library that is now
upstream (last commit fc0cf10c04f4).

This series of patches consist of the following parts:

 (0) Update kdoc comments to remove some kdoc builder warnings.

 (1) Push reponding to CHALLENGE packets over to recvmsg() or the kernel
     equivalent so that the application layer can include user-defined
     information in the RESPONSE packet.  In a follow-up patch set, this
     will allow the callback channel to be secured by the AFS filesystem.

 (2) Add the AF_RXRPC RxGK security class that uses a key obtained from the
     AFS GSS security service to do Kerberos 5-based encryption instead of
     pcbc(fcrypt) and pcbc(des).

 (3) Add support for callback channel encryption in kafs.

 (4) Provide the test rxperf server module with some fixed krb5 keys.
====================

Link: https://patch.msgid.link/20250411095303.2316168-1-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

40 files changed, 4272 insertions, 245 deletions

diff --git a/Documentation/networking/rxrpc.rst b/Documentation/networking/rxrpc.rst
index e807e18ba32a..fe2ea73be441 100644
--- a/Documentation/networking/rxrpc.rst
+++ b/Documentation/networking/rxrpc.rst
@@ -1172,3 +1172,18 @@ adjusted through sysctls in /proc/net/rxrpc/:
      header plus exactly 1412 bytes of data.  The terminal packet must contain
      a four byte header plus any amount of data.  In any event, a jumbo packet
      may not exceed rxrpc_rx_mtu in size.
+
+
+API Function Reference
+======================
+
+.. kernel-doc:: net/rxrpc/af_rxrpc.c
+.. kernel-doc:: net/rxrpc/call_object.c
+.. kernel-doc:: net/rxrpc/key.c
+.. kernel-doc:: net/rxrpc/oob.c
+.. kernel-doc:: net/rxrpc/peer_object.c
+.. kernel-doc:: net/rxrpc/recvmsg.c
+.. kernel-doc:: net/rxrpc/rxgk.c
+.. kernel-doc:: net/rxrpc/rxkad.c
+.. kernel-doc:: net/rxrpc/sendmsg.c
+.. kernel-doc:: net/rxrpc/server_key.c
diff --git a/fs/afs/Kconfig b/fs/afs/Kconfig
index fc8ba9142f2f..682bd8ec2c10 100644
--- a/fs/afs/Kconfig
+++ b/fs/afs/Kconfig
@@ -5,6 +5,7 @@ config AFS_FS
 	select AF_RXRPC
 	select DNS_RESOLVER
 	select NETFS_SUPPORT
+	select CRYPTO_KRB5
 	help
 	  If you say Y here, you will get an experimental Andrew File System
 	  driver. It currently only supports unsecured read-only AFS access.
diff --git a/fs/afs/Makefile b/fs/afs/Makefile
index 5efd7e13b304..b49b8fe682f3 100644
--- a/fs/afs/Makefile
+++ b/fs/afs/Makefile
@@ -8,6 +8,7 @@ kafs-y := \
 	addr_prefs.o \
 	callback.o \
 	cell.o \
+	cm_security.o \
 	cmservice.o \
 	dir.o \
 	dir_edit.o \
diff --git a/fs/afs/cm_security.c b/fs/afs/cm_security.c
new file mode 100644
index 000000000000..edcbd249d202
--- /dev/null
+++ b/fs/afs/cm_security.c
@@ -0,0 +1,340 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Cache manager security.
+ *
+ * Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/slab.h>
+#include <crypto/krb5.h>
+#include "internal.h"
+#include "afs_cm.h"
+#include "afs_fs.h"
+#include "protocol_yfs.h"
+#define RXRPC_TRACE_ONLY_DEFINE_ENUMS
+#include <trace/events/rxrpc.h>
+
+#define RXGK_SERVER_ENC_TOKEN 1036U // 0x40c
+#define xdr_round_up(x) (round_up((x), sizeof(__be32)))
+#define xdr_len_object(x) (4 + round_up((x), sizeof(__be32)))
+
+#ifdef CONFIG_RXGK
+static int afs_create_yfs_cm_token(struct sk_buff *challenge,
+				   struct afs_server *server);
+#endif
+
+/*
+ * Respond to an RxGK challenge, adding appdata.
+ */
+static int afs_respond_to_challenge(struct sk_buff *challenge)
+{
+#ifdef CONFIG_RXGK
+	struct krb5_buffer appdata = {};
+	struct afs_server *server;
+#endif
+	struct rxrpc_peer *peer;
+	unsigned long peer_data;
+	u16 service_id;
+	u8 security_index;
+
+	rxrpc_kernel_query_challenge(challenge, &peer, &peer_data,
+				     &service_id, &security_index);
+
+	_enter("%u,%u", service_id, security_index);
+
+	switch (service_id) {
+		/* We don't send CM_SERVICE RPCs, so don't expect a challenge
+		 * therefrom.
+		 */
+	case FS_SERVICE:
+	case VL_SERVICE:
+	case YFS_FS_SERVICE:
+	case YFS_VL_SERVICE:
+		break;
+	default:
+		pr_warn("Can't respond to unknown challenge %u:%u",
+			service_id, security_index);
+		return rxrpc_kernel_reject_challenge(challenge, RX_USER_ABORT, -EPROTO,
+						     afs_abort_unsupported_sec_class);
+	}
+
+	switch (security_index) {
+#ifdef CONFIG_RXKAD
+	case RXRPC_SECURITY_RXKAD:
+		return rxkad_kernel_respond_to_challenge(challenge);
+#endif
+
+#ifdef CONFIG_RXGK
+	case RXRPC_SECURITY_RXGK:
+		return rxgk_kernel_respond_to_challenge(challenge, &appdata);
+
+	case RXRPC_SECURITY_YFS_RXGK:
+		switch (service_id) {
+		case FS_SERVICE:
+		case YFS_FS_SERVICE:
+			server = (struct afs_server *)peer_data;
+			if (!server->cm_rxgk_appdata.data) {
+				mutex_lock(&server->cm_token_lock);
+				if (!server->cm_rxgk_appdata.data)
+					afs_create_yfs_cm_token(challenge, server);
+				mutex_unlock(&server->cm_token_lock);
+			}
+			if (server->cm_rxgk_appdata.data)
+				appdata = server->cm_rxgk_appdata;
+			break;
+		}
+		return rxgk_kernel_respond_to_challenge(challenge, &appdata);
+#endif
+
+	default:
+		return rxrpc_kernel_reject_challenge(challenge, RX_USER_ABORT, -EPROTO,
+						     afs_abort_unsupported_sec_class);
+	}
+}
+
+/*
+ * Process the OOB message queue, processing challenge packets.
+ */
+void afs_process_oob_queue(struct work_struct *work)
+{
+	struct afs_net *net = container_of(work, struct afs_net, rx_oob_work);
+	struct sk_buff *oob;
+	enum rxrpc_oob_type type;
+
+	while ((oob = rxrpc_kernel_dequeue_oob(net->socket, &type))) {
+		switch (type) {
+		case RXRPC_OOB_CHALLENGE:
+			afs_respond_to_challenge(oob);
+			break;
+		}
+		rxrpc_kernel_free_oob(oob);
+	}
+}
+
+#ifdef CONFIG_RXGK
+/*
+ * Create a securities keyring for the cache manager and attach a key to it for
+ * the RxGK tokens we want to use to secure the callback connection back from
+ * the fileserver.
+ */
+int afs_create_token_key(struct afs_net *net, struct socket *socket)
+{
+	const struct krb5_enctype *krb5;
+	struct key *ring;
+	key_ref_t key;
+	char K0[32], *desc;
+	int ret;
+
+	ring = keyring_alloc("kafs",
+			     GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, current_cred(),
+			     KEY_POS_SEARCH | KEY_POS_WRITE |
+			     KEY_USR_VIEW | KEY_USR_READ | KEY_USR_SEARCH,
+			     KEY_ALLOC_NOT_IN_QUOTA,
+			     NULL, NULL);
+	if (IS_ERR(ring))
+		return PTR_ERR(ring);
+
+	ret = rxrpc_sock_set_security_keyring(socket->sk, ring);
+	if (ret < 0)
+		goto out;
+
+	ret = -ENOPKG;
+	krb5 = crypto_krb5_find_enctype(KRB5_ENCTYPE_AES128_CTS_HMAC_SHA1_96);
+	if (!krb5)
+		goto out;
+
+	if (WARN_ON_ONCE(krb5->key_len > sizeof(K0)))
+		goto out;
+
+	ret = -ENOMEM;
+	desc = kasprintf(GFP_KERNEL, "%u:%u:%u:%u",
+			 YFS_CM_SERVICE, RXRPC_SECURITY_YFS_RXGK, 1, krb5->etype);
+	if (!desc)
+		goto out;
+
+	wait_for_random_bytes();
+	get_random_bytes(K0, krb5->key_len);
+
+	key = key_create(make_key_ref(ring, true),
+			 "rxrpc_s", desc,
+			 K0, krb5->key_len,
+			 KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH | KEY_USR_VIEW,
+			 KEY_ALLOC_NOT_IN_QUOTA);
+	kfree(desc);
+	if (IS_ERR(key)) {
+		ret = PTR_ERR(key);
+		goto out;
+	}
+
+	net->fs_cm_token_key = key_ref_to_ptr(key);
+	ret = 0;
+out:
+	key_put(ring);
+	return ret;
+}
+
+/*
+ * Create an YFS RxGK GSS token to use as a ticket to the specified fileserver.
+ */
+static int afs_create_yfs_cm_token(struct sk_buff *challenge,
+				   struct afs_server *server)
+{
+	const struct krb5_enctype *conn_krb5, *token_krb5;
+	const struct krb5_buffer *token_key;
+	struct crypto_aead *aead;
+	struct scatterlist sg;
+	struct afs_net *net = server->cell->net;
+	const struct key *key = net->fs_cm_token_key;
+	size_t keysize, uuidsize, authsize, toksize, encsize, contsize, adatasize, offset;
+	__be32 caps[1] = {
+		[0] = htonl(AFS_CAP_ERROR_TRANSLATION),
+	};
+	__be32 *xdr;
+	void *appdata, *K0, *encbase;
+	u32 enctype;
+	int ret;
+
+	if (!key)
+		return -ENOKEY;
+
+	/* Assume that the fileserver is happy to use the same encoding type as
+	 * we were told to use by the token obtained by the user.
+	 */
+	enctype = rxgk_kernel_query_challenge(challenge);
+
+	conn_krb5 = crypto_krb5_find_enctype(enctype);
+	if (!conn_krb5)
+		return -ENOPKG;
+	token_krb5 = key->payload.data[0];
+	token_key = (const struct krb5_buffer *)&key->payload.data[2];
+
+	/* struct rxgk_key {
+	 *	afs_uint32	enctype;
+	 *	opaque		key<>;
+	 * };
+	 */
+	keysize = 4 + xdr_len_object(conn_krb5->key_len);
+
+	/* struct RXGK_AuthName {
+	 *	afs_int32	kind;
+	 *	opaque		data<AUTHDATAMAX>;
+	 *	opaque		display<AUTHPRINTABLEMAX>;
+	 * };
+	 */
+	uuidsize = sizeof(server->uuid);
+	authsize = 4 + xdr_len_object(uuidsize) + xdr_len_object(0);
+
+	/* struct RXGK_Token {
+	 *	rxgk_key		K0;
+	 *	RXGK_Level		level;
+	 *	rxgkTime		starttime;
+	 *	afs_int32		lifetime;
+	 *	afs_int32		bytelife;
+	 *	rxgkTime		expirationtime;
+	 *	struct RXGK_AuthName	identities<>;
+	 * };
+	 */
+	toksize = keysize + 8 + 4 + 4 + 8 + xdr_len_object(authsize);
+
+	offset = 0;
+	encsize = crypto_krb5_how_much_buffer(token_krb5, KRB5_ENCRYPT_MODE, toksize, &offset);
+
+	/* struct RXGK_TokenContainer {
+	 *	afs_int32	kvno;
+	 *	afs_int32	enctype;
+	 *	opaque		encrypted_token<>;
+	 * };
+	 */
+	contsize = 4 + 4 + xdr_len_object(encsize);
+
+	/* struct YFSAppData {
+	 *	opr_uuid	initiatorUuid;
+	 *	opr_uuid	acceptorUuid;
+	 *	Capabilities	caps;
+	 *	afs_int32	enctype;
+	 *	opaque		callbackKey<>;
+	 *	opaque		callbackToken<>;
+	 * };
+	 */
+	adatasize = 16 + 16 +
+		xdr_len_object(sizeof(caps)) +
+		4 +
+		xdr_len_object(conn_krb5->key_len) +
+		xdr_len_object(contsize);
+
+	ret = -ENOMEM;
+	appdata = kzalloc(adatasize, GFP_KERNEL);
+	if (!appdata)
+		goto out;
+	xdr = appdata;
+
+	memcpy(xdr, &net->uuid, 16);		/* appdata.initiatorUuid */
+	xdr += 16 / 4;
+	memcpy(xdr, &server->uuid, 16);		/* appdata.acceptorUuid */
+	xdr += 16 / 4;
+	*xdr++ = htonl(ARRAY_SIZE(caps));	/* appdata.caps.len */
+	memcpy(xdr, &caps, sizeof(caps));	/* appdata.caps */
+	xdr += ARRAY_SIZE(caps);
+	*xdr++ = htonl(conn_krb5->etype);	/* appdata.enctype */
+
+	*xdr++ = htonl(conn_krb5->key_len);	/* appdata.callbackKey.len */
+	K0 = xdr;
+	get_random_bytes(K0, conn_krb5->key_len); /* appdata.callbackKey.data */
+	xdr += xdr_round_up(conn_krb5->key_len) / 4;
+
+	*xdr++ = htonl(contsize);		/* appdata.callbackToken.len */
+	*xdr++ = htonl(1);			/* cont.kvno */
+	*xdr++ = htonl(token_krb5->etype);	/* cont.enctype */
+	*xdr++ = htonl(encsize);		/* cont.encrypted_token.len */
+
+	encbase = xdr;
+	xdr += offset / 4;
+	*xdr++ = htonl(conn_krb5->etype);	/* token.K0.enctype */
+	*xdr++ = htonl(conn_krb5->key_len);	/* token.K0.key.len */
+	memcpy(xdr, K0, conn_krb5->key_len);	/* token.K0.key.data */
+	xdr += xdr_round_up(conn_krb5->key_len) / 4;
+
+	*xdr++ = htonl(RXRPC_SECURITY_ENCRYPT);	/* token.level */
+	*xdr++ = htonl(0);			/* token.starttime */
+	*xdr++ = htonl(0);			/* " */
+	*xdr++ = htonl(0);			/* token.lifetime */
+	*xdr++ = htonl(0);			/* token.bytelife */
+	*xdr++ = htonl(0);			/* token.expirationtime */
+	*xdr++ = htonl(0);			/* " */
+	*xdr++ = htonl(1);			/* token.identities.count */
+	*xdr++ = htonl(0);			/* token.identities[0].kind */
+	*xdr++ = htonl(uuidsize);		/* token.identities[0].data.len */
+	memcpy(xdr, &server->uuid, uuidsize);
+	xdr += xdr_round_up(uuidsize) / 4;
+	*xdr++ = htonl(0);			/* token.identities[0].display.len */
+
+	xdr = encbase + xdr_round_up(encsize);
+
+	if ((unsigned long)xdr - (unsigned long)appdata != adatasize)
+		pr_err("Appdata size incorrect %lx != %zx\n",
+		       (unsigned long)xdr - (unsigned long)appdata, adatasize);
+
+	aead = crypto_krb5_prepare_encryption(token_krb5, token_key, RXGK_SERVER_ENC_TOKEN,
+					      GFP_KERNEL);
+	if (IS_ERR(aead)) {
+		ret = PTR_ERR(aead);
+		goto out_token;
+	}
+
+	sg_init_one(&sg, encbase, encsize);
+	ret = crypto_krb5_encrypt(token_krb5, aead, &sg, 1, encsize, offset, toksize, false);
+	if (ret < 0)
+		goto out_aead;
+
+	server->cm_rxgk_appdata.len  = adatasize;
+	server->cm_rxgk_appdata.data = appdata;
+	appdata = NULL;
+
+out_aead:
+	crypto_free_aead(aead);
+out_token:
+	kfree(appdata);
+out:
+	return ret;
+}
+#endif /* CONFIG_RXGK */
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 440b0e731093..1124ea4000cb 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -20,6 +20,7 @@
 #include <linux/uuid.h>
 #include <linux/mm_types.h>
 #include <linux/dns_resolver.h>
+#include <crypto/krb5.h>
 #include <net/net_namespace.h>
 #include <net/netns/generic.h>
 #include <net/sock.h>
@@ -176,8 +177,10 @@ struct afs_call {
 	bool			intr;		/* T if interruptible */
 	bool			unmarshalling_error; /* T if an unmarshalling error occurred */
 	bool			responded;	/* Got a response from the call (may be abort) */
+	u8			security_ix;	/* Security class */
 	u16			service_id;	/* Actual service ID (after upgrade) */
 	unsigned int		debug_id;	/* Trace ID */
+	u32			enctype;	/* Security encoding type */
 	u32			operation_ID;	/* operation ID for an incoming call */
 	u32			count;		/* count for use in unmarshalling */
 	union {					/* place to extract temporary data */
@@ -281,6 +284,7 @@ struct afs_net {
 	struct socket		*socket;
 	struct afs_call		*spare_incoming_call;
 	struct work_struct	charge_preallocation_work;
+	struct work_struct	rx_oob_work;
 	struct mutex		socket_mutex;
 	atomic_t		nr_outstanding_calls;
 	atomic_t		nr_superblocks;
@@ -305,6 +309,7 @@ struct afs_net {
 	struct list_head	fs_probe_slow;	/* List of afs_server to probe at 5m intervals */
 	struct hlist_head	fs_proc;	/* procfs servers list */
 
+	struct key		*fs_cm_token_key; /* Key for creating CM tokens */
 	struct work_struct	fs_prober;
 	struct timer_list	fs_probe_timer;
 	atomic_t		servers_outstanding;
@@ -540,6 +545,8 @@ struct afs_server {
 	struct list_head	volumes;	/* RCU list of afs_server_entry objects */
 	struct work_struct	destroyer;	/* Work item to try and destroy a server */
 	struct timer_list	timer;		/* Management timer */
+	struct mutex		cm_token_lock;	/* Lock governing creation of appdata */
+	struct krb5_buffer	cm_rxgk_appdata; /* Appdata to be included in RESPONSE packet */
 	time64_t		unuse_time;	/* Time at which last unused */
 	unsigned long		flags;
 #define AFS_SERVER_FL_RESPONDING 0		/* The server is responding */
@@ -1059,6 +1066,19 @@ extern void __net_exit afs_cell_purge(struct afs_net *);
 extern bool afs_cm_incoming_call(struct afs_call *);
 
 /*
+ * cm_security.c
+ */
+void afs_process_oob_queue(struct work_struct *work);
+#ifdef CONFIG_RXGK
+int afs_create_token_key(struct afs_net *net, struct socket *socket);
+#else
+static inline int afs_create_token_key(struct afs_net *net, struct socket *socket)
+{
+	return 0;
+}
+#endif
+
+/*
  * dir.c
  */
 extern const struct file_operations afs_dir_file_operations;
diff --git a/fs/afs/main.c b/fs/afs/main.c
index c845c5daaeba..02475d415d88 100644
--- a/fs/afs/main.c
+++ b/fs/afs/main.c
@@ -73,6 +73,7 @@ static int __net_init afs_net_init(struct net *net_ns)
 	generate_random_uuid((unsigned char *)&net->uuid);
 
 	INIT_WORK(&net->charge_preallocation_work, afs_charge_preallocation);
+	INIT_WORK(&net->rx_oob_work, afs_process_oob_queue);
 	mutex_init(&net->socket_mutex);
 
 	net->cells = RB_ROOT;
diff --git a/fs/afs/misc.c b/fs/afs/misc.c
index b8180bf2281f..8f2b3a177690 100644
--- a/fs/afs/misc.c
+++ b/fs/afs/misc.c
@@ -8,6 +8,7 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/errno.h>
+#include <crypto/krb5.h>
 #include "internal.h"
 #include "afs_fs.h"
 #include "protocol_uae.h"
@@ -103,6 +104,32 @@ int afs_abort_to_error(u32 abort_code)
 	case RXKADDATALEN:	return -EKEYREJECTED;
 	case RXKADILLEGALLEVEL:	return -EKEYREJECTED;
 
+	case RXGK_INCONSISTENCY:	return -EPROTO;
+	case RXGK_PACKETSHORT:		return -EPROTO;
+	case RXGK_BADCHALLENGE:		return -EPROTO;
+	case RXGK_SEALEDINCON:		return -EKEYREJECTED;
+	case RXGK_NOTAUTH:		return -EKEYREJECTED;
+	case RXGK_EXPIRED:		return -EKEYEXPIRED;
+	case RXGK_BADLEVEL:		return -EKEYREJECTED;
+	case RXGK_BADKEYNO:		return -EKEYREJECTED;
+	case RXGK_NOTRXGK:		return -EKEYREJECTED;
+	case RXGK_UNSUPPORTED:		return -EKEYREJECTED;
+	case RXGK_GSSERROR:		return -EKEYREJECTED;
+#ifdef RXGK_BADETYPE
+	case RXGK_BADETYPE:		return -ENOPKG;
+#endif
+#ifdef RXGK_BADTOKEN
+	case RXGK_BADTOKEN:		return -EKEYREJECTED;
+#endif
+#ifdef RXGK_BADETYPE
+	case RXGK_DATALEN:		return -EPROTO;
+#endif
+#ifdef RXGK_BADQOP
+	case RXGK_BADQOP:		return -EKEYREJECTED;
+#endif
+
+	case KRB5_PROG_KEYTYPE_NOSUPP:	return -ENOPKG;
+
 	case RXGEN_OPCODE:	return -ENOTSUPP;
 
 	default:		return -EREMOTEIO;
diff --git a/fs/afs/rxrpc.c b/fs/afs/rxrpc.c
index d5e480a33859..c1cadf8fb346 100644
--- a/fs/afs/rxrpc.c
+++ b/fs/afs/rxrpc.c
@@ -24,8 +24,17 @@ static void afs_wake_up_async_call(struct sock *, struct rxrpc_call *, unsigned
 static void afs_process_async_call(struct work_struct *);
 static void afs_rx_new_call(struct sock *, struct rxrpc_call *, unsigned long);
 static void afs_rx_discard_new_call(struct rxrpc_call *, unsigned long);
+static void afs_rx_attach(struct rxrpc_call *rxcall, unsigned long user_call_ID);
+static void afs_rx_notify_oob(struct sock *sk, struct sk_buff *oob);
 static int afs_deliver_cm_op_id(struct afs_call *);
 
+static const struct rxrpc_kernel_ops afs_rxrpc_callback_ops = {
+	.notify_new_call	= afs_rx_new_call,
+	.discard_new_call	= afs_rx_discard_new_call,
+	.user_attach_call	= afs_rx_attach,
+	.notify_oob		= afs_rx_notify_oob,
+};
+
 /* asynchronous incoming call initial processing */
 static const struct afs_call_type afs_RXCMxxxx = {
 	.name		= "CB.xxxx",
@@ -49,6 +58,7 @@ int afs_open_socket(struct afs_net *net)
 		goto error_1;
 
 	socket->sk->sk_allocation = GFP_NOFS;
+	socket->sk->sk_user_data = net;
 
 	/* bind the callback manager's address to make this a server socket */
 	memset(&srx, 0, sizeof(srx));
@@ -64,6 +74,14 @@ int afs_open_socket(struct afs_net *net)
 	if (ret < 0)
 		goto error_2;
 
+	ret = rxrpc_sock_set_manage_response(socket->sk, true);
+	if (ret < 0)
+		goto error_2;
+
+	ret = afs_create_token_key(net, socket);
+	if (ret < 0)
+		pr_err("Couldn't create RxGK CM key: %d\n", ret);
+
 	ret = kernel_bind(socket, (struct sockaddr *) &srx, sizeof(srx));
 	if (ret == -EADDRINUSE) {
 		srx.transport.sin6.sin6_port = 0;
@@ -84,8 +102,7 @@ int afs_open_socket(struct afs_net *net)
 	 * it sends back to us.
 	 */
 
-	rxrpc_kernel_new_call_notification(socket, afs_rx_new_call,
-					   afs_rx_discard_new_call);
+	rxrpc_kernel_set_notifications(socket, &afs_rxrpc_callback_ops);
 
 	ret = kernel_listen(socket, INT_MAX);
 	if (ret < 0)
@@ -125,7 +142,9 @@ void afs_close_socket(struct afs_net *net)
 
 	kernel_sock_shutdown(net->socket, SHUT_RDWR);
 	flush_workqueue(afs_async_calls);
+	net->socket->sk->sk_user_data = NULL;
 	sock_release(net->socket);
+	key_put(net->fs_cm_token_key);
 
 	_debug("dework");
 	_leave("");
@@ -738,7 +757,6 @@ void afs_charge_preallocation(struct work_struct *work)
 
 		if (rxrpc_kernel_charge_accept(net->socket,
 					       afs_wake_up_async_call,
-					       afs_rx_attach,
 					       (unsigned long)call,
 					       GFP_KERNEL,
 					       call->debug_id) < 0)
@@ -800,10 +818,14 @@ static int afs_deliver_cm_op_id(struct afs_call *call)
 	if (!afs_cm_incoming_call(call))
 		return -ENOTSUPP;
 
+	call->security_ix = rxrpc_kernel_query_call_security(call->rxcall,
+							     &call->service_id,
+							     &call->enctype);
+
 	trace_afs_cb_call(call);
 	call->work.func = call->type->work;
 
-	/* pass responsibility for the remainer of this message off to the
+	/* pass responsibility for the remainder of this message off to the
 	 * cache manager op */
 	return call->type->deliver(call);
 }
@@ -952,3 +974,13 @@ noinline int afs_protocol_error(struct afs_call *call,
 		call->unmarshalling_error = true;
 	return -EBADMSG;
 }
+
+/*
+ * Wake up OOB notification processing.
+ */
+static void afs_rx_notify_oob(struct sock *sk, struct sk_buff *oob)
+{
+	struct afs_net *net = sk->sk_user_data;
+
+	schedule_work(&net->rx_oob_work);
+}
diff --git a/fs/afs/server.c b/fs/afs/server.c
index 8755f2703815..a97562f831eb 100644
--- a/fs/afs/server.c
+++ b/fs/afs/server.c
@@ -131,6 +131,7 @@ static struct afs_server *afs_alloc_server(struct afs_cell *cell, const uuid_t *
 	timer_setup(&server->timer, afs_server_timer, 0);
 	INIT_LIST_HEAD(&server->volumes);
 	init_waitqueue_head(&server->probe_wq);
+	mutex_init(&server->cm_token_lock);
 	INIT_LIST_HEAD(&server->probe_link);
 	INIT_HLIST_NODE(&server->proc_link);
 	spin_lock_init(&server->probe_lock);
@@ -396,6 +397,7 @@ static void afs_server_rcu(struct rcu_head *rcu)
 	afs_put_endpoint_state(rcu_access_pointer(server->endpoint_state),
 			       afs_estate_trace_put_server);
 	afs_put_cell(server->cell, afs_cell_trace_put_server);
+	kfree(server->cm_rxgk_appdata.data);
 	kfree(server);
 }
 
diff --git a/include/crypto/krb5.h b/include/crypto/krb5.h
index 62d998e62f47..71dd38f59be1 100644
--- a/include/crypto/krb5.h
+++ b/include/crypto/krb5.h
@@ -64,6 +64,11 @@ struct scatterlist;
 #define KEY_USAGE_SEED_INTEGRITY        (0x55)
 
 /*
+ * Standard Kerberos error codes.
+ */
+#define KRB5_PROG_KEYTYPE_NOSUPP		-1765328233
+
+/*
  * Mode of operation.
  */
 enum krb5_crypto_mode {
diff --git a/include/keys/rxrpc-type.h b/include/keys/rxrpc-type.h
index 333c0f49a9cd..0ddbe197a261 100644
--- a/include/keys/rxrpc-type.h
+++ b/include/keys/rxrpc-type.h
@@ -9,6 +9,7 @@
 #define _KEYS_RXRPC_TYPE_H
 
 #include <linux/key.h>
+#include <crypto/krb5.h>
 
 /*
  * key type for AF_RXRPC keys
@@ -32,6 +33,21 @@ struct rxkad_key {
 };
 
 /*
+ * RxRPC key for YFS-RxGK (type-6 security)
+ */
+struct rxgk_key {
+	s64		begintime;	/* Time at which the ticket starts */
+	s64		endtime;	/* Time at which the ticket ends */
+	u64		lifetime;	/* Maximum lifespan of a connection (seconds) */
+	u64		bytelife;	/* Maximum number of bytes on a connection */
+	unsigned int	enctype;	/* Encoding type */
+	s8		level;		/* Negotiated security RXRPC_SECURITY_PLAIN/AUTH/ENCRYPT */
+	struct krb5_buffer key;		/* Master key, K0 */
+	struct krb5_buffer ticket;	/* Ticket to be passed to server */
+	u8		_key[];		/* Key storage */
+};
+
+/*
  * list of tokens attached to an rxrpc key
  */
 struct rxrpc_key_token {
@@ -40,6 +56,7 @@ struct rxrpc_key_token {
 	struct rxrpc_key_token *next;	/* the next token in the list */
 	union {
 		struct rxkad_key *kad;
+		struct rxgk_key *rxgk;
 	};
 };
 
diff --git a/include/net/af_rxrpc.h b/include/net/af_rxrpc.h
index cf793d18e5df..f15341594cc8 100644
--- a/include/net/af_rxrpc.h
+++ b/include/net/af_rxrpc.h
@@ -16,6 +16,7 @@ struct sock;
 struct socket;
 struct rxrpc_call;
 struct rxrpc_peer;
+struct krb5_buffer;
 enum rxrpc_abort_reason;
 
 enum rxrpc_interruptibility {
@@ -24,23 +25,33 @@ enum rxrpc_interruptibility {
 	RXRPC_UNINTERRUPTIBLE,	/* Call should not be interruptible at all */
 };
 
+enum rxrpc_oob_type {
+	RXRPC_OOB_CHALLENGE,	/* Security challenge for a connection */
+};
+
 /*
  * Debug ID counter for tracing.
  */
 extern atomic_t rxrpc_debug_id;
 
+/*
+ * Operations table for rxrpc to call out to a kernel application (e.g. kAFS).
+ */
+struct rxrpc_kernel_ops {
+	void (*notify_new_call)(struct sock *sk, struct rxrpc_call *call,
+				unsigned long user_call_ID);
+	void (*discard_new_call)(struct rxrpc_call *call, unsigned long user_call_ID);
+	void (*user_attach_call)(struct rxrpc_call *call, unsigned long user_call_ID);
+	void (*notify_oob)(struct sock *sk, struct sk_buff *oob);
+};
+
 typedef void (*rxrpc_notify_rx_t)(struct sock *, struct rxrpc_call *,
 				  unsigned long);
 typedef void (*rxrpc_notify_end_tx_t)(struct sock *, struct rxrpc_call *,
 				      unsigned long);
-typedef void (*rxrpc_notify_new_call_t)(struct sock *, struct rxrpc_call *,
-					unsigned long);
-typedef void (*rxrpc_discard_new_call_t)(struct rxrpc_call *, unsigned long);
-typedef void (*rxrpc_user_attach_call_t)(struct rxrpc_call *, unsigned long);
 
-void rxrpc_kernel_new_call_notification(struct socket *,
-					rxrpc_notify_new_call_t,
-					rxrpc_discard_new_call_t);
+void rxrpc_kernel_set_notifications(struct socket *sock,
+				    const struct rxrpc_kernel_ops *app_ops);
 struct rxrpc_call *rxrpc_kernel_begin_call(struct socket *sock,
 					   struct rxrpc_peer *peer,
 					   struct key *key,
@@ -72,9 +83,9 @@ const struct sockaddr *rxrpc_kernel_remote_addr(const struct rxrpc_peer *peer);
 unsigned long rxrpc_kernel_set_peer_data(struct rxrpc_peer *peer, unsigned long app_data);
 unsigned long rxrpc_kernel_get_peer_data(const struct rxrpc_peer *peer);
 unsigned int rxrpc_kernel_get_srtt(const struct rxrpc_peer *);
-int rxrpc_kernel_charge_accept(struct socket *, rxrpc_notify_rx_t,
-			       rxrpc_user_attach_call_t, unsigned long, gfp_t,
-			       unsigned int);
+int rxrpc_kernel_charge_accept(struct socket *sock, rxrpc_notify_rx_t notify_rx,
+			       unsigned long user_call_ID, gfp_t gfp,
+			       unsigned int debug_id);
 void rxrpc_kernel_set_tx_length(struct socket *, struct rxrpc_call *, s64);
 bool rxrpc_kernel_check_life(const struct socket *, const struct rxrpc_call *);
 u32 rxrpc_kernel_get_epoch(struct socket *, struct rxrpc_call *);
@@ -83,5 +94,25 @@ void rxrpc_kernel_set_max_life(struct socket *, struct rxrpc_call *,
 
 int rxrpc_sock_set_min_security_level(struct sock *sk, unsigned int val);
 int rxrpc_sock_set_security_keyring(struct sock *, struct key *);
+int rxrpc_sock_set_manage_response(struct sock *sk, bool set);
+
+enum rxrpc_oob_type rxrpc_kernel_query_oob(struct sk_buff *oob,
+					   struct rxrpc_peer **_peer,
+					   unsigned long *_peer_appdata);
+struct sk_buff *rxrpc_kernel_dequeue_oob(struct socket *sock,
+					 enum rxrpc_oob_type *_type);
+void rxrpc_kernel_free_oob(struct sk_buff *oob);
+void rxrpc_kernel_query_challenge(struct sk_buff *challenge,
+				  struct rxrpc_peer **_peer,
+				  unsigned long *_peer_appdata,
+				  u16 *_service_id, u8 *_security_index);
+int rxrpc_kernel_reject_challenge(struct sk_buff *challenge, u32 abort_code,
+				  int error, enum rxrpc_abort_reason why);
+int rxkad_kernel_respond_to_challenge(struct sk_buff *challenge);
+u32 rxgk_kernel_query_challenge(struct sk_buff *challenge);
+int rxgk_kernel_respond_to_challenge(struct sk_buff *challenge,
+				     struct krb5_buffer *appdata);
+u8 rxrpc_kernel_query_call_security(struct rxrpc_call *call,
+				    u16 *_service_id, u32 *_enctype);
 
 #endif /* _NET_RXRPC_H */
diff --git a/include/trace/events/afs.h b/include/trace/events/afs.h
index 8857f5ea77d4..7f83d242c8e9 100644
--- a/include/trace/events/afs.h
+++ b/include/trace/events/afs.h
@@ -663,19 +663,26 @@ TRACE_EVENT(afs_cb_call,
 		    __field(unsigned int,		call)
 		    __field(u32,			op)
 		    __field(u16,			service_id)
+		    __field(u8,				security_ix)
+		    __field(u32,			enctype)
 			     ),
 
 	    TP_fast_assign(
 		    __entry->call	= call->debug_id;
 		    __entry->op		= call->operation_ID;
 		    __entry->service_id	= call->service_id;
+		    __entry->security_ix = call->security_ix;
+		    __entry->enctype	= call->enctype;
 			   ),
 
-	    TP_printk("c=%08x %s",
+	    TP_printk("c=%08x %s sv=%u sx=%u en=%u",
 		      __entry->call,
 		      __entry->service_id == 2501 ?
 		      __print_symbolic(__entry->op, yfs_cm_operations) :
-		      __print_symbolic(__entry->op, afs_cm_operations))
+		      __print_symbolic(__entry->op, afs_cm_operations),
+		      __entry->service_id,
+		      __entry->security_ix,
+		      __entry->enctype)
 	    );
 
 TRACE_EVENT(afs_call,
diff --git a/include/trace/events/rxrpc.h b/include/trace/events/rxrpc.h
index cad50d91077e..378d2dfc7392 100644
--- a/include/trace/events/rxrpc.h
+++ b/include/trace/events/rxrpc.h
@@ -25,6 +25,7 @@
 	EM(afs_abort_probeuuid_negative,	"afs-probeuuid-neg")	\
 	EM(afs_abort_send_data_error,		"afs-send-data")	\
 	EM(afs_abort_unmarshal_error,		"afs-unmarshal")	\
+	EM(afs_abort_unsupported_sec_class,	"afs-unsup-sec-class")	\
 	/* rxperf errors */						\
 	EM(rxperf_abort_general_error,		"rxperf-error")		\
 	EM(rxperf_abort_oom,			"rxperf-oom")		\
@@ -68,6 +69,38 @@
 	EM(rxkad_abort_resp_tkt_sname,		"rxkad-resp-tk-sname")	\
 	EM(rxkad_abort_resp_unknown_tkt,	"rxkad-resp-unknown-tkt") \
 	EM(rxkad_abort_resp_version,		"rxkad-resp-version")	\
+	/* RxGK security errors */					\
+	EM(rxgk_abort_1_verify_mic_eproto,	"rxgk1-vfy-mic-eproto")	\
+	EM(rxgk_abort_2_decrypt_eproto,		"rxgk2-dec-eproto")	\
+	EM(rxgk_abort_2_short_data,		"rxgk2-short-data")	\
+	EM(rxgk_abort_2_short_encdata,		"rxgk2-short-encdata")	\
+	EM(rxgk_abort_2_short_header,		"rxgk2-short-hdr")	\
+	EM(rxgk_abort_bad_key_number,		"rxgk-bad-key-num")	\
+	EM(rxgk_abort_chall_key_expired,	"rxgk-chall-key-exp")	\
+	EM(rxgk_abort_chall_no_key,		"rxgk-chall-nokey")	\
+	EM(rxgk_abort_chall_short,		"rxgk-chall-short")	\
+	EM(rxgk_abort_resp_auth_dec,		"rxgk-resp-auth-dec")	\
+	EM(rxgk_abort_resp_bad_callid,		"rxgk-resp-bad-callid")	\
+	EM(rxgk_abort_resp_bad_nonce,		"rxgk-resp-bad-nonce")	\
+	EM(rxgk_abort_resp_bad_param,		"rxgk-resp-bad-param")	\
+	EM(rxgk_abort_resp_call_ctr,		"rxgk-resp-call-ctr")	\
+	EM(rxgk_abort_resp_call_state,		"rxgk-resp-call-state")	\
+	EM(rxgk_abort_resp_internal_error,	"rxgk-resp-int-error")	\
+	EM(rxgk_abort_resp_nopkg,		"rxgk-resp-nopkg")	\
+	EM(rxgk_abort_resp_short_applen,	"rxgk-resp-short-applen") \
+	EM(rxgk_abort_resp_short_auth,		"rxgk-resp-short-auth") \
+	EM(rxgk_abort_resp_short_call_list,	"rxgk-resp-short-callls") \
+	EM(rxgk_abort_resp_short_packet,	"rxgk-resp-short-packet") \
+	EM(rxgk_abort_resp_short_yfs_klen,	"rxgk-resp-short-yfs-klen") \
+	EM(rxgk_abort_resp_short_yfs_key,	"rxgk-resp-short-yfs-key") \
+	EM(rxgk_abort_resp_short_yfs_tkt,	"rxgk-resp-short-yfs-tkt") \
+	EM(rxgk_abort_resp_tok_dec,		"rxgk-resp-tok-dec")	\
+	EM(rxgk_abort_resp_tok_internal_error,	"rxgk-resp-tok-int-err") \
+	EM(rxgk_abort_resp_tok_keyerr,		"rxgk-resp-tok-keyerr")	\
+	EM(rxgk_abort_resp_tok_nokey,		"rxgk-resp-tok-nokey")	\
+	EM(rxgk_abort_resp_tok_nopkg,		"rxgk-resp-tok-nopkg")	\
+	EM(rxgk_abort_resp_tok_short,		"rxgk-resp-tok-short")	\
+	EM(rxgk_abort_resp_xdr_align,		"rxgk-resp-xdr-align")	\
 	/* rxrpc errors */						\
 	EM(rxrpc_abort_call_improper_term,	"call-improper-term")	\
 	EM(rxrpc_abort_call_reset,		"call-reset")		\
@@ -77,6 +110,7 @@
 	EM(rxrpc_abort_call_timeout,		"call-timeout")		\
 	EM(rxrpc_abort_no_service_key,		"no-serv-key")		\
 	EM(rxrpc_abort_nomem,			"nomem")		\
+	EM(rxrpc_abort_response_sendmsg,	"resp-sendmsg")		\
 	EM(rxrpc_abort_service_not_offered,	"serv-not-offered")	\
 	EM(rxrpc_abort_shut_down,		"shut-down")		\
 	EM(rxrpc_abort_unsupported_security,	"unsup-sec")		\
@@ -133,24 +167,33 @@
 	EM(rxrpc_skb_get_conn_secured,		"GET conn-secd") \
 	EM(rxrpc_skb_get_conn_work,		"GET conn-work") \
 	EM(rxrpc_skb_get_local_work,		"GET locl-work") \
+	EM(rxrpc_skb_get_post_oob,		"GET post-oob ") \
 	EM(rxrpc_skb_get_reject_work,		"GET rej-work ") \
 	EM(rxrpc_skb_get_to_recvmsg,		"GET to-recv  ") \
 	EM(rxrpc_skb_get_to_recvmsg_oos,	"GET to-recv-o") \
 	EM(rxrpc_skb_new_encap_rcv,		"NEW encap-rcv") \
 	EM(rxrpc_skb_new_error_report,		"NEW error-rpt") \
 	EM(rxrpc_skb_new_jumbo_subpacket,	"NEW jumbo-sub") \
+	EM(rxrpc_skb_new_response_rxgk,		"NEW resp-rxgk") \
+	EM(rxrpc_skb_new_response_rxkad,	"NEW resp-rxkd") \
 	EM(rxrpc_skb_new_unshared,		"NEW unshared ") \
 	EM(rxrpc_skb_put_call_rx,		"PUT call-rx  ") \
+	EM(rxrpc_skb_put_challenge,		"PUT challenge") \
 	EM(rxrpc_skb_put_conn_secured,		"PUT conn-secd") \
 	EM(rxrpc_skb_put_conn_work,		"PUT conn-work") \
 	EM(rxrpc_skb_put_error_report,		"PUT error-rep") \
 	EM(rxrpc_skb_put_input,			"PUT input    ") \
 	EM(rxrpc_skb_put_jumbo_subpacket,	"PUT jumbo-sub") \
+	EM(rxrpc_skb_put_oob,			"PUT oob      ") \
 	EM(rxrpc_skb_put_purge,			"PUT purge    ") \
+	EM(rxrpc_skb_put_purge_oob,		"PUT purge-oob") \
+	EM(rxrpc_skb_put_response,		"PUT response ") \
 	EM(rxrpc_skb_put_rotate,		"PUT rotate   ") \
 	EM(rxrpc_skb_put_unknown,		"PUT unknown  ") \
 	EM(rxrpc_skb_see_conn_work,		"SEE conn-work") \
+	EM(rxrpc_skb_see_oob_challenge,		"SEE oob-chall") \
 	EM(rxrpc_skb_see_recvmsg,		"SEE recvmsg  ") \
+	EM(rxrpc_skb_see_recvmsg_oob,		"SEE recvm-oob") \
 	EM(rxrpc_skb_see_reject,		"SEE reject   ") \
 	EM(rxrpc_skb_see_rotate,		"SEE rotate   ") \
 	E_(rxrpc_skb_see_version,		"SEE version  ")
@@ -216,9 +259,11 @@
 	EM(rxrpc_conn_free,			"FREE        ") \
 	EM(rxrpc_conn_get_activate_call,	"GET act-call") \
 	EM(rxrpc_conn_get_call_input,		"GET inp-call") \
+	EM(rxrpc_conn_get_challenge_input,	"GET inp-chal") \
 	EM(rxrpc_conn_get_conn_input,		"GET inp-conn") \
 	EM(rxrpc_conn_get_idle,			"GET idle    ") \
 	EM(rxrpc_conn_get_poke_abort,		"GET pk-abort") \
+	EM(rxrpc_conn_get_poke_response,	"GET response") \
 	EM(rxrpc_conn_get_poke_secured,		"GET secured ") \
 	EM(rxrpc_conn_get_poke_timer,		"GET poke    ") \
 	EM(rxrpc_conn_get_service_conn,		"GET svc-conn") \
@@ -226,10 +271,12 @@
 	EM(rxrpc_conn_new_service,		"NEW service ") \
 	EM(rxrpc_conn_put_call,			"PUT call    ") \
 	EM(rxrpc_conn_put_call_input,		"PUT inp-call") \
+	EM(rxrpc_conn_put_challenge_input,	"PUT inp-chal") \
 	EM(rxrpc_conn_put_conn_input,		"PUT inp-conn") \
 	EM(rxrpc_conn_put_discard_idle,		"PUT disc-idl") \
 	EM(rxrpc_conn_put_local_dead,		"PUT loc-dead") \
 	EM(rxrpc_conn_put_noreuse,		"PUT noreuse ") \
+	EM(rxrpc_conn_put_oob,			"PUT oob     ") \
 	EM(rxrpc_conn_put_poke,			"PUT poke    ") \
 	EM(rxrpc_conn_put_service_reaped,	"PUT svc-reap") \
 	EM(rxrpc_conn_put_unbundle,		"PUT unbundle") \
@@ -331,6 +378,7 @@
 	EM(rxrpc_recvmsg_full,			"FULL") \
 	EM(rxrpc_recvmsg_hole,			"HOLE") \
 	EM(rxrpc_recvmsg_next,			"NEXT") \
+	EM(rxrpc_recvmsg_oobq,			"OOBQ") \
 	EM(rxrpc_recvmsg_requeue,		"REQU") \
 	EM(rxrpc_recvmsg_return,		"RETN") \
 	EM(rxrpc_recvmsg_terminal,		"TERM") \
@@ -455,8 +503,9 @@
 	EM(rxrpc_tx_point_call_final_resend,	"CallFinalResend") \
 	EM(rxrpc_tx_point_conn_abort,		"ConnAbort") \
 	EM(rxrpc_tx_point_reject,		"Reject") \
+	EM(rxrpc_tx_point_rxgk_challenge,	"RxGKChall") \
 	EM(rxrpc_tx_point_rxkad_challenge,	"RxkadChall") \
-	EM(rxrpc_tx_point_rxkad_response,	"RxkadResp") \
+	EM(rxrpc_tx_point_response,		"Response") \
 	EM(rxrpc_tx_point_version_keepalive,	"VerKeepalive") \
 	E_(rxrpc_tx_point_version_reply,	"VerReply")
 
@@ -473,6 +522,7 @@
 
 #define rxrpc_txbuf_traces \
 	EM(rxrpc_txbuf_alloc_data,		"ALLOC DATA ")	\
+	EM(rxrpc_txbuf_alloc_response,		"ALLOC RESP ")	\
 	EM(rxrpc_txbuf_free,			"FREE       ")	\
 	EM(rxrpc_txbuf_get_buffer,		"GET BUFFER ")	\
 	EM(rxrpc_txbuf_get_trans,		"GET TRANS  ")	\
@@ -480,6 +530,7 @@
 	EM(rxrpc_txbuf_put_cleaned,		"PUT CLEANED")	\
 	EM(rxrpc_txbuf_put_nomem,		"PUT NOMEM  ")	\
 	EM(rxrpc_txbuf_put_rotated,		"PUT ROTATED")	\
+	EM(rxrpc_txbuf_put_response_tx,		"PUT RESP TX")	\
 	EM(rxrpc_txbuf_put_send_aborted,	"PUT SEND-X ")	\
 	EM(rxrpc_txbuf_put_trans,		"PUT TRANS  ")	\
 	EM(rxrpc_txbuf_see_lost,		"SEE LOST   ")	\
@@ -1150,6 +1201,39 @@ TRACE_EVENT(rxrpc_rx_conn_abort,
 		      __entry->abort_code)
 	    );
 
+TRACE_EVENT(rxrpc_tx_challenge,
+	    TP_PROTO(struct rxrpc_connection *conn, rxrpc_serial_t serial,
+		     u32 version, u32 nonce),
+
+	    TP_ARGS(conn, serial, version, nonce),
+
+	    TP_STRUCT__entry(
+		    __field(unsigned int,	conn)
+		    __field(rxrpc_serial_t,	serial)
+		    __field(u32,		version)
+		    __field(u32,		nonce)
+		    __field(u16,		service_id)
+		    __field(u8,			security_ix)
+			     ),
+
+	    TP_fast_assign(
+		    __entry->conn = conn->debug_id;
+		    __entry->serial = serial;
+		    __entry->version = version;
+		    __entry->nonce = nonce;
+		    __entry->service_id = conn->service_id;
+		    __entry->security_ix = conn->security_ix;
+			   ),
+
+	    TP_printk("C=%08x CHALLENGE r=%08x sv=%u+%u v=%x n=%x",
+		      __entry->conn,
+		      __entry->serial,
+		      __entry->service_id,
+		      __entry->security_ix,
+		      __entry->version,
+		      __entry->nonce)
+	    );
+
 TRACE_EVENT(rxrpc_rx_challenge,
 	    TP_PROTO(struct rxrpc_connection *conn, rxrpc_serial_t serial,
 		     u32 version, u32 nonce, u32 min_level),
@@ -1162,6 +1246,8 @@ TRACE_EVENT(rxrpc_rx_challenge,
 		    __field(u32,		version)
 		    __field(u32,		nonce)
 		    __field(u32,		min_level)
+		    __field(u16,		service_id)
+		    __field(u8,			security_ix)
 			     ),
 
 	    TP_fast_assign(
@@ -1170,16 +1256,60 @@ TRACE_EVENT(rxrpc_rx_challenge,
 		    __entry->version = version;
 		    __entry->nonce = nonce;
 		    __entry->min_level = min_level;
+		    __entry->service_id = conn->service_id;
+		    __entry->security_ix = conn->security_ix;
 			   ),
 
-	    TP_printk("C=%08x CHALLENGE %08x v=%x n=%x ml=%x",
+	    TP_printk("C=%08x CHALLENGE r=%08x sv=%u+%u v=%x n=%x ml=%x",
 		      __entry->conn,
 		      __entry->serial,
+		      __entry->service_id,
+		      __entry->security_ix,
 		      __entry->version,
 		      __entry->nonce,
 		      __entry->min_level)
 	    );
 
+TRACE_EVENT(rxrpc_tx_response,
+	    TP_PROTO(struct rxrpc_connection *conn, rxrpc_serial_t serial,
+		     struct rxrpc_skb_priv *rsp),
+
+	    TP_ARGS(conn, serial, rsp),
+
+	    TP_STRUCT__entry(
+		    __field(unsigned int,	conn)
+		    __field(rxrpc_serial_t,	serial)
+		    __field(rxrpc_serial_t,	challenge)
+		    __field(u32,		version)
+		    __field(u32,		kvno)
+		    __field(u16,		ticket_len)
+		    __field(u16,		appdata_len)
+		    __field(u16,		service_id)
+		    __field(u8,			security_ix)
+			     ),
+
+	    TP_fast_assign(
+		    __entry->conn	= conn->debug_id;
+		    __entry->serial	= serial;
+		    __entry->challenge	= rsp->resp.challenge_serial;
+		    __entry->version	= rsp->resp.version;
+		    __entry->kvno	= rsp->resp.kvno;
+		    __entry->ticket_len = rsp->resp.ticket_len;
+		    __entry->service_id = conn->service_id;
+		    __entry->security_ix = conn->security_ix;
+			   ),
+
+	    TP_printk("C=%08x RESPONSE r=%08x cr=%08x sv=%u+%u v=%x kv=%x tl=%u",
+		      __entry->conn,
+		      __entry->serial,
+		      __entry->challenge,
+		      __entry->service_id,
+		      __entry->security_ix,
+		      __entry->version,
+		      __entry->kvno,
+		      __entry->ticket_len)
+	    );
+
 TRACE_EVENT(rxrpc_rx_response,
 	    TP_PROTO(struct rxrpc_connection *conn, rxrpc_serial_t serial,
 		     u32 version, u32 kvno, u32 ticket_len),
@@ -1192,6 +1322,7 @@ TRACE_EVENT(rxrpc_rx_response,
 		    __field(u32,		version)
 		    __field(u32,		kvno)
 		    __field(u32,		ticket_len)
+		    __field(u8,			security_ix)
 			     ),
 
 	    TP_fast_assign(
@@ -1200,11 +1331,13 @@ TRACE_EVENT(rxrpc_rx_response,
 		    __entry->version = version;
 		    __entry->kvno = kvno;
 		    __entry->ticket_len = ticket_len;
+		    __entry->security_ix = conn->security_ix;
 			   ),
 
-	    TP_printk("C=%08x RESPONSE %08x v=%x kvno=%x tl=%x",
+	    TP_printk("C=%08x RESPONSE r=%08x sx=%u v=%x kvno=%x tl=%x",
 		      __entry->conn,
 		      __entry->serial,
+		      __entry->security_ix,
 		      __entry->version,
 		      __entry->kvno,
 		      __entry->ticket_len)
@@ -2668,6 +2801,30 @@ TRACE_EVENT(rxrpc_rack_timer,
 		      ktime_to_us(__entry->delay))
 	    );
 
+TRACE_EVENT(rxrpc_rxgk_rekey,
+	    TP_PROTO(struct rxrpc_connection *conn,
+		     unsigned int current_key, unsigned int requested_key),
+
+	    TP_ARGS(conn, current_key, requested_key),
+
+	    TP_STRUCT__entry(
+		    __field(unsigned int,	conn)
+		    __field(unsigned int,	current_key)
+		    __field(unsigned int,	requested_key)
+			     ),
+
+	    TP_fast_assign(
+		    __entry->conn		= conn->debug_id;
+		    __entry->current_key	= current_key;
+		    __entry->requested_key	= requested_key;
+			   ),
+
+	    TP_printk("C=%08x cur=%x req=%x",
+		      __entry->conn,
+		      __entry->current_key,
+		      __entry->requested_key)
+	    );
+
 #undef EM
 #undef E_
 
diff --git a/include/uapi/linux/rxrpc.h b/include/uapi/linux/rxrpc.h
index 8f8dc7a937a4..d9735abd4c79 100644
--- a/include/uapi/linux/rxrpc.h
+++ b/include/uapi/linux/rxrpc.h
@@ -36,26 +36,33 @@ struct sockaddr_rxrpc {
 #define RXRPC_MIN_SECURITY_LEVEL	4	/* minimum security level */
 #define RXRPC_UPGRADEABLE_SERVICE	5	/* Upgrade service[0] -> service[1] */
 #define RXRPC_SUPPORTED_CMSG		6	/* Get highest supported control message type */
+#define RXRPC_MANAGE_RESPONSE		7	/* [clnt] Want to manage RESPONSE packets */
 
 /*
  * RxRPC control messages
  * - If neither abort or accept are specified, the message is a data message.
  * - terminal messages mean that a user call ID tag can be recycled
+ * - C/S/- indicate whether these are applicable to client, server or both
  * - s/r/- indicate whether these are applicable to sendmsg() and/or recvmsg()
  */
 enum rxrpc_cmsg_type {
-	RXRPC_USER_CALL_ID	= 1,	/* sr: user call ID specifier */
-	RXRPC_ABORT		= 2,	/* sr: abort request / notification [terminal] */
-	RXRPC_ACK		= 3,	/* -r: [Service] RPC op final ACK received [terminal] */
-	RXRPC_NET_ERROR		= 5,	/* -r: network error received [terminal] */
-	RXRPC_BUSY		= 6,	/* -r: server busy received [terminal] */
-	RXRPC_LOCAL_ERROR	= 7,	/* -r: local error generated [terminal] */
-	RXRPC_NEW_CALL		= 8,	/* -r: [Service] new incoming call notification */
-	RXRPC_EXCLUSIVE_CALL	= 10,	/* s-: Call should be on exclusive connection */
-	RXRPC_UPGRADE_SERVICE	= 11,	/* s-: Request service upgrade for client call */
-	RXRPC_TX_LENGTH		= 12,	/* s-: Total length of Tx data */
-	RXRPC_SET_CALL_TIMEOUT	= 13,	/* s-: Set one or more call timeouts */
-	RXRPC_CHARGE_ACCEPT	= 14,	/* s-: Charge the accept pool with a user call ID */
+	RXRPC_USER_CALL_ID	= 1,	/* -sr: User call ID specifier */
+	RXRPC_ABORT		= 2,	/* -sr: Abort request / notification [terminal] */
+	RXRPC_ACK		= 3,	/* S-r: RPC op final ACK received [terminal] */
+	RXRPC_NET_ERROR		= 5,	/* --r: Network error received [terminal] */
+	RXRPC_BUSY		= 6,	/* C-r: Server busy received [terminal] */
+	RXRPC_LOCAL_ERROR	= 7,	/* --r: Local error generated [terminal] */
+	RXRPC_NEW_CALL		= 8,	/* S-r: New incoming call notification */
+	RXRPC_EXCLUSIVE_CALL	= 10,	/* Cs-: Call should be on exclusive connection */
+	RXRPC_UPGRADE_SERVICE	= 11,	/* Cs-: Request service upgrade for client call */
+	RXRPC_TX_LENGTH		= 12,	/* -s-: Total length of Tx data */
+	RXRPC_SET_CALL_TIMEOUT	= 13,	/* -s-: Set one or more call timeouts */
+	RXRPC_CHARGE_ACCEPT	= 14,	/* Ss-: Charge the accept pool with a user call ID */
+	RXRPC_OOB_ID		= 15,	/* -sr: OOB message ID */
+	RXRPC_CHALLENGED	= 16,	/* C-r: Info on a received CHALLENGE */
+	RXRPC_RESPOND		= 17,	/* Cs-: Respond to a challenge */
+	RXRPC_RESPONDED		= 18,	/* S-r: Data received in RESPONSE */
+	RXRPC_RESP_RXGK_APPDATA	= 19,	/* Cs-: RESPONSE: RxGK app data to include */
 	RXRPC__SUPPORTED
 };
 
@@ -73,6 +80,7 @@ enum rxrpc_cmsg_type {
 #define RXRPC_SECURITY_RXKAD	2	/* kaserver or kerberos 4 */
 #define RXRPC_SECURITY_RXGK	4	/* gssapi-based */
 #define RXRPC_SECURITY_RXK5	5	/* kerberos 5 */
+#define RXRPC_SECURITY_YFS_RXGK	6	/* YFS gssapi-based */
 
 /*
  * RxRPC-level abort codes
@@ -118,4 +126,49 @@ enum rxrpc_cmsg_type {
 #define RXKADDATALEN		19270411	/* user data too long */
 #define RXKADILLEGALLEVEL	19270412	/* caller not authorised to use encrypted conns */
 
+/*
+ * RxGK GSSAPI security abort codes.
+ */
+#if 0 /* Original standard abort codes (used by OpenAFS) */
+#define RXGK_INCONSISTENCY	1233242880	/* Security module structure inconsistent */
+#define RXGK_PACKETSHORT	1233242881	/* Packet too short for security challenge */
+#define RXGK_BADCHALLENGE	1233242882	/* Invalid security challenge */
+#define RXGK_BADETYPE		1233242883	/* Invalid or impermissible encryption type */
+#define RXGK_BADLEVEL		1233242884	/* Invalid or impermissible security level */
+#define RXGK_BADKEYNO		1233242885	/* Key version number not found */
+#define RXGK_EXPIRED		1233242886	/* Token has expired */
+#define RXGK_NOTAUTH		1233242887	/* Caller not authorized */
+#define RXGK_BAD_TOKEN		1233242888	/* Security object was passed a bad token */
+#define RXGK_SEALED_INCON	1233242889	/* Sealed data inconsistent */
+#define RXGK_DATA_LEN		1233242890	/* User data too long */
+#define RXGK_BAD_QOP		1233242891	/* Inadequate quality of protection available */
+#else /* Revised standard abort codes (used by YFS) */
+#define RXGK_INCONSISTENCY	1233242880	/* Security module structure inconsistent */
+#define RXGK_PACKETSHORT	1233242881	/* Packet too short for security challenge */
+#define RXGK_BADCHALLENGE	1233242882	/* Security challenge/response failed */
+#define RXGK_SEALEDINCON	1233242883	/* Sealed data is inconsistent */
+#define RXGK_NOTAUTH		1233242884	/* Caller not authorised */
+#define RXGK_EXPIRED		1233242885	/* Authentication expired */
+#define RXGK_BADLEVEL		1233242886	/* Unsupported or not permitted security level */
+#define RXGK_BADKEYNO		1233242887	/* Bad transport key number */
+#define RXGK_NOTRXGK		1233242888	/* Security layer is not rxgk */
+#define RXGK_UNSUPPORTED	1233242889	/* Endpoint does not support rxgk */
+#define RXGK_GSSERROR		1233242890	/* GSSAPI mechanism error */
+#endif
+
+/*
+ * Challenge information in the RXRPC_CHALLENGED control message.
+ */
+struct rxrpc_challenge {
+	__u16		service_id;	/* The service ID of the connection (may be upgraded) */
+	__u8		security_index;	/* The security index of the connection */
+	__u8		pad;		/* Round out to a multiple of 4 bytes. */
+	/* ... The security class gets to append extra information ... */
+};
+
+struct rxgk_challenge {
+	struct rxrpc_challenge	base;
+	__u32			enctype;	/* Krb5 encoding type */
+};
+
 #endif /* _UAPI_LINUX_RXRPC_H */
diff --git a/net/rxrpc/Kconfig b/net/rxrpc/Kconfig
index a20986806fea..f60b81c66078 100644
--- a/net/rxrpc/Kconfig
+++ b/net/rxrpc/Kconfig
@@ -67,6 +67,29 @@ config RXKAD
 
 	  See Documentation/networking/rxrpc.rst.
 
+config RXGK
+	bool "RxRPC GSSAPI security"
+	select CRYPTO_KRB5
+	select CRYPTO_MANAGER
+	select CRYPTO_KRB5ENC
+	select CRYPTO_AUTHENC
+	select CRYPTO_SKCIPHER
+	select CRYPTO_HASH_INFO
+	select CRYPTO_HMAC
+	select CRYPTO_CMAC
+	select CRYPTO_SHA1
+	select CRYPTO_SHA256
+	select CRYPTO_SHA512
+	select CRYPTO_CBC
+	select CRYPTO_CTS
+	select CRYPTO_AES
+	select CRYPTO_CAMELLIA
+	help
+	  Provide the GSSAPI-based RxGK security class for AFS.  Keys are added
+	  with add_key().
+
+	  See Documentation/networking/rxrpc.rst.
+
 config RXPERF
 	tristate "RxRPC test service"
 	help
diff --git a/net/rxrpc/Makefile b/net/rxrpc/Makefile
index 210b75e3179e..c0542bae719e 100644
--- a/net/rxrpc/Makefile
+++ b/net/rxrpc/Makefile
@@ -24,6 +24,7 @@ rxrpc-y := \
 	local_object.o \
 	misc.o \
 	net_ns.o \
+	oob.o \
 	output.o \
 	peer_event.o \
 	peer_object.o \
@@ -39,6 +40,9 @@ rxrpc-y := \
 rxrpc-$(CONFIG_PROC_FS) += proc.o
 rxrpc-$(CONFIG_RXKAD) += rxkad.o
 rxrpc-$(CONFIG_SYSCTL) += sysctl.o
-
+rxrpc-$(CONFIG_RXGK) += \
+	rxgk.o \
+	rxgk_app.o \
+	rxgk_kdf.o
 
 obj-$(CONFIG_RXPERF) += rxperf.o
diff --git a/net/rxrpc/af_rxrpc.c b/net/rxrpc/af_rxrpc.c
index 86873399f7d5..3a558c1a541e 100644
--- a/net/rxrpc/af_rxrpc.c
+++ b/net/rxrpc/af_rxrpc.c
@@ -265,7 +265,10 @@ static int rxrpc_listen(struct socket *sock, int backlog)
  * @gfp: Allocation flags
  *
  * Lookup or create a remote transport endpoint record for the specified
- * address and return it with a ref held.
+ * address.
+ *
+ * Return: The peer record found with a reference, %NULL if no record is found
+ * or a negative error code if the address is invalid or unsupported.
  */
 struct rxrpc_peer *rxrpc_kernel_lookup_peer(struct socket *sock,
 					    struct sockaddr_rxrpc *srx, gfp_t gfp)
@@ -283,9 +286,11 @@ EXPORT_SYMBOL(rxrpc_kernel_lookup_peer);
 
 /**
  * rxrpc_kernel_get_peer - Get a reference on a peer
- * @peer: The peer to get a reference on.
+ * @peer: The peer to get a reference on (may be NULL).
+ *
+ * Get a reference for a remote peer record (if not NULL).
  *
- * Get a record for the remote peer in a call.
+ * Return: The @peer argument.
  */
 struct rxrpc_peer *rxrpc_kernel_get_peer(struct rxrpc_peer *peer)
 {
@@ -296,6 +301,8 @@ EXPORT_SYMBOL(rxrpc_kernel_get_peer);
 /**
  * rxrpc_kernel_put_peer - Allow a kernel app to drop a peer reference
  * @peer: The peer to drop a ref on
+ *
+ * Drop a reference on a peer record.
  */
 void rxrpc_kernel_put_peer(struct rxrpc_peer *peer)
 {
@@ -320,10 +327,12 @@ EXPORT_SYMBOL(rxrpc_kernel_put_peer);
  *
  * Allow a kernel service to begin a call on the nominated socket.  This just
  * sets up all the internal tracking structures and allocates connection and
- * call IDs as appropriate.  The call to be used is returned.
+ * call IDs as appropriate.
  *
  * The default socket destination address and security may be overridden by
  * supplying @srx and @key.
+ *
+ * Return: The new call or an error code.
  */
 struct rxrpc_call *rxrpc_kernel_begin_call(struct socket *sock,
 					   struct rxrpc_peer *peer,
@@ -437,6 +446,8 @@ EXPORT_SYMBOL(rxrpc_kernel_put_call);
  *
  * Allow a kernel service to find out whether a call is still alive - whether
  * it has completed successfully and all received data has been consumed.
+ *
+ * Return: %true if the call is still ongoing and %false if it has completed.
  */
 bool rxrpc_kernel_check_life(const struct socket *sock,
 			     const struct rxrpc_call *call)
@@ -456,6 +467,8 @@ EXPORT_SYMBOL(rxrpc_kernel_check_life);
  *
  * Allow a kernel service to retrieve the epoch value from a service call to
  * see if the client at the other end rebooted.
+ *
+ * Return: The epoch of the call's connection.
  */
 u32 rxrpc_kernel_get_epoch(struct socket *sock, struct rxrpc_call *call)
 {
@@ -464,24 +477,20 @@ u32 rxrpc_kernel_get_epoch(struct socket *sock, struct rxrpc_call *call)
 EXPORT_SYMBOL(rxrpc_kernel_get_epoch);
 
 /**
- * rxrpc_kernel_new_call_notification - Get notifications of new calls
- * @sock: The socket to intercept received messages on
- * @notify_new_call: Function to be called when new calls appear
- * @discard_new_call: Function to discard preallocated calls
+ * rxrpc_kernel_set_notifications - Set table of callback operations
+ * @sock: The socket to install table upon
+ * @app_ops: Callback operation table to set
  *
- * Allow a kernel service to be given notifications about new calls.
+ * Allow a kernel service to set a table of event notifications on a socket.
  */
-void rxrpc_kernel_new_call_notification(
-	struct socket *sock,
-	rxrpc_notify_new_call_t notify_new_call,
-	rxrpc_discard_new_call_t discard_new_call)
+void rxrpc_kernel_set_notifications(struct socket *sock,
+				    const struct rxrpc_kernel_ops *app_ops)
 {
 	struct rxrpc_sock *rx = rxrpc_sk(sock->sk);
 
-	rx->notify_new_call = notify_new_call;
-	rx->discard_new_call = discard_new_call;
+	rx->app_ops = app_ops;
 }
-EXPORT_SYMBOL(rxrpc_kernel_new_call_notification);
+EXPORT_SYMBOL(rxrpc_kernel_set_notifications);
 
 /**
  * rxrpc_kernel_set_max_life - Set maximum lifespan on a call
@@ -624,7 +633,10 @@ static int rxrpc_sendmsg(struct socket *sock, struct msghdr *m, size_t len)
 		fallthrough;
 	case RXRPC_SERVER_BOUND:
 	case RXRPC_SERVER_LISTENING:
-		ret = rxrpc_do_sendmsg(rx, m, len);
+		if (m->msg_flags & MSG_OOB)
+			ret = rxrpc_sendmsg_oob(rx, m, len);
+		else
+			ret = rxrpc_do_sendmsg(rx, m, len);
 		/* The socket has been unlocked */
 		goto out;
 	default:
@@ -659,7 +671,7 @@ static int rxrpc_setsockopt(struct socket *sock, int level, int optname,
 			    sockptr_t optval, unsigned int optlen)
 {
 	struct rxrpc_sock *rx = rxrpc_sk(sock->sk);
-	unsigned int min_sec_level;
+	unsigned int min_sec_level, val;
 	u16 service_upgrade[2];
 	int ret;
 
@@ -740,6 +752,26 @@ static int rxrpc_setsockopt(struct socket *sock, int level, int optname,
 			rx->service_upgrade.to = service_upgrade[1];
 			goto success;
 
+		case RXRPC_MANAGE_RESPONSE:
+			ret = -EINVAL;
+			if (optlen != sizeof(unsigned int))
+				goto error;
+			ret = -EISCONN;
+			if (rx->sk.sk_state != RXRPC_UNBOUND)
+				goto error;
+			ret = copy_safe_from_sockptr(&val, sizeof(val),
+						     optval, optlen);
+			if (ret)
+				goto error;
+			ret = -EINVAL;
+			if (val > 1)
+				goto error;
+			if (val)
+				set_bit(RXRPC_SOCK_MANAGE_RESPONSE, &rx->flags);
+			else
+				clear_bit(RXRPC_SOCK_MANAGE_RESPONSE, &rx->flags);
+			goto success;
+
 		default:
 			break;
 		}
@@ -846,6 +878,8 @@ static int rxrpc_create(struct net *net, struct socket *sock, int protocol,
 	rx->calls = RB_ROOT;
 
 	spin_lock_init(&rx->incoming_lock);
+	skb_queue_head_init(&rx->recvmsg_oobq);
+	rx->pending_oobq = RB_ROOT;
 	INIT_LIST_HEAD(&rx->sock_calls);
 	INIT_LIST_HEAD(&rx->to_be_accepted);
 	INIT_LIST_HEAD(&rx->recvmsg_q);
@@ -879,8 +913,10 @@ static int rxrpc_shutdown(struct socket *sock, int flags)
 	lock_sock(sk);
 
 	if (sk->sk_state < RXRPC_CLOSE) {
+		spin_lock_irq(&rx->recvmsg_lock);
 		sk->sk_state = RXRPC_CLOSE;
 		sk->sk_shutdown = SHUTDOWN_MASK;
+		spin_unlock_irq(&rx->recvmsg_lock);
 	} else {
 		ret = -ESHUTDOWN;
 	}
@@ -892,12 +928,30 @@ static int rxrpc_shutdown(struct socket *sock, int flags)
 }
 
 /*
+ * Purge the out-of-band queue.
+ */
+static void rxrpc_purge_oob_queue(struct sock *sk)
+{
+	struct rxrpc_sock *rx = rxrpc_sk(sk);
+	struct sk_buff *skb;
+
+	while ((skb = skb_dequeue(&rx->recvmsg_oobq)))
+		rxrpc_kernel_free_oob(skb);
+	while (!RB_EMPTY_ROOT(&rx->pending_oobq)) {
+		skb = rb_entry(rx->pending_oobq.rb_node, struct sk_buff, rbnode);
+		rb_erase(&skb->rbnode, &rx->pending_oobq);
+		rxrpc_kernel_free_oob(skb);
+	}
+}
+
+/*
  * RxRPC socket destructor
  */
 static void rxrpc_sock_destructor(struct sock *sk)
 {
 	_enter("%p", sk);
 
+	rxrpc_purge_oob_queue(sk);
 	rxrpc_purge_queue(&sk->sk_receive_queue);
 
 	WARN_ON(refcount_read(&sk->sk_wmem_alloc));
@@ -936,7 +990,9 @@ static int rxrpc_release_sock(struct sock *sk)
 		break;
 	}
 
+	spin_lock_irq(&rx->recvmsg_lock);
 	sk->sk_state = RXRPC_CLOSE;
+	spin_unlock_irq(&rx->recvmsg_lock);
 
 	if (rx->local && rx->local->service == rx) {
 		write_lock(&rx->local->services_lock);
@@ -948,6 +1004,7 @@ static int rxrpc_release_sock(struct sock *sk)
 	rxrpc_discard_prealloc(rx);
 	rxrpc_release_calls_on_socket(rx);
 	flush_workqueue(rxrpc_workqueue);
+	rxrpc_purge_oob_queue(sk);
 	rxrpc_purge_queue(&sk->sk_receive_queue);
 
 	rxrpc_unuse_local(rx->local, rxrpc_local_unuse_release_sock);
diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index 3cc3af15086f..ca62a1db3286 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -31,6 +31,7 @@ struct key_preparsed_payload;
 struct rxrpc_connection;
 struct rxrpc_txbuf;
 struct rxrpc_txqueue;
+struct rxgk_context;
 
 /*
  * Mark applied to socket buffers in skb->mark.  skb->priority is used
@@ -39,6 +40,7 @@ struct rxrpc_txqueue;
 enum rxrpc_skb_mark {
 	RXRPC_SKB_MARK_PACKET,		/* Received packet */
 	RXRPC_SKB_MARK_ERROR,		/* Error notification */
+	RXRPC_SKB_MARK_CHALLENGE,	/* Challenge notification */
 	RXRPC_SKB_MARK_SERVICE_CONN_SECURED, /* Service connection response has been verified */
 	RXRPC_SKB_MARK_REJECT_BUSY,	/* Reject with BUSY */
 	RXRPC_SKB_MARK_REJECT_ABORT,	/* Reject with ABORT (code in skb->priority) */
@@ -146,10 +148,12 @@ struct rxrpc_backlog {
 struct rxrpc_sock {
 	/* WARNING: sk has to be the first member */
 	struct sock		sk;
-	rxrpc_notify_new_call_t	notify_new_call; /* Func to notify of new call */
-	rxrpc_discard_new_call_t discard_new_call; /* Func to discard a new call */
+	const struct rxrpc_kernel_ops *app_ops;	/* Table of kernel app notification funcs */
 	struct rxrpc_local	*local;		/* local endpoint */
 	struct rxrpc_backlog	*backlog;	/* Preallocation for services */
+	struct sk_buff_head	recvmsg_oobq;	/* OOB messages for recvmsg to pick up */
+	struct rb_root		pending_oobq;	/* OOB messages awaiting userspace to respond to */
+	u64			oob_id_counter;	/* OOB message ID counter */
 	spinlock_t		incoming_lock;	/* Incoming call vs service shutdown lock */
 	struct list_head	sock_calls;	/* List of calls owned by this socket */
 	struct list_head	to_be_accepted;	/* calls awaiting acceptance */
@@ -160,6 +164,7 @@ struct rxrpc_sock {
 	struct rb_root		calls;		/* User ID -> call mapping */
 	unsigned long		flags;
 #define RXRPC_SOCK_CONNECTED		0	/* connect_srx is set */
+#define RXRPC_SOCK_MANAGE_RESPONSE	1	/* User wants to manage RESPONSE packets */
 	rwlock_t		call_lock;	/* lock for calls */
 	u32			min_sec_level;	/* minimum security level */
 #define RXRPC_SECURITY_MAX	RXRPC_SECURITY_ENCRYPT
@@ -203,7 +208,7 @@ struct rxrpc_host_header {
  */
 struct rxrpc_skb_priv {
 	union {
-		struct rxrpc_connection *conn;	/* Connection referred to (poke packet) */
+		struct rxrpc_connection *poke_conn;	/* Conn referred to (poke packet) */
 		struct {
 			u16		offset;		/* Offset of data */
 			u16		len;		/* Length of data */
@@ -217,6 +222,19 @@ struct rxrpc_skb_priv {
 			u16		nr_acks;	/* Number of acks+nacks */
 			u8		reason;		/* Reason for ack */
 		} ack;
+		struct {
+			struct rxrpc_connection *conn;	/* Connection referred to */
+			union {
+				u32 rxkad_nonce;
+			};
+		} chall;
+		struct {
+			rxrpc_serial_t	challenge_serial;
+			u32		kvno;
+			u32		version;
+			u16		len;
+			u16		ticket_len;
+		} resp;
 	};
 	struct rxrpc_host_header hdr;	/* RxRPC packet header from this packet */
 };
@@ -270,9 +288,24 @@ struct rxrpc_security {
 	/* issue a challenge */
 	int (*issue_challenge)(struct rxrpc_connection *);
 
+	/* Validate a challenge packet */
+	bool (*validate_challenge)(struct rxrpc_connection *conn,
+				   struct sk_buff *skb);
+
+	/* Fill out the cmsg for recvmsg() to pass on a challenge to userspace.
+	 * The security class gets to add additional information.
+	 */
+	int (*challenge_to_recvmsg)(struct rxrpc_connection *conn,
+				    struct sk_buff *challenge,
+				    struct msghdr *msg);
+
+	/* Parse sendmsg() control message and respond to challenge. */
+	int (*sendmsg_respond_to_challenge)(struct sk_buff *challenge,
+					    struct msghdr *msg);
+
 	/* respond to a challenge */
-	int (*respond_to_challenge)(struct rxrpc_connection *,
-				    struct sk_buff *);
+	int (*respond_to_challenge)(struct rxrpc_connection *conn,
+				    struct sk_buff *challenge);
 
 	/* verify a response */
 	int (*verify_response)(struct rxrpc_connection *,
@@ -280,6 +313,11 @@ struct rxrpc_security {
 
 	/* clear connection security */
 	void (*clear)(struct rxrpc_connection *);
+
+	/* Default ticket -> key decoder */
+	int (*default_decode_ticket)(struct rxrpc_connection *conn, struct sk_buff *skb,
+				     unsigned int ticket_offset, unsigned int ticket_len,
+				     struct key **_key);
 };
 
 /*
@@ -526,7 +564,17 @@ struct rxrpc_connection {
 			struct rxrpc_crypt csum_iv;	/* packet checksum base */
 			u32	nonce;		/* response re-use preventer */
 		} rxkad;
+		struct {
+			struct rxgk_context *keys[4]; /* (Re-)keying buffer */
+			u64	start_time;	/* The start time for TK derivation */
+			u8	nonce[20];	/* Response re-use preventer */
+			u32	enctype;	/* Kerberos 5 encoding type */
+			u32	key_number;	/* Current key number */
+		} rxgk;
 	};
+	rwlock_t		security_use_lock; /* Security use/modification lock */
+	struct sk_buff		*tx_response;	/* Response packet to be transmitted */
+
 	unsigned long		flags;
 	unsigned long		events;
 	unsigned long		idle_timestamp;	/* Time at which last became idle */
@@ -692,6 +740,7 @@ struct rxrpc_call {
 	u32			call_id;	/* call ID on connection  */
 	u32			cid;		/* connection ID plus channel index */
 	u32			security_level;	/* Security level selected */
+	u32			security_enctype; /* Security-specific encoding type (or 0) */
 	int			debug_id;	/* debug ID for printks */
 	unsigned short		rx_pkt_offset;	/* Current recvmsg packet offset */
 	unsigned short		rx_pkt_len;	/* Current recvmsg packet len */
@@ -867,6 +916,8 @@ struct rxrpc_txbuf {
 	unsigned short		len;		/* Amount of data in buffer */
 	unsigned short		space;		/* Remaining data space */
 	unsigned short		offset;		/* Offset of fill point */
+	unsigned short		crypto_header;	/* Size of crypto header */
+	unsigned short		sec_header;	/* Size of security header */
 	unsigned short		pkt_len;	/* Size of packet content */
 	unsigned short		alloc_size;	/* Amount of bufferage allocated */
 	unsigned int		flags;
@@ -1001,7 +1052,9 @@ struct rxrpc_call *rxrpc_alloc_call(struct rxrpc_sock *, gfp_t, unsigned int);
 struct rxrpc_call *rxrpc_new_client_call(struct rxrpc_sock *,
 					 struct rxrpc_conn_parameters *,
 					 struct rxrpc_call_params *, gfp_t,
-					 unsigned int);
+					 unsigned int)
+	__releases(&rx->sk.sk_lock)
+	__acquires(&call->user_mutex);
 void rxrpc_start_call_timer(struct rxrpc_call *call);
 void rxrpc_incoming_call(struct rxrpc_sock *, struct rxrpc_call *,
 			 struct sk_buff *);
@@ -1198,8 +1251,11 @@ void rxrpc_error_report(struct sock *);
 bool rxrpc_direct_abort(struct sk_buff *skb, enum rxrpc_abort_reason why,
 			s32 abort_code, int err);
 int rxrpc_io_thread(void *data);
+void rxrpc_post_response(struct rxrpc_connection *conn, struct sk_buff *skb);
 static inline void rxrpc_wake_up_io_thread(struct rxrpc_local *local)
 {
+	if (!local->io_thread)
+		return;
 	wake_up_process(READ_ONCE(local->io_thread));
 }
 
@@ -1289,8 +1345,16 @@ static inline struct rxrpc_net *rxrpc_net(struct net *net)
 }
 
 /*
+ * out_of_band.c
+ */
+void rxrpc_notify_socket_oob(struct rxrpc_call *call, struct sk_buff *skb);
+void rxrpc_add_pending_oob(struct rxrpc_sock *rx, struct sk_buff *skb);
+int rxrpc_sendmsg_oob(struct rxrpc_sock *rx, struct msghdr *msg, size_t len);
+
+/*
  * output.c
  */
+ssize_t do_udp_sendmsg(struct socket *socket, struct msghdr *msg, size_t len);
 void rxrpc_send_ACK(struct rxrpc_call *call, u8 ack_reason,
 		    rxrpc_serial_t serial, enum rxrpc_propose_ack_trace why);
 void rxrpc_send_probe_for_pmtud(struct rxrpc_call *call);
@@ -1299,6 +1363,7 @@ void rxrpc_send_data_packet(struct rxrpc_call *call, struct rxrpc_send_data_req
 void rxrpc_send_conn_abort(struct rxrpc_connection *conn);
 void rxrpc_reject_packet(struct rxrpc_local *local, struct sk_buff *skb);
 void rxrpc_send_keepalive(struct rxrpc_peer *);
+void rxrpc_send_response(struct rxrpc_connection *conn, struct sk_buff *skb);
 
 /*
  * peer_event.c
@@ -1363,6 +1428,11 @@ ktime_t rxrpc_get_rto_backoff(struct rxrpc_call *call, bool retrans);
 void rxrpc_call_init_rtt(struct rxrpc_call *call);
 
 /*
+ * rxgk.c
+ */
+extern const struct rxrpc_security rxgk_yfs;
+
+/*
  * rxkad.c
  */
 #ifdef CONFIG_RXKAD
diff --git a/net/rxrpc/call_accept.c b/net/rxrpc/call_accept.c
index e685034ce4f7..a4b363b47cca 100644
--- a/net/rxrpc/call_accept.c
+++ b/net/rxrpc/call_accept.c
@@ -34,7 +34,6 @@ static void rxrpc_dummy_notify(struct sock *sk, struct rxrpc_call *call,
 static int rxrpc_service_prealloc_one(struct rxrpc_sock *rx,
 				      struct rxrpc_backlog *b,
 				      rxrpc_notify_rx_t notify_rx,
-				      rxrpc_user_attach_call_t user_attach_call,
 				      unsigned long user_call_ID, gfp_t gfp,
 				      unsigned int debug_id)
 {
@@ -123,9 +122,10 @@ static int rxrpc_service_prealloc_one(struct rxrpc_sock *rx,
 
 	call->user_call_ID = user_call_ID;
 	call->notify_rx = notify_rx;
-	if (user_attach_call) {
+	if (rx->app_ops &&
+	    rx->app_ops->user_attach_call) {
 		rxrpc_get_call(call, rxrpc_call_get_kernel_service);
-		user_attach_call(call, user_call_ID);
+		rx->app_ops->user_attach_call(call, user_call_ID);
 	}
 
 	rxrpc_get_call(call, rxrpc_call_get_userid);
@@ -219,9 +219,10 @@ void rxrpc_discard_prealloc(struct rxrpc_sock *rx)
 	while (CIRC_CNT(head, tail, size) > 0) {
 		struct rxrpc_call *call = b->call_backlog[tail];
 		rcu_assign_pointer(call->socket, rx);
-		if (rx->discard_new_call) {
+		if (rx->app_ops &&
+		    rx->app_ops->discard_new_call) {
 			_debug("discard %lx", call->user_call_ID);
-			rx->discard_new_call(call, call->user_call_ID);
+			rx->app_ops->discard_new_call(call, call->user_call_ID);
 			if (call->notify_rx)
 				call->notify_rx = rxrpc_dummy_notify;
 			rxrpc_put_call(call, rxrpc_call_put_kernel);
@@ -387,8 +388,9 @@ bool rxrpc_new_incoming_call(struct rxrpc_local *local,
 	rxrpc_incoming_call(rx, call, skb);
 	conn = call->conn;
 
-	if (rx->notify_new_call)
-		rx->notify_new_call(&rx->sk, call, call->user_call_ID);
+	if (rx->app_ops &&
+	    rx->app_ops->notify_new_call)
+		rx->app_ops->notify_new_call(&rx->sk, call, call->user_call_ID);
 
 	spin_lock(&conn->state_lock);
 	if (conn->state == RXRPC_CONN_SERVICE_UNSECURED) {
@@ -440,8 +442,7 @@ int rxrpc_user_charge_accept(struct rxrpc_sock *rx, unsigned long user_call_ID)
 	if (rx->sk.sk_state == RXRPC_CLOSE)
 		return -ESHUTDOWN;
 
-	return rxrpc_service_prealloc_one(rx, b, NULL, NULL, user_call_ID,
-					  GFP_KERNEL,
+	return rxrpc_service_prealloc_one(rx, b, NULL, user_call_ID, GFP_KERNEL,
 					  atomic_inc_return(&rxrpc_debug_id));
 }
 
@@ -449,20 +450,18 @@ int rxrpc_user_charge_accept(struct rxrpc_sock *rx, unsigned long user_call_ID)
  * rxrpc_kernel_charge_accept - Charge up socket with preallocated calls
  * @sock: The socket on which to preallocate
  * @notify_rx: Event notification function for the call
- * @user_attach_call: Func to attach call to user_call_ID
  * @user_call_ID: The tag to attach to the preallocated call
  * @gfp: The allocation conditions.
  * @debug_id: The tracing debug ID.
  *
- * Charge up the socket with preallocated calls, each with a user ID.  A
- * function should be provided to effect the attachment from the user's side.
- * The user is given a ref to hold on the call.
+ * Charge up the socket with preallocated calls, each with a user ID.  The
+ * ->user_attach_call() callback function should be provided to effect the
+ * attachment from the user's side.  The user is given a ref to hold on the
+ * call.
  *
  * Note that the call may be come connected before this function returns.
  */
-int rxrpc_kernel_charge_accept(struct socket *sock,
-			       rxrpc_notify_rx_t notify_rx,
-			       rxrpc_user_attach_call_t user_attach_call,
+int rxrpc_kernel_charge_accept(struct socket *sock, rxrpc_notify_rx_t notify_rx,
 			       unsigned long user_call_ID, gfp_t gfp,
 			       unsigned int debug_id)
 {
@@ -472,8 +471,7 @@ int rxrpc_kernel_charge_accept(struct socket *sock,
 	if (sock->sk->sk_state == RXRPC_CLOSE)
 		return -ESHUTDOWN;
 
-	return rxrpc_service_prealloc_one(rx, b, notify_rx,
-					  user_attach_call, user_call_ID,
+	return rxrpc_service_prealloc_one(rx, b, notify_rx, user_call_ID,
 					  gfp, debug_id);
 }
 EXPORT_SYMBOL(rxrpc_kernel_charge_accept);
diff --git a/net/rxrpc/call_object.c b/net/rxrpc/call_object.c
index fce58be65e7c..e9e8f0ef3fd5 100644
--- a/net/rxrpc/call_object.c
+++ b/net/rxrpc/call_object.c
@@ -145,8 +145,8 @@ struct rxrpc_call *rxrpc_alloc_call(struct rxrpc_sock *rx, gfp_t gfp,
 	INIT_LIST_HEAD(&call->recvmsg_link);
 	INIT_LIST_HEAD(&call->sock_link);
 	INIT_LIST_HEAD(&call->attend_link);
-	skb_queue_head_init(&call->rx_queue);
 	skb_queue_head_init(&call->recvmsg_queue);
+	skb_queue_head_init(&call->rx_queue);
 	skb_queue_head_init(&call->rx_oos_queue);
 	init_waitqueue_head(&call->waitq);
 	spin_lock_init(&call->notify_lock);
@@ -322,7 +322,7 @@ struct rxrpc_call *rxrpc_new_client_call(struct rxrpc_sock *rx,
 					 struct rxrpc_call_params *p,
 					 gfp_t gfp,
 					 unsigned int debug_id)
-	__releases(&rx->sk.sk_lock.slock)
+	__releases(&rx->sk.sk_lock)
 	__acquires(&call->user_mutex)
 {
 	struct rxrpc_call *call, *xcall;
@@ -760,3 +760,23 @@ void rxrpc_destroy_all_calls(struct rxrpc_net *rxnet)
 	atomic_dec(&rxnet->nr_calls);
 	wait_var_event(&rxnet->nr_calls, !atomic_read(&rxnet->nr_calls));
 }
+
+/**
+ * rxrpc_kernel_query_call_security - Query call's security parameters
+ * @call: The call to query
+ * @_service_id: Where to return the service ID
+ * @_enctype: Where to return the "encoding type"
+ *
+ * This queries the security parameters of a call, setting *@_service_id and
+ * *@_enctype and returning the security class.
+ *
+ * Return: The security class protocol number.
+ */
+u8 rxrpc_kernel_query_call_security(struct rxrpc_call *call,
+				    u16 *_service_id, u32 *_enctype)
+{
+	*_service_id = call->dest_srx.srx_service;
+	*_enctype = call->security_enctype;
+	return call->security_ix;
+}
+EXPORT_SYMBOL(rxrpc_kernel_query_call_security);
diff --git a/net/rxrpc/conn_event.c b/net/rxrpc/conn_event.c
index 4d9c5e21ba78..232b6986da83 100644
--- a/net/rxrpc/conn_event.c
+++ b/net/rxrpc/conn_event.c
@@ -19,7 +19,7 @@
 /*
  * Set the completion state on an aborted connection.
  */
-static bool rxrpc_set_conn_aborted(struct rxrpc_connection *conn, struct sk_buff *skb,
+static bool rxrpc_set_conn_aborted(struct rxrpc_connection *conn,
 				   s32 abort_code, int err,
 				   enum rxrpc_call_completion compl)
 {
@@ -49,12 +49,20 @@ static bool rxrpc_set_conn_aborted(struct rxrpc_connection *conn, struct sk_buff
 int rxrpc_abort_conn(struct rxrpc_connection *conn, struct sk_buff *skb,
 		     s32 abort_code, int err, enum rxrpc_abort_reason why)
 {
-	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
 
-	if (rxrpc_set_conn_aborted(conn, skb, abort_code, err,
+	u32 cid = conn->proto.cid, call = 0, seq = 0;
+
+	if (skb) {
+		struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+
+		cid  = sp->hdr.cid;
+		call = sp->hdr.callNumber;
+		seq  = sp->hdr.seq;
+	}
+
+	if (rxrpc_set_conn_aborted(conn, abort_code, err,
 				   RXRPC_CALL_LOCALLY_ABORTED)) {
-		trace_rxrpc_abort(0, why, sp->hdr.cid, sp->hdr.callNumber,
-				  sp->hdr.seq, abort_code, err);
+		trace_rxrpc_abort(0, why, cid, call, seq, abort_code, err);
 		rxrpc_poke_conn(conn, rxrpc_conn_get_poke_abort);
 	}
 	return -EPROTO;
@@ -67,7 +75,7 @@ static void rxrpc_input_conn_abort(struct rxrpc_connection *conn,
 				   struct sk_buff *skb)
 {
 	trace_rxrpc_rx_conn_abort(conn, skb);
-	rxrpc_set_conn_aborted(conn, skb, skb->priority, -ECONNABORTED,
+	rxrpc_set_conn_aborted(conn, skb->priority, -ECONNABORTED,
 			       RXRPC_CALL_REMOTELY_ABORTED);
 }
 
@@ -248,7 +256,10 @@ static int rxrpc_process_event(struct rxrpc_connection *conn,
 
 	switch (sp->hdr.type) {
 	case RXRPC_PACKET_TYPE_CHALLENGE:
-		return conn->security->respond_to_challenge(conn, skb);
+		ret = conn->security->respond_to_challenge(conn, skb);
+		sp->chall.conn = NULL;
+		rxrpc_put_connection(conn, rxrpc_conn_put_challenge_input);
+		return ret;
 
 	case RXRPC_PACKET_TYPE_RESPONSE:
 		ret = conn->security->verify_response(conn, skb);
@@ -270,7 +281,8 @@ static int rxrpc_process_event(struct rxrpc_connection *conn,
 			 * we've already received the packet, put it on the
 			 * front of the queue.
 			 */
-			sp->conn = rxrpc_get_connection(conn, rxrpc_conn_get_poke_secured);
+			sp->poke_conn = rxrpc_get_connection(
+				conn, rxrpc_conn_get_poke_secured);
 			skb->mark = RXRPC_SKB_MARK_SERVICE_CONN_SECURED;
 			rxrpc_get_skb(skb, rxrpc_skb_get_conn_secured);
 			skb_queue_head(&conn->local->rx_queue, skb);
@@ -392,6 +404,61 @@ static void rxrpc_post_packet_to_conn(struct rxrpc_connection *conn,
 }
 
 /*
+ * Post a CHALLENGE packet to the socket of one of a connection's calls so that
+ * it can get application data to include in the packet, possibly querying
+ * userspace.
+ */
+static bool rxrpc_post_challenge(struct rxrpc_connection *conn,
+				 struct sk_buff *skb)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+	struct rxrpc_call *call = NULL;
+	struct rxrpc_sock *rx;
+	bool respond = false;
+
+	sp->chall.conn =
+		rxrpc_get_connection(conn, rxrpc_conn_get_challenge_input);
+
+	if (!conn->security->challenge_to_recvmsg) {
+		rxrpc_post_packet_to_conn(conn, skb);
+		return true;
+	}
+
+	rcu_read_lock();
+
+	for (int i = 0; i < ARRAY_SIZE(conn->channels); i++) {
+		if (conn->channels[i].call) {
+			call = conn->channels[i].call;
+			rx = rcu_dereference(call->socket);
+			if (!rx) {
+				call = NULL;
+				continue;
+			}
+
+			respond = true;
+			if (test_bit(RXRPC_SOCK_MANAGE_RESPONSE, &rx->flags))
+				break;
+			call = NULL;
+		}
+	}
+
+	if (!respond) {
+		rcu_read_unlock();
+		rxrpc_put_connection(conn, rxrpc_conn_put_challenge_input);
+		sp->chall.conn = NULL;
+		return false;
+	}
+
+	if (call)
+		rxrpc_notify_socket_oob(call, skb);
+	rcu_read_unlock();
+
+	if (!call)
+		rxrpc_post_packet_to_conn(conn, skb);
+	return true;
+}
+
+/*
  * Input a connection-level packet.
  */
 bool rxrpc_input_conn_packet(struct rxrpc_connection *conn, struct sk_buff *skb)
@@ -411,6 +478,16 @@ bool rxrpc_input_conn_packet(struct rxrpc_connection *conn, struct sk_buff *skb)
 		return true;
 
 	case RXRPC_PACKET_TYPE_CHALLENGE:
+		rxrpc_see_skb(skb, rxrpc_skb_see_oob_challenge);
+		if (rxrpc_is_conn_aborted(conn)) {
+			if (conn->completion == RXRPC_CALL_LOCALLY_ABORTED)
+				rxrpc_send_conn_abort(conn);
+			return true;
+		}
+		if (!conn->security->validate_challenge(conn, skb))
+			return false;
+		return rxrpc_post_challenge(conn, skb);
+
 	case RXRPC_PACKET_TYPE_RESPONSE:
 		if (rxrpc_is_conn_aborted(conn)) {
 			if (conn->completion == RXRPC_CALL_LOCALLY_ABORTED)
@@ -436,6 +513,19 @@ void rxrpc_input_conn_event(struct rxrpc_connection *conn, struct sk_buff *skb)
 	if (test_and_clear_bit(RXRPC_CONN_EV_ABORT_CALLS, &conn->events))
 		rxrpc_abort_calls(conn);
 
+	if (conn->tx_response) {
+		struct sk_buff *skb;
+
+		spin_lock_irq(&conn->local->lock);
+		skb = conn->tx_response;
+		conn->tx_response = NULL;
+		spin_unlock_irq(&conn->local->lock);
+
+		if (conn->state != RXRPC_CONN_ABORTED)
+			rxrpc_send_response(conn, skb);
+		rxrpc_free_skb(skb, rxrpc_skb_put_response);
+	}
+
 	if (skb) {
 		switch (skb->mark) {
 		case RXRPC_SKB_MARK_SERVICE_CONN_SECURED:
@@ -452,3 +542,31 @@ void rxrpc_input_conn_event(struct rxrpc_connection *conn, struct sk_buff *skb)
 	if (conn->flags & RXRPC_CONN_FINAL_ACK_MASK)
 		rxrpc_process_delayed_final_acks(conn, false);
 }
+
+/*
+ * Post a RESPONSE message to the I/O thread for transmission.
+ */
+void rxrpc_post_response(struct rxrpc_connection *conn, struct sk_buff *skb)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+	struct rxrpc_local *local = conn->local;
+	struct sk_buff *old;
+
+	_enter("%x", sp->resp.challenge_serial);
+
+	spin_lock_irq(&local->lock);
+	old = conn->tx_response;
+	if (old) {
+		struct rxrpc_skb_priv *osp = rxrpc_skb(skb);
+
+		/* Always go with the response to the most recent challenge. */
+		if (after(sp->resp.challenge_serial, osp->resp.challenge_serial))
+			conn->tx_response = old;
+		else
+			old = skb;
+	} else {
+		conn->tx_response = skb;
+	}
+	spin_unlock_irq(&local->lock);
+	rxrpc_poke_conn(conn, rxrpc_conn_get_poke_response);
+}
diff --git a/net/rxrpc/conn_object.c b/net/rxrpc/conn_object.c
index 8ac22dde8b39..37340becb224 100644
--- a/net/rxrpc/conn_object.c
+++ b/net/rxrpc/conn_object.c
@@ -73,6 +73,7 @@ struct rxrpc_connection *rxrpc_alloc_connection(struct rxrpc_net *rxnet,
 		skb_queue_head_init(&conn->rx_queue);
 		conn->rxnet = rxnet;
 		conn->security = &rxrpc_no_security;
+		rwlock_init(&conn->security_use_lock);
 		spin_lock_init(&conn->state_lock);
 		conn->debug_id = atomic_inc_return(&rxrpc_debug_id);
 		conn->idle_timestamp = jiffies;
@@ -329,6 +330,7 @@ static void rxrpc_clean_up_connection(struct work_struct *work)
 	}
 
 	rxrpc_purge_queue(&conn->rx_queue);
+	rxrpc_free_skb(conn->tx_response, rxrpc_skb_put_response);
 
 	rxrpc_kill_client_conn(conn);
 
diff --git a/net/rxrpc/insecure.c b/net/rxrpc/insecure.c
index e068f9b79d02..1f7c136d6d0e 100644
--- a/net/rxrpc/insecure.c
+++ b/net/rxrpc/insecure.c
@@ -42,13 +42,19 @@ static void none_free_call_crypto(struct rxrpc_call *call)
 {
 }
 
-static int none_respond_to_challenge(struct rxrpc_connection *conn,
-				     struct sk_buff *skb)
+static bool none_validate_challenge(struct rxrpc_connection *conn,
+				    struct sk_buff *skb)
 {
 	return rxrpc_abort_conn(conn, skb, RX_PROTOCOL_ERROR, -EPROTO,
 				rxrpc_eproto_rxnull_challenge);
 }
 
+static int none_sendmsg_respond_to_challenge(struct sk_buff *challenge,
+					     struct msghdr *msg)
+{
+	return -EINVAL;
+}
+
 static int none_verify_response(struct rxrpc_connection *conn,
 				struct sk_buff *skb)
 {
@@ -82,7 +88,8 @@ const struct rxrpc_security rxrpc_no_security = {
 	.alloc_txbuf			= none_alloc_txbuf,
 	.secure_packet			= none_secure_packet,
 	.verify_packet			= none_verify_packet,
-	.respond_to_challenge		= none_respond_to_challenge,
+	.validate_challenge		= none_validate_challenge,
+	.sendmsg_respond_to_challenge	= none_sendmsg_respond_to_challenge,
 	.verify_response		= none_verify_response,
 	.clear				= none_clear,
 };
diff --git a/net/rxrpc/io_thread.c b/net/rxrpc/io_thread.c
index 64f8d77b8731..27b650d30f4d 100644
--- a/net/rxrpc/io_thread.c
+++ b/net/rxrpc/io_thread.c
@@ -489,8 +489,8 @@ int rxrpc_io_thread(void *data)
 				rxrpc_free_skb(skb, rxrpc_skb_put_error_report);
 				break;
 			case RXRPC_SKB_MARK_SERVICE_CONN_SECURED:
-				rxrpc_input_conn_event(sp->conn, skb);
-				rxrpc_put_connection(sp->conn, rxrpc_conn_put_poke);
+				rxrpc_input_conn_event(sp->poke_conn, skb);
+				rxrpc_put_connection(sp->poke_conn, rxrpc_conn_put_poke);
 				rxrpc_free_skb(skb, rxrpc_skb_put_conn_secured);
 				break;
 			default:
@@ -501,9 +501,11 @@ int rxrpc_io_thread(void *data)
 		}
 
 		/* Deal with connections that want immediate attention. */
-		spin_lock_irq(&local->lock);
-		list_splice_tail_init(&local->conn_attend_q, &conn_attend_q);
-		spin_unlock_irq(&local->lock);
+		if (!list_empty_careful(&local->conn_attend_q)) {
+			spin_lock_irq(&local->lock);
+			list_splice_tail_init(&local->conn_attend_q, &conn_attend_q);
+			spin_unlock_irq(&local->lock);
+		}
 
 		while ((conn = list_first_entry_or_null(&conn_attend_q,
 							struct rxrpc_connection,
diff --git a/net/rxrpc/key.c b/net/rxrpc/key.c
index 33e8302a79e3..9fdc1f031c9d 100644
--- a/net/rxrpc/key.c
+++ b/net/rxrpc/key.c
@@ -129,6 +129,160 @@ static int rxrpc_preparse_xdr_rxkad(struct key_preparsed_payload *prep,
 	return 0;
 }
 
+static u64 xdr_dec64(const __be32 *xdr)
+{
+	return (u64)ntohl(xdr[0]) << 32 | (u64)ntohl(xdr[1]);
+}
+
+static time64_t rxrpc_s64_to_time64(s64 time_in_100ns)
+{
+	bool neg = false;
+	u64 tmp = time_in_100ns;
+
+	if (time_in_100ns < 0) {
+		tmp = -time_in_100ns;
+		neg = true;
+	}
+	do_div(tmp, 10000000);
+	return neg ? -tmp : tmp;
+}
+
+/*
+ * Parse a YFS-RxGK type XDR format token
+ * - the caller guarantees we have at least 4 words
+ *
+ * struct token_rxgk {
+ *	opr_time begintime;
+ *	opr_time endtime;
+ *	afs_int64 level;
+ *	afs_int64 lifetime;
+ *	afs_int64 bytelife;
+ *	afs_int64 enctype;
+ *	opaque key<>;
+ *	opaque ticket<>;
+ * };
+ */
+static int rxrpc_preparse_xdr_yfs_rxgk(struct key_preparsed_payload *prep,
+				       size_t datalen,
+				       const __be32 *xdr, unsigned int toklen)
+{
+	struct rxrpc_key_token *token, **pptoken;
+	time64_t expiry;
+	size_t plen;
+	const __be32 *ticket, *key;
+	s64 tmp;
+	u32 tktlen, keylen;
+
+	_enter(",{%x,%x,%x,%x},%x",
+	       ntohl(xdr[0]), ntohl(xdr[1]), ntohl(xdr[2]), ntohl(xdr[3]),
+	       toklen);
+
+	if (6 * 2 + 2 > toklen / 4)
+		goto reject;
+
+	key = xdr + (6 * 2 + 1);
+	keylen = ntohl(key[-1]);
+	_debug("keylen: %x", keylen);
+	keylen = round_up(keylen, 4);
+	if ((6 * 2 + 2) * 4 + keylen > toklen)
+		goto reject;
+
+	ticket = xdr + (6 * 2 + 1 + (keylen / 4) + 1);
+	tktlen = ntohl(ticket[-1]);
+	_debug("tktlen: %x", tktlen);
+	tktlen = round_up(tktlen, 4);
+	if ((6 * 2 + 2) * 4 + keylen + tktlen != toklen) {
+		kleave(" = -EKEYREJECTED [%x!=%x, %x,%x]",
+		       (6 * 2 + 2) * 4 + keylen + tktlen, toklen,
+		       keylen, tktlen);
+		goto reject;
+	}
+
+	plen = sizeof(*token) + sizeof(*token->rxgk) + tktlen + keylen;
+	prep->quotalen = datalen + plen;
+
+	plen -= sizeof(*token);
+	token = kzalloc(sizeof(*token), GFP_KERNEL);
+	if (!token)
+		goto nomem;
+
+	token->rxgk = kzalloc(sizeof(*token->rxgk) + keylen, GFP_KERNEL);
+	if (!token->rxgk)
+		goto nomem_token;
+
+	token->security_index	= RXRPC_SECURITY_YFS_RXGK;
+	token->rxgk->begintime	= xdr_dec64(xdr + 0 * 2);
+	token->rxgk->endtime	= xdr_dec64(xdr + 1 * 2);
+	token->rxgk->level	= tmp = xdr_dec64(xdr + 2 * 2);
+	if (tmp < -1LL || tmp > RXRPC_SECURITY_ENCRYPT)
+		goto reject_token;
+	token->rxgk->lifetime	= xdr_dec64(xdr + 3 * 2);
+	token->rxgk->bytelife	= xdr_dec64(xdr + 4 * 2);
+	token->rxgk->enctype	= tmp = xdr_dec64(xdr + 5 * 2);
+	if (tmp < 0 || tmp > UINT_MAX)
+		goto reject_token;
+	token->rxgk->key.len	= ntohl(key[-1]);
+	token->rxgk->key.data	= token->rxgk->_key;
+	token->rxgk->ticket.len = ntohl(ticket[-1]);
+
+	if (token->rxgk->endtime != 0) {
+		expiry = rxrpc_s64_to_time64(token->rxgk->endtime);
+		if (expiry < 0)
+			goto expired;
+		if (expiry < prep->expiry)
+			prep->expiry = expiry;
+	}
+
+	memcpy(token->rxgk->key.data, key, token->rxgk->key.len);
+
+	/* Pad the ticket so that we can use it directly in XDR */
+	token->rxgk->ticket.data = kzalloc(round_up(token->rxgk->ticket.len, 4),
+					   GFP_KERNEL);
+	if (!token->rxgk->ticket.data)
+		goto nomem_yrxgk;
+	memcpy(token->rxgk->ticket.data, ticket, token->rxgk->ticket.len);
+
+	_debug("SCIX: %u",	token->security_index);
+	_debug("EXPY: %llx",	token->rxgk->endtime);
+	_debug("LIFE: %llx",	token->rxgk->lifetime);
+	_debug("BYTE: %llx",	token->rxgk->bytelife);
+	_debug("ENC : %u",	token->rxgk->enctype);
+	_debug("LEVL: %u",	token->rxgk->level);
+	_debug("KLEN: %u",	token->rxgk->key.len);
+	_debug("TLEN: %u",	token->rxgk->ticket.len);
+	_debug("KEY0: %*phN",	token->rxgk->key.len, token->rxgk->key.data);
+	_debug("TICK: %*phN",
+	       min_t(u32, token->rxgk->ticket.len, 32), token->rxgk->ticket.data);
+
+	/* count the number of tokens attached */
+	prep->payload.data[1] = (void *)((unsigned long)prep->payload.data[1] + 1);
+
+	/* attach the data */
+	for (pptoken = (struct rxrpc_key_token **)&prep->payload.data[0];
+	     *pptoken;
+	     pptoken = &(*pptoken)->next)
+		continue;
+	*pptoken = token;
+
+	_leave(" = 0");
+	return 0;
+
+nomem_yrxgk:
+	kfree(token->rxgk);
+nomem_token:
+	kfree(token);
+nomem:
+	return -ENOMEM;
+reject_token:
+	kfree(token);
+reject:
+	return -EKEYREJECTED;
+expired:
+	kfree(token->rxgk);
+	kfree(token);
+	return -EKEYEXPIRED;
+}
+
 /*
  * attempt to parse the data as the XDR format
  * - the caller guarantees we have more than 7 words
@@ -228,6 +382,9 @@ static int rxrpc_preparse_xdr(struct key_preparsed_payload *prep)
 		case RXRPC_SECURITY_RXKAD:
 			ret2 = rxrpc_preparse_xdr_rxkad(prep, datalen, token, toklen);
 			break;
+		case RXRPC_SECURITY_YFS_RXGK:
+			ret2 = rxrpc_preparse_xdr_yfs_rxgk(prep, datalen, token, toklen);
+			break;
 		default:
 			ret2 = -EPROTONOSUPPORT;
 			break;
@@ -390,6 +547,10 @@ static void rxrpc_free_token_list(struct rxrpc_key_token *token)
 		case RXRPC_SECURITY_RXKAD:
 			kfree(token->kad);
 			break;
+		case RXRPC_SECURITY_YFS_RXGK:
+			kfree(token->rxgk->ticket.data);
+			kfree(token->rxgk);
+			break;
 		default:
 			pr_err("Unknown token type %x on rxrpc key\n",
 			       token->security_index);
@@ -433,6 +594,9 @@ static void rxrpc_describe(const struct key *key, struct seq_file *m)
 		case RXRPC_SECURITY_RXKAD:
 			seq_puts(m, "ka");
 			break;
+		case RXRPC_SECURITY_YFS_RXGK:
+			seq_puts(m, "ygk");
+			break;
 		default: /* we have a ticket we can't encode */
 			seq_printf(m, "%u", token->security_index);
 			break;
@@ -531,6 +695,8 @@ EXPORT_SYMBOL(rxrpc_get_server_data_key);
  *
  * Generate a null RxRPC key that can be used to indicate anonymous security is
  * required for a particular domain.
+ *
+ * Return: The new key or a negative error code.
  */
 struct key *rxrpc_get_null_key(const char *keyname)
 {
@@ -595,6 +761,13 @@ static long rxrpc_read(const struct key *key,
 				toksize += RND(token->kad->ticket_len);
 			break;
 
+		case RXRPC_SECURITY_YFS_RXGK:
+			toksize += 6 * 8 + 2 * 4;
+			if (!token->no_leak_key)
+				toksize += RND(token->rxgk->key.len);
+			toksize += RND(token->rxgk->ticket.len);
+			break;
+
 		default: /* we have a ticket we can't encode */
 			pr_err("Unsupported key token type (%u)\n",
 			       token->security_index);
@@ -674,6 +847,20 @@ static long rxrpc_read(const struct key *key,
 				ENCODE_DATA(token->kad->ticket_len, token->kad->ticket);
 			break;
 
+		case RXRPC_SECURITY_YFS_RXGK:
+			ENCODE64(token->rxgk->begintime);
+			ENCODE64(token->rxgk->endtime);
+			ENCODE64(token->rxgk->level);
+			ENCODE64(token->rxgk->lifetime);
+			ENCODE64(token->rxgk->bytelife);
+			ENCODE64(token->rxgk->enctype);
+			if (token->no_leak_key)
+				ENCODE(0);
+			else
+				ENCODE_DATA(token->rxgk->key.len, token->rxgk->key.data);
+			ENCODE_DATA(token->rxgk->ticket.len, token->rxgk->ticket.data);
+			break;
+
 		default:
 			pr_err("Unsupported key token type (%u)\n",
 			       token->security_index);
diff --git a/net/rxrpc/oob.c b/net/rxrpc/oob.c
new file mode 100644
index 000000000000..05ca9c1faa57
--- /dev/null
+++ b/net/rxrpc/oob.c
@@ -0,0 +1,379 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Out of band message handling (e.g. challenge-response)
+ *
+ * Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/net.h>
+#include <linux/gfp.h>
+#include <linux/skbuff.h>
+#include <linux/export.h>
+#include <linux/sched/signal.h>
+#include <net/sock.h>
+#include <net/af_rxrpc.h>
+#include "ar-internal.h"
+
+enum rxrpc_oob_command {
+	RXRPC_OOB_CMD_UNSET,
+	RXRPC_OOB_CMD_RESPOND,
+} __mode(byte);
+
+struct rxrpc_oob_params {
+	u64			oob_id;		/* ID number of message if reply */
+	s32			abort_code;
+	enum rxrpc_oob_command	command;
+	bool			have_oob_id:1;
+};
+
+/*
+ * Post an out-of-band message for attention by the socket or kernel service
+ * associated with a reference call.
+ */
+void rxrpc_notify_socket_oob(struct rxrpc_call *call, struct sk_buff *skb)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+	struct rxrpc_sock *rx;
+	struct sock *sk;
+
+	rcu_read_lock();
+
+	rx = rcu_dereference(call->socket);
+	if (rx) {
+		sk = &rx->sk;
+		spin_lock_irq(&rx->recvmsg_lock);
+
+		if (sk->sk_state < RXRPC_CLOSE) {
+			skb->skb_mstamp_ns = rx->oob_id_counter++;
+			rxrpc_get_skb(skb, rxrpc_skb_get_post_oob);
+			skb_queue_tail(&rx->recvmsg_oobq, skb);
+
+			trace_rxrpc_notify_socket(call->debug_id, sp->hdr.serial);
+			if (rx->app_ops)
+				rx->app_ops->notify_oob(sk, skb);
+		}
+
+		spin_unlock_irq(&rx->recvmsg_lock);
+		if (!rx->app_ops && !sock_flag(sk, SOCK_DEAD))
+			sk->sk_data_ready(sk);
+	}
+
+	rcu_read_unlock();
+}
+
+/*
+ * Locate the OOB message to respond to by its ID.
+ */
+static struct sk_buff *rxrpc_find_pending_oob(struct rxrpc_sock *rx, u64 oob_id)
+{
+	struct rb_node *p;
+	struct sk_buff *skb;
+
+	p = rx->pending_oobq.rb_node;
+	while (p) {
+		skb = rb_entry(p, struct sk_buff, rbnode);
+
+		if (oob_id < skb->skb_mstamp_ns)
+			p = p->rb_left;
+		else if (oob_id > skb->skb_mstamp_ns)
+			p = p->rb_right;
+		else
+			return skb;
+	}
+
+	return NULL;
+}
+
+/*
+ * Add an OOB message into the pending-response set.  We always assign the next
+ * value from a 64-bit counter to the oob_id, so just assume we're always going
+ * to be on the right-hand edge of the tree and that the counter won't wrap.
+ * The tree is also given a ref to the message.
+ */
+void rxrpc_add_pending_oob(struct rxrpc_sock *rx, struct sk_buff *skb)
+{
+	struct rb_node **pp = &rx->pending_oobq.rb_node, *p = NULL;
+
+	while (*pp) {
+		p = *pp;
+		pp = &(*pp)->rb_right;
+	}
+
+	rb_link_node(&skb->rbnode, p, pp);
+	rb_insert_color(&skb->rbnode, &rx->pending_oobq);
+}
+
+/*
+ * Extract control messages from the sendmsg() control buffer.
+ */
+static int rxrpc_sendmsg_oob_cmsg(struct msghdr *msg, struct rxrpc_oob_params *p)
+{
+	struct cmsghdr *cmsg;
+	int len;
+
+	if (msg->msg_controllen == 0)
+		return -EINVAL;
+
+	for_each_cmsghdr(cmsg, msg) {
+		if (!CMSG_OK(msg, cmsg))
+			return -EINVAL;
+
+		len = cmsg->cmsg_len - sizeof(struct cmsghdr);
+		_debug("CMSG %d, %d, %d",
+		       cmsg->cmsg_level, cmsg->cmsg_type, len);
+
+		if (cmsg->cmsg_level != SOL_RXRPC)
+			continue;
+
+		switch (cmsg->cmsg_type) {
+		case RXRPC_OOB_ID:
+			if (len != sizeof(p->oob_id) || p->have_oob_id)
+				return -EINVAL;
+			memcpy(&p->oob_id, CMSG_DATA(cmsg), sizeof(p->oob_id));
+			p->have_oob_id = true;
+			break;
+		case RXRPC_RESPOND:
+			if (p->command != RXRPC_OOB_CMD_UNSET)
+				return -EINVAL;
+			p->command = RXRPC_OOB_CMD_RESPOND;
+			break;
+		case RXRPC_ABORT:
+			if (len != sizeof(p->abort_code) || p->abort_code)
+				return -EINVAL;
+			memcpy(&p->abort_code, CMSG_DATA(cmsg), sizeof(p->abort_code));
+			if (p->abort_code == 0)
+				return -EINVAL;
+			break;
+		case RXRPC_RESP_RXGK_APPDATA:
+			if (p->command != RXRPC_OOB_CMD_RESPOND)
+				return -EINVAL;
+			break;
+		default:
+			return -EINVAL;
+		}
+	}
+
+	switch (p->command) {
+	case RXRPC_OOB_CMD_RESPOND:
+		if (!p->have_oob_id)
+			return -EBADSLT;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/*
+ * Allow userspace to respond to an OOB using sendmsg().
+ */
+static int rxrpc_respond_to_oob(struct rxrpc_sock *rx,
+				struct rxrpc_oob_params *p,
+				struct msghdr *msg)
+{
+	struct rxrpc_connection *conn;
+	struct rxrpc_skb_priv *sp;
+	struct sk_buff *skb;
+	int ret;
+
+	skb = rxrpc_find_pending_oob(rx, p->oob_id);
+	if (skb)
+		rb_erase(&skb->rbnode, &rx->pending_oobq);
+	release_sock(&rx->sk);
+	if (!skb)
+		return -EBADSLT;
+
+	sp = rxrpc_skb(skb);
+
+	switch (p->command) {
+	case RXRPC_OOB_CMD_RESPOND:
+		ret = -EPROTO;
+		if (skb->mark != RXRPC_OOB_CHALLENGE)
+			break;
+		conn = sp->chall.conn;
+		ret = -EOPNOTSUPP;
+		if (!conn->security->sendmsg_respond_to_challenge)
+			break;
+		if (p->abort_code) {
+			rxrpc_abort_conn(conn, NULL, p->abort_code, -ECONNABORTED,
+					 rxrpc_abort_response_sendmsg);
+			ret = 0;
+		} else {
+			ret = conn->security->sendmsg_respond_to_challenge(skb, msg);
+		}
+		break;
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+	rxrpc_free_skb(skb, rxrpc_skb_put_oob);
+	return ret;
+}
+
+/*
+ * Send an out-of-band message or respond to a received out-of-band message.
+ * - caller gives us the socket lock
+ * - the socket may be either a client socket or a server socket
+ */
+int rxrpc_sendmsg_oob(struct rxrpc_sock *rx, struct msghdr *msg, size_t len)
+{
+	struct rxrpc_oob_params p = {};
+	int ret;
+
+	_enter("");
+
+	ret = rxrpc_sendmsg_oob_cmsg(msg, &p);
+	if (ret < 0)
+		goto error_release_sock;
+
+	if (p.have_oob_id)
+		return rxrpc_respond_to_oob(rx, &p, msg);
+
+	release_sock(&rx->sk);
+
+	switch (p.command) {
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+	_leave(" = %d", ret);
+	return ret;
+
+error_release_sock:
+	release_sock(&rx->sk);
+	return ret;
+}
+
+/**
+ * rxrpc_kernel_query_oob - Query the parameters of an out-of-band message
+ * @oob: The message to query
+ * @_peer: Where to return the peer record
+ * @_peer_appdata: The application data attached to a peer record
+ *
+ * Extract useful parameters from an out-of-band message.  The source peer
+ * parameters are returned through the argument list and the message type is
+ * returned.
+ *
+ * Return:
+ * * %RXRPC_OOB_CHALLENGE - Challenge wanting a response.
+ */
+enum rxrpc_oob_type rxrpc_kernel_query_oob(struct sk_buff *oob,
+					   struct rxrpc_peer **_peer,
+					   unsigned long *_peer_appdata)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(oob);
+	enum rxrpc_oob_type type = oob->mark;
+
+	switch (type) {
+	case RXRPC_OOB_CHALLENGE:
+		*_peer		= sp->chall.conn->peer;
+		*_peer_appdata	= sp->chall.conn->peer->app_data;
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		*_peer		= NULL;
+		*_peer_appdata	= 0;
+		break;
+	}
+
+	return type;
+}
+EXPORT_SYMBOL(rxrpc_kernel_query_oob);
+
+/**
+ * rxrpc_kernel_dequeue_oob - Dequeue and return the front OOB message
+ * @sock: The socket to query
+ * @_type: Where to return the message type
+ *
+ * Dequeue the front OOB message, if there is one, and return it and
+ * its type.
+ *
+ * Return: The sk_buff representing the OOB message or %NULL if the queue was
+ * empty.
+ */
+struct sk_buff *rxrpc_kernel_dequeue_oob(struct socket *sock,
+					 enum rxrpc_oob_type *_type)
+{
+	struct rxrpc_sock *rx = rxrpc_sk(sock->sk);
+	struct sk_buff *oob;
+
+	oob = skb_dequeue(&rx->recvmsg_oobq);
+	if (oob)
+		*_type = oob->mark;
+	return oob;
+}
+EXPORT_SYMBOL(rxrpc_kernel_dequeue_oob);
+
+/**
+ * rxrpc_kernel_free_oob - Free an out-of-band message
+ * @oob: The OOB message to free
+ *
+ * Free an OOB message along with any resources it holds.
+ */
+void rxrpc_kernel_free_oob(struct sk_buff *oob)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(oob);
+
+	switch (oob->mark) {
+	case RXRPC_OOB_CHALLENGE:
+		rxrpc_put_connection(sp->chall.conn, rxrpc_conn_put_oob);
+		break;
+	}
+
+	rxrpc_free_skb(oob, rxrpc_skb_put_purge_oob);
+}
+EXPORT_SYMBOL(rxrpc_kernel_free_oob);
+
+/**
+ * rxrpc_kernel_query_challenge - Query the parameters of a challenge
+ * @challenge: The challenge to query
+ * @_peer: Where to return the peer record
+ * @_peer_appdata: The application data attached to a peer record
+ * @_service_id: Where to return the connection service ID
+ * @_security_index: Where to return the connection security index
+ *
+ * Extract useful parameters from a CHALLENGE message.
+ */
+void rxrpc_kernel_query_challenge(struct sk_buff *challenge,
+				  struct rxrpc_peer **_peer,
+				  unsigned long *_peer_appdata,
+				  u16 *_service_id, u8 *_security_index)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(challenge);
+
+	*_peer		= sp->chall.conn->peer;
+	*_peer_appdata	= sp->chall.conn->peer->app_data;
+	*_service_id	= sp->hdr.serviceId;
+	*_security_index = sp->hdr.securityIndex;
+}
+EXPORT_SYMBOL(rxrpc_kernel_query_challenge);
+
+/**
+ * rxrpc_kernel_reject_challenge - Allow a kernel service to reject a challenge
+ * @challenge: The challenge to be rejected
+ * @abort_code: The abort code to stick into the ABORT packet
+ * @error: Local error value
+ * @why: Indication as to why.
+ *
+ * Allow a kernel service to reject a challenge by aborting the connection if
+ * it's still in an abortable state.  The error is returned so this function
+ * can be used with a return statement.
+ *
+ * Return: The %error parameter.
+ */
+int rxrpc_kernel_reject_challenge(struct sk_buff *challenge, u32 abort_code,
+				  int error, enum rxrpc_abort_reason why)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(challenge);
+
+	_enter("{%x},%d,%d,%u", sp->hdr.serial, abort_code, error, why);
+
+	rxrpc_abort_conn(sp->chall.conn, NULL, abort_code, error, why);
+	return error;
+}
+EXPORT_SYMBOL(rxrpc_kernel_reject_challenge);
diff --git a/net/rxrpc/output.c b/net/rxrpc/output.c
index 95905b85a8d7..0af19bcdc80a 100644
--- a/net/rxrpc/output.c
+++ b/net/rxrpc/output.c
@@ -18,7 +18,7 @@
 
 extern int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len);
 
-static ssize_t do_udp_sendmsg(struct socket *socket, struct msghdr *msg, size_t len)
+ssize_t do_udp_sendmsg(struct socket *socket, struct msghdr *msg, size_t len)
 {
 	struct sockaddr *sa = msg->msg_name;
 	struct sock *sk = socket->sk;
@@ -916,3 +916,61 @@ void rxrpc_send_keepalive(struct rxrpc_peer *peer)
 	peer->last_tx_at = ktime_get_seconds();
 	_leave("");
 }
+
+/*
+ * Send a RESPONSE message.
+ */
+void rxrpc_send_response(struct rxrpc_connection *conn, struct sk_buff *response)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(response);
+	struct scatterlist sg[16];
+	struct bio_vec bvec[16];
+	struct msghdr msg;
+	size_t len = sp->resp.len;
+	__be32 wserial;
+	u32 serial = 0;
+	int ret, nr_sg;
+
+	_enter("C=%x,%x", conn->debug_id, sp->resp.challenge_serial);
+
+	sg_init_table(sg, ARRAY_SIZE(sg));
+	ret = skb_to_sgvec(response, sg, 0, len);
+	if (ret < 0)
+		goto fail;
+	nr_sg = ret;
+
+	for (int i = 0; i < nr_sg; i++)
+		bvec_set_page(&bvec[i], sg_page(&sg[i]), sg[i].length, sg[i].offset);
+
+	iov_iter_bvec(&msg.msg_iter, WRITE, bvec, nr_sg, len);
+
+	msg.msg_name	= &conn->peer->srx.transport;
+	msg.msg_namelen	= conn->peer->srx.transport_len;
+	msg.msg_control	= NULL;
+	msg.msg_controllen = 0;
+	msg.msg_flags	= MSG_SPLICE_PAGES;
+
+	serial = rxrpc_get_next_serials(conn, 1);
+	wserial = htonl(serial);
+
+	trace_rxrpc_tx_response(conn, serial, sp);
+
+	ret = skb_store_bits(response, offsetof(struct rxrpc_wire_header, serial),
+			     &wserial, sizeof(wserial));
+	if (ret < 0)
+		goto fail;
+
+	rxrpc_local_dont_fragment(conn->local, false);
+
+	ret = do_udp_sendmsg(conn->local->socket, &msg, len);
+	if (ret < 0)
+		goto fail;
+
+	conn->peer->last_tx_at = ktime_get_seconds();
+	return;
+
+fail:
+	trace_rxrpc_tx_fail(conn->debug_id, serial, ret,
+			    rxrpc_tx_point_response);
+	kleave(" = %d", ret);
+}
diff --git a/net/rxrpc/peer_object.c b/net/rxrpc/peer_object.c
index 71b6e07bf161..e2f35e6c04d6 100644
--- a/net/rxrpc/peer_object.c
+++ b/net/rxrpc/peer_object.c
@@ -475,6 +475,8 @@ void rxrpc_destroy_all_peers(struct rxrpc_net *rxnet)
  * @call: The call to query
  *
  * Get a record for the remote peer in a call.
+ *
+ * Return: The call's peer record.
  */
 struct rxrpc_peer *rxrpc_kernel_get_call_peer(struct socket *sock, struct rxrpc_call *call)
 {
@@ -486,7 +488,9 @@ EXPORT_SYMBOL(rxrpc_kernel_get_call_peer);
  * rxrpc_kernel_get_srtt - Get a call's peer smoothed RTT
  * @peer: The peer to query
  *
- * Get the call's peer smoothed RTT in uS or UINT_MAX if we have no samples.
+ * Get the call's peer smoothed RTT.
+ *
+ * Return: The RTT in uS or %UINT_MAX if we have no samples.
  */
 unsigned int rxrpc_kernel_get_srtt(const struct rxrpc_peer *peer)
 {
@@ -499,7 +503,10 @@ EXPORT_SYMBOL(rxrpc_kernel_get_srtt);
  * @peer: The peer to query
  *
  * Get a pointer to the address from a peer record.  The caller is responsible
- * for making sure that the address is not deallocated.
+ * for making sure that the address is not deallocated.  A fake address will be
+ * substituted if %peer in NULL.
+ *
+ * Return: The rxrpc address record or a fake record.
  */
 const struct sockaddr_rxrpc *rxrpc_kernel_remote_srx(const struct rxrpc_peer *peer)
 {
@@ -512,7 +519,10 @@ EXPORT_SYMBOL(rxrpc_kernel_remote_srx);
  * @peer: The peer to query
  *
  * Get a pointer to the transport address from a peer record.  The caller is
- * responsible for making sure that the address is not deallocated.
+ * responsible for making sure that the address is not deallocated.  A fake
+ * address will be substituted if %peer in NULL.
+ *
+ * Return: The transport address record or a fake record.
  */
 const struct sockaddr *rxrpc_kernel_remote_addr(const struct rxrpc_peer *peer)
 {
@@ -527,7 +537,9 @@ EXPORT_SYMBOL(rxrpc_kernel_remote_addr);
  * @app_data: The data to set
  *
  * Set the app-specific data on a peer.  AF_RXRPC makes no effort to retain
- * anything the data might refer to.  The previous app_data is returned.
+ * anything the data might refer to.
+ *
+ * Return: The previous app_data.
  */
 unsigned long rxrpc_kernel_set_peer_data(struct rxrpc_peer *peer, unsigned long app_data)
 {
@@ -540,6 +552,8 @@ EXPORT_SYMBOL(rxrpc_kernel_set_peer_data);
  * @peer: The peer to query
  *
  * Retrieve the app-specific data from a peer.
+ *
+ * Return: The peer's app data.
  */
 unsigned long rxrpc_kernel_get_peer_data(const struct rxrpc_peer *peer)
 {
diff --git a/net/rxrpc/protocol.h b/net/rxrpc/protocol.h
index 42f70e4636f8..f8bfec12bc7e 100644
--- a/net/rxrpc/protocol.h
+++ b/net/rxrpc/protocol.h
@@ -181,4 +181,24 @@ struct rxkad_response {
 	__be32		ticket_len;	/* Kerberos ticket length  */
 } __packed;
 
+/*
+ * GSSAPI security type-4 and type-6 data header.
+ */
+struct rxgk_header {
+	__be32	epoch;
+	__be32	cid;
+	__be32	call_number;
+	__be32	seq;
+	__be32	sec_index;
+	__be32	data_len;
+} __packed;
+
+/*
+ * GSSAPI security type-4 and type-6 response packet header.
+ */
+struct rxgk_response {
+	__be64	start_time;
+	__be32	token_len;
+} __packed;
+
 #endif /* _LINUX_RXRPC_PACKET_H */
diff --git a/net/rxrpc/recvmsg.c b/net/rxrpc/recvmsg.c
index 32cd5f1d541d..86a27fb55a1c 100644
--- a/net/rxrpc/recvmsg.c
+++ b/net/rxrpc/recvmsg.c
@@ -155,6 +155,82 @@ static int rxrpc_verify_data(struct rxrpc_call *call, struct sk_buff *skb)
 }
 
 /*
+ * Transcribe a call's user ID to a control message.
+ */
+static int rxrpc_recvmsg_user_id(struct rxrpc_call *call, struct msghdr *msg,
+				 int flags)
+{
+	if (!test_bit(RXRPC_CALL_HAS_USERID, &call->flags))
+		return 0;
+
+	if (flags & MSG_CMSG_COMPAT) {
+		unsigned int id32 = call->user_call_ID;
+
+		return put_cmsg(msg, SOL_RXRPC, RXRPC_USER_CALL_ID,
+				sizeof(unsigned int), &id32);
+	} else {
+		unsigned long idl = call->user_call_ID;
+
+		return put_cmsg(msg, SOL_RXRPC, RXRPC_USER_CALL_ID,
+				sizeof(unsigned long), &idl);
+	}
+}
+
+/*
+ * Deal with a CHALLENGE packet.
+ */
+static int rxrpc_recvmsg_challenge(struct socket *sock, struct msghdr *msg,
+				   struct sk_buff *challenge, unsigned int flags)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(challenge);
+	struct rxrpc_connection *conn = sp->chall.conn;
+
+	return conn->security->challenge_to_recvmsg(conn, challenge, msg);
+}
+
+/*
+ * Process OOB packets.  Called with the socket locked.
+ */
+static int rxrpc_recvmsg_oob(struct socket *sock, struct msghdr *msg,
+			     unsigned int flags)
+{
+	struct rxrpc_sock *rx = rxrpc_sk(sock->sk);
+	struct sk_buff *skb;
+	bool need_response = false;
+	int ret;
+
+	skb = skb_peek(&rx->recvmsg_oobq);
+	if (!skb)
+		return -EAGAIN;
+	rxrpc_see_skb(skb, rxrpc_skb_see_recvmsg);
+
+	ret = put_cmsg(msg, SOL_RXRPC, RXRPC_OOB_ID, sizeof(u64),
+		       &skb->skb_mstamp_ns);
+	if (ret < 0)
+		return ret;
+
+	switch ((enum rxrpc_oob_type)skb->mark) {
+	case RXRPC_OOB_CHALLENGE:
+		need_response = true;
+		ret = rxrpc_recvmsg_challenge(sock, msg, skb, flags);
+		break;
+	default:
+		WARN_ONCE(1, "recvmsg() can't process unknown OOB type %u\n",
+			  skb->mark);
+		ret = -EIO;
+		break;
+	}
+
+	if (!(flags & MSG_PEEK))
+		skb_unlink(skb, &rx->recvmsg_oobq);
+	if (need_response)
+		rxrpc_add_pending_oob(rx, skb);
+	else
+		rxrpc_free_skb(skb, rxrpc_skb_put_oob);
+	return ret;
+}
+
+/*
  * Deliver messages to a call.  This keeps processing packets until the buffer
  * is filled and we find either more DATA (returns 0) or the end of the DATA
  * (returns 1).  If more packets are required, it returns -EAGAIN and if the
@@ -165,6 +241,7 @@ static int rxrpc_recvmsg_data(struct socket *sock, struct rxrpc_call *call,
 			      size_t len, int flags, size_t *_offset)
 {
 	struct rxrpc_skb_priv *sp;
+	struct rxrpc_sock *rx = rxrpc_sk(sock->sk);
 	struct sk_buff *skb;
 	rxrpc_seq_t seq = 0;
 	size_t remain;
@@ -207,7 +284,6 @@ static int rxrpc_recvmsg_data(struct socket *sock, struct rxrpc_call *call,
 			trace_rxrpc_recvdata(call, rxrpc_recvmsg_next, seq,
 					     sp->offset, sp->len, ret2);
 			if (ret2 < 0) {
-				kdebug("verify = %d", ret2);
 				ret = ret2;
 				goto out;
 			}
@@ -255,6 +331,13 @@ static int rxrpc_recvmsg_data(struct socket *sock, struct rxrpc_call *call,
 
 		if (!(flags & MSG_PEEK))
 			rxrpc_rotate_rx_window(call);
+
+		if (!rx->app_ops &&
+		    !skb_queue_empty_lockless(&rx->recvmsg_oobq)) {
+			trace_rxrpc_recvdata(call, rxrpc_recvmsg_oobq, seq,
+					     rx_pkt_offset, rx_pkt_len, ret);
+			break;
+		}
 	}
 
 out:
@@ -262,6 +345,7 @@ out:
 		call->rx_pkt_offset = rx_pkt_offset;
 		call->rx_pkt_len = rx_pkt_len;
 	}
+
 done:
 	trace_rxrpc_recvdata(call, rxrpc_recvmsg_data_return, seq,
 			     rx_pkt_offset, rx_pkt_len, ret);
@@ -301,6 +385,7 @@ try_again:
 	/* Return immediately if a client socket has no outstanding calls */
 	if (RB_EMPTY_ROOT(&rx->calls) &&
 	    list_empty(&rx->recvmsg_q) &&
+	    skb_queue_empty_lockless(&rx->recvmsg_oobq) &&
 	    rx->sk.sk_state != RXRPC_SERVER_LISTENING) {
 		release_sock(&rx->sk);
 		return -EAGAIN;
@@ -322,7 +407,8 @@ try_again:
 		if (ret)
 			goto wait_error;
 
-		if (list_empty(&rx->recvmsg_q)) {
+		if (list_empty(&rx->recvmsg_q) &&
+		    skb_queue_empty_lockless(&rx->recvmsg_oobq)) {
 			if (signal_pending(current))
 				goto wait_interrupted;
 			trace_rxrpc_recvmsg(0, rxrpc_recvmsg_wait, 0);
@@ -332,6 +418,15 @@ try_again:
 		goto try_again;
 	}
 
+	/* Deal with OOB messages before we consider getting normal data. */
+	if (!skb_queue_empty_lockless(&rx->recvmsg_oobq)) {
+		ret = rxrpc_recvmsg_oob(sock, msg, flags);
+		release_sock(&rx->sk);
+		if (ret == -EAGAIN)
+			goto try_again;
+		goto error_no_call;
+	}
+
 	/* Find the next call and dequeue it if we're not just peeking.  If we
 	 * do dequeue it, that comes with a ref that we will need to release.
 	 * We also want to weed out calls that got requeued whilst we were
@@ -342,7 +437,8 @@ try_again:
 	call = list_entry(l, struct rxrpc_call, recvmsg_link);
 
 	if (!rxrpc_call_is_complete(call) &&
-	    skb_queue_empty(&call->recvmsg_queue)) {
+	    skb_queue_empty(&call->recvmsg_queue) &&
+	    skb_queue_empty(&rx->recvmsg_oobq)) {
 		list_del_init(&call->recvmsg_link);
 		spin_unlock_irq(&rx->recvmsg_lock);
 		release_sock(&rx->sk);
@@ -377,21 +473,9 @@ try_again:
 	if (test_bit(RXRPC_CALL_RELEASED, &call->flags))
 		BUG();
 
-	if (test_bit(RXRPC_CALL_HAS_USERID, &call->flags)) {
-		if (flags & MSG_CMSG_COMPAT) {
-			unsigned int id32 = call->user_call_ID;
-
-			ret = put_cmsg(msg, SOL_RXRPC, RXRPC_USER_CALL_ID,
-				       sizeof(unsigned int), &id32);
-		} else {
-			unsigned long idl = call->user_call_ID;
-
-			ret = put_cmsg(msg, SOL_RXRPC, RXRPC_USER_CALL_ID,
-				       sizeof(unsigned long), &idl);
-		}
-		if (ret < 0)
-			goto error_unlock_call;
-	}
+	ret = rxrpc_recvmsg_user_id(call, msg, flags);
+	if (ret < 0)
+		goto error_unlock_call;
 
 	if (msg->msg_name && call->peer) {
 		size_t len = sizeof(call->dest_srx);
@@ -477,14 +561,14 @@ wait_error:
  * @_service: Where to store the actual service ID (may be upgraded)
  *
  * Allow a kernel service to receive data and pick up information about the
- * state of a call.  Returns 0 if got what was asked for and there's more
- * available, 1 if we got what was asked for and we're at the end of the data
- * and -EAGAIN if we need more data.
+ * state of a call.  Note that *@_abort should also be initialised to %0.
  *
- * Note that we may return -EAGAIN to drain empty packets at the end of the
- * data, even if we've already copied over the requested data.
+ * Note that we may return %-EAGAIN to drain empty packets at the end
+ * of the data, even if we've already copied over the requested data.
  *
- * *_abort should also be initialised to 0.
+ * Return: %0 if got what was asked for and there's more available, %1
+ * if we got what was asked for and we're at the end of the data and
+ * %-EAGAIN if we need more data.
  */
 int rxrpc_kernel_recv_data(struct socket *sock, struct rxrpc_call *call,
 			   struct iov_iter *iter, size_t *_len,
diff --git a/net/rxrpc/rxgk.c b/net/rxrpc/rxgk.c
new file mode 100644
index 000000000000..ba8bc201b8d3
--- /dev/null
+++ b/net/rxrpc/rxgk.c
@@ -0,0 +1,1367 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* GSSAPI-based RxRPC security
+ *
+ * Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/net.h>
+#include <linux/skbuff.h>
+#include <linux/slab.h>
+#include <linux/key-type.h>
+#include "ar-internal.h"
+#include "rxgk_common.h"
+
+/*
+ * Parse the information from a server key
+ */
+static int rxgk_preparse_server_key(struct key_preparsed_payload *prep)
+{
+	const struct krb5_enctype *krb5;
+	struct krb5_buffer *server_key = (void *)&prep->payload.data[2];
+	unsigned int service, sec_class, kvno, enctype;
+	int n = 0;
+
+	_enter("%zu", prep->datalen);
+
+	if (sscanf(prep->orig_description, "%u:%u:%u:%u%n",
+		   &service, &sec_class, &kvno, &enctype, &n) != 4)
+		return -EINVAL;
+
+	if (prep->orig_description[n])
+		return -EINVAL;
+
+	krb5 = crypto_krb5_find_enctype(enctype);
+	if (!krb5)
+		return -ENOPKG;
+
+	prep->payload.data[0] = (struct krb5_enctype *)krb5;
+
+	if (prep->datalen != krb5->key_len)
+		return -EKEYREJECTED;
+
+	server_key->len = prep->datalen;
+	server_key->data = kmemdup(prep->data, prep->datalen, GFP_KERNEL);
+	if (!server_key->data)
+		return -ENOMEM;
+
+	_leave(" = 0");
+	return 0;
+}
+
+static void rxgk_free_server_key(union key_payload *payload)
+{
+	struct krb5_buffer *server_key = (void *)&payload->data[2];
+
+	kfree_sensitive(server_key->data);
+}
+
+static void rxgk_free_preparse_server_key(struct key_preparsed_payload *prep)
+{
+	rxgk_free_server_key(&prep->payload);
+}
+
+static void rxgk_destroy_server_key(struct key *key)
+{
+	rxgk_free_server_key(&key->payload);
+}
+
+static void rxgk_describe_server_key(const struct key *key, struct seq_file *m)
+{
+	const struct krb5_enctype *krb5 = key->payload.data[0];
+
+	if (krb5)
+		seq_printf(m, ": %s", krb5->name);
+}
+
+/*
+ * Handle rekeying the connection when we see our limits overrun or when the
+ * far side decided to rekey.
+ *
+ * Returns a ref on the context if successful or -ESTALE if the key is out of
+ * date.
+ */
+static struct rxgk_context *rxgk_rekey(struct rxrpc_connection *conn,
+				       const u16 *specific_key_number)
+{
+	struct rxgk_context *gk, *dead = NULL;
+	unsigned int key_number, current_key, mask = ARRAY_SIZE(conn->rxgk.keys) - 1;
+	bool crank = false;
+
+	_enter("%d", specific_key_number ? *specific_key_number : -1);
+
+	mutex_lock(&conn->security_lock);
+
+	current_key = conn->rxgk.key_number;
+	if (!specific_key_number) {
+		key_number = current_key;
+	} else {
+		if (*specific_key_number == (u16)current_key)
+			key_number = current_key;
+		else if (*specific_key_number == (u16)(current_key - 1))
+			key_number = current_key - 1;
+		else if (*specific_key_number == (u16)(current_key + 1))
+			goto crank_window;
+		else
+			goto bad_key;
+	}
+
+	gk = conn->rxgk.keys[key_number & mask];
+	if (!gk)
+		goto generate_key;
+	if (!specific_key_number &&
+	    test_bit(RXGK_TK_NEEDS_REKEY, &gk->flags))
+		goto crank_window;
+
+grab:
+	refcount_inc(&gk->usage);
+	mutex_unlock(&conn->security_lock);
+	rxgk_put(dead);
+	return gk;
+
+crank_window:
+	trace_rxrpc_rxgk_rekey(conn, current_key,
+			       specific_key_number ? *specific_key_number : -1);
+	if (current_key == UINT_MAX)
+		goto bad_key;
+	if (current_key + 1 == UINT_MAX)
+		set_bit(RXRPC_CONN_DONT_REUSE, &conn->flags);
+
+	key_number = current_key + 1;
+	if (WARN_ON(conn->rxgk.keys[key_number & mask]))
+		goto bad_key;
+	crank = true;
+
+generate_key:
+	gk = conn->rxgk.keys[current_key & mask];
+	gk = rxgk_generate_transport_key(conn, gk->key, key_number, GFP_NOFS);
+	if (IS_ERR(gk)) {
+		mutex_unlock(&conn->security_lock);
+		return gk;
+	}
+
+	write_lock(&conn->security_use_lock);
+	if (crank) {
+		current_key++;
+		conn->rxgk.key_number = current_key;
+		dead = conn->rxgk.keys[(current_key - 2) & mask];
+		conn->rxgk.keys[(current_key - 2) & mask] = NULL;
+	}
+	conn->rxgk.keys[current_key & mask] = gk;
+	write_unlock(&conn->security_use_lock);
+	goto grab;
+
+bad_key:
+	mutex_unlock(&conn->security_lock);
+	return ERR_PTR(-ESTALE);
+}
+
+/*
+ * Get the specified keying context.
+ *
+ * Returns a ref on the context if successful or -ESTALE if the key is out of
+ * date.
+ */
+static struct rxgk_context *rxgk_get_key(struct rxrpc_connection *conn,
+					 const u16 *specific_key_number)
+{
+	struct rxgk_context *gk;
+	unsigned int key_number, current_key, mask = ARRAY_SIZE(conn->rxgk.keys) - 1;
+
+	_enter("{%u},%d",
+	       conn->rxgk.key_number, specific_key_number ? *specific_key_number : -1);
+
+	read_lock(&conn->security_use_lock);
+
+	current_key = conn->rxgk.key_number;
+	if (!specific_key_number) {
+		key_number = current_key;
+	} else {
+		/* Only the bottom 16 bits of the key number are exposed in the
+		 * header, so we try and keep the upper 16 bits in step.  The
+		 * whole 32 bits are used to generate the TK.
+		 */
+		if (*specific_key_number == (u16)current_key)
+			key_number = current_key;
+		else if (*specific_key_number == (u16)(current_key - 1))
+			key_number = current_key - 1;
+		else if (*specific_key_number == (u16)(current_key + 1))
+			goto rekey;
+		else
+			goto bad_key;
+	}
+
+	gk = conn->rxgk.keys[key_number & mask];
+	if (!gk)
+		goto slow_path;
+	if (!specific_key_number &&
+	    key_number < UINT_MAX) {
+		if (time_after(jiffies, gk->expiry) ||
+		    gk->bytes_remaining < 0) {
+			set_bit(RXGK_TK_NEEDS_REKEY, &gk->flags);
+			goto slow_path;
+		}
+
+		if (test_bit(RXGK_TK_NEEDS_REKEY, &gk->flags))
+			goto slow_path;
+	}
+
+	refcount_inc(&gk->usage);
+	read_unlock(&conn->security_use_lock);
+	return gk;
+
+rekey:
+	_debug("rekey");
+	if (current_key == UINT_MAX)
+		goto bad_key;
+	gk = conn->rxgk.keys[current_key & mask];
+	if (gk)
+		set_bit(RXGK_TK_NEEDS_REKEY, &gk->flags);
+slow_path:
+	read_unlock(&conn->security_use_lock);
+	return rxgk_rekey(conn, specific_key_number);
+bad_key:
+	read_unlock(&conn->security_use_lock);
+	return ERR_PTR(-ESTALE);
+}
+
+/*
+ * initialise connection security
+ */
+static int rxgk_init_connection_security(struct rxrpc_connection *conn,
+					 struct rxrpc_key_token *token)
+{
+	struct rxgk_context *gk;
+	int ret;
+
+	_enter("{%d,%u},{%x}",
+	       conn->debug_id, conn->rxgk.key_number, key_serial(conn->key));
+
+	conn->security_ix = token->security_index;
+	conn->security_level = token->rxgk->level;
+
+	if (rxrpc_conn_is_client(conn)) {
+		conn->rxgk.start_time = ktime_get();
+		do_div(conn->rxgk.start_time, 100);
+	}
+
+	gk = rxgk_generate_transport_key(conn, token->rxgk, conn->rxgk.key_number,
+					 GFP_NOFS);
+	if (IS_ERR(gk))
+		return PTR_ERR(gk);
+	conn->rxgk.enctype = gk->krb5->etype;
+	conn->rxgk.keys[gk->key_number & 3] = gk;
+
+	switch (conn->security_level) {
+	case RXRPC_SECURITY_PLAIN:
+	case RXRPC_SECURITY_AUTH:
+	case RXRPC_SECURITY_ENCRYPT:
+		break;
+	default:
+		ret = -EKEYREJECTED;
+		goto error;
+	}
+
+	ret = 0;
+error:
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * Clean up the crypto on a call.
+ */
+static void rxgk_free_call_crypto(struct rxrpc_call *call)
+{
+}
+
+/*
+ * Work out how much data we can put in a packet.
+ */
+static struct rxrpc_txbuf *rxgk_alloc_txbuf(struct rxrpc_call *call, size_t remain, gfp_t gfp)
+{
+	enum krb5_crypto_mode mode;
+	struct rxgk_context *gk;
+	struct rxrpc_txbuf *txb;
+	size_t shdr, alloc, limit, part, offset, gap;
+
+	switch (call->conn->security_level) {
+	default:
+		alloc = umin(remain, RXRPC_JUMBO_DATALEN);
+		return rxrpc_alloc_data_txbuf(call, alloc, 1, gfp);
+	case RXRPC_SECURITY_AUTH:
+		shdr = 0;
+		mode = KRB5_CHECKSUM_MODE;
+		break;
+	case RXRPC_SECURITY_ENCRYPT:
+		shdr = sizeof(struct rxgk_header);
+		mode = KRB5_ENCRYPT_MODE;
+		break;
+	}
+
+	gk = rxgk_get_key(call->conn, NULL);
+	if (IS_ERR(gk))
+		return NULL;
+
+	/* Work out the maximum amount of data that will fit. */
+	alloc = RXRPC_JUMBO_DATALEN;
+	limit = crypto_krb5_how_much_data(gk->krb5, mode, &alloc, &offset);
+
+	if (remain < limit - shdr) {
+		part = remain;
+		alloc = crypto_krb5_how_much_buffer(gk->krb5, mode,
+						    shdr + part, &offset);
+		gap = 0;
+	} else {
+		part = limit - shdr;
+		gap = RXRPC_JUMBO_DATALEN - alloc;
+		alloc = RXRPC_JUMBO_DATALEN;
+	}
+
+	rxgk_put(gk);
+
+	txb = rxrpc_alloc_data_txbuf(call, alloc, 16, gfp);
+	if (!txb)
+		return NULL;
+
+	txb->crypto_header	= offset;
+	txb->sec_header		= shdr;
+	txb->offset		+= offset + shdr;
+	txb->space		= part;
+
+	/* Clear excess space in the packet */
+	if (gap)
+		memset(txb->data + alloc - gap, 0, gap);
+	return txb;
+}
+
+/*
+ * Integrity mode (sign a packet - level 1 security)
+ */
+static int rxgk_secure_packet_integrity(const struct rxrpc_call *call,
+					struct rxgk_context *gk,
+					struct rxrpc_txbuf *txb)
+{
+	struct rxgk_header *hdr;
+	struct scatterlist sg[1];
+	struct krb5_buffer metadata;
+	int ret = -ENOMEM;
+
+	_enter("");
+
+	hdr = kzalloc(sizeof(*hdr), GFP_NOFS);
+	if (!hdr)
+		goto error_gk;
+
+	hdr->epoch	= htonl(call->conn->proto.epoch);
+	hdr->cid	= htonl(call->cid);
+	hdr->call_number = htonl(call->call_id);
+	hdr->seq	= htonl(txb->seq);
+	hdr->sec_index	= htonl(call->security_ix);
+	hdr->data_len	= htonl(txb->len);
+	metadata.len = sizeof(*hdr);
+	metadata.data = hdr;
+
+	sg_init_table(sg, 1);
+	sg_set_buf(&sg[0], txb->data, txb->alloc_size);
+
+	ret = crypto_krb5_get_mic(gk->krb5, gk->tx_Kc, &metadata,
+				  sg, 1, txb->alloc_size,
+				  txb->crypto_header, txb->sec_header + txb->len);
+	if (ret >= 0) {
+		txb->pkt_len = ret;
+		if (txb->alloc_size == RXRPC_JUMBO_DATALEN)
+			txb->jumboable = true;
+		gk->bytes_remaining -= ret;
+	}
+	kfree(hdr);
+error_gk:
+	rxgk_put(gk);
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * wholly encrypt a packet (level 2 security)
+ */
+static int rxgk_secure_packet_encrypted(const struct rxrpc_call *call,
+					struct rxgk_context *gk,
+					struct rxrpc_txbuf *txb)
+{
+	struct rxgk_header *hdr;
+	struct scatterlist sg[1];
+	int ret;
+
+	_enter("%x", txb->len);
+
+	/* Insert the header into the buffer. */
+	hdr = txb->data + txb->crypto_header;
+	hdr->epoch	 = htonl(call->conn->proto.epoch);
+	hdr->cid	 = htonl(call->cid);
+	hdr->call_number = htonl(call->call_id);
+	hdr->seq	 = htonl(txb->seq);
+	hdr->sec_index	 = htonl(call->security_ix);
+	hdr->data_len	 = htonl(txb->len);
+
+	sg_init_table(sg, 1);
+	sg_set_buf(&sg[0], txb->data, txb->alloc_size);
+
+	ret = crypto_krb5_encrypt(gk->krb5, gk->tx_enc,
+				  sg, 1, txb->alloc_size,
+				  txb->crypto_header, txb->sec_header + txb->len,
+				  false);
+	if (ret >= 0) {
+		txb->pkt_len = ret;
+		if (txb->alloc_size == RXRPC_JUMBO_DATALEN)
+			txb->jumboable = true;
+		gk->bytes_remaining -= ret;
+	}
+
+	rxgk_put(gk);
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * checksum an RxRPC packet header
+ */
+static int rxgk_secure_packet(struct rxrpc_call *call, struct rxrpc_txbuf *txb)
+{
+	struct rxgk_context *gk;
+	int ret;
+
+	_enter("{%d{%x}},{#%u},%u,",
+	       call->debug_id, key_serial(call->conn->key), txb->seq, txb->len);
+
+	gk = rxgk_get_key(call->conn, NULL);
+	if (IS_ERR(gk))
+		return PTR_ERR(gk) == -ESTALE ? -EKEYREJECTED : PTR_ERR(gk);
+
+	ret = key_validate(call->conn->key);
+	if (ret < 0)
+		return ret;
+
+	call->security_enctype = gk->krb5->etype;
+	txb->cksum = htons(gk->key_number);
+
+	switch (call->conn->security_level) {
+	case RXRPC_SECURITY_PLAIN:
+		rxgk_put(gk);
+		txb->pkt_len = txb->len;
+		return 0;
+	case RXRPC_SECURITY_AUTH:
+		return rxgk_secure_packet_integrity(call, gk, txb);
+	case RXRPC_SECURITY_ENCRYPT:
+		return rxgk_secure_packet_encrypted(call, gk, txb);
+	default:
+		rxgk_put(gk);
+		return -EPERM;
+	}
+}
+
+/*
+ * Integrity mode (check the signature on a packet - level 1 security)
+ */
+static int rxgk_verify_packet_integrity(struct rxrpc_call *call,
+					struct rxgk_context *gk,
+					struct sk_buff *skb)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+	struct rxgk_header *hdr;
+	struct krb5_buffer metadata;
+	unsigned int offset = sp->offset, len = sp->len;
+	size_t data_offset = 0, data_len = len;
+	u32 ac;
+	int ret = -ENOMEM;
+
+	_enter("");
+
+	crypto_krb5_where_is_the_data(gk->krb5, KRB5_CHECKSUM_MODE,
+				      &data_offset, &data_len);
+
+	hdr = kzalloc(sizeof(*hdr), GFP_NOFS);
+	if (!hdr)
+		return -ENOMEM;
+
+	hdr->epoch	= htonl(call->conn->proto.epoch);
+	hdr->cid	= htonl(call->cid);
+	hdr->call_number = htonl(call->call_id);
+	hdr->seq	= htonl(sp->hdr.seq);
+	hdr->sec_index	= htonl(call->security_ix);
+	hdr->data_len	= htonl(data_len);
+
+	metadata.len = sizeof(*hdr);
+	metadata.data = hdr;
+	ret = rxgk_verify_mic_skb(gk->krb5, gk->rx_Kc, &metadata,
+				  skb, &offset, &len, &ac);
+	kfree(hdr);
+	if (ret == -EPROTO) {
+		rxrpc_abort_eproto(call, skb, ac,
+				   rxgk_abort_1_verify_mic_eproto);
+	} else {
+		sp->offset = offset;
+		sp->len = len;
+	}
+
+	rxgk_put(gk);
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * Decrypt an encrypted packet (level 2 security).
+ */
+static int rxgk_verify_packet_encrypted(struct rxrpc_call *call,
+					struct rxgk_context *gk,
+					struct sk_buff *skb)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+	struct rxgk_header hdr;
+	unsigned int offset = sp->offset, len = sp->len;
+	int ret;
+	u32 ac;
+
+	_enter("");
+
+	ret = rxgk_decrypt_skb(gk->krb5, gk->rx_enc, skb, &offset, &len, &ac);
+	if (ret == -EPROTO)
+		rxrpc_abort_eproto(call, skb, ac, rxgk_abort_2_decrypt_eproto);
+	if (ret < 0)
+		goto error;
+
+	if (len < sizeof(hdr)) {
+		ret = rxrpc_abort_eproto(call, skb, RXGK_PACKETSHORT,
+					 rxgk_abort_2_short_header);
+		goto error;
+	}
+
+	/* Extract the header from the skb */
+	ret = skb_copy_bits(skb, offset, &hdr, sizeof(hdr));
+	if (ret < 0) {
+		ret = rxrpc_abort_eproto(call, skb, RXGK_PACKETSHORT,
+					 rxgk_abort_2_short_encdata);
+		goto error;
+	}
+	offset += sizeof(hdr);
+	len -= sizeof(hdr);
+
+	if (ntohl(hdr.epoch)		!= call->conn->proto.epoch ||
+	    ntohl(hdr.cid)		!= call->cid ||
+	    ntohl(hdr.call_number)	!= call->call_id ||
+	    ntohl(hdr.seq)		!= sp->hdr.seq ||
+	    ntohl(hdr.sec_index)	!= call->security_ix ||
+	    ntohl(hdr.data_len)		> len) {
+		ret = rxrpc_abort_eproto(call, skb, RXGK_SEALEDINCON,
+					 rxgk_abort_2_short_data);
+		goto error;
+	}
+
+	sp->offset = offset;
+	sp->len = ntohl(hdr.data_len);
+	ret = 0;
+error:
+	rxgk_put(gk);
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * Verify the security on a received packet or subpacket (if part of a
+ * jumbo packet).
+ */
+static int rxgk_verify_packet(struct rxrpc_call *call, struct sk_buff *skb)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+	struct rxgk_context *gk;
+	u16 key_number = sp->hdr.cksum;
+
+	_enter("{%d{%x}},{#%u}",
+	       call->debug_id, key_serial(call->conn->key), sp->hdr.seq);
+
+	gk = rxgk_get_key(call->conn, &key_number);
+	if (IS_ERR(gk)) {
+		switch (PTR_ERR(gk)) {
+		case -ESTALE:
+			return rxrpc_abort_eproto(call, skb, RXGK_BADKEYNO,
+						  rxgk_abort_bad_key_number);
+		default:
+			return PTR_ERR(gk);
+		}
+	}
+
+	call->security_enctype = gk->krb5->etype;
+	switch (call->conn->security_level) {
+	case RXRPC_SECURITY_PLAIN:
+		return 0;
+	case RXRPC_SECURITY_AUTH:
+		return rxgk_verify_packet_integrity(call, gk, skb);
+	case RXRPC_SECURITY_ENCRYPT:
+		return rxgk_verify_packet_encrypted(call, gk, skb);
+	default:
+		rxgk_put(gk);
+		return -ENOANO;
+	}
+}
+
+/*
+ * Allocate memory to hold a challenge or a response packet.  We're not running
+ * in the io_thread, so we can't use ->tx_alloc.
+ */
+static struct page *rxgk_alloc_packet(size_t total_len)
+{
+	gfp_t gfp = GFP_NOFS;
+	int order;
+
+	order = get_order(total_len);
+	if (order > 0)
+		gfp |= __GFP_COMP;
+	return alloc_pages(gfp, order);
+}
+
+/*
+ * Issue a challenge.
+ */
+static int rxgk_issue_challenge(struct rxrpc_connection *conn)
+{
+	struct rxrpc_wire_header *whdr;
+	struct bio_vec bvec[1];
+	struct msghdr msg;
+	struct page *page;
+	size_t len = sizeof(*whdr) + sizeof(conn->rxgk.nonce);
+	u32 serial;
+	int ret;
+
+	_enter("{%d}", conn->debug_id);
+
+	get_random_bytes(&conn->rxgk.nonce, sizeof(conn->rxgk.nonce));
+
+	/* We can't use conn->tx_alloc without a lock */
+	page = rxgk_alloc_packet(sizeof(*whdr) + sizeof(conn->rxgk.nonce));
+	if (!page)
+		return -ENOMEM;
+
+	bvec_set_page(&bvec[0], page, len, 0);
+	iov_iter_bvec(&msg.msg_iter, WRITE, bvec, 1, len);
+
+	msg.msg_name	= &conn->peer->srx.transport;
+	msg.msg_namelen	= conn->peer->srx.transport_len;
+	msg.msg_control	= NULL;
+	msg.msg_controllen = 0;
+	msg.msg_flags	= MSG_SPLICE_PAGES;
+
+	whdr = page_address(page);
+	whdr->epoch	= htonl(conn->proto.epoch);
+	whdr->cid	= htonl(conn->proto.cid);
+	whdr->callNumber = 0;
+	whdr->seq	= 0;
+	whdr->type	= RXRPC_PACKET_TYPE_CHALLENGE;
+	whdr->flags	= conn->out_clientflag;
+	whdr->userStatus = 0;
+	whdr->securityIndex = conn->security_ix;
+	whdr->_rsvd	= 0;
+	whdr->serviceId	= htons(conn->service_id);
+
+	memcpy(whdr + 1, conn->rxgk.nonce, sizeof(conn->rxgk.nonce));
+
+	serial = rxrpc_get_next_serials(conn, 1);
+	whdr->serial = htonl(serial);
+
+	trace_rxrpc_tx_challenge(conn, serial, 0, *(u32 *)&conn->rxgk.nonce);
+
+	ret = do_udp_sendmsg(conn->local->socket, &msg, len);
+	if (ret > 0)
+		conn->peer->last_tx_at = ktime_get_seconds();
+	__free_page(page);
+
+	if (ret < 0) {
+		trace_rxrpc_tx_fail(conn->debug_id, serial, ret,
+				    rxrpc_tx_point_rxgk_challenge);
+		return -EAGAIN;
+	}
+
+	trace_rxrpc_tx_packet(conn->debug_id, whdr,
+			      rxrpc_tx_point_rxgk_challenge);
+	_leave(" = 0");
+	return 0;
+}
+
+/*
+ * Validate a challenge packet.
+ */
+static bool rxgk_validate_challenge(struct rxrpc_connection *conn,
+				    struct sk_buff *skb)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+	u8 nonce[20];
+
+	if (!conn->key) {
+		rxrpc_abort_conn(conn, skb, RX_PROTOCOL_ERROR, -EPROTO,
+				 rxgk_abort_chall_no_key);
+		return false;
+	}
+
+	if (key_validate(conn->key) < 0) {
+		rxrpc_abort_conn(conn, skb, RXGK_EXPIRED, -EPROTO,
+				 rxgk_abort_chall_key_expired);
+		return false;
+	}
+
+	if (skb_copy_bits(skb, sizeof(struct rxrpc_wire_header),
+			  nonce, sizeof(nonce)) < 0) {
+		rxrpc_abort_conn(conn, skb, RXGK_PACKETSHORT, -EPROTO,
+				 rxgk_abort_chall_short);
+		return false;
+	}
+
+	trace_rxrpc_rx_challenge(conn, sp->hdr.serial, 0, *(u32 *)nonce, 0);
+	return true;
+}
+
+/**
+ * rxgk_kernel_query_challenge - Query RxGK-specific challenge parameters
+ * @challenge: The challenge packet to query
+ *
+ * Return: The Kerberos 5 encoding type for the challenged connection.
+ */
+u32 rxgk_kernel_query_challenge(struct sk_buff *challenge)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(challenge);
+
+	return sp->chall.conn->rxgk.enctype;
+}
+EXPORT_SYMBOL(rxgk_kernel_query_challenge);
+
+/*
+ * Fill out the control message to pass to userspace to inform about the
+ * challenge.
+ */
+static int rxgk_challenge_to_recvmsg(struct rxrpc_connection *conn,
+				     struct sk_buff *challenge,
+				     struct msghdr *msg)
+{
+	struct rxgk_challenge chall;
+
+	chall.base.service_id		= conn->service_id;
+	chall.base.security_index	= conn->security_ix;
+	chall.enctype			= conn->rxgk.enctype;
+
+	return put_cmsg(msg, SOL_RXRPC, RXRPC_CHALLENGED, sizeof(chall), &chall);
+}
+
+/*
+ * Insert the requisite amount of XDR padding for the length given.
+ */
+static int rxgk_pad_out(struct sk_buff *response, size_t len, size_t offset)
+{
+	__be32 zero = 0;
+	size_t pad = xdr_round_up(len) - len;
+	int ret;
+
+	if (!pad)
+		return 0;
+
+	ret = skb_store_bits(response, offset, &zero, pad);
+	if (ret < 0)
+		return ret;
+	return pad;
+}
+
+/*
+ * Insert the header into the response.
+ */
+static noinline ssize_t rxgk_insert_response_header(struct rxrpc_connection *conn,
+						    struct rxgk_context *gk,
+						    struct sk_buff *response,
+						    size_t offset)
+{
+	struct rxrpc_skb_priv *rsp = rxrpc_skb(response);
+
+	struct {
+		struct rxrpc_wire_header whdr;
+		__be32 start_time_msw;
+		__be32 start_time_lsw;
+		__be32 ticket_len;
+	} h;
+	int ret;
+
+	rsp->resp.kvno		= gk->key_number;
+	rsp->resp.version	= gk->krb5->etype;
+
+	h.whdr.epoch		= htonl(conn->proto.epoch);
+	h.whdr.cid		= htonl(conn->proto.cid);
+	h.whdr.callNumber	= 0;
+	h.whdr.serial		= 0;
+	h.whdr.seq		= 0;
+	h.whdr.type		= RXRPC_PACKET_TYPE_RESPONSE;
+	h.whdr.flags		= conn->out_clientflag;
+	h.whdr.userStatus	= 0;
+	h.whdr.securityIndex	= conn->security_ix;
+	h.whdr.cksum		= htons(gk->key_number);
+	h.whdr.serviceId	= htons(conn->service_id);
+	h.start_time_msw	= htonl(upper_32_bits(conn->rxgk.start_time));
+	h.start_time_lsw	= htonl(lower_32_bits(conn->rxgk.start_time));
+	h.ticket_len		= htonl(gk->key->ticket.len);
+
+	ret = skb_store_bits(response, offset, &h, sizeof(h));
+	return ret < 0 ? ret : sizeof(h);
+}
+
+/*
+ * Construct the authenticator to go in the response packet
+ *
+ * struct RXGK_Authenticator {
+ *	opaque nonce[20];
+ *	opaque appdata<>;
+ *	RXGK_Level level;
+ *	unsigned int epoch;
+ *	unsigned int cid;
+ *	unsigned int call_numbers<>;
+ * };
+ */
+static ssize_t rxgk_construct_authenticator(struct rxrpc_connection *conn,
+					    struct sk_buff *challenge,
+					    const struct krb5_buffer *appdata,
+					    struct sk_buff *response,
+					    size_t offset)
+{
+	struct {
+		u8	nonce[20];
+		__be32	appdata_len;
+	} a;
+	struct {
+		__be32	level;
+		__be32	epoch;
+		__be32	cid;
+		__be32	call_numbers_count;
+		__be32	call_numbers[4];
+	} b;
+	int ret;
+
+	ret = skb_copy_bits(challenge, sizeof(struct rxrpc_wire_header),
+			    a.nonce, sizeof(a.nonce));
+	if (ret < 0)
+		return -EPROTO;
+
+	a.appdata_len = htonl(appdata->len);
+
+	ret = skb_store_bits(response, offset, &a, sizeof(a));
+	if (ret < 0)
+		return ret;
+	offset += sizeof(a);
+
+	if (appdata->len) {
+		ret = skb_store_bits(response, offset, appdata->data, appdata->len);
+		if (ret < 0)
+			return ret;
+		offset += appdata->len;
+
+		ret = rxgk_pad_out(response, appdata->len, offset);
+		if (ret < 0)
+			return ret;
+		offset += ret;
+	}
+
+	b.level			= htonl(conn->security_level);
+	b.epoch			= htonl(conn->proto.epoch);
+	b.cid			= htonl(conn->proto.cid);
+	b.call_numbers_count	= htonl(4);
+	b.call_numbers[0]	= htonl(conn->channels[0].call_counter);
+	b.call_numbers[1]	= htonl(conn->channels[1].call_counter);
+	b.call_numbers[2]	= htonl(conn->channels[2].call_counter);
+	b.call_numbers[3]	= htonl(conn->channels[3].call_counter);
+
+	ret = skb_store_bits(response, offset, &b, sizeof(b));
+	if (ret < 0)
+		return ret;
+	return sizeof(a) + xdr_round_up(appdata->len) + sizeof(b);
+}
+
+static ssize_t rxgk_encrypt_authenticator(struct rxrpc_connection *conn,
+					  struct rxgk_context *gk,
+					  struct sk_buff *response,
+					  size_t offset,
+					  size_t alloc_len,
+					  size_t auth_offset,
+					  size_t auth_len)
+{
+	struct scatterlist sg[16];
+	int nr_sg;
+
+	sg_init_table(sg, ARRAY_SIZE(sg));
+	nr_sg = skb_to_sgvec(response, sg, offset, alloc_len);
+	if (unlikely(nr_sg < 0))
+		return nr_sg;
+	return crypto_krb5_encrypt(gk->krb5, gk->resp_enc, sg, nr_sg, alloc_len,
+				   auth_offset, auth_len, false);
+}
+
+/*
+ * Construct the response.
+ *
+ * struct RXGK_Response {
+ *	rxgkTime start_time;
+ *	RXGK_Data token;
+ *	opaque authenticator<RXGK_MAXAUTHENTICATOR>
+ * };
+ */
+static int rxgk_construct_response(struct rxrpc_connection *conn,
+				   struct sk_buff *challenge,
+				   struct krb5_buffer *appdata)
+{
+	struct rxrpc_skb_priv *csp, *rsp;
+	struct rxgk_context *gk;
+	struct sk_buff *response;
+	size_t len, auth_len, authx_len, offset, auth_offset, authx_offset;
+	__be32 tmp;
+	int ret;
+
+	gk = rxgk_get_key(conn, NULL);
+	if (IS_ERR(gk))
+		return PTR_ERR(gk);
+
+	auth_len = 20 + (4 + appdata->len) + 12 + (1 + 4) * 4;
+	authx_len = crypto_krb5_how_much_buffer(gk->krb5, KRB5_ENCRYPT_MODE,
+						auth_len, &auth_offset);
+	len = sizeof(struct rxrpc_wire_header) +
+		8 + (4 + xdr_round_up(gk->key->ticket.len)) + (4 + authx_len);
+
+	response = alloc_skb_with_frags(0, len, 0, &ret, GFP_NOFS);
+	if (!response)
+		goto error;
+	rxrpc_new_skb(response, rxrpc_skb_new_response_rxgk);
+	response->len = len;
+	response->data_len = len;
+
+	ret = rxgk_insert_response_header(conn, gk, response, 0);
+	if (ret < 0)
+		goto error;
+	offset = ret;
+
+	ret = skb_store_bits(response, offset, gk->key->ticket.data, gk->key->ticket.len);
+	if (ret < 0)
+		goto error;
+	offset += gk->key->ticket.len;
+	ret = rxgk_pad_out(response, gk->key->ticket.len, offset);
+	if (ret < 0)
+		goto error;
+
+	authx_offset = offset + ret + 4; /* Leave a gap for the length. */
+
+	ret = rxgk_construct_authenticator(conn, challenge, appdata, response,
+					   authx_offset + auth_offset);
+	if (ret < 0)
+		goto error;
+	auth_len = ret;
+
+	ret = rxgk_encrypt_authenticator(conn, gk, response,
+					 authx_offset, authx_len,
+					 auth_offset, auth_len);
+	if (ret < 0)
+		goto error;
+	authx_len = ret;
+
+	tmp = htonl(authx_len);
+	ret = skb_store_bits(response, authx_offset - 4, &tmp, 4);
+	if (ret < 0)
+		goto error;
+
+	ret = rxgk_pad_out(response, authx_len, authx_offset + authx_len);
+	if (ret < 0)
+		return ret;
+	len = authx_offset + authx_len + ret;
+
+	if (len != response->len) {
+		response->len = len;
+		response->data_len = len;
+	}
+
+	csp = rxrpc_skb(challenge);
+	rsp = rxrpc_skb(response);
+	rsp->resp.len = len;
+	rsp->resp.challenge_serial = csp->hdr.serial;
+	rxrpc_post_response(conn, response);
+	response = NULL;
+	ret = 0;
+
+error:
+	rxrpc_free_skb(response, rxrpc_skb_put_response);
+	rxgk_put(gk);
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * Respond to a challenge packet.
+ */
+static int rxgk_respond_to_challenge(struct rxrpc_connection *conn,
+				     struct sk_buff *challenge,
+				     struct krb5_buffer *appdata)
+{
+	_enter("{%d,%x}", conn->debug_id, key_serial(conn->key));
+
+	if (key_validate(conn->key) < 0)
+		return rxrpc_abort_conn(conn, NULL, RXGK_EXPIRED, -EPROTO,
+					rxgk_abort_chall_key_expired);
+
+	return rxgk_construct_response(conn, challenge, appdata);
+}
+
+static int rxgk_respond_to_challenge_no_appdata(struct rxrpc_connection *conn,
+						struct sk_buff *challenge)
+{
+	struct krb5_buffer appdata = {};
+
+	return rxgk_respond_to_challenge(conn, challenge, &appdata);
+}
+
+/**
+ * rxgk_kernel_respond_to_challenge - Respond to a challenge with appdata
+ * @challenge: The challenge to respond to
+ * @appdata: The application data to include in the RESPONSE authenticator
+ *
+ * Allow a kernel application to respond to a CHALLENGE with application data
+ * to be included in the RxGK RESPONSE Authenticator.
+ *
+ * Return: %0 if successful and a negative error code otherwise.
+ */
+int rxgk_kernel_respond_to_challenge(struct sk_buff *challenge,
+				     struct krb5_buffer *appdata)
+{
+	struct rxrpc_skb_priv *csp = rxrpc_skb(challenge);
+
+	return rxgk_respond_to_challenge(csp->chall.conn, challenge, appdata);
+}
+EXPORT_SYMBOL(rxgk_kernel_respond_to_challenge);
+
+/*
+ * Parse sendmsg() control message and respond to challenge.  We need to see if
+ * there's an appdata to fish out.
+ */
+static int rxgk_sendmsg_respond_to_challenge(struct sk_buff *challenge,
+					     struct msghdr *msg)
+{
+	struct krb5_buffer appdata = {};
+	struct cmsghdr *cmsg;
+
+	for_each_cmsghdr(cmsg, msg) {
+		if (cmsg->cmsg_level != SOL_RXRPC ||
+		    cmsg->cmsg_type != RXRPC_RESP_RXGK_APPDATA)
+			continue;
+		if (appdata.data)
+			return -EINVAL;
+		appdata.data = CMSG_DATA(cmsg);
+		appdata.len = cmsg->cmsg_len - sizeof(struct cmsghdr);
+	}
+
+	return rxgk_kernel_respond_to_challenge(challenge, &appdata);
+}
+
+/*
+ * Verify the authenticator.
+ *
+ * struct RXGK_Authenticator {
+ *	opaque nonce[20];
+ *	opaque appdata<>;
+ *	RXGK_Level level;
+ *	unsigned int epoch;
+ *	unsigned int cid;
+ *	unsigned int call_numbers<>;
+ * };
+ */
+static int rxgk_do_verify_authenticator(struct rxrpc_connection *conn,
+					const struct krb5_enctype *krb5,
+					struct sk_buff *skb,
+					__be32 *p, __be32 *end)
+{
+	u32 app_len, call_count, level, epoch, cid, i;
+
+	_enter("");
+
+	if (memcmp(p, conn->rxgk.nonce, 20) != 0)
+		return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+					rxgk_abort_resp_bad_nonce);
+	p += 20 / sizeof(__be32);
+
+	app_len	= ntohl(*p++);
+	if (app_len > (end - p) * sizeof(__be32))
+		return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+					rxgk_abort_resp_short_applen);
+
+	p += xdr_round_up(app_len) / sizeof(__be32);
+	if (end - p < 4)
+		return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+					rxgk_abort_resp_short_applen);
+
+	level	= ntohl(*p++);
+	epoch	= ntohl(*p++);
+	cid	= ntohl(*p++);
+	call_count = ntohl(*p++);
+
+	if (level	!= conn->security_level ||
+	    epoch	!= conn->proto.epoch ||
+	    cid		!= conn->proto.cid ||
+	    call_count	> 4)
+		return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+					rxgk_abort_resp_bad_param);
+
+	if (end - p < call_count)
+		return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+					rxgk_abort_resp_short_call_list);
+
+	for (i = 0; i < call_count; i++) {
+		u32 call_id = ntohl(*p++);
+
+		if (call_id > INT_MAX)
+			return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+						rxgk_abort_resp_bad_callid);
+
+		if (call_id < conn->channels[i].call_counter)
+			return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+						rxgk_abort_resp_call_ctr);
+
+		if (call_id > conn->channels[i].call_counter) {
+			if (conn->channels[i].call)
+				return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+							rxgk_abort_resp_call_state);
+
+			conn->channels[i].call_counter = call_id;
+		}
+	}
+
+	_leave(" = 0");
+	return 0;
+}
+
+/*
+ * Extract the authenticator and verify it.
+ */
+static int rxgk_verify_authenticator(struct rxrpc_connection *conn,
+				     const struct krb5_enctype *krb5,
+				     struct sk_buff *skb,
+				     unsigned int auth_offset, unsigned int auth_len)
+{
+	void *auth;
+	__be32 *p;
+	int ret;
+
+	auth = kmalloc(auth_len, GFP_NOFS);
+	if (!auth)
+		return -ENOMEM;
+
+	ret = skb_copy_bits(skb, auth_offset, auth, auth_len);
+	if (ret < 0) {
+		ret = rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+				       rxgk_abort_resp_short_auth);
+		goto error;
+	}
+
+	p = auth;
+	ret = rxgk_do_verify_authenticator(conn, krb5, skb, p, p + auth_len);
+error:
+	kfree(auth);
+	return ret;
+}
+
+/*
+ * Verify a response.
+ *
+ * struct RXGK_Response {
+ *	rxgkTime	start_time;
+ *	RXGK_Data	token;
+ *	opaque		authenticator<RXGK_MAXAUTHENTICATOR>
+ * };
+ */
+static int rxgk_verify_response(struct rxrpc_connection *conn,
+				struct sk_buff *skb)
+{
+	const struct krb5_enctype *krb5;
+	struct rxrpc_key_token *token;
+	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+	struct rxgk_response rhdr;
+	struct rxgk_context *gk;
+	struct key *key = NULL;
+	unsigned int offset = sizeof(struct rxrpc_wire_header);
+	unsigned int len = skb->len - sizeof(struct rxrpc_wire_header);
+	unsigned int token_offset, token_len;
+	unsigned int auth_offset, auth_len;
+	__be32 xauth_len;
+	int ret, ec;
+
+	_enter("{%d}", conn->debug_id);
+
+	/* Parse the RXGK_Response object */
+	if (sizeof(rhdr) + sizeof(__be32) > len)
+		goto short_packet;
+
+	if (skb_copy_bits(skb, offset, &rhdr, sizeof(rhdr)) < 0)
+		goto short_packet;
+	offset	+= sizeof(rhdr);
+	len	-= sizeof(rhdr);
+
+	token_offset	= offset;
+	token_len	= ntohl(rhdr.token_len);
+	if (xdr_round_up(token_len) + sizeof(__be32) > len)
+		goto short_packet;
+
+	trace_rxrpc_rx_response(conn, sp->hdr.serial, 0, sp->hdr.cksum, token_len);
+
+	offset	+= xdr_round_up(token_len);
+	len	-= xdr_round_up(token_len);
+
+	if (skb_copy_bits(skb, offset, &xauth_len, sizeof(xauth_len)) < 0)
+		goto short_packet;
+	offset	+= sizeof(xauth_len);
+	len	-= sizeof(xauth_len);
+
+	auth_offset	= offset;
+	auth_len	= ntohl(xauth_len);
+	if (auth_len < len)
+		goto short_packet;
+	if (auth_len & 3)
+		goto inconsistent;
+	if (auth_len < 20 + 9 * 4)
+		goto auth_too_short;
+
+	/* We need to extract and decrypt the token and instantiate a session
+	 * key for it.  This bit, however, is application-specific.  If
+	 * possible, we use a default parser, but we might end up bumping this
+	 * to the app to deal with - which might mean a round trip to
+	 * userspace.
+	 */
+	ret = rxgk_extract_token(conn, skb, token_offset, token_len, &key);
+	if (ret < 0)
+		goto out;
+
+	/* We now have a key instantiated from the decrypted ticket.  We can
+	 * pass this to the application so that they can parse the ticket
+	 * content and we can use the session key it contains to derive the
+	 * keys we need.
+	 *
+	 * Note that we have to switch enctype at this point as the enctype of
+	 * the ticket doesn't necessarily match that of the transport.
+	 */
+	token = key->payload.data[0];
+	conn->security_level = token->rxgk->level;
+	conn->rxgk.start_time = __be64_to_cpu(rhdr.start_time);
+
+	gk = rxgk_generate_transport_key(conn, token->rxgk, sp->hdr.cksum, GFP_NOFS);
+	if (IS_ERR(gk)) {
+		ret = PTR_ERR(gk);
+		goto cant_get_token;
+	}
+
+	krb5 = gk->krb5;
+
+	trace_rxrpc_rx_response(conn, sp->hdr.serial, krb5->etype, sp->hdr.cksum, token_len);
+
+	/* Decrypt, parse and verify the authenticator. */
+	ret = rxgk_decrypt_skb(krb5, gk->resp_enc, skb,
+			       &auth_offset, &auth_len, &ec);
+	if (ret < 0) {
+		rxrpc_abort_conn(conn, skb, RXGK_SEALEDINCON, ret,
+				 rxgk_abort_resp_auth_dec);
+		goto out;
+	}
+
+	ret = rxgk_verify_authenticator(conn, krb5, skb, auth_offset, auth_len);
+	if (ret < 0)
+		goto out;
+
+	conn->key = key;
+	key = NULL;
+	ret = 0;
+out:
+	key_put(key);
+	_leave(" = %d", ret);
+	return ret;
+
+inconsistent:
+	ret = rxrpc_abort_conn(conn, skb, RXGK_INCONSISTENCY, -EPROTO,
+			       rxgk_abort_resp_xdr_align);
+	goto out;
+auth_too_short:
+	ret = rxrpc_abort_conn(conn, skb, RXGK_PACKETSHORT, -EPROTO,
+			       rxgk_abort_resp_short_auth);
+	goto out;
+short_packet:
+	ret = rxrpc_abort_conn(conn, skb, RXGK_PACKETSHORT, -EPROTO,
+			       rxgk_abort_resp_short_packet);
+	goto out;
+
+cant_get_token:
+	switch (ret) {
+	case -ENOMEM:
+		goto temporary_error;
+	case -EINVAL:
+		ret = rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EKEYREJECTED,
+				       rxgk_abort_resp_internal_error);
+		goto out;
+	case -ENOPKG:
+		ret = rxrpc_abort_conn(conn, skb, KRB5_PROG_KEYTYPE_NOSUPP,
+				       -EKEYREJECTED, rxgk_abort_resp_nopkg);
+		goto out;
+	}
+
+temporary_error:
+	/* Ignore the response packet if we got a temporary error such as
+	 * ENOMEM.  We just want to send the challenge again.  Note that we
+	 * also come out this way if the ticket decryption fails.
+	 */
+	goto out;
+}
+
+/*
+ * clear the connection security
+ */
+static void rxgk_clear(struct rxrpc_connection *conn)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(conn->rxgk.keys); i++)
+		rxgk_put(conn->rxgk.keys[i]);
+}
+
+/*
+ * Initialise the RxGK security service.
+ */
+static int rxgk_init(void)
+{
+	return 0;
+}
+
+/*
+ * Clean up the RxGK security service.
+ */
+static void rxgk_exit(void)
+{
+}
+
+/*
+ * RxRPC YFS GSSAPI-based security
+ */
+const struct rxrpc_security rxgk_yfs = {
+	.name				= "yfs-rxgk",
+	.security_index			= RXRPC_SECURITY_YFS_RXGK,
+	.no_key_abort			= RXGK_NOTAUTH,
+	.init				= rxgk_init,
+	.exit				= rxgk_exit,
+	.preparse_server_key		= rxgk_preparse_server_key,
+	.free_preparse_server_key	= rxgk_free_preparse_server_key,
+	.destroy_server_key		= rxgk_destroy_server_key,
+	.describe_server_key		= rxgk_describe_server_key,
+	.init_connection_security	= rxgk_init_connection_security,
+	.alloc_txbuf			= rxgk_alloc_txbuf,
+	.secure_packet			= rxgk_secure_packet,
+	.verify_packet			= rxgk_verify_packet,
+	.free_call_crypto		= rxgk_free_call_crypto,
+	.issue_challenge		= rxgk_issue_challenge,
+	.validate_challenge		= rxgk_validate_challenge,
+	.challenge_to_recvmsg		= rxgk_challenge_to_recvmsg,
+	.sendmsg_respond_to_challenge	= rxgk_sendmsg_respond_to_challenge,
+	.respond_to_challenge		= rxgk_respond_to_challenge_no_appdata,
+	.verify_response		= rxgk_verify_response,
+	.clear				= rxgk_clear,
+	.default_decode_ticket		= rxgk_yfs_decode_ticket,
+};
diff --git a/net/rxrpc/rxgk_app.c b/net/rxrpc/rxgk_app.c
new file mode 100644
index 000000000000..6206a84395b8
--- /dev/null
+++ b/net/rxrpc/rxgk_app.c
@@ -0,0 +1,285 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Application-specific bits for GSSAPI-based RxRPC security
+ *
+ * Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/net.h>
+#include <linux/skbuff.h>
+#include <linux/slab.h>
+#include <linux/key-type.h>
+#include "ar-internal.h"
+#include "rxgk_common.h"
+
+/*
+ * Decode a default-style YFS ticket in a response and turn it into an
+ * rxrpc-type key.
+ *
+ * struct rxgk_key {
+ *	afs_uint32	enctype;
+ *	opaque		key<>;
+ * };
+ *
+ * struct RXGK_AuthName {
+ *	afs_int32	kind;
+ *	opaque		data<AUTHDATAMAX>;
+ *	opaque		display<AUTHPRINTABLEMAX>;
+ * };
+ *
+ * struct RXGK_Token {
+ *	rxgk_key		K0;
+ *	RXGK_Level		level;
+ *	rxgkTime		starttime;
+ *	afs_int32		lifetime;
+ *	afs_int32		bytelife;
+ *	rxgkTime		expirationtime;
+ *	struct RXGK_AuthName	identities<>;
+ * };
+ */
+int rxgk_yfs_decode_ticket(struct rxrpc_connection *conn, struct sk_buff *skb,
+			   unsigned int ticket_offset, unsigned int ticket_len,
+			   struct key **_key)
+{
+	struct rxrpc_key_token *token;
+	const struct cred *cred = current_cred(); // TODO - use socket creds
+	struct key *key;
+	size_t pre_ticket_len, payload_len;
+	unsigned int klen, enctype;
+	void *payload, *ticket;
+	__be32 *t, *p, *q, tmp[2];
+	int ret;
+
+	_enter("");
+
+	/* Get the session key length */
+	ret = skb_copy_bits(skb, ticket_offset, tmp, sizeof(tmp));
+	if (ret < 0)
+		return rxrpc_abort_conn(conn, skb, RXGK_INCONSISTENCY, -EPROTO,
+					rxgk_abort_resp_short_yfs_klen);
+	enctype = ntohl(tmp[0]);
+	klen = ntohl(tmp[1]);
+
+	if (klen > ticket_len - 10 * sizeof(__be32))
+		return rxrpc_abort_conn(conn, skb, RXGK_INCONSISTENCY, -EPROTO,
+					rxgk_abort_resp_short_yfs_key);
+
+	pre_ticket_len = ((5 + 14) * sizeof(__be32) +
+			  xdr_round_up(klen) +
+			  sizeof(__be32));
+	payload_len = pre_ticket_len + xdr_round_up(ticket_len);
+
+	payload = kzalloc(payload_len, GFP_NOFS);
+	if (!payload)
+		return -ENOMEM;
+
+	/* We need to fill out the XDR form for a key payload that we can pass
+	 * to add_key().  Start by copying in the ticket so that we can parse
+	 * it.
+	 */
+	ticket = payload + pre_ticket_len;
+	ret = skb_copy_bits(skb, ticket_offset, ticket, ticket_len);
+	if (ret < 0) {
+		ret = rxrpc_abort_conn(conn, skb, RXGK_INCONSISTENCY, -EPROTO,
+				       rxgk_abort_resp_short_yfs_tkt);
+		goto error;
+	}
+
+	/* Fill out the form header. */
+	p = payload;
+	p[0] = htonl(0); /* Flags */
+	p[1] = htonl(1); /* len(cellname) */
+	p[2] = htonl(0x20000000); /* Cellname " " */
+	p[3] = htonl(1); /* #tokens */
+	p[4] = htonl(15 * sizeof(__be32) + xdr_round_up(klen) +
+		     xdr_round_up(ticket_len)); /* Token len */
+
+	/* Now fill in the body.  Most of this we can just scrape directly from
+	 * the ticket.
+	 */
+	t = ticket + sizeof(__be32) * 2 + xdr_round_up(klen);
+	q = payload + 5 * sizeof(__be32);
+	q[0]  = htonl(RXRPC_SECURITY_YFS_RXGK);
+	q[1]  = t[1];		/* begintime - msw */
+	q[2]  = t[2];		/* - lsw */
+	q[3]  = t[5];		/* endtime - msw */
+	q[4]  = t[6];		/* - lsw */
+	q[5]  = 0;		/* level - msw */
+	q[6]  = t[0];		/* - lsw */
+	q[7]  = 0;		/* lifetime - msw */
+	q[8]  = t[3];		/* - lsw */
+	q[9]  = 0;		/* bytelife - msw */
+	q[10] = t[4];		/* - lsw */
+	q[11] = 0;		/* enctype - msw */
+	q[12] = htonl(enctype);	/* - lsw */
+	q[13] = htonl(klen);	/* Key length */
+
+	q += 14;
+
+	memcpy(q, ticket + sizeof(__be32) * 2, klen);
+	q += xdr_round_up(klen) / 4;
+	q[0] = htonl(ticket_len);
+	q++;
+	if (WARN_ON((unsigned long)q != (unsigned long)ticket)) {
+		ret = -EIO;
+		goto error;
+	}
+
+	/* Ticket read in with skb_copy_bits above */
+	q += xdr_round_up(ticket_len) / 4;
+	if (WARN_ON((unsigned long)q - (unsigned long)payload != payload_len)) {
+		ret = -EIO;
+		goto error;
+	}
+
+	/* Now turn that into a key. */
+	key = key_alloc(&key_type_rxrpc, "x",
+			GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred, // TODO: Use socket owner
+			KEY_USR_VIEW,
+			KEY_ALLOC_NOT_IN_QUOTA, NULL);
+	if (IS_ERR(key)) {
+		_leave(" = -ENOMEM [alloc %ld]", PTR_ERR(key));
+		goto error;
+	}
+
+	_debug("key %d", key_serial(key));
+
+	ret = key_instantiate_and_link(key, payload, payload_len, NULL, NULL);
+	if (ret < 0)
+		goto error_key;
+
+	token = key->payload.data[0];
+	token->no_leak_key = true;
+	*_key = key;
+	key = NULL;
+	ret = 0;
+	goto error;
+
+error_key:
+	key_put(key);
+error:
+	kfree_sensitive(payload);
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * Extract the token and set up a session key from the details.
+ *
+ * struct RXGK_TokenContainer {
+ *	afs_int32	kvno;
+ *	afs_int32	enctype;
+ *	opaque		encrypted_token<>;
+ * };
+ *
+ * [tools.ietf.org/html/draft-wilkinson-afs3-rxgk-afs-08 sec 6.1]
+ */
+int rxgk_extract_token(struct rxrpc_connection *conn, struct sk_buff *skb,
+		       unsigned int token_offset, unsigned int token_len,
+		       struct key **_key)
+{
+	const struct krb5_enctype *krb5;
+	const struct krb5_buffer *server_secret;
+	struct crypto_aead *token_enc = NULL;
+	struct key *server_key;
+	unsigned int ticket_offset, ticket_len;
+	u32 kvno, enctype;
+	int ret, ec;
+
+	struct {
+		__be32 kvno;
+		__be32 enctype;
+		__be32 token_len;
+	} container;
+
+	/* Decode the RXGK_TokenContainer object.  This tells us which server
+	 * key we should be using.  We can then fetch the key, get the secret
+	 * and set up the crypto to extract the token.
+	 */
+	if (skb_copy_bits(skb, token_offset, &container, sizeof(container)) < 0)
+		return rxrpc_abort_conn(conn, skb, RXGK_PACKETSHORT, -EPROTO,
+					rxgk_abort_resp_tok_short);
+
+	kvno		= ntohl(container.kvno);
+	enctype		= ntohl(container.enctype);
+	ticket_len	= ntohl(container.token_len);
+	ticket_offset	= token_offset + sizeof(container);
+
+	if (xdr_round_up(ticket_len) > token_len - 3 * 4)
+		return rxrpc_abort_conn(conn, skb, RXGK_PACKETSHORT, -EPROTO,
+					rxgk_abort_resp_tok_short);
+
+	_debug("KVNO %u", kvno);
+	_debug("ENC  %u", enctype);
+	_debug("TLEN %u", ticket_len);
+
+	server_key = rxrpc_look_up_server_security(conn, skb, kvno, enctype);
+	if (IS_ERR(server_key))
+		goto cant_get_server_key;
+
+	down_read(&server_key->sem);
+	server_secret = (const void *)&server_key->payload.data[2];
+	ret = rxgk_set_up_token_cipher(server_secret, &token_enc, enctype, &krb5, GFP_NOFS);
+	up_read(&server_key->sem);
+	key_put(server_key);
+	if (ret < 0)
+		goto cant_get_token;
+
+	/* We can now decrypt and parse the token/ticket.  This allows us to
+	 * gain access to K0, from which we can derive the transport key and
+	 * thence decode the authenticator.
+	 */
+	ret = rxgk_decrypt_skb(krb5, token_enc, skb,
+			       &ticket_offset, &ticket_len, &ec);
+	crypto_free_aead(token_enc);
+	token_enc = NULL;
+	if (ret < 0)
+		return rxrpc_abort_conn(conn, skb, ec, ret,
+					rxgk_abort_resp_tok_dec);
+
+	ret = conn->security->default_decode_ticket(conn, skb, ticket_offset,
+						    ticket_len, _key);
+	if (ret < 0)
+		goto cant_get_token;
+
+	_leave(" = 0");
+	return ret;
+
+cant_get_server_key:
+	ret = PTR_ERR(server_key);
+	switch (ret) {
+	case -ENOMEM:
+		goto temporary_error;
+	case -ENOKEY:
+	case -EKEYREJECTED:
+	case -EKEYEXPIRED:
+	case -EKEYREVOKED:
+	case -EPERM:
+		return rxrpc_abort_conn(conn, skb, RXGK_BADKEYNO, -EKEYREJECTED,
+					rxgk_abort_resp_tok_nokey);
+	default:
+		return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EKEYREJECTED,
+					rxgk_abort_resp_tok_keyerr);
+	}
+
+cant_get_token:
+	switch (ret) {
+	case -ENOMEM:
+		goto temporary_error;
+	case -EINVAL:
+		return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EKEYREJECTED,
+					rxgk_abort_resp_tok_internal_error);
+	case -ENOPKG:
+		return rxrpc_abort_conn(conn, skb, KRB5_PROG_KEYTYPE_NOSUPP,
+					-EKEYREJECTED, rxgk_abort_resp_tok_nopkg);
+	}
+
+temporary_error:
+	/* Ignore the response packet if we got a temporary error such as
+	 * ENOMEM.  We just want to send the challenge again.  Note that we
+	 * also come out this way if the ticket decryption fails.
+	 */
+	return ret;
+}
diff --git a/net/rxrpc/rxgk_common.h b/net/rxrpc/rxgk_common.h
new file mode 100644
index 000000000000..7370a5655985
--- /dev/null
+++ b/net/rxrpc/rxgk_common.h
@@ -0,0 +1,139 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Common bits for GSSAPI-based RxRPC security.
+ *
+ * Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <crypto/krb5.h>
+#include <crypto/skcipher.h>
+#include <crypto/hash.h>
+
+/*
+ * Per-key number context.  This is replaced when the connection is rekeyed.
+ */
+struct rxgk_context {
+	refcount_t		usage;
+	unsigned int		key_number;	/* Rekeying number (goes in the rx header) */
+	unsigned long		flags;
+#define RXGK_TK_NEEDS_REKEY	0		/* Set if this needs rekeying */
+	unsigned long		expiry;		/* Expiration time of this key */
+	long long		bytes_remaining; /* Remaining Tx lifetime of this key */
+	const struct krb5_enctype *krb5;	/* RxGK encryption type */
+	const struct rxgk_key	*key;
+
+	/* We need up to 7 keys derived from the transport key, but we don't
+	 * actually need the transport key.  Each key is derived by
+	 * DK(TK,constant).
+	 */
+	struct crypto_aead	*tx_enc;	/* Transmission key */
+	struct crypto_aead	*rx_enc;	/* Reception key */
+	struct crypto_shash	*tx_Kc;		/* Transmission checksum key */
+	struct crypto_shash	*rx_Kc;		/* Reception checksum key */
+	struct crypto_aead	*resp_enc;	/* Response packet enc key */
+};
+
+#define xdr_round_up(x) (round_up((x), sizeof(__be32)))
+#define xdr_object_len(x) (4 + xdr_round_up(x))
+
+/*
+ * rxgk_app.c
+ */
+int rxgk_yfs_decode_ticket(struct rxrpc_connection *conn, struct sk_buff *skb,
+			   unsigned int ticket_offset, unsigned int ticket_len,
+			   struct key **_key);
+int rxgk_extract_token(struct rxrpc_connection *conn, struct sk_buff *skb,
+		       unsigned int token_offset, unsigned int token_len,
+		       struct key **_key);
+
+/*
+ * rxgk_kdf.c
+ */
+void rxgk_put(struct rxgk_context *gk);
+struct rxgk_context *rxgk_generate_transport_key(struct rxrpc_connection *conn,
+						 const struct rxgk_key *key,
+						 unsigned int key_number,
+						 gfp_t gfp);
+int rxgk_set_up_token_cipher(const struct krb5_buffer *server_key,
+			     struct crypto_aead **token_key,
+			     unsigned int enctype,
+			     const struct krb5_enctype **_krb5,
+			     gfp_t gfp);
+
+/*
+ * Apply decryption and checksumming functions to part of an skbuff.  The
+ * offset and length are updated to reflect the actual content of the encrypted
+ * region.
+ */
+static inline
+int rxgk_decrypt_skb(const struct krb5_enctype *krb5,
+		     struct crypto_aead *aead,
+		     struct sk_buff *skb,
+		     unsigned int *_offset, unsigned int *_len,
+		     int *_error_code)
+{
+	struct scatterlist sg[16];
+	size_t offset = 0, len = *_len;
+	int nr_sg, ret;
+
+	sg_init_table(sg, ARRAY_SIZE(sg));
+	nr_sg = skb_to_sgvec(skb, sg, *_offset, len);
+	if (unlikely(nr_sg < 0))
+		return nr_sg;
+
+	ret = crypto_krb5_decrypt(krb5, aead, sg, nr_sg,
+				  &offset, &len);
+	switch (ret) {
+	case 0:
+		*_offset += offset;
+		*_len = len;
+		break;
+	case -EPROTO:
+	case -EBADMSG:
+		*_error_code = RXGK_SEALEDINCON;
+		break;
+	default:
+		break;
+	}
+
+	return ret;
+}
+
+/*
+ * Check the MIC on a region of an skbuff.  The offset and length are updated
+ * to reflect the actual content of the secure region.
+ */
+static inline
+int rxgk_verify_mic_skb(const struct krb5_enctype *krb5,
+			struct crypto_shash *shash,
+			const struct krb5_buffer *metadata,
+			struct sk_buff *skb,
+			unsigned int *_offset, unsigned int *_len,
+			u32 *_error_code)
+{
+	struct scatterlist sg[16];
+	size_t offset = 0, len = *_len;
+	int nr_sg, ret;
+
+	sg_init_table(sg, ARRAY_SIZE(sg));
+	nr_sg = skb_to_sgvec(skb, sg, *_offset, len);
+	if (unlikely(nr_sg < 0))
+		return nr_sg;
+
+	ret = crypto_krb5_verify_mic(krb5, shash, metadata, sg, nr_sg,
+				     &offset, &len);
+	switch (ret) {
+	case 0:
+		*_offset += offset;
+		*_len = len;
+		break;
+	case -EPROTO:
+	case -EBADMSG:
+		*_error_code = RXGK_SEALEDINCON;
+		break;
+	default:
+		break;
+	}
+
+	return ret;
+}
diff --git a/net/rxrpc/rxgk_kdf.c b/net/rxrpc/rxgk_kdf.c
new file mode 100644
index 000000000000..b4db5aa30e5b
--- /dev/null
+++ b/net/rxrpc/rxgk_kdf.c
@@ -0,0 +1,288 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* RxGK transport key derivation.
+ *
+ * Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/key-type.h>
+#include <linux/slab.h>
+#include <keys/rxrpc-type.h>
+#include "ar-internal.h"
+#include "rxgk_common.h"
+
+#define round16(x) (((x) + 15) & ~15)
+
+/*
+ * Constants used to derive the keys and hmacs actually used for doing stuff.
+ */
+#define RXGK_CLIENT_ENC_PACKET		1026U // 0x402
+#define RXGK_CLIENT_MIC_PACKET          1027U // 0x403
+#define RXGK_SERVER_ENC_PACKET          1028U // 0x404
+#define RXGK_SERVER_MIC_PACKET          1029U // 0x405
+#define RXGK_CLIENT_ENC_RESPONSE        1030U // 0x406
+#define RXGK_SERVER_ENC_TOKEN           1036U // 0x40c
+
+static void rxgk_free(struct rxgk_context *gk)
+{
+	if (gk->tx_Kc)
+		crypto_free_shash(gk->tx_Kc);
+	if (gk->rx_Kc)
+		crypto_free_shash(gk->rx_Kc);
+	if (gk->tx_enc)
+		crypto_free_aead(gk->tx_enc);
+	if (gk->rx_enc)
+		crypto_free_aead(gk->rx_enc);
+	if (gk->resp_enc)
+		crypto_free_aead(gk->resp_enc);
+	kfree(gk);
+}
+
+void rxgk_put(struct rxgk_context *gk)
+{
+	if (gk && refcount_dec_and_test(&gk->usage))
+		rxgk_free(gk);
+}
+
+/*
+ * Transport key derivation function.
+ *
+ *      TK = random-to-key(PRF+(K0, L,
+ *                         epoch || cid || start_time || key_number))
+ *      [tools.ietf.org/html/draft-wilkinson-afs3-rxgk-11 sec 8.3]
+ */
+static int rxgk_derive_transport_key(struct rxrpc_connection *conn,
+				     struct rxgk_context *gk,
+				     const struct rxgk_key *rxgk,
+				     struct krb5_buffer *TK,
+				     gfp_t gfp)
+{
+	const struct krb5_enctype *krb5 = gk->krb5;
+	struct krb5_buffer conn_info;
+	unsigned int L = krb5->key_bytes;
+	__be32 *info;
+	u8 *buffer;
+	int ret;
+
+	_enter("");
+
+	conn_info.len = sizeof(__be32) * 5;
+
+	buffer = kzalloc(round16(conn_info.len), gfp);
+	if (!buffer)
+		return -ENOMEM;
+
+	conn_info.data = buffer;
+
+	info = (__be32 *)conn_info.data;
+	info[0] = htonl(conn->proto.epoch);
+	info[1] = htonl(conn->proto.cid);
+	info[2] = htonl(conn->rxgk.start_time >> 32);
+	info[3] = htonl(conn->rxgk.start_time >>  0);
+	info[4] = htonl(gk->key_number);
+
+	ret = crypto_krb5_calc_PRFplus(krb5, &rxgk->key, L, &conn_info, TK, gfp);
+	kfree_sensitive(buffer);
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * Set up the ciphers for the usage keys.
+ */
+static int rxgk_set_up_ciphers(struct rxrpc_connection *conn,
+			       struct rxgk_context *gk,
+			       const struct rxgk_key *rxgk,
+			       gfp_t gfp)
+{
+	const struct krb5_enctype *krb5 = gk->krb5;
+	struct crypto_shash *shash;
+	struct crypto_aead *aead;
+	struct krb5_buffer TK;
+	bool service = rxrpc_conn_is_service(conn);
+	int ret;
+	u8 *buffer;
+
+	buffer = kzalloc(krb5->key_bytes, gfp);
+	if (!buffer)
+		return -ENOMEM;
+
+	TK.len = krb5->key_bytes;
+	TK.data = buffer;
+
+	ret = rxgk_derive_transport_key(conn, gk, rxgk, &TK, gfp);
+	if (ret < 0)
+		goto out;
+
+	aead = crypto_krb5_prepare_encryption(krb5, &TK, RXGK_CLIENT_ENC_RESPONSE, gfp);
+	if (IS_ERR(aead))
+		goto aead_error;
+	gk->resp_enc = aead;
+
+	if (crypto_aead_blocksize(gk->resp_enc) != krb5->block_len ||
+	    crypto_aead_authsize(gk->resp_enc) != krb5->cksum_len) {
+		pr_notice("algo inconsistent with krb5 table %u!=%u or %u!=%u\n",
+			  crypto_aead_blocksize(gk->resp_enc), krb5->block_len,
+			  crypto_aead_authsize(gk->resp_enc), krb5->cksum_len);
+		ret = -EINVAL;
+		goto out;
+	}
+
+	if (service) {
+		switch (conn->security_level) {
+		case RXRPC_SECURITY_AUTH:
+			shash = crypto_krb5_prepare_checksum(
+				krb5, &TK, RXGK_SERVER_MIC_PACKET, gfp);
+			if (IS_ERR(shash))
+				goto hash_error;
+			gk->tx_Kc = shash;
+			shash = crypto_krb5_prepare_checksum(
+				krb5, &TK, RXGK_CLIENT_MIC_PACKET, gfp);
+			if (IS_ERR(shash))
+				goto hash_error;
+			gk->rx_Kc = shash;
+			break;
+		case RXRPC_SECURITY_ENCRYPT:
+			aead = crypto_krb5_prepare_encryption(
+				krb5, &TK, RXGK_SERVER_ENC_PACKET, gfp);
+			if (IS_ERR(aead))
+				goto aead_error;
+			gk->tx_enc = aead;
+			aead = crypto_krb5_prepare_encryption(
+				krb5, &TK, RXGK_CLIENT_ENC_PACKET, gfp);
+			if (IS_ERR(aead))
+				goto aead_error;
+			gk->rx_enc = aead;
+			break;
+		}
+	} else {
+		switch (conn->security_level) {
+		case RXRPC_SECURITY_AUTH:
+			shash = crypto_krb5_prepare_checksum(
+				krb5, &TK, RXGK_CLIENT_MIC_PACKET, gfp);
+			if (IS_ERR(shash))
+				goto hash_error;
+			gk->tx_Kc = shash;
+			shash = crypto_krb5_prepare_checksum(
+				krb5, &TK, RXGK_SERVER_MIC_PACKET, gfp);
+			if (IS_ERR(shash))
+				goto hash_error;
+			gk->rx_Kc = shash;
+			break;
+		case RXRPC_SECURITY_ENCRYPT:
+			aead = crypto_krb5_prepare_encryption(
+				krb5, &TK, RXGK_CLIENT_ENC_PACKET, gfp);
+			if (IS_ERR(aead))
+				goto aead_error;
+			gk->tx_enc = aead;
+			aead = crypto_krb5_prepare_encryption(
+				krb5, &TK, RXGK_SERVER_ENC_PACKET, gfp);
+			if (IS_ERR(aead))
+				goto aead_error;
+			gk->rx_enc = aead;
+			break;
+		}
+	}
+
+	ret = 0;
+out:
+	kfree_sensitive(buffer);
+	return ret;
+aead_error:
+	ret = PTR_ERR(aead);
+	goto out;
+hash_error:
+	ret = PTR_ERR(shash);
+	goto out;
+}
+
+/*
+ * Derive a transport key for a connection and then derive a bunch of usage
+ * keys from it and set up ciphers using them.
+ */
+struct rxgk_context *rxgk_generate_transport_key(struct rxrpc_connection *conn,
+						 const struct rxgk_key *key,
+						 unsigned int key_number,
+						 gfp_t gfp)
+{
+	struct rxgk_context *gk;
+	unsigned long lifetime;
+	int ret = -ENOPKG;
+
+	_enter("");
+
+	gk = kzalloc(sizeof(*gk), GFP_KERNEL);
+	if (!gk)
+		return ERR_PTR(-ENOMEM);
+	refcount_set(&gk->usage, 1);
+	gk->key		= key;
+	gk->key_number	= key_number;
+
+	gk->krb5 = crypto_krb5_find_enctype(key->enctype);
+	if (!gk->krb5)
+		goto err_tk;
+
+	ret = rxgk_set_up_ciphers(conn, gk, key, gfp);
+	if (ret)
+		goto err_tk;
+
+	/* Set the remaining number of bytes encrypted with this key that may
+	 * be transmitted before rekeying.  Note that the spec has been
+	 * interpreted differently on this point...
+	 */
+	switch (key->bytelife) {
+	case 0:
+	case 63:
+		gk->bytes_remaining = LLONG_MAX;
+		break;
+	case 1 ... 62:
+		gk->bytes_remaining = 1LL << key->bytelife;
+		break;
+	default:
+		gk->bytes_remaining = key->bytelife;
+		break;
+	}
+
+	/* Set the time after which rekeying must occur */
+	if (key->lifetime) {
+		lifetime = min_t(u64, key->lifetime, INT_MAX / HZ);
+		lifetime *= HZ;
+	} else {
+		lifetime = MAX_JIFFY_OFFSET;
+	}
+	gk->expiry = jiffies + lifetime;
+	return gk;
+
+err_tk:
+	rxgk_put(gk);
+	_leave(" = %d", ret);
+	return ERR_PTR(ret);
+}
+
+/*
+ * Use the server secret key to set up the ciphers that will be used to extract
+ * the token from a response packet.
+ */
+int rxgk_set_up_token_cipher(const struct krb5_buffer *server_key,
+			     struct crypto_aead **token_aead,
+			     unsigned int enctype,
+			     const struct krb5_enctype **_krb5,
+			     gfp_t gfp)
+{
+	const struct krb5_enctype *krb5;
+	struct crypto_aead *aead;
+
+	krb5 = crypto_krb5_find_enctype(enctype);
+	if (!krb5)
+		return -ENOPKG;
+
+	aead = crypto_krb5_prepare_encryption(krb5, server_key, RXGK_SERVER_ENC_TOKEN, gfp);
+	if (IS_ERR(aead))
+		return PTR_ERR(aead);
+
+	*_krb5 = krb5;
+	*token_aead = aead;
+	return 0;
+}
diff --git a/net/rxrpc/rxkad.c b/net/rxrpc/rxkad.c
index 6cb37b0eb77f..3657c0661cdc 100644
--- a/net/rxrpc/rxkad.c
+++ b/net/rxrpc/rxkad.c
@@ -177,8 +177,10 @@ static struct rxrpc_txbuf *rxkad_alloc_txbuf(struct rxrpc_call *call, size_t rem
 	if (!txb)
 		return NULL;
 
-	txb->offset += shdr;
-	txb->space = part;
+	txb->crypto_header	= 0;
+	txb->sec_header		= shdr;
+	txb->offset		+= shdr;
+	txb->space		= part;
 	return txb;
 }
 
@@ -683,6 +685,8 @@ static int rxkad_issue_challenge(struct rxrpc_connection *conn)
 	serial = rxrpc_get_next_serial(conn);
 	whdr.serial = htonl(serial);
 
+	trace_rxrpc_tx_challenge(conn, serial, 0, conn->rxkad.nonce);
+
 	ret = kernel_sendmsg(conn->local->socket, &msg, iov, 2, len);
 	if (ret < 0) {
 		trace_rxrpc_tx_fail(conn->debug_id, serial, ret,
@@ -698,62 +702,6 @@ static int rxkad_issue_challenge(struct rxrpc_connection *conn)
 }
 
 /*
- * send a Kerberos security response
- */
-static int rxkad_send_response(struct rxrpc_connection *conn,
-			       struct rxrpc_host_header *hdr,
-			       struct rxkad_response *resp,
-			       const struct rxkad_key *s2)
-{
-	struct rxrpc_wire_header whdr;
-	struct msghdr msg;
-	struct kvec iov[3];
-	size_t len;
-	u32 serial;
-	int ret;
-
-	_enter("");
-
-	msg.msg_name	= &conn->peer->srx.transport;
-	msg.msg_namelen	= conn->peer->srx.transport_len;
-	msg.msg_control	= NULL;
-	msg.msg_controllen = 0;
-	msg.msg_flags	= 0;
-
-	memset(&whdr, 0, sizeof(whdr));
-	whdr.epoch	= htonl(hdr->epoch);
-	whdr.cid	= htonl(hdr->cid);
-	whdr.type	= RXRPC_PACKET_TYPE_RESPONSE;
-	whdr.flags	= conn->out_clientflag;
-	whdr.securityIndex = hdr->securityIndex;
-	whdr.serviceId	= htons(hdr->serviceId);
-
-	iov[0].iov_base	= &whdr;
-	iov[0].iov_len	= sizeof(whdr);
-	iov[1].iov_base	= resp;
-	iov[1].iov_len	= sizeof(*resp);
-	iov[2].iov_base	= (void *)s2->ticket;
-	iov[2].iov_len	= s2->ticket_len;
-
-	len = iov[0].iov_len + iov[1].iov_len + iov[2].iov_len;
-
-	serial = rxrpc_get_next_serial(conn);
-	whdr.serial = htonl(serial);
-
-	rxrpc_local_dont_fragment(conn->local, false);
-	ret = kernel_sendmsg(conn->local->socket, &msg, iov, 3, len);
-	if (ret < 0) {
-		trace_rxrpc_tx_fail(conn->debug_id, serial, ret,
-				    rxrpc_tx_point_rxkad_response);
-		return -EAGAIN;
-	}
-
-	conn->peer->last_tx_at = ktime_get_seconds();
-	_leave(" = 0");
-	return 0;
-}
-
-/*
  * calculate the response checksum
  */
 static void rxkad_calc_response_checksum(struct rxkad_response *response)
@@ -772,12 +720,21 @@ static void rxkad_calc_response_checksum(struct rxkad_response *response)
  * encrypt the response packet
  */
 static int rxkad_encrypt_response(struct rxrpc_connection *conn,
-				  struct rxkad_response *resp,
+				  struct sk_buff *response,
 				  const struct rxkad_key *s2)
 {
 	struct skcipher_request *req;
 	struct rxrpc_crypt iv;
 	struct scatterlist sg[1];
+	size_t encsize = sizeof(((struct rxkad_response *)0)->encrypted);
+	int ret;
+
+	sg_init_table(sg, ARRAY_SIZE(sg));
+	ret = skb_to_sgvec(response, sg,
+			   sizeof(struct rxrpc_wire_header) +
+			   offsetof(struct rxkad_response, encrypted), encsize);
+	if (ret < 0)
+		return ret;
 
 	req = skcipher_request_alloc(&conn->rxkad.cipher->base, GFP_NOFS);
 	if (!req)
@@ -786,89 +743,206 @@ static int rxkad_encrypt_response(struct rxrpc_connection *conn,
 	/* continue encrypting from where we left off */
 	memcpy(&iv, s2->session_key, sizeof(iv));
 
-	sg_init_table(sg, 1);
-	sg_set_buf(sg, &resp->encrypted, sizeof(resp->encrypted));
 	skcipher_request_set_sync_tfm(req, conn->rxkad.cipher);
 	skcipher_request_set_callback(req, 0, NULL, NULL);
-	skcipher_request_set_crypt(req, sg, sg, sizeof(resp->encrypted), iv.x);
-	crypto_skcipher_encrypt(req);
+	skcipher_request_set_crypt(req, sg, sg, encsize, iv.x);
+	ret = crypto_skcipher_encrypt(req);
 	skcipher_request_free(req);
-	return 0;
+	return ret;
 }
 
 /*
- * respond to a challenge packet
+ * Validate a challenge packet.
  */
-static int rxkad_respond_to_challenge(struct rxrpc_connection *conn,
-				      struct sk_buff *skb)
+static bool rxkad_validate_challenge(struct rxrpc_connection *conn,
+				     struct sk_buff *skb)
 {
-	const struct rxrpc_key_token *token;
 	struct rxkad_challenge challenge;
-	struct rxkad_response *resp;
 	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
-	u32 version, nonce, min_level;
-	int ret = -EPROTO;
+	u32 version, min_level;
+	int ret;
 
 	_enter("{%d,%x}", conn->debug_id, key_serial(conn->key));
 
-	if (!conn->key)
-		return rxrpc_abort_conn(conn, skb, RX_PROTOCOL_ERROR, -EPROTO,
-					rxkad_abort_chall_no_key);
+	if (!conn->key) {
+		rxrpc_abort_conn(conn, skb, RX_PROTOCOL_ERROR, -EPROTO,
+				 rxkad_abort_chall_no_key);
+		return false;
+	}
 
 	ret = key_validate(conn->key);
-	if (ret < 0)
-		return rxrpc_abort_conn(conn, skb, RXKADEXPIRED, ret,
-					rxkad_abort_chall_key_expired);
+	if (ret < 0) {
+		rxrpc_abort_conn(conn, skb, RXKADEXPIRED, ret,
+				 rxkad_abort_chall_key_expired);
+		return false;
+	}
 
 	if (skb_copy_bits(skb, sizeof(struct rxrpc_wire_header),
-			  &challenge, sizeof(challenge)) < 0)
-		return rxrpc_abort_conn(conn, skb, RXKADPACKETSHORT, -EPROTO,
-					rxkad_abort_chall_short);
+			  &challenge, sizeof(challenge)) < 0) {
+		rxrpc_abort_conn(conn, skb, RXKADPACKETSHORT, -EPROTO,
+				 rxkad_abort_chall_short);
+		return false;
+	}
 
 	version = ntohl(challenge.version);
-	nonce = ntohl(challenge.nonce);
+	sp->chall.rxkad_nonce = ntohl(challenge.nonce);
 	min_level = ntohl(challenge.min_level);
 
-	trace_rxrpc_rx_challenge(conn, sp->hdr.serial, version, nonce, min_level);
+	trace_rxrpc_rx_challenge(conn, sp->hdr.serial, version,
+				 sp->chall.rxkad_nonce, min_level);
+
+	if (version != RXKAD_VERSION) {
+		rxrpc_abort_conn(conn, skb, RXKADINCONSISTENCY, -EPROTO,
+				 rxkad_abort_chall_version);
+		return false;
+	}
 
-	if (version != RXKAD_VERSION)
-		return rxrpc_abort_conn(conn, skb, RXKADINCONSISTENCY, -EPROTO,
-					rxkad_abort_chall_version);
+	if (conn->security_level < min_level) {
+		rxrpc_abort_conn(conn, skb, RXKADLEVELFAIL, -EACCES,
+				 rxkad_abort_chall_level);
+		return false;
+	}
+	return true;
+}
+
+/*
+ * Insert the header into the response.
+ */
+static noinline
+int rxkad_insert_response_header(struct rxrpc_connection *conn,
+				 const struct rxrpc_key_token *token,
+				 struct sk_buff *challenge,
+				 struct sk_buff *response,
+				 size_t *offset)
+{
+	struct rxrpc_skb_priv *csp = rxrpc_skb(challenge);
+	struct {
+		struct rxrpc_wire_header whdr;
+		struct rxkad_response	resp;
+	} h;
+	int ret;
 
-	if (conn->security_level < min_level)
-		return rxrpc_abort_conn(conn, skb, RXKADLEVELFAIL, -EACCES,
-					rxkad_abort_chall_level);
+	h.whdr.epoch			= htonl(conn->proto.epoch);
+	h.whdr.cid			= htonl(conn->proto.cid);
+	h.whdr.callNumber		= 0;
+	h.whdr.serial			= 0;
+	h.whdr.seq			= 0;
+	h.whdr.type			= RXRPC_PACKET_TYPE_RESPONSE;
+	h.whdr.flags			= conn->out_clientflag;
+	h.whdr.userStatus		= 0;
+	h.whdr.securityIndex		= conn->security_ix;
+	h.whdr.cksum			= 0;
+	h.whdr.serviceId		= htons(conn->service_id);
+	h.resp.version			= htonl(RXKAD_VERSION);
+	h.resp.__pad			= 0;
+	h.resp.encrypted.epoch		= htonl(conn->proto.epoch);
+	h.resp.encrypted.cid		= htonl(conn->proto.cid);
+	h.resp.encrypted.checksum	= 0;
+	h.resp.encrypted.securityIndex	= htonl(conn->security_ix);
+	h.resp.encrypted.call_id[0]	= htonl(conn->channels[0].call_counter);
+	h.resp.encrypted.call_id[1]	= htonl(conn->channels[1].call_counter);
+	h.resp.encrypted.call_id[2]	= htonl(conn->channels[2].call_counter);
+	h.resp.encrypted.call_id[3]	= htonl(conn->channels[3].call_counter);
+	h.resp.encrypted.inc_nonce	= htonl(csp->chall.rxkad_nonce + 1);
+	h.resp.encrypted.level		= htonl(conn->security_level);
+	h.resp.kvno			= htonl(token->kad->kvno);
+	h.resp.ticket_len		= htonl(token->kad->ticket_len);
+
+	rxkad_calc_response_checksum(&h.resp);
+
+	ret = skb_store_bits(response, *offset, &h, sizeof(h));
+	*offset += sizeof(h);
+	return ret;
+}
+
+/*
+ * respond to a challenge packet
+ */
+static int rxkad_respond_to_challenge(struct rxrpc_connection *conn,
+				      struct sk_buff *challenge)
+{
+	const struct rxrpc_key_token *token;
+	struct rxrpc_skb_priv *csp, *rsp;
+	struct sk_buff *response;
+	size_t len, offset = 0;
+	int ret = -EPROTO;
+
+	_enter("{%d,%x}", conn->debug_id, key_serial(conn->key));
+
+	ret = key_validate(conn->key);
+	if (ret < 0)
+		return rxrpc_abort_conn(conn, challenge, RXKADEXPIRED, ret,
+					rxkad_abort_chall_key_expired);
 
 	token = conn->key->payload.data[0];
 
 	/* build the response packet */
-	resp = kzalloc(sizeof(struct rxkad_response), GFP_NOFS);
-	if (!resp)
-		return -ENOMEM;
+	len = sizeof(struct rxrpc_wire_header) +
+		sizeof(struct rxkad_response) +
+		token->kad->ticket_len;
+
+	response = alloc_skb_with_frags(0, len, 0, &ret, GFP_NOFS);
+	if (!response)
+		goto error;
+	rxrpc_new_skb(response, rxrpc_skb_new_response_rxkad);
+	response->len = len;
+	response->data_len = len;
+
+	offset = 0;
+	ret = rxkad_insert_response_header(conn, token, challenge, response,
+					   &offset);
+	if (ret < 0)
+		goto error;
+
+	ret = rxkad_encrypt_response(conn, response, token->kad);
+	if (ret < 0)
+		goto error;
+
+	ret = skb_store_bits(response, offset, token->kad->ticket,
+			     token->kad->ticket_len);
+	if (ret < 0)
+		goto error;
 
-	resp->version			= htonl(RXKAD_VERSION);
-	resp->encrypted.epoch		= htonl(conn->proto.epoch);
-	resp->encrypted.cid		= htonl(conn->proto.cid);
-	resp->encrypted.securityIndex	= htonl(conn->security_ix);
-	resp->encrypted.inc_nonce	= htonl(nonce + 1);
-	resp->encrypted.level		= htonl(conn->security_level);
-	resp->kvno			= htonl(token->kad->kvno);
-	resp->ticket_len		= htonl(token->kad->ticket_len);
-	resp->encrypted.call_id[0]	= htonl(conn->channels[0].call_counter);
-	resp->encrypted.call_id[1]	= htonl(conn->channels[1].call_counter);
-	resp->encrypted.call_id[2]	= htonl(conn->channels[2].call_counter);
-	resp->encrypted.call_id[3]	= htonl(conn->channels[3].call_counter);
-
-	/* calculate the response checksum and then do the encryption */
-	rxkad_calc_response_checksum(resp);
-	ret = rxkad_encrypt_response(conn, resp, token->kad);
-	if (ret == 0)
-		ret = rxkad_send_response(conn, &sp->hdr, resp, token->kad);
-	kfree(resp);
+	csp = rxrpc_skb(challenge);
+	rsp = rxrpc_skb(response);
+	rsp->resp.len = len;
+	rsp->resp.challenge_serial = csp->hdr.serial;
+	rxrpc_post_response(conn, response);
+	response = NULL;
+	ret = 0;
+
+error:
+	rxrpc_free_skb(response, rxrpc_skb_put_response);
 	return ret;
 }
 
 /*
+ * RxKAD does automatic response only as there's nothing to manage that isn't
+ * already in the key.
+ */
+static int rxkad_sendmsg_respond_to_challenge(struct sk_buff *challenge,
+					      struct msghdr *msg)
+{
+	return -EINVAL;
+}
+
+/**
+ * rxkad_kernel_respond_to_challenge - Respond to a challenge with appdata
+ * @challenge: The challenge to respond to
+ *
+ * Allow a kernel application to respond to a CHALLENGE.
+ *
+ * Return: %0 if successful and a negative error code otherwise.
+ */
+int rxkad_kernel_respond_to_challenge(struct sk_buff *challenge)
+{
+	struct rxrpc_skb_priv *csp = rxrpc_skb(challenge);
+
+	return rxkad_respond_to_challenge(csp->chall.conn, challenge);
+}
+EXPORT_SYMBOL(rxkad_kernel_respond_to_challenge);
+
+/*
  * decrypt the kerberos IV ticket in the response
  */
 static int rxkad_decrypt_ticket(struct rxrpc_connection *conn,
@@ -1276,6 +1350,8 @@ const struct rxrpc_security rxkad = {
 	.verify_packet			= rxkad_verify_packet,
 	.free_call_crypto		= rxkad_free_call_crypto,
 	.issue_challenge		= rxkad_issue_challenge,
+	.validate_challenge		= rxkad_validate_challenge,
+	.sendmsg_respond_to_challenge	= rxkad_sendmsg_respond_to_challenge,
 	.respond_to_challenge		= rxkad_respond_to_challenge,
 	.verify_response		= rxkad_verify_response,
 	.clear				= rxkad_clear,
diff --git a/net/rxrpc/rxperf.c b/net/rxrpc/rxperf.c
index e848a4777b8c..0377301156b0 100644
--- a/net/rxrpc/rxperf.c
+++ b/net/rxrpc/rxperf.c
@@ -8,6 +8,7 @@
 #define pr_fmt(fmt) "rxperf: " fmt
 #include <linux/module.h>
 #include <linux/slab.h>
+#include <crypto/krb5.h>
 #include <net/sock.h>
 #include <net/af_rxrpc.h>
 #define RXRPC_TRACE_ONLY_DEFINE_ENUMS
@@ -136,6 +137,12 @@ static void rxperf_notify_end_reply_tx(struct sock *sock,
 			      RXPERF_CALL_SV_AWAIT_ACK);
 }
 
+static const struct rxrpc_kernel_ops rxperf_rxrpc_callback_ops = {
+	.notify_new_call	= rxperf_rx_new_call,
+	.discard_new_call	= rxperf_rx_discard_new_call,
+	.user_attach_call	= rxperf_rx_attach,
+};
+
 /*
  * Charge the incoming call preallocation.
  */
@@ -161,7 +168,6 @@ static void rxperf_charge_preallocation(struct work_struct *work)
 
 		if (rxrpc_kernel_charge_accept(rxperf_socket,
 					       rxperf_notify_rx,
-					       rxperf_rx_attach,
 					       (unsigned long)call,
 					       GFP_KERNEL,
 					       call->debug_id) < 0)
@@ -209,8 +215,7 @@ static int rxperf_open_socket(void)
 	if (ret < 0)
 		goto error_2;
 
-	rxrpc_kernel_new_call_notification(socket, rxperf_rx_new_call,
-					   rxperf_rx_discard_new_call);
+	rxrpc_kernel_set_notifications(socket, &rxperf_rxrpc_callback_ops);
 
 	ret = kernel_listen(socket, INT_MAX);
 	if (ret < 0)
@@ -546,9 +551,9 @@ static int rxperf_process_call(struct rxperf_call *call)
 }
 
 /*
- * Add a key to the security keyring.
+ * Add an rxkad key to the security keyring.
  */
-static int rxperf_add_key(struct key *keyring)
+static int rxperf_add_rxkad_key(struct key *keyring)
 {
 	key_ref_t kref;
 	int ret;
@@ -574,6 +579,47 @@ static int rxperf_add_key(struct key *keyring)
 	return ret;
 }
 
+#ifdef CONFIG_RXGK
+/*
+ * Add a yfs-rxgk key to the security keyring.
+ */
+static int rxperf_add_yfs_rxgk_key(struct key *keyring, u32 enctype)
+{
+	const struct krb5_enctype *krb5 = crypto_krb5_find_enctype(enctype);
+	key_ref_t kref;
+	char name[64];
+	int ret;
+	u8 key[32];
+
+	if (!krb5 || krb5->key_len > sizeof(key))
+		return 0;
+
+	/* The key is just { 0, 1, 2, 3, 4, ... } */
+	for (int i = 0; i < krb5->key_len; i++)
+		key[i] = i;
+
+	sprintf(name, "%u:6:1:%u", RX_PERF_SERVICE, enctype);
+
+	kref = key_create_or_update(make_key_ref(keyring, true),
+				    "rxrpc_s", name,
+				    key, krb5->key_len,
+				    KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH |
+				    KEY_USR_VIEW,
+				    KEY_ALLOC_NOT_IN_QUOTA);
+
+	if (IS_ERR(kref)) {
+		pr_err("Can't allocate rxperf server key: %ld\n", PTR_ERR(kref));
+		return PTR_ERR(kref);
+	}
+
+	ret = key_link(keyring, key_ref_to_ptr(kref));
+	if (ret < 0)
+		pr_err("Can't link rxperf server key: %d\n", ret);
+	key_ref_put(kref);
+	return ret;
+}
+#endif
+
 /*
  * Initialise the rxperf server.
  */
@@ -603,9 +649,29 @@ static int __init rxperf_init(void)
 		goto error_keyring;
 	}
 	rxperf_sec_keyring = keyring;
-	ret = rxperf_add_key(keyring);
+	ret = rxperf_add_rxkad_key(keyring);
+	if (ret < 0)
+		goto error_key;
+#ifdef CONFIG_RXGK
+	ret = rxperf_add_yfs_rxgk_key(keyring, KRB5_ENCTYPE_AES128_CTS_HMAC_SHA1_96);
+	if (ret < 0)
+		goto error_key;
+	ret = rxperf_add_yfs_rxgk_key(keyring, KRB5_ENCTYPE_AES256_CTS_HMAC_SHA1_96);
+	if (ret < 0)
+		goto error_key;
+	ret = rxperf_add_yfs_rxgk_key(keyring, KRB5_ENCTYPE_AES128_CTS_HMAC_SHA256_128);
+	if (ret < 0)
+		goto error_key;
+	ret = rxperf_add_yfs_rxgk_key(keyring, KRB5_ENCTYPE_AES256_CTS_HMAC_SHA384_192);
+	if (ret < 0)
+		goto error_key;
+	ret = rxperf_add_yfs_rxgk_key(keyring, KRB5_ENCTYPE_CAMELLIA128_CTS_CMAC);
+	if (ret < 0)
+		goto error_key;
+	ret = rxperf_add_yfs_rxgk_key(keyring, KRB5_ENCTYPE_CAMELLIA256_CTS_CMAC);
 	if (ret < 0)
 		goto error_key;
+#endif
 
 	ret = rxperf_open_socket();
 	if (ret < 0)
diff --git a/net/rxrpc/security.c b/net/rxrpc/security.c
index 9784adc8f275..078d91a6b77f 100644
--- a/net/rxrpc/security.c
+++ b/net/rxrpc/security.c
@@ -20,6 +20,9 @@ static const struct rxrpc_security *rxrpc_security_types[] = {
 #ifdef CONFIG_RXKAD
 	[RXRPC_SECURITY_RXKAD]	= &rxkad,
 #endif
+#ifdef CONFIG_RXGK
+	[RXRPC_SECURITY_YFS_RXGK] = &rxgk_yfs,
+#endif
 };
 
 int __init rxrpc_init_security(void)
diff --git a/net/rxrpc/sendmsg.c b/net/rxrpc/sendmsg.c
index 84dc6c94f23b..ebbb78b842de 100644
--- a/net/rxrpc/sendmsg.c
+++ b/net/rxrpc/sendmsg.c
@@ -607,7 +607,7 @@ static int rxrpc_sendmsg_cmsg(struct msghdr *msg, struct rxrpc_send_params *p)
 static struct rxrpc_call *
 rxrpc_new_client_call_for_sendmsg(struct rxrpc_sock *rx, struct msghdr *msg,
 				  struct rxrpc_send_params *p)
-	__releases(&rx->sk.sk_lock.slock)
+	__releases(&rx->sk.sk_lock)
 	__acquires(&call->user_mutex)
 {
 	struct rxrpc_conn_parameters cp;
@@ -657,7 +657,6 @@ rxrpc_new_client_call_for_sendmsg(struct rxrpc_sock *rx, struct msghdr *msg,
  * - the socket may be either a client socket or a server socket
  */
 int rxrpc_do_sendmsg(struct rxrpc_sock *rx, struct msghdr *msg, size_t len)
-	__releases(&rx->sk.sk_lock.slock)
 {
 	struct rxrpc_call *call;
 	bool dropped_lock = false;
@@ -759,14 +758,21 @@ int rxrpc_do_sendmsg(struct rxrpc_sock *rx, struct msghdr *msg, size_t len)
 	if (rxrpc_call_is_complete(call)) {
 		/* it's too late for this call */
 		ret = -ESHUTDOWN;
-	} else if (p.command == RXRPC_CMD_SEND_ABORT) {
+		goto out_put_unlock;
+	}
+
+	switch (p.command) {
+	case RXRPC_CMD_SEND_ABORT:
 		rxrpc_propose_abort(call, p.abort_code, -ECONNABORTED,
 				    rxrpc_abort_call_sendmsg);
 		ret = 0;
-	} else if (p.command != RXRPC_CMD_SEND_DATA) {
-		ret = -EINVAL;
-	} else {
+		break;
+	case RXRPC_CMD_SEND_DATA:
 		ret = rxrpc_send_data(rx, call, msg, len, NULL, &dropped_lock);
+		break;
+	default:
+		ret = -EINVAL;
+		break;
 	}
 
 out_put_unlock:
@@ -794,6 +800,8 @@ error_release_sock:
  * appropriate to sending data.  No control data should be supplied in @msg,
  * nor should an address be supplied.  MSG_MORE should be flagged if there's
  * more data to come, otherwise this data will end the transmission phase.
+ *
+ * Return: %0 if successful and a negative error code otherwise.
  */
 int rxrpc_kernel_send_data(struct socket *sock, struct rxrpc_call *call,
 			   struct msghdr *msg, size_t len,
@@ -829,8 +837,9 @@ EXPORT_SYMBOL(rxrpc_kernel_send_data);
  * @error: Local error value
  * @why: Indication as to why.
  *
- * Allow a kernel service to abort a call, if it's still in an abortable state
- * and return true if the call was aborted, false if it was already complete.
+ * Allow a kernel service to abort a call if it's still in an abortable state.
+ *
+ * Return: %true if the call was aborted, %false if it was already complete.
  */
 bool rxrpc_kernel_abort_call(struct socket *sock, struct rxrpc_call *call,
 			     u32 abort_code, int error, enum rxrpc_abort_reason why)
diff --git a/net/rxrpc/server_key.c b/net/rxrpc/server_key.c
index e51940589ee5..36b05fd842a7 100644
--- a/net/rxrpc/server_key.c
+++ b/net/rxrpc/server_key.c
@@ -152,6 +152,8 @@ int rxrpc_server_keyring(struct rxrpc_sock *rx, sockptr_t optval, int optlen)
  *
  * Set the server security keyring on an rxrpc socket.  This is used to provide
  * the encryption keys for a kernel service.
+ *
+ * Return: %0 if successful and a negative error code otherwise.
  */
 int rxrpc_sock_set_security_keyring(struct sock *sk, struct key *keyring)
 {
@@ -169,3 +171,43 @@ int rxrpc_sock_set_security_keyring(struct sock *sk, struct key *keyring)
 	return ret;
 }
 EXPORT_SYMBOL(rxrpc_sock_set_security_keyring);
+
+/**
+ * rxrpc_sock_set_manage_response - Set the manage-response flag for a kernel service
+ * @sk: The socket to set the keyring on
+ * @set: True to set, false to clear the flag
+ *
+ * Set the flag on an rxrpc socket to say that the caller wants to manage the
+ * RESPONSE packet and the user-defined data it may contain.  Setting this
+ * means that recvmsg() will return messages with RXRPC_CHALLENGED in the
+ * control message buffer containing information about the challenge.
+ *
+ * The user should respond to the challenge by passing RXRPC_RESPOND or
+ * RXRPC_RESPOND_ABORT control messages with sendmsg() to the same call.
+ * Supplementary control messages, such as RXRPC_RESP_RXGK_APPDATA, may be
+ * included to indicate the parts the user wants to supply.
+ *
+ * The server will be passed the response data with a RXRPC_RESPONDED control
+ * message when it gets the first data from each call.
+ *
+ * Note that this is only honoured by security classes that need auxiliary data
+ * (e.g. RxGK).  Those that don't offer the facility (e.g. RxKAD) respond
+ * without consulting userspace.
+ *
+ * Return: The previous setting.
+ */
+int rxrpc_sock_set_manage_response(struct sock *sk, bool set)
+{
+	struct rxrpc_sock *rx = rxrpc_sk(sk);
+	int ret;
+
+	lock_sock(sk);
+	ret = !!test_bit(RXRPC_SOCK_MANAGE_RESPONSE, &rx->flags);
+	if (set)
+		set_bit(RXRPC_SOCK_MANAGE_RESPONSE, &rx->flags);
+	else
+		clear_bit(RXRPC_SOCK_MANAGE_RESPONSE, &rx->flags);
+	release_sock(sk);
+	return ret;
+}
+EXPORT_SYMBOL(rxrpc_sock_set_manage_response);