rxrpc: Allow CHALLENGEs to the passed to the app for a RESPONSE

Allow the app to request that CHALLENGEs be passed to it through an
out-of-band queue that allows recvmsg() to pick it up so that the app can
add data to it with sendmsg().

This will allow the application (AFS or userspace) to interact with the
process if it wants to and put values into user-defined fields.  This will
be used by AFS when talking to a fileserver to supply that fileserver with
a crypto key by which callback RPCs can be encrypted (ie. notifications
from the fileserver to the client).

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
Link: https://patch.msgid.link/20250411095303.2316168-5-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

5 files changed, 99 insertions, 0 deletions

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..efe6a23c8477
--- /dev/null
+++ b/fs/afs/cm_security.c
@@ -0,0 +1,73 @@
+// 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 "internal.h"
+#include "afs_fs.h"
+#include "protocol_yfs.h"
+#define RXRPC_TRACE_ONLY_DEFINE_ENUMS
+#include <trace/events/rxrpc.h>
+
+/*
+ * Respond to an RxGK challenge, adding appdata.
+ */
+static int afs_respond_to_challenge(struct sk_buff *challenge)
+{
+	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) {
+	case RXRPC_SECURITY_RXKAD:
+		return rxkad_kernel_respond_to_challenge(challenge);
+
+	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);
+	}
+}
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 440b0e731093..b3612b700c6a 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -281,6 +281,7 @@ 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;
@@ -1059,6 +1060,11 @@ 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);
+
+/*
  * 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/rxrpc.c b/fs/afs/rxrpc.c
index a4734304e542..212af2aa85bf 100644
--- a/fs/afs/rxrpc.c
+++ b/fs/afs/rxrpc.c
@@ -25,12 +25,14 @@ 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 */
@@ -56,6 +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));
@@ -71,6 +74,10 @@ 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 = kernel_bind(socket, (struct sockaddr *) &srx, sizeof(srx));
 	if (ret == -EADDRINUSE) {
 		srx.transport.sin6.sin6_port = 0;
@@ -131,6 +138,7 @@ 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);
 
 	_debug("dework");
@@ -957,3 +965,13 @@ 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);
+}