1 files changed, 1357 insertions, 256 deletions

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 65122edf60aa..02a54d59697b 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -9,6 +9,8 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/netdevice.h>
+#include <crypto/algapi.h>
+#include <crypto/sha2.h>
 #include <net/sock.h>
 #include <net/inet_common.h>
 #include <net/inet_hashtables.h>
@@ -16,24 +18,21 @@
 #include <net/tcp.h>
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
 #include <net/ip6_route.h>
+#include <net/transp_v6.h>
 #endif
 #include <net/mptcp.h>
+#include <uapi/linux/mptcp.h>
 #include "protocol.h"
+#include "mib.h"
 
-static int subflow_rebuild_header(struct sock *sk)
-{
-	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
-	int err = 0;
+#include <trace/events/mptcp.h>
 
-	if (subflow->request_mptcp && !subflow->token) {
-		pr_debug("subflow=%p", sk);
-		err = mptcp_token_new_connect(sk);
-	}
-
-	if (err)
-		return err;
+static void mptcp_subflow_ops_undo_override(struct sock *ssk);
 
-	return subflow->icsk_af_ops->rebuild_header(sk);
+static void SUBFLOW_REQ_INC_STATS(struct request_sock *req,
+				  enum linux_mptcp_mib_field field)
+{
+	MPTCP_INC_STATS(sock_net(req_to_sk(req)), field);
 }
 
 static void subflow_req_destructor(struct request_sock *req)
@@ -42,91 +41,496 @@ static void subflow_req_destructor(struct request_sock *req)
 
 	pr_debug("subflow_req=%p", subflow_req);
 
-	if (subflow_req->mp_capable)
-		mptcp_token_destroy_request(subflow_req->token);
+	if (subflow_req->msk)
+		sock_put((struct sock *)subflow_req->msk);
+
+	mptcp_token_destroy_request(req);
 	tcp_request_sock_ops.destructor(req);
 }
 
-static void subflow_init_req(struct request_sock *req,
+static void subflow_generate_hmac(u64 key1, u64 key2, u32 nonce1, u32 nonce2,
+				  void *hmac)
+{
+	u8 msg[8];
+
+	put_unaligned_be32(nonce1, &msg[0]);
+	put_unaligned_be32(nonce2, &msg[4]);
+
+	mptcp_crypto_hmac_sha(key1, key2, msg, 8, hmac);
+}
+
+static bool mptcp_can_accept_new_subflow(const struct mptcp_sock *msk)
+{
+	return mptcp_is_fully_established((void *)msk) &&
+		((mptcp_pm_is_userspace(msk) &&
+		  mptcp_userspace_pm_active(msk)) ||
+		 READ_ONCE(msk->pm.accept_subflow));
+}
+
+/* validate received token and create truncated hmac and nonce for SYN-ACK */
+static void subflow_req_create_thmac(struct mptcp_subflow_request_sock *subflow_req)
+{
+	struct mptcp_sock *msk = subflow_req->msk;
+	u8 hmac[SHA256_DIGEST_SIZE];
+
+	get_random_bytes(&subflow_req->local_nonce, sizeof(u32));
+
+	subflow_generate_hmac(msk->local_key, msk->remote_key,
+			      subflow_req->local_nonce,
+			      subflow_req->remote_nonce, hmac);
+
+	subflow_req->thmac = get_unaligned_be64(hmac);
+}
+
+static struct mptcp_sock *subflow_token_join_request(struct request_sock *req)
+{
+	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
+	struct mptcp_sock *msk;
+	int local_id;
+
+	msk = mptcp_token_get_sock(sock_net(req_to_sk(req)), subflow_req->token);
+	if (!msk) {
+		SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINNOTOKEN);
+		return NULL;
+	}
+
+	local_id = mptcp_pm_get_local_id(msk, (struct sock_common *)req);
+	if (local_id < 0) {
+		sock_put((struct sock *)msk);
+		return NULL;
+	}
+	subflow_req->local_id = local_id;
+
+	return msk;
+}
+
+static void subflow_init_req(struct request_sock *req, const struct sock *sk_listener)
+{
+	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
+
+	subflow_req->mp_capable = 0;
+	subflow_req->mp_join = 0;
+	subflow_req->csum_reqd = mptcp_is_checksum_enabled(sock_net(sk_listener));
+	subflow_req->allow_join_id0 = mptcp_allow_join_id0(sock_net(sk_listener));
+	subflow_req->msk = NULL;
+	mptcp_token_init_request(req);
+}
+
+static bool subflow_use_different_sport(struct mptcp_sock *msk, const struct sock *sk)
+{
+	return inet_sk(sk)->inet_sport != inet_sk((struct sock *)msk)->inet_sport;
+}
+
+static void subflow_add_reset_reason(struct sk_buff *skb, u8 reason)
+{
+	struct mptcp_ext *mpext = skb_ext_add(skb, SKB_EXT_MPTCP);
+
+	if (mpext) {
+		memset(mpext, 0, sizeof(*mpext));
+		mpext->reset_reason = reason;
+	}
+}
+
+/* Init mptcp request socket.
+ *
+ * Returns an error code if a JOIN has failed and a TCP reset
+ * should be sent.
+ */
+static int subflow_check_req(struct request_sock *req,
 			     const struct sock *sk_listener,
 			     struct sk_buff *skb)
 {
 	struct mptcp_subflow_context *listener = mptcp_subflow_ctx(sk_listener);
 	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
-	struct tcp_options_received rx_opt;
+	struct mptcp_options_received mp_opt;
+	bool opt_mp_capable, opt_mp_join;
 
 	pr_debug("subflow_req=%p, listener=%p", subflow_req, listener);
 
-	memset(&rx_opt.mptcp, 0, sizeof(rx_opt.mptcp));
-	mptcp_get_options(skb, &rx_opt);
-
-	subflow_req->mp_capable = 0;
-	subflow_req->remote_key_valid = 0;
-
 #ifdef CONFIG_TCP_MD5SIG
 	/* no MPTCP if MD5SIG is enabled on this socket or we may run out of
 	 * TCP option space.
 	 */
 	if (rcu_access_pointer(tcp_sk(sk_listener)->md5sig_info))
-		return;
+		return -EINVAL;
 #endif
 
-	if (rx_opt.mptcp.mp_capable && listener->request_mptcp) {
-		int err;
+	mptcp_get_options(skb, &mp_opt);
+
+	opt_mp_capable = !!(mp_opt.suboptions & OPTIONS_MPTCP_MPC);
+	opt_mp_join = !!(mp_opt.suboptions & OPTIONS_MPTCP_MPJ);
+	if (opt_mp_capable) {
+		SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_MPCAPABLEPASSIVE);
+
+		if (opt_mp_join)
+			return 0;
+	} else if (opt_mp_join) {
+		SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINSYNRX);
+	}
+
+	if (opt_mp_capable && listener->request_mptcp) {
+		int err, retries = MPTCP_TOKEN_MAX_RETRIES;
+
+		subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq;
+again:
+		do {
+			get_random_bytes(&subflow_req->local_key, sizeof(subflow_req->local_key));
+		} while (subflow_req->local_key == 0);
+
+		if (unlikely(req->syncookie)) {
+			mptcp_crypto_key_sha(subflow_req->local_key,
+					     &subflow_req->token,
+					     &subflow_req->idsn);
+			if (mptcp_token_exists(subflow_req->token)) {
+				if (retries-- > 0)
+					goto again;
+				SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_TOKENFALLBACKINIT);
+			} else {
+				subflow_req->mp_capable = 1;
+			}
+			return 0;
+		}
 
 		err = mptcp_token_new_request(req);
 		if (err == 0)
 			subflow_req->mp_capable = 1;
+		else if (retries-- > 0)
+			goto again;
+		else
+			SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_TOKENFALLBACKINIT);
 
+	} else if (opt_mp_join && listener->request_mptcp) {
 		subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq;
+		subflow_req->mp_join = 1;
+		subflow_req->backup = mp_opt.backup;
+		subflow_req->remote_id = mp_opt.join_id;
+		subflow_req->token = mp_opt.token;
+		subflow_req->remote_nonce = mp_opt.nonce;
+		subflow_req->msk = subflow_token_join_request(req);
+
+		/* Can't fall back to TCP in this case. */
+		if (!subflow_req->msk) {
+			subflow_add_reset_reason(skb, MPTCP_RST_EMPTCP);
+			return -EPERM;
+		}
+
+		if (subflow_use_different_sport(subflow_req->msk, sk_listener)) {
+			pr_debug("syn inet_sport=%d %d",
+				 ntohs(inet_sk(sk_listener)->inet_sport),
+				 ntohs(inet_sk((struct sock *)subflow_req->msk)->inet_sport));
+			if (!mptcp_pm_sport_in_anno_list(subflow_req->msk, sk_listener)) {
+				SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_MISMATCHPORTSYNRX);
+				return -EPERM;
+			}
+			SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINPORTSYNRX);
+		}
+
+		subflow_req_create_thmac(subflow_req);
+
+		if (unlikely(req->syncookie)) {
+			if (mptcp_can_accept_new_subflow(subflow_req->msk))
+				subflow_init_req_cookie_join_save(subflow_req, skb);
+			else
+				return -EPERM;
+		}
+
+		pr_debug("token=%u, remote_nonce=%u msk=%p", subflow_req->token,
+			 subflow_req->remote_nonce, subflow_req->msk);
+	}
+
+	return 0;
+}
+
+int mptcp_subflow_init_cookie_req(struct request_sock *req,
+				  const struct sock *sk_listener,
+				  struct sk_buff *skb)
+{
+	struct mptcp_subflow_context *listener = mptcp_subflow_ctx(sk_listener);
+	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
+	struct mptcp_options_received mp_opt;
+	bool opt_mp_capable, opt_mp_join;
+	int err;
+
+	subflow_init_req(req, sk_listener);
+	mptcp_get_options(skb, &mp_opt);
+
+	opt_mp_capable = !!(mp_opt.suboptions & OPTIONS_MPTCP_MPC);
+	opt_mp_join = !!(mp_opt.suboptions & OPTIONS_MPTCP_MPJ);
+	if (opt_mp_capable && opt_mp_join)
+		return -EINVAL;
+
+	if (opt_mp_capable && listener->request_mptcp) {
+		if (mp_opt.sndr_key == 0)
+			return -EINVAL;
+
+		subflow_req->local_key = mp_opt.rcvr_key;
+		err = mptcp_token_new_request(req);
+		if (err)
+			return err;
+
+		subflow_req->mp_capable = 1;
+		subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq - 1;
+	} else if (opt_mp_join && listener->request_mptcp) {
+		if (!mptcp_token_join_cookie_init_state(subflow_req, skb))
+			return -EINVAL;
+
+		subflow_req->mp_join = 1;
+		subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq - 1;
 	}
+
+	return 0;
 }
+EXPORT_SYMBOL_GPL(mptcp_subflow_init_cookie_req);
 
-static void subflow_v4_init_req(struct request_sock *req,
-				const struct sock *sk_listener,
-				struct sk_buff *skb)
+static struct dst_entry *subflow_v4_route_req(const struct sock *sk,
+					      struct sk_buff *skb,
+					      struct flowi *fl,
+					      struct request_sock *req)
 {
+	struct dst_entry *dst;
+	int err;
+
 	tcp_rsk(req)->is_mptcp = 1;
+	subflow_init_req(req, sk);
+
+	dst = tcp_request_sock_ipv4_ops.route_req(sk, skb, fl, req);
+	if (!dst)
+		return NULL;
 
-	tcp_request_sock_ipv4_ops.init_req(req, sk_listener, skb);
+	err = subflow_check_req(req, sk, skb);
+	if (err == 0)
+		return dst;
 
-	subflow_init_req(req, sk_listener, skb);
+	dst_release(dst);
+	if (!req->syncookie)
+		tcp_request_sock_ops.send_reset(sk, skb);
+	return NULL;
 }
 
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
-static void subflow_v6_init_req(struct request_sock *req,
-				const struct sock *sk_listener,
-				struct sk_buff *skb)
+static struct dst_entry *subflow_v6_route_req(const struct sock *sk,
+					      struct sk_buff *skb,
+					      struct flowi *fl,
+					      struct request_sock *req)
 {
+	struct dst_entry *dst;
+	int err;
+
 	tcp_rsk(req)->is_mptcp = 1;
+	subflow_init_req(req, sk);
 
-	tcp_request_sock_ipv6_ops.init_req(req, sk_listener, skb);
+	dst = tcp_request_sock_ipv6_ops.route_req(sk, skb, fl, req);
+	if (!dst)
+		return NULL;
+
+	err = subflow_check_req(req, sk, skb);
+	if (err == 0)
+		return dst;
 
-	subflow_init_req(req, sk_listener, skb);
+	dst_release(dst);
+	if (!req->syncookie)
+		tcp6_request_sock_ops.send_reset(sk, skb);
+	return NULL;
 }
 #endif
 
+/* validate received truncated hmac and create hmac for third ACK */
+static bool subflow_thmac_valid(struct mptcp_subflow_context *subflow)
+{
+	u8 hmac[SHA256_DIGEST_SIZE];
+	u64 thmac;
+
+	subflow_generate_hmac(subflow->remote_key, subflow->local_key,
+			      subflow->remote_nonce, subflow->local_nonce,
+			      hmac);
+
+	thmac = get_unaligned_be64(hmac);
+	pr_debug("subflow=%p, token=%u, thmac=%llu, subflow->thmac=%llu\n",
+		 subflow, subflow->token, thmac, subflow->thmac);
+
+	return thmac == subflow->thmac;
+}
+
+void mptcp_subflow_reset(struct sock *ssk)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+	struct sock *sk = subflow->conn;
+
+	/* must hold: tcp_done() could drop last reference on parent */
+	sock_hold(sk);
+
+	tcp_set_state(ssk, TCP_CLOSE);
+	tcp_send_active_reset(ssk, GFP_ATOMIC);
+	tcp_done(ssk);
+	if (!test_and_set_bit(MPTCP_WORK_CLOSE_SUBFLOW, &mptcp_sk(sk)->flags) &&
+	    schedule_work(&mptcp_sk(sk)->work))
+		return; /* worker will put sk for us */
+
+	sock_put(sk);
+}
+
+static bool subflow_use_different_dport(struct mptcp_sock *msk, const struct sock *sk)
+{
+	return inet_sk(sk)->inet_dport != inet_sk((struct sock *)msk)->inet_dport;
+}
+
+void __mptcp_set_connected(struct sock *sk)
+{
+	if (sk->sk_state == TCP_SYN_SENT) {
+		inet_sk_state_store(sk, TCP_ESTABLISHED);
+		sk->sk_state_change(sk);
+	}
+}
+
+static void mptcp_set_connected(struct sock *sk)
+{
+	mptcp_data_lock(sk);
+	if (!sock_owned_by_user(sk))
+		__mptcp_set_connected(sk);
+	else
+		__set_bit(MPTCP_CONNECTED, &mptcp_sk(sk)->cb_flags);
+	mptcp_data_unlock(sk);
+}
+
 static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct mptcp_options_received mp_opt;
+	struct sock *parent = subflow->conn;
 
 	subflow->icsk_af_ops->sk_rx_dst_set(sk, skb);
 
-	if (subflow->conn && !subflow->conn_finished) {
-		pr_debug("subflow=%p, remote_key=%llu", mptcp_subflow_ctx(sk),
+	/* be sure no special action on any packet other than syn-ack */
+	if (subflow->conn_finished)
+		return;
+
+	mptcp_propagate_sndbuf(parent, sk);
+	subflow->rel_write_seq = 1;
+	subflow->conn_finished = 1;
+	subflow->ssn_offset = TCP_SKB_CB(skb)->seq;
+	pr_debug("subflow=%p synack seq=%x", subflow, subflow->ssn_offset);
+
+	mptcp_get_options(skb, &mp_opt);
+	if (subflow->request_mptcp) {
+		if (!(mp_opt.suboptions & OPTIONS_MPTCP_MPC)) {
+			MPTCP_INC_STATS(sock_net(sk),
+					MPTCP_MIB_MPCAPABLEACTIVEFALLBACK);
+			mptcp_do_fallback(sk);
+			pr_fallback(mptcp_sk(subflow->conn));
+			goto fallback;
+		}
+
+		if (mp_opt.suboptions & OPTION_MPTCP_CSUMREQD)
+			WRITE_ONCE(mptcp_sk(parent)->csum_enabled, true);
+		if (mp_opt.deny_join_id0)
+			WRITE_ONCE(mptcp_sk(parent)->pm.remote_deny_join_id0, true);
+		subflow->mp_capable = 1;
+		subflow->can_ack = 1;
+		subflow->remote_key = mp_opt.sndr_key;
+		pr_debug("subflow=%p, remote_key=%llu", subflow,
 			 subflow->remote_key);
+		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPCAPABLEACTIVEACK);
 		mptcp_finish_connect(sk);
-		subflow->conn_finished = 1;
+		mptcp_set_connected(parent);
+	} else if (subflow->request_join) {
+		u8 hmac[SHA256_DIGEST_SIZE];
+
+		if (!(mp_opt.suboptions & OPTIONS_MPTCP_MPJ)) {
+			subflow->reset_reason = MPTCP_RST_EMPTCP;
+			goto do_reset;
+		}
 
-		if (skb) {
-			pr_debug("synack seq=%u", TCP_SKB_CB(skb)->seq);
-			subflow->ssn_offset = TCP_SKB_CB(skb)->seq;
+		subflow->backup = mp_opt.backup;
+		subflow->thmac = mp_opt.thmac;
+		subflow->remote_nonce = mp_opt.nonce;
+		subflow->remote_id = mp_opt.join_id;
+		pr_debug("subflow=%p, thmac=%llu, remote_nonce=%u backup=%d",
+			 subflow, subflow->thmac, subflow->remote_nonce,
+			 subflow->backup);
+
+		if (!subflow_thmac_valid(subflow)) {
+			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_JOINACKMAC);
+			subflow->reset_reason = MPTCP_RST_EMPTCP;
+			goto do_reset;
 		}
+
+		if (!mptcp_finish_join(sk))
+			goto do_reset;
+
+		subflow_generate_hmac(subflow->local_key, subflow->remote_key,
+				      subflow->local_nonce,
+				      subflow->remote_nonce,
+				      hmac);
+		memcpy(subflow->hmac, hmac, MPTCPOPT_HMAC_LEN);
+
+		subflow->mp_join = 1;
+		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_JOINSYNACKRX);
+
+		if (subflow_use_different_dport(mptcp_sk(parent), sk)) {
+			pr_debug("synack inet_dport=%d %d",
+				 ntohs(inet_sk(sk)->inet_dport),
+				 ntohs(inet_sk(parent)->inet_dport));
+			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_JOINPORTSYNACKRX);
+		}
+	} else if (mptcp_check_fallback(sk)) {
+fallback:
+		mptcp_rcv_space_init(mptcp_sk(parent), sk);
+		mptcp_set_connected(parent);
 	}
+	return;
+
+do_reset:
+	subflow->reset_transient = 0;
+	mptcp_subflow_reset(sk);
+}
+
+static void subflow_set_local_id(struct mptcp_subflow_context *subflow, int local_id)
+{
+	subflow->local_id = local_id;
+	subflow->local_id_valid = 1;
+}
+
+static int subflow_chk_local_id(struct sock *sk)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
+	int err;
+
+	if (likely(subflow->local_id_valid))
+		return 0;
+
+	err = mptcp_pm_get_local_id(msk, (struct sock_common *)sk);
+	if (err < 0)
+		return err;
+
+	subflow_set_local_id(subflow, err);
+	return 0;
+}
+
+static int subflow_rebuild_header(struct sock *sk)
+{
+	int err = subflow_chk_local_id(sk);
+
+	if (unlikely(err < 0))
+		return err;
+
+	return inet_sk_rebuild_header(sk);
+}
+
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+static int subflow_v6_rebuild_header(struct sock *sk)
+{
+	int err = subflow_chk_local_id(sk);
+
+	if (unlikely(err < 0))
+		return err;
+
+	return inet6_sk_rebuild_header(sk);
 }
+#endif
 
-static struct request_sock_ops subflow_request_sock_ops;
-static struct tcp_request_sock_ops subflow_request_sock_ipv4_ops;
+struct request_sock_ops mptcp_subflow_request_sock_ops;
+static struct tcp_request_sock_ops subflow_request_sock_ipv4_ops __ro_after_init;
 
 static int subflow_v4_conn_request(struct sock *sk, struct sk_buff *skb)
 {
@@ -138,7 +542,7 @@ static int subflow_v4_conn_request(struct sock *sk, struct sk_buff *skb)
 	if (skb_rtable(skb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
 		goto drop;
 
-	return tcp_conn_request(&subflow_request_sock_ops,
+	return tcp_conn_request(&mptcp_subflow_request_sock_ops,
 				&subflow_request_sock_ipv4_ops,
 				sk, skb);
 drop:
@@ -147,9 +551,10 @@ drop:
 }
 
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
-static struct tcp_request_sock_ops subflow_request_sock_ipv6_ops;
-static struct inet_connection_sock_af_ops subflow_v6_specific;
-static struct inet_connection_sock_af_ops subflow_v6m_specific;
+static struct tcp_request_sock_ops subflow_request_sock_ipv6_ops __ro_after_init;
+static struct inet_connection_sock_af_ops subflow_v6_specific __ro_after_init;
+static struct inet_connection_sock_af_ops subflow_v6m_specific __ro_after_init;
+static struct proto tcpv6_prot_override;
 
 static int subflow_v6_conn_request(struct sock *sk, struct sk_buff *skb)
 {
@@ -163,7 +568,12 @@ static int subflow_v6_conn_request(struct sock *sk, struct sk_buff *skb)
 	if (!ipv6_unicast_destination(skb))
 		goto drop;
 
-	return tcp_conn_request(&subflow_request_sock_ops,
+	if (ipv6_addr_v4mapped(&ipv6_hdr(skb)->saddr)) {
+		__IP6_INC_STATS(sock_net(sk), NULL, IPSTATS_MIB_INHDRERRORS);
+		return 0;
+	}
+
+	return tcp_conn_request(&mptcp_subflow_request_sock_ops,
 				&subflow_request_sock_ipv6_ops, sk, skb);
 
 drop:
@@ -172,6 +582,71 @@ drop:
 }
 #endif
 
+/* validate hmac received in third ACK */
+static bool subflow_hmac_valid(const struct request_sock *req,
+			       const struct mptcp_options_received *mp_opt)
+{
+	const struct mptcp_subflow_request_sock *subflow_req;
+	u8 hmac[SHA256_DIGEST_SIZE];
+	struct mptcp_sock *msk;
+
+	subflow_req = mptcp_subflow_rsk(req);
+	msk = subflow_req->msk;
+	if (!msk)
+		return false;
+
+	subflow_generate_hmac(msk->remote_key, msk->local_key,
+			      subflow_req->remote_nonce,
+			      subflow_req->local_nonce, hmac);
+
+	return !crypto_memneq(hmac, mp_opt->hmac, MPTCPOPT_HMAC_LEN);
+}
+
+static void mptcp_force_close(struct sock *sk)
+{
+	/* the msk is not yet exposed to user-space */
+	inet_sk_state_store(sk, TCP_CLOSE);
+	sk_common_release(sk);
+}
+
+static void subflow_ulp_fallback(struct sock *sk,
+				 struct mptcp_subflow_context *old_ctx)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+
+	mptcp_subflow_tcp_fallback(sk, old_ctx);
+	icsk->icsk_ulp_ops = NULL;
+	rcu_assign_pointer(icsk->icsk_ulp_data, NULL);
+	tcp_sk(sk)->is_mptcp = 0;
+
+	mptcp_subflow_ops_undo_override(sk);
+}
+
+static void subflow_drop_ctx(struct sock *ssk)
+{
+	struct mptcp_subflow_context *ctx = mptcp_subflow_ctx(ssk);
+
+	if (!ctx)
+		return;
+
+	subflow_ulp_fallback(ssk, ctx);
+	if (ctx->conn)
+		sock_put(ctx->conn);
+
+	kfree_rcu(ctx, rcu);
+}
+
+void mptcp_subflow_fully_established(struct mptcp_subflow_context *subflow,
+				     struct mptcp_options_received *mp_opt)
+{
+	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
+
+	subflow->remote_key = mp_opt->sndr_key;
+	subflow->fully_established = 1;
+	subflow->can_ack = 1;
+	WRITE_ONCE(msk->fully_established, true);
+}
+
 static struct sock *subflow_syn_recv_sock(const struct sock *sk,
 					  struct sk_buff *skb,
 					  struct request_sock *req,
@@ -181,32 +656,51 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
 {
 	struct mptcp_subflow_context *listener = mptcp_subflow_ctx(sk);
 	struct mptcp_subflow_request_sock *subflow_req;
-	struct tcp_options_received opt_rx;
+	struct mptcp_options_received mp_opt;
+	bool fallback, fallback_is_fatal;
+	struct sock *new_msk = NULL;
 	struct sock *child;
 
 	pr_debug("listener=%p, req=%p, conn=%p", listener, req, listener->conn);
 
-	if (tcp_rsk(req)->is_mptcp == 0)
+	/* After child creation we must look for MPC even when options
+	 * are not parsed
+	 */
+	mp_opt.suboptions = 0;
+
+	/* hopefully temporary handling for MP_JOIN+syncookie */
+	subflow_req = mptcp_subflow_rsk(req);
+	fallback_is_fatal = tcp_rsk(req)->is_mptcp && subflow_req->mp_join;
+	fallback = !tcp_rsk(req)->is_mptcp;
+	if (fallback)
 		goto create_child;
 
 	/* if the sk is MP_CAPABLE, we try to fetch the client key */
-	subflow_req = mptcp_subflow_rsk(req);
 	if (subflow_req->mp_capable) {
-		if (TCP_SKB_CB(skb)->seq != subflow_req->ssn_offset + 1) {
-			/* here we can receive and accept an in-window,
-			 * out-of-order pkt, which will not carry the MP_CAPABLE
-			 * opt even on mptcp enabled paths
-			 */
+		/* we can receive and accept an in-window, out-of-order pkt,
+		 * which may not carry the MP_CAPABLE opt even on mptcp enabled
+		 * paths: always try to extract the peer key, and fallback
+		 * for packets missing it.
+		 * Even OoO DSS packets coming legitly after dropped or
+		 * reordered MPC will cause fallback, but we don't have other
+		 * options.
+		 */
+		mptcp_get_options(skb, &mp_opt);
+		if (!(mp_opt.suboptions & OPTIONS_MPTCP_MPC)) {
+			fallback = true;
 			goto create_child;
 		}
 
-		opt_rx.mptcp.mp_capable = 0;
-		mptcp_get_options(skb, &opt_rx);
-		if (opt_rx.mptcp.mp_capable) {
-			subflow_req->remote_key = opt_rx.mptcp.sndr_key;
-			subflow_req->remote_key_valid = 1;
-		} else {
-			subflow_req->mp_capable = 0;
+		new_msk = mptcp_sk_clone(listener->conn, &mp_opt, req);
+		if (!new_msk)
+			fallback = true;
+	} else if (subflow_req->mp_join) {
+		mptcp_get_options(skb, &mp_opt);
+		if (!(mp_opt.suboptions & OPTIONS_MPTCP_MPJ) ||
+		    !subflow_hmac_valid(req, &mp_opt) ||
+		    !mptcp_can_accept_new_subflow(subflow_req->msk)) {
+			SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINACKMAC);
+			fallback = true;
 		}
 	}
 
@@ -217,50 +711,129 @@ create_child:
 	if (child && *own_req) {
 		struct mptcp_subflow_context *ctx = mptcp_subflow_ctx(child);
 
-		/* we have null ctx on TCP fallback, not fatal on MPC
-		 * handshake
+		tcp_rsk(req)->drop_req = false;
+
+		/* we need to fallback on ctx allocation failure and on pre-reqs
+		 * checking above. In the latter scenario we additionally need
+		 * to reset the context to non MPTCP status.
 		 */
-		if (!ctx)
-			return child;
+		if (!ctx || fallback) {
+			if (fallback_is_fatal) {
+				subflow_add_reset_reason(skb, MPTCP_RST_EMPTCP);
+				goto dispose_child;
+			}
+
+			if (new_msk)
+				mptcp_copy_inaddrs(new_msk, child);
+			subflow_drop_ctx(child);
+			goto out;
+		}
+
+		/* ssk inherits options of listener sk */
+		ctx->setsockopt_seq = listener->setsockopt_seq;
 
 		if (ctx->mp_capable) {
-			if (mptcp_token_new_accept(ctx->token))
-				goto close_child;
+			/* this can't race with mptcp_close(), as the msk is
+			 * not yet exposted to user-space
+			 */
+			inet_sk_state_store((void *)new_msk, TCP_ESTABLISHED);
+
+			/* record the newly created socket as the first msk
+			 * subflow, but don't link it yet into conn_list
+			 */
+			WRITE_ONCE(mptcp_sk(new_msk)->first, child);
+
+			/* new mpc subflow takes ownership of the newly
+			 * created mptcp socket
+			 */
+			mptcp_sk(new_msk)->setsockopt_seq = ctx->setsockopt_seq;
+			mptcp_pm_new_connection(mptcp_sk(new_msk), child, 1);
+			mptcp_token_accept(subflow_req, mptcp_sk(new_msk));
+			ctx->conn = new_msk;
+			new_msk = NULL;
+
+			/* set msk addresses early to ensure mptcp_pm_get_local_id()
+			 * uses the correct data
+			 */
+			mptcp_copy_inaddrs(ctx->conn, child);
+
+			/* with OoO packets we can reach here without ingress
+			 * mpc option
+			 */
+			if (mp_opt.suboptions & OPTIONS_MPTCP_MPC)
+				mptcp_subflow_fully_established(ctx, &mp_opt);
+		} else if (ctx->mp_join) {
+			struct mptcp_sock *owner;
+
+			owner = subflow_req->msk;
+			if (!owner) {
+				subflow_add_reset_reason(skb, MPTCP_RST_EPROHIBIT);
+				goto dispose_child;
+			}
+
+			/* move the msk reference ownership to the subflow */
+			subflow_req->msk = NULL;
+			ctx->conn = (struct sock *)owner;
+
+			if (subflow_use_different_sport(owner, sk)) {
+				pr_debug("ack inet_sport=%d %d",
+					 ntohs(inet_sk(sk)->inet_sport),
+					 ntohs(inet_sk((struct sock *)owner)->inet_sport));
+				if (!mptcp_pm_sport_in_anno_list(owner, sk)) {
+					SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_MISMATCHPORTACKRX);
+					goto dispose_child;
+				}
+				SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINPORTACKRX);
+			}
+
+			if (!mptcp_finish_join(child))
+				goto dispose_child;
+
+			SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINACKRX);
+			tcp_rsk(req)->drop_req = true;
 		}
 	}
 
+out:
+	/* dispose of the left over mptcp master, if any */
+	if (unlikely(new_msk))
+		mptcp_force_close(new_msk);
+
+	/* check for expected invariant - should never trigger, just help
+	 * catching eariler subtle bugs
+	 */
+	WARN_ON_ONCE(child && *own_req && tcp_sk(child)->is_mptcp &&
+		     (!mptcp_subflow_ctx(child) ||
+		      !mptcp_subflow_ctx(child)->conn));
 	return child;
 
-close_child:
-	pr_debug("closing child socket");
-	tcp_send_active_reset(child, GFP_ATOMIC);
-	inet_csk_prepare_forced_close(child);
+dispose_child:
+	subflow_drop_ctx(child);
+	tcp_rsk(req)->drop_req = true;
+	inet_csk_prepare_for_destroy_sock(child);
 	tcp_done(child);
-	return NULL;
+	req->rsk_ops->send_reset(sk, skb);
+
+	/* The last child reference will be released by the caller */
+	return child;
 }
 
-static struct inet_connection_sock_af_ops subflow_specific;
+static struct inet_connection_sock_af_ops subflow_specific __ro_after_init;
+static struct proto tcp_prot_override;
 
 enum mapping_status {
 	MAPPING_OK,
 	MAPPING_INVALID,
 	MAPPING_EMPTY,
-	MAPPING_DATA_FIN
+	MAPPING_DATA_FIN,
+	MAPPING_DUMMY,
+	MAPPING_BAD_CSUM
 };
 
-static u64 expand_seq(u64 old_seq, u16 old_data_len, u64 seq)
-{
-	if ((u32)seq == (u32)old_seq)
-		return old_seq;
-
-	/* Assume map covers data not mapped yet. */
-	return seq | ((old_seq + old_data_len + 1) & GENMASK_ULL(63, 32));
-}
-
-static void warn_bad_map(struct mptcp_subflow_context *subflow, u32 ssn)
+static void dbg_bad_map(struct mptcp_subflow_context *subflow, u32 ssn)
 {
-	WARN_ONCE(1, "Bad mapping: ssn=%d map_seq=%d map_data_len=%d",
-		  ssn, subflow->map_subflow_seq, subflow->map_data_len);
+	pr_debug("Bad mapping: ssn=%d map_seq=%d map_data_len=%d",
+		 ssn, subflow->map_subflow_seq, subflow->map_data_len);
 }
 
 static bool skb_is_fully_mapped(struct sock *ssk, struct sk_buff *skb)
@@ -285,21 +858,102 @@ static bool validate_mapping(struct sock *ssk, struct sk_buff *skb)
 		/* Mapping covers data later in the subflow stream,
 		 * currently unsupported.
 		 */
-		warn_bad_map(subflow, ssn);
+		dbg_bad_map(subflow, ssn);
 		return false;
 	}
 	if (unlikely(!before(ssn, subflow->map_subflow_seq +
 				  subflow->map_data_len))) {
 		/* Mapping does covers past subflow data, invalid */
-		warn_bad_map(subflow, ssn + skb->len);
+		dbg_bad_map(subflow, ssn);
 		return false;
 	}
 	return true;
 }
 
-static enum mapping_status get_mapping_status(struct sock *ssk)
+static enum mapping_status validate_data_csum(struct sock *ssk, struct sk_buff *skb,
+					      bool csum_reqd)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+	u32 offset, seq, delta;
+	__sum16 csum;
+	int len;
+
+	if (!csum_reqd)
+		return MAPPING_OK;
+
+	/* mapping already validated on previous traversal */
+	if (subflow->map_csum_len == subflow->map_data_len)
+		return MAPPING_OK;
+
+	/* traverse the receive queue, ensuring it contains a full
+	 * DSS mapping and accumulating the related csum.
+	 * Preserve the accoumlate csum across multiple calls, to compute
+	 * the csum only once
+	 */
+	delta = subflow->map_data_len - subflow->map_csum_len;
+	for (;;) {
+		seq = tcp_sk(ssk)->copied_seq + subflow->map_csum_len;
+		offset = seq - TCP_SKB_CB(skb)->seq;
+
+		/* if the current skb has not been accounted yet, csum its contents
+		 * up to the amount covered by the current DSS
+		 */
+		if (offset < skb->len) {
+			__wsum csum;
+
+			len = min(skb->len - offset, delta);
+			csum = skb_checksum(skb, offset, len, 0);
+			subflow->map_data_csum = csum_block_add(subflow->map_data_csum, csum,
+								subflow->map_csum_len);
+
+			delta -= len;
+			subflow->map_csum_len += len;
+		}
+		if (delta == 0)
+			break;
+
+		if (skb_queue_is_last(&ssk->sk_receive_queue, skb)) {
+			/* if this subflow is closed, the partial mapping
+			 * will be never completed; flush the pending skbs, so
+			 * that subflow_sched_work_if_closed() can kick in
+			 */
+			if (unlikely(ssk->sk_state == TCP_CLOSE))
+				while ((skb = skb_peek(&ssk->sk_receive_queue)))
+					sk_eat_skb(ssk, skb);
+
+			/* not enough data to validate the csum */
+			return MAPPING_EMPTY;
+		}
+
+		/* the DSS mapping for next skbs will be validated later,
+		 * when a get_mapping_status call will process such skb
+		 */
+		skb = skb->next;
+	}
+
+	/* note that 'map_data_len' accounts only for the carried data, does
+	 * not include the eventual seq increment due to the data fin,
+	 * while the pseudo header requires the original DSS data len,
+	 * including that
+	 */
+	csum = __mptcp_make_csum(subflow->map_seq,
+				 subflow->map_subflow_seq,
+				 subflow->map_data_len + subflow->map_data_fin,
+				 subflow->map_data_csum);
+	if (unlikely(csum)) {
+		MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DATACSUMERR);
+		return MAPPING_BAD_CSUM;
+	}
+
+	subflow->valid_csum_seen = 1;
+	return MAPPING_OK;
+}
+
+static enum mapping_status get_mapping_status(struct sock *ssk,
+					      struct mptcp_sock *msk)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+	bool csum_reqd = READ_ONCE(msk->csum_enabled);
 	struct mptcp_ext *mpext;
 	struct sk_buff *skb;
 	u16 data_len;
@@ -309,6 +963,9 @@ static enum mapping_status get_mapping_status(struct sock *ssk)
 	if (!skb)
 		return MAPPING_EMPTY;
 
+	if (mptcp_check_fallback(ssk))
+		return MAPPING_DUMMY;
+
 	mpext = mptcp_get_ext(skb);
 	if (!mpext || !mpext->use_map) {
 		if (!subflow->map_valid && !skb->len) {
@@ -331,19 +988,21 @@ static enum mapping_status get_mapping_status(struct sock *ssk)
 		goto validate_seq;
 	}
 
-	pr_debug("seq=%llu is64=%d ssn=%u data_len=%u data_fin=%d",
-		 mpext->data_seq, mpext->dsn64, mpext->subflow_seq,
-		 mpext->data_len, mpext->data_fin);
+	trace_get_mapping_status(mpext);
 
 	data_len = mpext->data_len;
 	if (data_len == 0) {
-		pr_err("Infinite mapping not handled");
+		pr_debug("infinite mapping received");
+		MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_INFINITEMAPRX);
+		subflow->map_data_len = 0;
 		return MAPPING_INVALID;
 	}
 
 	if (mpext->data_fin == 1) {
 		if (data_len == 1) {
-			pr_debug("DATA_FIN with no payload");
+			bool updated = mptcp_update_rcv_data_fin(msk, mpext->data_seq,
+								 mpext->dsn64);
+			pr_debug("DATA_FIN with no payload seq=%llu", mpext->data_seq);
 			if (subflow->map_valid) {
 				/* A DATA_FIN might arrive in a DSS
 				 * option before the previous mapping
@@ -353,59 +1012,160 @@ static enum mapping_status get_mapping_status(struct sock *ssk)
 				skb_ext_del(skb, SKB_EXT_MPTCP);
 				return MAPPING_OK;
 			} else {
+				if (updated && schedule_work(&msk->work))
+					sock_hold((struct sock *)msk);
+
 				return MAPPING_DATA_FIN;
 			}
+		} else {
+			u64 data_fin_seq = mpext->data_seq + data_len - 1;
+
+			/* If mpext->data_seq is a 32-bit value, data_fin_seq
+			 * must also be limited to 32 bits.
+			 */
+			if (!mpext->dsn64)
+				data_fin_seq &= GENMASK_ULL(31, 0);
+
+			mptcp_update_rcv_data_fin(msk, data_fin_seq, mpext->dsn64);
+			pr_debug("DATA_FIN with mapping seq=%llu dsn64=%d",
+				 data_fin_seq, mpext->dsn64);
 		}
 
 		/* Adjust for DATA_FIN using 1 byte of sequence space */
 		data_len--;
 	}
 
-	if (!mpext->dsn64) {
-		map_seq = expand_seq(subflow->map_seq, subflow->map_data_len,
-				     mpext->data_seq);
-		pr_debug("expanded seq=%llu", subflow->map_seq);
-	} else {
-		map_seq = mpext->data_seq;
-	}
+	map_seq = mptcp_expand_seq(READ_ONCE(msk->ack_seq), mpext->data_seq, mpext->dsn64);
+	WRITE_ONCE(mptcp_sk(subflow->conn)->use_64bit_ack, !!mpext->dsn64);
 
 	if (subflow->map_valid) {
 		/* Allow replacing only with an identical map */
 		if (subflow->map_seq == map_seq &&
 		    subflow->map_subflow_seq == mpext->subflow_seq &&
-		    subflow->map_data_len == data_len) {
+		    subflow->map_data_len == data_len &&
+		    subflow->map_csum_reqd == mpext->csum_reqd) {
 			skb_ext_del(skb, SKB_EXT_MPTCP);
-			return MAPPING_OK;
+			goto validate_csum;
 		}
 
 		/* If this skb data are fully covered by the current mapping,
 		 * the new map would need caching, which is not supported
 		 */
-		if (skb_is_fully_mapped(ssk, skb))
+		if (skb_is_fully_mapped(ssk, skb)) {
+			MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DSSNOMATCH);
 			return MAPPING_INVALID;
+		}
 
 		/* will validate the next map after consuming the current one */
-		return MAPPING_OK;
+		goto validate_csum;
 	}
 
 	subflow->map_seq = map_seq;
 	subflow->map_subflow_seq = mpext->subflow_seq;
 	subflow->map_data_len = data_len;
 	subflow->map_valid = 1;
+	subflow->map_data_fin = mpext->data_fin;
 	subflow->mpc_map = mpext->mpc_map;
-	pr_debug("new map seq=%llu subflow_seq=%u data_len=%u",
+	subflow->map_csum_reqd = mpext->csum_reqd;
+	subflow->map_csum_len = 0;
+	subflow->map_data_csum = csum_unfold(mpext->csum);
+
+	/* Cfr RFC 8684 Section 3.3.0 */
+	if (unlikely(subflow->map_csum_reqd != csum_reqd))
+		return MAPPING_INVALID;
+
+	pr_debug("new map seq=%llu subflow_seq=%u data_len=%u csum=%d:%u",
 		 subflow->map_seq, subflow->map_subflow_seq,
-		 subflow->map_data_len);
+		 subflow->map_data_len, subflow->map_csum_reqd,
+		 subflow->map_data_csum);
 
 validate_seq:
 	/* we revalidate valid mapping on new skb, because we must ensure
 	 * the current skb is completely covered by the available mapping
 	 */
-	if (!validate_mapping(ssk, skb))
+	if (!validate_mapping(ssk, skb)) {
+		MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DSSTCPMISMATCH);
 		return MAPPING_INVALID;
+	}
 
 	skb_ext_del(skb, SKB_EXT_MPTCP);
-	return MAPPING_OK;
+
+validate_csum:
+	return validate_data_csum(ssk, skb, csum_reqd);
+}
+
+static void mptcp_subflow_discard_data(struct sock *ssk, struct sk_buff *skb,
+				       u64 limit)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+	bool fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
+	u32 incr;
+
+	incr = limit >= skb->len ? skb->len + fin : limit;
+
+	pr_debug("discarding=%d len=%d seq=%d", incr, skb->len,
+		 subflow->map_subflow_seq);
+	MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DUPDATA);
+	tcp_sk(ssk)->copied_seq += incr;
+	if (!before(tcp_sk(ssk)->copied_seq, TCP_SKB_CB(skb)->end_seq))
+		sk_eat_skb(ssk, skb);
+	if (mptcp_subflow_get_map_offset(subflow) >= subflow->map_data_len)
+		subflow->map_valid = 0;
+}
+
+/* sched mptcp worker to remove the subflow if no more data is pending */
+static void subflow_sched_work_if_closed(struct mptcp_sock *msk, struct sock *ssk)
+{
+	struct sock *sk = (struct sock *)msk;
+
+	if (likely(ssk->sk_state != TCP_CLOSE))
+		return;
+
+	if (skb_queue_empty(&ssk->sk_receive_queue) &&
+	    !test_and_set_bit(MPTCP_WORK_CLOSE_SUBFLOW, &msk->flags)) {
+		sock_hold(sk);
+		if (!schedule_work(&msk->work))
+			sock_put(sk);
+	}
+}
+
+static bool subflow_can_fallback(struct mptcp_subflow_context *subflow)
+{
+	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
+
+	if (subflow->mp_join)
+		return false;
+	else if (READ_ONCE(msk->csum_enabled))
+		return !subflow->valid_csum_seen;
+	else
+		return !subflow->fully_established;
+}
+
+static void mptcp_subflow_fail(struct mptcp_sock *msk, struct sock *ssk)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+	unsigned long fail_tout;
+
+	/* greceful failure can happen only on the MPC subflow */
+	if (WARN_ON_ONCE(ssk != READ_ONCE(msk->first)))
+		return;
+
+	/* since the close timeout take precedence on the fail one,
+	 * no need to start the latter when the first is already set
+	 */
+	if (sock_flag((struct sock *)msk, SOCK_DEAD))
+		return;
+
+	/* we don't need extreme accuracy here, use a zero fail_tout as special
+	 * value meaning no fail timeout at all;
+	 */
+	fail_tout = jiffies + TCP_RTO_MAX;
+	if (!fail_tout)
+		fail_tout = 1;
+	WRITE_ONCE(subflow->fail_tout, fail_tout);
+	tcp_send_ack(ssk);
+
+	mptcp_reset_timeout(msk, subflow->fail_tout);
 }
 
 static bool subflow_check_data_avail(struct sock *ssk)
@@ -415,43 +1175,35 @@ static bool subflow_check_data_avail(struct sock *ssk)
 	struct mptcp_sock *msk;
 	struct sk_buff *skb;
 
-	pr_debug("msk=%p ssk=%p data_avail=%d skb=%p", subflow->conn, ssk,
-		 subflow->data_avail, skb_peek(&ssk->sk_receive_queue));
+	if (!skb_peek(&ssk->sk_receive_queue))
+		WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_NODATA);
 	if (subflow->data_avail)
 		return true;
 
-	if (!subflow->conn)
-		return false;
-
 	msk = mptcp_sk(subflow->conn);
 	for (;;) {
-		u32 map_remaining;
-		size_t delta;
 		u64 ack_seq;
 		u64 old_ack;
 
-		status = get_mapping_status(ssk);
-		pr_debug("msk=%p ssk=%p status=%d", msk, ssk, status);
-		if (status == MAPPING_INVALID) {
-			ssk->sk_err = EBADMSG;
-			goto fatal;
-		}
+		status = get_mapping_status(ssk, msk);
+		trace_subflow_check_data_avail(status, skb_peek(&ssk->sk_receive_queue));
+		if (unlikely(status == MAPPING_INVALID || status == MAPPING_DUMMY ||
+			     status == MAPPING_BAD_CSUM))
+			goto fallback;
 
 		if (status != MAPPING_OK)
-			return false;
+			goto no_data;
 
 		skb = skb_peek(&ssk->sk_receive_queue);
 		if (WARN_ON_ONCE(!skb))
-			return false;
+			goto no_data;
 
 		/* if msk lacks the remote key, this subflow must provide an
 		 * MP_CAPABLE-based mapping
 		 */
 		if (unlikely(!READ_ONCE(msk->can_ack))) {
-			if (!subflow->mpc_map) {
-				ssk->sk_err = EBADMSG;
-				goto fatal;
-			}
+			if (!subflow->mpc_map)
+				goto fallback;
 			WRITE_ONCE(msk->remote_key, subflow->remote_key);
 			WRITE_ONCE(msk->ack_seq, subflow->map_seq);
 			WRITE_ONCE(msk->can_ack, true);
@@ -461,121 +1213,179 @@ static bool subflow_check_data_avail(struct sock *ssk)
 		ack_seq = mptcp_subflow_get_mapped_dsn(subflow);
 		pr_debug("msk ack_seq=%llx subflow ack_seq=%llx", old_ack,
 			 ack_seq);
-		if (ack_seq == old_ack)
-			break;
-
-		/* only accept in-sequence mapping. Old values are spurious
-		 * retransmission; we can hit "future" values on active backup
-		 * subflow switch, we relay on retransmissions to get
-		 * in-sequence data.
-		 * Cuncurrent subflows support will require subflow data
-		 * reordering
-		 */
-		map_remaining = subflow->map_data_len -
-				mptcp_subflow_get_map_offset(subflow);
-		if (before64(ack_seq, old_ack))
-			delta = min_t(size_t, old_ack - ack_seq, map_remaining);
-		else
-			delta = min_t(size_t, ack_seq - old_ack, map_remaining);
-
-		/* discard mapped data */
-		pr_debug("discarding %zu bytes, current map len=%d", delta,
-			 map_remaining);
-		if (delta) {
-			struct mptcp_read_arg arg = {
-				.msg = NULL,
-			};
-			read_descriptor_t desc = {
-				.count = delta,
-				.arg.data = &arg,
-			};
-			int ret;
-
-			ret = tcp_read_sock(ssk, &desc, mptcp_read_actor);
-			if (ret < 0) {
-				ssk->sk_err = -ret;
-				goto fatal;
-			}
-			if (ret < delta)
-				return false;
-			if (delta == map_remaining)
-				subflow->map_valid = 0;
+		if (unlikely(before64(ack_seq, old_ack))) {
+			mptcp_subflow_discard_data(ssk, skb, old_ack - ack_seq);
+			continue;
 		}
+
+		WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_DATA_AVAIL);
+		break;
 	}
 	return true;
 
-fatal:
-	/* fatal protocol error, close the socket */
-	/* This barrier is coupled with smp_rmb() in tcp_poll() */
-	smp_wmb();
-	ssk->sk_error_report(ssk);
-	tcp_set_state(ssk, TCP_CLOSE);
-	tcp_send_active_reset(ssk, GFP_ATOMIC);
+no_data:
+	subflow_sched_work_if_closed(msk, ssk);
 	return false;
+
+fallback:
+	if (!__mptcp_check_fallback(msk)) {
+		/* RFC 8684 section 3.7. */
+		if (status == MAPPING_BAD_CSUM &&
+		    (subflow->mp_join || subflow->valid_csum_seen)) {
+			subflow->send_mp_fail = 1;
+
+			if (!READ_ONCE(msk->allow_infinite_fallback)) {
+				subflow->reset_transient = 0;
+				subflow->reset_reason = MPTCP_RST_EMIDDLEBOX;
+				goto reset;
+			}
+			mptcp_subflow_fail(msk, ssk);
+			WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_DATA_AVAIL);
+			return true;
+		}
+
+		if (!subflow_can_fallback(subflow) && subflow->map_data_len) {
+			/* fatal protocol error, close the socket.
+			 * subflow_error_report() will introduce the appropriate barriers
+			 */
+			subflow->reset_transient = 0;
+			subflow->reset_reason = MPTCP_RST_EMPTCP;
+
+reset:
+			ssk->sk_err = EBADMSG;
+			tcp_set_state(ssk, TCP_CLOSE);
+			while ((skb = skb_peek(&ssk->sk_receive_queue)))
+				sk_eat_skb(ssk, skb);
+			tcp_send_active_reset(ssk, GFP_ATOMIC);
+			WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_NODATA);
+			return false;
+		}
+
+		mptcp_do_fallback(ssk);
+	}
+
+	skb = skb_peek(&ssk->sk_receive_queue);
+	subflow->map_valid = 1;
+	subflow->map_seq = READ_ONCE(msk->ack_seq);
+	subflow->map_data_len = skb->len;
+	subflow->map_subflow_seq = tcp_sk(ssk)->copied_seq - subflow->ssn_offset;
+	WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_DATA_AVAIL);
+	return true;
 }
 
 bool mptcp_subflow_data_available(struct sock *sk)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
-	struct sk_buff *skb;
 
 	/* check if current mapping is still valid */
 	if (subflow->map_valid &&
 	    mptcp_subflow_get_map_offset(subflow) >= subflow->map_data_len) {
 		subflow->map_valid = 0;
-		subflow->data_avail = 0;
+		WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_NODATA);
 
 		pr_debug("Done with mapping: seq=%u data_len=%u",
 			 subflow->map_subflow_seq,
 			 subflow->map_data_len);
 	}
 
-	if (!subflow_check_data_avail(sk)) {
-		subflow->data_avail = 0;
-		return false;
+	return subflow_check_data_avail(sk);
+}
+
+/* If ssk has an mptcp parent socket, use the mptcp rcvbuf occupancy,
+ * not the ssk one.
+ *
+ * In mptcp, rwin is about the mptcp-level connection data.
+ *
+ * Data that is still on the ssk rx queue can thus be ignored,
+ * as far as mptcp peer is concerned that data is still inflight.
+ * DSS ACK is updated when skb is moved to the mptcp rx queue.
+ */
+void mptcp_space(const struct sock *ssk, int *space, int *full_space)
+{
+	const struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+	const struct sock *sk = subflow->conn;
+
+	*space = __mptcp_space(sk);
+	*full_space = tcp_full_space(sk);
+}
+
+void __mptcp_error_report(struct sock *sk)
+{
+	struct mptcp_subflow_context *subflow;
+	struct mptcp_sock *msk = mptcp_sk(sk);
+
+	mptcp_for_each_subflow(msk, subflow) {
+		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
+		int err = sock_error(ssk);
+
+		if (!err)
+			continue;
+
+		/* only propagate errors on fallen-back sockets or
+		 * on MPC connect
+		 */
+		if (sk->sk_state != TCP_SYN_SENT && !__mptcp_check_fallback(msk))
+			continue;
+
+		inet_sk_state_store(sk, inet_sk_state_load(ssk));
+		sk->sk_err = -err;
+
+		/* This barrier is coupled with smp_rmb() in mptcp_poll() */
+		smp_wmb();
+		sk_error_report(sk);
+		break;
 	}
+}
 
-	skb = skb_peek(&sk->sk_receive_queue);
-	subflow->data_avail = skb &&
-		       before(tcp_sk(sk)->copied_seq, TCP_SKB_CB(skb)->end_seq);
-	return subflow->data_avail;
+static void subflow_error_report(struct sock *ssk)
+{
+	struct sock *sk = mptcp_subflow_ctx(ssk)->conn;
+
+	mptcp_data_lock(sk);
+	if (!sock_owned_by_user(sk))
+		__mptcp_error_report(sk);
+	else
+		__set_bit(MPTCP_ERROR_REPORT,  &mptcp_sk(sk)->cb_flags);
+	mptcp_data_unlock(sk);
 }
 
 static void subflow_data_ready(struct sock *sk)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	u16 state = 1 << inet_sk_state_load(sk);
 	struct sock *parent = subflow->conn;
+	struct mptcp_sock *msk;
 
-	if (!parent || !subflow->mp_capable) {
-		subflow->tcp_data_ready(sk);
+	msk = mptcp_sk(parent);
+	if (state & TCPF_LISTEN) {
+		/* MPJ subflow are removed from accept queue before reaching here,
+		 * avoid stray wakeups
+		 */
+		if (reqsk_queue_empty(&inet_csk(sk)->icsk_accept_queue))
+			return;
 
-		if (parent)
-			parent->sk_data_ready(parent);
+		parent->sk_data_ready(parent);
 		return;
 	}
 
-	if (mptcp_subflow_data_available(sk)) {
-		set_bit(MPTCP_DATA_READY, &mptcp_sk(parent)->flags);
+	WARN_ON_ONCE(!__mptcp_check_fallback(msk) && !subflow->mp_capable &&
+		     !subflow->mp_join && !(state & TCPF_CLOSE));
 
-		parent->sk_data_ready(parent);
-	}
+	if (mptcp_subflow_data_available(sk))
+		mptcp_data_ready(parent, sk);
+	else if (unlikely(sk->sk_err))
+		subflow_error_report(sk);
 }
 
-static void subflow_write_space(struct sock *sk)
+static void subflow_write_space(struct sock *ssk)
 {
-	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
-	struct sock *parent = subflow->conn;
+	struct sock *sk = mptcp_subflow_ctx(ssk)->conn;
 
-	sk_stream_write_space(sk);
-	if (parent && sk_stream_is_writeable(sk)) {
-		set_bit(MPTCP_SEND_SPACE, &mptcp_sk(parent)->flags);
-		smp_mb__after_atomic();
-		/* set SEND_SPACE before sk_stream_write_space clears NOSPACE */
-		sk_stream_write_space(parent);
-	}
+	mptcp_propagate_sndbuf(sk, ssk);
+	mptcp_write_space(sk);
 }
 
-static struct inet_connection_sock_af_ops *
+static const struct inet_connection_sock_af_ops *
 subflow_default_af_ops(struct sock *sk)
 {
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
@@ -590,7 +1400,7 @@ void mptcpv6_handle_mapped(struct sock *sk, bool mapped)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 	struct inet_connection_sock *icsk = inet_csk(sk);
-	struct inet_connection_sock_af_ops *target;
+	const struct inet_connection_sock_af_ops *target;
 
 	target = mapped ? &subflow_v6m_specific : subflow_default_af_ops(sk);
 
@@ -605,6 +1415,168 @@ void mptcpv6_handle_mapped(struct sock *sk, bool mapped)
 }
 #endif
 
+void mptcp_info2sockaddr(const struct mptcp_addr_info *info,
+			 struct sockaddr_storage *addr,
+			 unsigned short family)
+{
+	memset(addr, 0, sizeof(*addr));
+	addr->ss_family = family;
+	if (addr->ss_family == AF_INET) {
+		struct sockaddr_in *in_addr = (struct sockaddr_in *)addr;
+
+		if (info->family == AF_INET)
+			in_addr->sin_addr = info->addr;
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+		else if (ipv6_addr_v4mapped(&info->addr6))
+			in_addr->sin_addr.s_addr = info->addr6.s6_addr32[3];
+#endif
+		in_addr->sin_port = info->port;
+	}
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	else if (addr->ss_family == AF_INET6) {
+		struct sockaddr_in6 *in6_addr = (struct sockaddr_in6 *)addr;
+
+		if (info->family == AF_INET)
+			ipv6_addr_set_v4mapped(info->addr.s_addr,
+					       &in6_addr->sin6_addr);
+		else
+			in6_addr->sin6_addr = info->addr6;
+		in6_addr->sin6_port = info->port;
+	}
+#endif
+}
+
+int __mptcp_subflow_connect(struct sock *sk, const struct mptcp_addr_info *loc,
+			    const struct mptcp_addr_info *remote)
+{
+	struct mptcp_sock *msk = mptcp_sk(sk);
+	struct mptcp_subflow_context *subflow;
+	struct sockaddr_storage addr;
+	int remote_id = remote->id;
+	int local_id = loc->id;
+	int err = -ENOTCONN;
+	struct socket *sf;
+	struct sock *ssk;
+	u32 remote_token;
+	int addrlen;
+	int ifindex;
+	u8 flags;
+
+	if (!mptcp_is_fully_established(sk))
+		goto err_out;
+
+	err = mptcp_subflow_create_socket(sk, &sf);
+	if (err)
+		goto err_out;
+
+	ssk = sf->sk;
+	subflow = mptcp_subflow_ctx(ssk);
+	do {
+		get_random_bytes(&subflow->local_nonce, sizeof(u32));
+	} while (!subflow->local_nonce);
+
+	if (local_id)
+		subflow_set_local_id(subflow, local_id);
+
+	mptcp_pm_get_flags_and_ifindex_by_id(msk, local_id,
+					     &flags, &ifindex);
+	subflow->remote_key = msk->remote_key;
+	subflow->local_key = msk->local_key;
+	subflow->token = msk->token;
+	mptcp_info2sockaddr(loc, &addr, ssk->sk_family);
+
+	addrlen = sizeof(struct sockaddr_in);
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	if (addr.ss_family == AF_INET6)
+		addrlen = sizeof(struct sockaddr_in6);
+#endif
+	mptcp_sockopt_sync(msk, ssk);
+
+	ssk->sk_bound_dev_if = ifindex;
+	err = kernel_bind(sf, (struct sockaddr *)&addr, addrlen);
+	if (err)
+		goto failed;
+
+	mptcp_crypto_key_sha(subflow->remote_key, &remote_token, NULL);
+	pr_debug("msk=%p remote_token=%u local_id=%d remote_id=%d", msk,
+		 remote_token, local_id, remote_id);
+	subflow->remote_token = remote_token;
+	subflow->remote_id = remote_id;
+	subflow->request_join = 1;
+	subflow->request_bkup = !!(flags & MPTCP_PM_ADDR_FLAG_BACKUP);
+	mptcp_info2sockaddr(remote, &addr, ssk->sk_family);
+
+	sock_hold(ssk);
+	list_add_tail(&subflow->node, &msk->conn_list);
+	err = kernel_connect(sf, (struct sockaddr *)&addr, addrlen, O_NONBLOCK);
+	if (err && err != -EINPROGRESS)
+		goto failed_unlink;
+
+	/* discard the subflow socket */
+	mptcp_sock_graft(ssk, sk->sk_socket);
+	iput(SOCK_INODE(sf));
+	WRITE_ONCE(msk->allow_infinite_fallback, false);
+	return 0;
+
+failed_unlink:
+	list_del(&subflow->node);
+	sock_put(mptcp_subflow_tcp_sock(subflow));
+
+failed:
+	subflow->disposable = 1;
+	sock_release(sf);
+
+err_out:
+	/* we account subflows before the creation, and this failures will not
+	 * be caught by sk_state_change()
+	 */
+	mptcp_pm_close_subflow(msk);
+	return err;
+}
+
+static void mptcp_attach_cgroup(struct sock *parent, struct sock *child)
+{
+#ifdef CONFIG_SOCK_CGROUP_DATA
+	struct sock_cgroup_data *parent_skcd = &parent->sk_cgrp_data,
+				*child_skcd = &child->sk_cgrp_data;
+
+	/* only the additional subflows created by kworkers have to be modified */
+	if (cgroup_id(sock_cgroup_ptr(parent_skcd)) !=
+	    cgroup_id(sock_cgroup_ptr(child_skcd))) {
+#ifdef CONFIG_MEMCG
+		struct mem_cgroup *memcg = parent->sk_memcg;
+
+		mem_cgroup_sk_free(child);
+		if (memcg && css_tryget(&memcg->css))
+			child->sk_memcg = memcg;
+#endif /* CONFIG_MEMCG */
+
+		cgroup_sk_free(child_skcd);
+		*child_skcd = *parent_skcd;
+		cgroup_sk_clone(child_skcd);
+	}
+#endif /* CONFIG_SOCK_CGROUP_DATA */
+}
+
+static void mptcp_subflow_ops_override(struct sock *ssk)
+{
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	if (ssk->sk_prot == &tcpv6_prot)
+		ssk->sk_prot = &tcpv6_prot_override;
+	else
+#endif
+		ssk->sk_prot = &tcp_prot_override;
+}
+
+static void mptcp_subflow_ops_undo_override(struct sock *ssk)
+{
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	if (ssk->sk_prot == &tcpv6_prot_override)
+		ssk->sk_prot = &tcpv6_prot;
+	else
+#endif
+		ssk->sk_prot = &tcp_prot;
+}
 int mptcp_subflow_create_socket(struct sock *sk, struct socket **new_sock)
 {
 	struct mptcp_subflow_context *subflow;
@@ -612,6 +1584,12 @@ int mptcp_subflow_create_socket(struct sock *sk, struct socket **new_sock)
 	struct socket *sf;
 	int err;
 
+	/* un-accepted server sockets can reach here - on bad configuration
+	 * bail early to avoid greater trouble later
+	 */
+	if (unlikely(!sk->sk_socket))
+		return -EINVAL;
+
 	err = sock_create_kern(net, sk->sk_family, SOCK_STREAM, IPPROTO_TCP,
 			       &sf);
 	if (err)
@@ -619,19 +1597,32 @@ int mptcp_subflow_create_socket(struct sock *sk, struct socket **new_sock)
 
 	lock_sock(sf->sk);
 
+	/* the newly created socket has to be in the same cgroup as its parent */
+	mptcp_attach_cgroup(sk, sf->sk);
+
 	/* kernel sockets do not by default acquire net ref, but TCP timer
 	 * needs it.
 	 */
 	sf->sk->sk_net_refcnt = 1;
-	get_net(net);
-#ifdef CONFIG_PROC_FS
-	this_cpu_add(*net->core.sock_inuse, 1);
-#endif
+	get_net_track(net, &sf->sk->ns_tracker, GFP_KERNEL);
+	sock_inuse_add(net, 1);
 	err = tcp_set_ulp(sf->sk, "mptcp");
 	release_sock(sf->sk);
 
-	if (err)
+	if (err) {
+		sock_release(sf);
 		return err;
+	}
+
+	/* the newly created socket really belongs to the owning MPTCP master
+	 * socket, even if for additional subflows the allocation is performed
+	 * by a kernel workqueue. Adjust inode references, so that the
+	 * procfs/diag interfaces really show this one belonging to the correct
+	 * user.
+	 */
+	SOCK_INODE(sf)->i_ino = SOCK_INODE(sk->sk_socket)->i_ino;
+	SOCK_INODE(sf)->i_uid = SOCK_INODE(sk->sk_socket)->i_uid;
+	SOCK_INODE(sf)->i_gid = SOCK_INODE(sk->sk_socket)->i_gid;
 
 	subflow = mptcp_subflow_ctx(sf->sk);
 	pr_debug("subflow=%p", subflow);
@@ -639,6 +1630,7 @@ int mptcp_subflow_create_socket(struct sock *sk, struct socket **new_sock)
 	*new_sock = sf;
 	sock_hold(sk);
 	subflow->conn = sk;
+	mptcp_subflow_ops_override(sf->sk);
 
 	return 0;
 }
@@ -655,6 +1647,7 @@ static struct mptcp_subflow_context *subflow_create_ctx(struct sock *sk,
 
 	rcu_assign_pointer(icsk->icsk_ulp_data, ctx);
 	INIT_LIST_HEAD(&ctx->node);
+	INIT_LIST_HEAD(&ctx->delegated_node);
 
 	pr_debug("subflow=%p", ctx);
 
@@ -682,28 +1675,95 @@ static bool subflow_is_done(const struct sock *sk)
 static void subflow_state_change(struct sock *sk)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
-	struct sock *parent = READ_ONCE(subflow->conn);
+	struct sock *parent = subflow->conn;
 
 	__subflow_state_change(sk);
 
+	if (subflow_simultaneous_connect(sk)) {
+		mptcp_propagate_sndbuf(parent, sk);
+		mptcp_do_fallback(sk);
+		mptcp_rcv_space_init(mptcp_sk(parent), sk);
+		pr_fallback(mptcp_sk(parent));
+		subflow->conn_finished = 1;
+		mptcp_set_connected(parent);
+	}
+
 	/* as recvmsg() does not acquire the subflow socket for ssk selection
 	 * a fin packet carrying a DSS can be unnoticed if we don't trigger
 	 * the data available machinery here.
 	 */
-	if (parent && subflow->mp_capable && mptcp_subflow_data_available(sk)) {
-		set_bit(MPTCP_DATA_READY, &mptcp_sk(parent)->flags);
+	if (mptcp_subflow_data_available(sk))
+		mptcp_data_ready(parent, sk);
+	else if (unlikely(sk->sk_err))
+		subflow_error_report(sk);
 
-		parent->sk_data_ready(parent);
-	}
+	subflow_sched_work_if_closed(mptcp_sk(parent), sk);
 
-	if (parent && !(parent->sk_shutdown & RCV_SHUTDOWN) &&
+	if (__mptcp_check_fallback(mptcp_sk(parent)) &&
 	    !subflow->rx_eof && subflow_is_done(sk)) {
 		subflow->rx_eof = 1;
-		parent->sk_shutdown |= RCV_SHUTDOWN;
-		__subflow_state_change(parent);
+		mptcp_subflow_eof(parent);
 	}
 }
 
+void mptcp_subflow_queue_clean(struct sock *listener_ssk)
+{
+	struct request_sock_queue *queue = &inet_csk(listener_ssk)->icsk_accept_queue;
+	struct mptcp_sock *msk, *next, *head = NULL;
+	struct request_sock *req;
+
+	/* build a list of all unaccepted mptcp sockets */
+	spin_lock_bh(&queue->rskq_lock);
+	for (req = queue->rskq_accept_head; req; req = req->dl_next) {
+		struct mptcp_subflow_context *subflow;
+		struct sock *ssk = req->sk;
+		struct mptcp_sock *msk;
+
+		if (!sk_is_mptcp(ssk))
+			continue;
+
+		subflow = mptcp_subflow_ctx(ssk);
+		if (!subflow || !subflow->conn)
+			continue;
+
+		/* skip if already in list */
+		msk = mptcp_sk(subflow->conn);
+		if (msk->dl_next || msk == head)
+			continue;
+
+		msk->dl_next = head;
+		head = msk;
+	}
+	spin_unlock_bh(&queue->rskq_lock);
+	if (!head)
+		return;
+
+	/* can't acquire the msk socket lock under the subflow one,
+	 * or will cause ABBA deadlock
+	 */
+	release_sock(listener_ssk);
+
+	for (msk = head; msk; msk = next) {
+		struct sock *sk = (struct sock *)msk;
+		bool slow, do_cancel_work;
+
+		sock_hold(sk);
+		slow = lock_sock_fast_nested(sk);
+		next = msk->dl_next;
+		msk->first = NULL;
+		msk->dl_next = NULL;
+
+		do_cancel_work = __mptcp_close(sk, 0);
+		unlock_sock_fast(sk, slow);
+		if (do_cancel_work)
+			mptcp_cancel_work(sk);
+		sock_put(sk);
+	}
+
+	/* we are still under the listener msk socket lock */
+	lock_sock_nested(listener_ssk, SINGLE_DEPTH_NESTING);
+}
+
 static int subflow_ulp_init(struct sock *sk)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
@@ -730,38 +1790,42 @@ static int subflow_ulp_init(struct sock *sk)
 	tp->is_mptcp = 1;
 	ctx->icsk_af_ops = icsk->icsk_af_ops;
 	icsk->icsk_af_ops = subflow_default_af_ops(sk);
-	ctx->tcp_data_ready = sk->sk_data_ready;
 	ctx->tcp_state_change = sk->sk_state_change;
-	ctx->tcp_write_space = sk->sk_write_space;
+	ctx->tcp_error_report = sk->sk_error_report;
+
+	WARN_ON_ONCE(sk->sk_data_ready != sock_def_readable);
+	WARN_ON_ONCE(sk->sk_write_space != sk_stream_write_space);
+
 	sk->sk_data_ready = subflow_data_ready;
 	sk->sk_write_space = subflow_write_space;
 	sk->sk_state_change = subflow_state_change;
+	sk->sk_error_report = subflow_error_report;
 out:
 	return err;
 }
 
-static void subflow_ulp_release(struct sock *sk)
+static void subflow_ulp_release(struct sock *ssk)
 {
-	struct mptcp_subflow_context *ctx = mptcp_subflow_ctx(sk);
+	struct mptcp_subflow_context *ctx = mptcp_subflow_ctx(ssk);
+	bool release = true;
+	struct sock *sk;
 
 	if (!ctx)
 		return;
 
-	if (ctx->conn)
-		sock_put(ctx->conn);
-
-	kfree_rcu(ctx, rcu);
-}
-
-static void subflow_ulp_fallback(struct sock *sk,
-				 struct mptcp_subflow_context *old_ctx)
-{
-	struct inet_connection_sock *icsk = inet_csk(sk);
+	sk = ctx->conn;
+	if (sk) {
+		/* if the msk has been orphaned, keep the ctx
+		 * alive, will be freed by __mptcp_close_ssk(),
+		 * when the subflow is still unaccepted
+		 */
+		release = ctx->disposable || list_empty(&ctx->node);
+		sock_put(sk);
+	}
 
-	mptcp_subflow_tcp_fallback(sk, old_ctx);
-	icsk->icsk_ulp_ops = NULL;
-	rcu_assign_pointer(icsk->icsk_ulp_data, NULL);
-	tcp_sk(sk)->is_mptcp = 0;
+	mptcp_subflow_ops_undo_override(ssk);
+	if (release)
+		kfree_rcu(ctx, rcu);
 }
 
 static void subflow_ulp_clone(const struct request_sock *req,
@@ -772,7 +1836,8 @@ static void subflow_ulp_clone(const struct request_sock *req,
 	struct mptcp_subflow_context *old_ctx = mptcp_subflow_ctx(newsk);
 	struct mptcp_subflow_context *new_ctx;
 
-	if (!tcp_rsk(req)->is_mptcp || !subflow_req->mp_capable) {
+	if (!tcp_rsk(req)->is_mptcp ||
+	    (!subflow_req->mp_capable && !subflow_req->mp_join)) {
 		subflow_ulp_fallback(newsk, old_ctx);
 		return;
 	}
@@ -783,22 +1848,49 @@ static void subflow_ulp_clone(const struct request_sock *req,
 		return;
 	}
 
-	/* see comments in subflow_syn_recv_sock(), MPTCP connection is fully
-	 * established only after we receive the remote key
-	 */
 	new_ctx->conn_finished = 1;
 	new_ctx->icsk_af_ops = old_ctx->icsk_af_ops;
-	new_ctx->tcp_data_ready = old_ctx->tcp_data_ready;
 	new_ctx->tcp_state_change = old_ctx->tcp_state_change;
-	new_ctx->tcp_write_space = old_ctx->tcp_write_space;
-	new_ctx->mp_capable = 1;
-	new_ctx->fourth_ack = subflow_req->remote_key_valid;
-	new_ctx->can_ack = subflow_req->remote_key_valid;
-	new_ctx->remote_key = subflow_req->remote_key;
-	new_ctx->local_key = subflow_req->local_key;
-	new_ctx->token = subflow_req->token;
-	new_ctx->ssn_offset = subflow_req->ssn_offset;
-	new_ctx->idsn = subflow_req->idsn;
+	new_ctx->tcp_error_report = old_ctx->tcp_error_report;
+	new_ctx->rel_write_seq = 1;
+	new_ctx->tcp_sock = newsk;
+
+	if (subflow_req->mp_capable) {
+		/* see comments in subflow_syn_recv_sock(), MPTCP connection
+		 * is fully established only after we receive the remote key
+		 */
+		new_ctx->mp_capable = 1;
+		new_ctx->local_key = subflow_req->local_key;
+		new_ctx->token = subflow_req->token;
+		new_ctx->ssn_offset = subflow_req->ssn_offset;
+		new_ctx->idsn = subflow_req->idsn;
+
+		/* this is the first subflow, id is always 0 */
+		new_ctx->local_id_valid = 1;
+	} else if (subflow_req->mp_join) {
+		new_ctx->ssn_offset = subflow_req->ssn_offset;
+		new_ctx->mp_join = 1;
+		new_ctx->fully_established = 1;
+		new_ctx->backup = subflow_req->backup;
+		new_ctx->remote_id = subflow_req->remote_id;
+		new_ctx->token = subflow_req->token;
+		new_ctx->thmac = subflow_req->thmac;
+
+		/* the subflow req id is valid, fetched via subflow_check_req()
+		 * and subflow_token_join_request()
+		 */
+		subflow_set_local_id(new_ctx, subflow_req->local_id);
+	}
+}
+
+static void tcp_release_cb_override(struct sock *ssk)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+
+	if (mptcp_subflow_has_delegated_action(subflow))
+		mptcp_subflow_process_delegated(ssk);
+
+	tcp_release_cb(ssk);
 }
 
 static struct tcp_ulp_ops subflow_ulp_ops __read_mostly = {
@@ -827,14 +1919,14 @@ static int subflow_ops_init(struct request_sock_ops *subflow_ops)
 	return 0;
 }
 
-void mptcp_subflow_init(void)
+void __init mptcp_subflow_init(void)
 {
-	subflow_request_sock_ops = tcp_request_sock_ops;
-	if (subflow_ops_init(&subflow_request_sock_ops) != 0)
+	mptcp_subflow_request_sock_ops = tcp_request_sock_ops;
+	if (subflow_ops_init(&mptcp_subflow_request_sock_ops) != 0)
 		panic("MPTCP: failed to init subflow request sock ops\n");
 
 	subflow_request_sock_ipv4_ops = tcp_request_sock_ipv4_ops;
-	subflow_request_sock_ipv4_ops.init_req = subflow_v4_init_req;
+	subflow_request_sock_ipv4_ops.route_req = subflow_v4_route_req;
 
 	subflow_specific = ipv4_specific;
 	subflow_specific.conn_request = subflow_v4_conn_request;
@@ -842,15 +1934,18 @@ void mptcp_subflow_init(void)
 	subflow_specific.sk_rx_dst_set = subflow_finish_connect;
 	subflow_specific.rebuild_header = subflow_rebuild_header;
 
+	tcp_prot_override = tcp_prot;
+	tcp_prot_override.release_cb = tcp_release_cb_override;
+
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
 	subflow_request_sock_ipv6_ops = tcp_request_sock_ipv6_ops;
-	subflow_request_sock_ipv6_ops.init_req = subflow_v6_init_req;
+	subflow_request_sock_ipv6_ops.route_req = subflow_v6_route_req;
 
 	subflow_v6_specific = ipv6_specific;
 	subflow_v6_specific.conn_request = subflow_v6_conn_request;
 	subflow_v6_specific.syn_recv_sock = subflow_syn_recv_sock;
 	subflow_v6_specific.sk_rx_dst_set = subflow_finish_connect;
-	subflow_v6_specific.rebuild_header = subflow_rebuild_header;
+	subflow_v6_specific.rebuild_header = subflow_v6_rebuild_header;
 
 	subflow_v6m_specific = subflow_v6_specific;
 	subflow_v6m_specific.queue_xmit = ipv4_specific.queue_xmit;
@@ -858,8 +1953,14 @@ void mptcp_subflow_init(void)
 	subflow_v6m_specific.net_header_len = ipv4_specific.net_header_len;
 	subflow_v6m_specific.mtu_reduced = ipv4_specific.mtu_reduced;
 	subflow_v6m_specific.net_frag_header_len = 0;
+	subflow_v6m_specific.rebuild_header = subflow_rebuild_header;
+
+	tcpv6_prot_override = tcpv6_prot;
+	tcpv6_prot_override.release_cb = tcp_release_cb_override;
 #endif
 
+	mptcp_diag_subflow_init(&subflow_ulp_ops);
+
 	if (tcp_register_ulp(&subflow_ulp_ops) != 0)
 		panic("MPTCP: failed to register subflows to ULP\n");
 }