Adding upstream version 5.10.209.upstream/5.10.209

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1469 insertions, 0 deletions

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
new file mode 100644
index 000000000..607519246
--- /dev/null
+++ b/net/mptcp/subflow.c
@@ -0,0 +1,1469 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Multipath TCP
+ *
+ * Copyright (c) 2017 - 2019, Intel Corporation.
+ */
+
+#define pr_fmt(fmt) "MPTCP: " fmt
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/netdevice.h>
+#include <crypto/algapi.h>
+#include <crypto/sha.h>
+#include <net/sock.h>
+#include <net/inet_common.h>
+#include <net/inet_hashtables.h>
+#include <net/protocol.h>
+#include <net/tcp.h>
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+#include <net/ip6_route.h>
+#endif
+#include <net/mptcp.h>
+#include <uapi/linux/mptcp.h>
+#include "protocol.h"
+#include "mib.h"
+
+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)
+{
+	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
+
+	pr_debug("subflow_req=%p", subflow_req);
+
+	if (subflow_req->msk)
+		sock_put((struct sock *)subflow_req->msk);
+
+	mptcp_token_destroy_request(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) &&
+	       READ_ONCE(msk->pm.accept_subflow);
+}
+
+/* validate received token and create truncated hmac and nonce for SYN-ACK */
+static struct mptcp_sock *subflow_token_join_request(struct request_sock *req,
+						     const struct sk_buff *skb)
+{
+	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
+	u8 hmac[SHA256_DIGEST_SIZE];
+	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;
+
+	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);
+	return msk;
+}
+
+static int __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->msk = NULL;
+	mptcp_token_init_request(req);
+
+#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 -EINVAL;
+#endif
+
+	return 0;
+}
+
+static void subflow_init_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;
+	int ret;
+
+	pr_debug("subflow_req=%p, listener=%p", subflow_req, listener);
+
+	ret = __subflow_init_req(req, sk_listener);
+	if (ret)
+		return;
+
+	mptcp_get_options(skb, &mp_opt);
+
+	if (mp_opt.mp_capable) {
+		SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_MPCAPABLEPASSIVE);
+
+		if (mp_opt.mp_join)
+			return;
+	} else if (mp_opt.mp_join) {
+		SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINSYNRX);
+	}
+
+	if (mp_opt.mp_capable && listener->request_mptcp) {
+		int err, retries = 4;
+
+		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;
+			} else {
+				subflow_req->mp_capable = 1;
+			}
+			return;
+		}
+
+		err = mptcp_token_new_request(req);
+		if (err == 0)
+			subflow_req->mp_capable = 1;
+		else if (retries-- > 0)
+			goto again;
+
+	} else if (mp_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, skb);
+
+		if (unlikely(req->syncookie) && subflow_req->msk) {
+			if (mptcp_can_accept_new_subflow(subflow_req->msk))
+				subflow_init_req_cookie_join_save(subflow_req, skb);
+		}
+
+		pr_debug("token=%u, remote_nonce=%u msk=%p", subflow_req->token,
+			 subflow_req->remote_nonce, subflow_req->msk);
+	}
+}
+
+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;
+	int err;
+
+	err = __subflow_init_req(req, sk_listener);
+	if (err)
+		return err;
+
+	mptcp_get_options(skb, &mp_opt);
+
+	if (mp_opt.mp_capable && mp_opt.mp_join)
+		return -EINVAL;
+
+	if (mp_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 (mp_opt.mp_join && listener->request_mptcp) {
+		if (!mptcp_token_join_cookie_init_state(subflow_req, skb))
+			return -EINVAL;
+
+		if (mptcp_can_accept_new_subflow(subflow_req->msk))
+			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)
+{
+	tcp_rsk(req)->is_mptcp = 1;
+
+	tcp_request_sock_ipv4_ops.init_req(req, sk_listener, skb);
+
+	subflow_init_req(req, sk_listener, skb);
+}
+
+#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)
+{
+	tcp_rsk(req)->is_mptcp = 1;
+
+	tcp_request_sock_ipv6_ops.init_req(req, sk_listener, skb);
+
+	subflow_init_req(req, sk_listener, skb);
+}
+#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,
+		 (unsigned long long)thmac,
+		 (unsigned long long)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;
+
+	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))
+		sock_hold(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 (inet_sk_state_load(parent) == TCP_SYN_SENT) {
+		inet_sk_state_store(parent, TCP_ESTABLISHED);
+		parent->sk_state_change(parent);
+	}
+
+	/* be sure no special action on any packet other than syn-ack */
+	if (subflow->conn_finished)
+		return;
+
+	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.mp_capable) {
+			MPTCP_INC_STATS(sock_net(sk),
+					MPTCP_MIB_MPCAPABLEACTIVEFALLBACK);
+			mptcp_do_fallback(sk);
+			pr_fallback(mptcp_sk(subflow->conn));
+			goto fallback;
+		}
+
+		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_finish_connect(sk);
+	} else if (subflow->request_join) {
+		u8 hmac[SHA256_DIGEST_SIZE];
+
+		if (!mp_opt.mp_join)
+			goto do_reset;
+
+		subflow->thmac = mp_opt.thmac;
+		subflow->remote_nonce = mp_opt.nonce;
+		pr_debug("subflow=%p, thmac=%llu, remote_nonce=%u", subflow,
+			 subflow->thmac, subflow->remote_nonce);
+
+		if (!subflow_thmac_valid(subflow)) {
+			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_JOINACKMAC);
+			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);
+	} else if (mptcp_check_fallback(sk)) {
+fallback:
+		mptcp_rcv_space_init(mptcp_sk(parent), sk);
+	}
+	return;
+
+do_reset:
+	mptcp_subflow_reset(sk);
+}
+
+static struct request_sock_ops mptcp_subflow_v4_request_sock_ops __ro_after_init;
+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)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+
+	pr_debug("subflow=%p", subflow);
+
+	/* Never answer to SYNs sent to broadcast or multicast */
+	if (skb_rtable(skb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
+		goto drop;
+
+	return tcp_conn_request(&mptcp_subflow_v4_request_sock_ops,
+				&subflow_request_sock_ipv4_ops,
+				sk, skb);
+drop:
+	tcp_listendrop(sk);
+	return 0;
+}
+
+static void subflow_v4_req_destructor(struct request_sock *req)
+{
+	subflow_req_destructor(req);
+	tcp_request_sock_ops.destructor(req);
+}
+
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+static struct request_sock_ops mptcp_subflow_v6_request_sock_ops __ro_after_init;
+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 int subflow_v6_conn_request(struct sock *sk, struct sk_buff *skb)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+
+	pr_debug("subflow=%p", subflow);
+
+	if (skb->protocol == htons(ETH_P_IP))
+		return subflow_v4_conn_request(sk, skb);
+
+	if (!ipv6_unicast_destination(skb))
+		goto drop;
+
+	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_v6_request_sock_ops,
+				&subflow_request_sock_ipv6_ops, sk, skb);
+
+drop:
+	tcp_listendrop(sk);
+	return 0; /* don't send reset */
+}
+
+static void subflow_v6_req_destructor(struct request_sock *req)
+{
+	subflow_req_destructor(req);
+	tcp6_request_sock_ops.destructor(req);
+}
+#endif
+
+struct request_sock *mptcp_subflow_reqsk_alloc(const struct request_sock_ops *ops,
+					       struct sock *sk_listener,
+					       bool attach_listener)
+{
+	if (ops->family == AF_INET)
+		ops = &mptcp_subflow_v4_request_sock_ops;
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	else if (ops->family == AF_INET6)
+		ops = &mptcp_subflow_v6_request_sock_ops;
+#endif
+
+	return inet_reqsk_alloc(ops, sk_listener, attach_listener);
+}
+EXPORT_SYMBOL(mptcp_subflow_reqsk_alloc);
+
+/* 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_sock_destruct(struct sock *sk)
+{
+	/* if new mptcp socket isn't accepted, it is free'd
+	 * from the tcp listener sockets request queue, linked
+	 * from req->sk.  The tcp socket is released.
+	 * This calls the ULP release function which will
+	 * also remove the mptcp socket, via
+	 * sock_put(ctx->conn).
+	 *
+	 * Problem is that the mptcp socket will be in
+	 * ESTABLISHED state and will not have the SOCK_DEAD flag.
+	 * Both result in warnings from inet_sock_destruct.
+	 */
+	if ((1 << sk->sk_state) & (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT)) {
+		sk->sk_state = TCP_CLOSE;
+		WARN_ON_ONCE(sk->sk_socket);
+		sock_orphan(sk);
+	}
+
+	mptcp_destroy_common(mptcp_sk(sk));
+	inet_sock_destruct(sk);
+}
+
+static void mptcp_force_close(struct sock *sk)
+{
+	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;
+}
+
+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,
+					  struct dst_entry *dst,
+					  struct request_sock *req_unhash,
+					  bool *own_req)
+{
+	struct mptcp_subflow_context *listener = mptcp_subflow_ctx(sk);
+	struct mptcp_subflow_request_sock *subflow_req;
+	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);
+
+	/* After child creation we must look for 'mp_capable' even when options
+	 * are not parsed
+	 */
+	mp_opt.mp_capable = 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 */
+	if (subflow_req->mp_capable) {
+		/* 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.mp_capable) {
+			fallback = true;
+			goto create_child;
+		}
+
+		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.mp_join || !subflow_hmac_valid(req, &mp_opt) ||
+		    !mptcp_can_accept_new_subflow(subflow_req->msk)) {
+			SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINACKMAC);
+			fallback = true;
+		}
+	}
+
+create_child:
+	child = listener->icsk_af_ops->syn_recv_sock(sk, skb, req, dst,
+						     req_unhash, own_req);
+
+	if (child && *own_req) {
+		struct mptcp_subflow_context *ctx = mptcp_subflow_ctx(child);
+
+		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 || fallback) {
+			if (fallback_is_fatal)
+				goto dispose_child;
+
+			subflow_drop_ctx(child);
+			goto out;
+		}
+
+		if (ctx->mp_capable) {
+			/* 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);
+
+			/* new mpc subflow takes ownership of the newly
+			 * created mptcp socket
+			 */
+			new_msk->sk_destruct = mptcp_sock_destruct;
+			mptcp_pm_new_connection(mptcp_sk(new_msk), 1);
+			mptcp_token_accept(subflow_req, mptcp_sk(new_msk));
+			ctx->conn = new_msk;
+			new_msk = NULL;
+
+			/* with OoO packets we can reach here without ingress
+			 * mpc option
+			 */
+			if (mp_opt.mp_capable)
+				mptcp_subflow_fully_established(ctx, &mp_opt);
+		} else if (ctx->mp_join) {
+			struct mptcp_sock *owner;
+
+			owner = subflow_req->msk;
+			if (!owner)
+				goto dispose_child;
+
+			/* move the msk reference ownership to the subflow */
+			subflow_req->msk = NULL;
+			ctx->conn = (struct sock *)owner;
+			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;
+
+dispose_child:
+	subflow_drop_ctx(child);
+	tcp_rsk(req)->drop_req = true;
+	inet_csk_prepare_for_destroy_sock(child);
+	tcp_done(child);
+	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 __ro_after_init;
+
+enum mapping_status {
+	MAPPING_OK,
+	MAPPING_INVALID,
+	MAPPING_EMPTY,
+	MAPPING_DATA_FIN,
+	MAPPING_DUMMY
+};
+
+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 dbg_bad_map(struct mptcp_subflow_context *subflow, u32 ssn)
+{
+	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)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+	unsigned int skb_consumed;
+
+	skb_consumed = tcp_sk(ssk)->copied_seq - TCP_SKB_CB(skb)->seq;
+	if (WARN_ON_ONCE(skb_consumed >= skb->len))
+		return true;
+
+	return skb->len - skb_consumed <= subflow->map_data_len -
+					  mptcp_subflow_get_map_offset(subflow);
+}
+
+static bool validate_mapping(struct sock *ssk, struct sk_buff *skb)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+	u32 ssn = tcp_sk(ssk)->copied_seq - subflow->ssn_offset;
+
+	if (unlikely(before(ssn, subflow->map_subflow_seq))) {
+		/* Mapping covers data later in the subflow stream,
+		 * currently unsupported.
+		 */
+		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 */
+		dbg_bad_map(subflow, ssn);
+		return false;
+	}
+	return true;
+}
+
+static enum mapping_status get_mapping_status(struct sock *ssk,
+					      struct mptcp_sock *msk)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+	struct mptcp_ext *mpext;
+	struct sk_buff *skb;
+	u16 data_len;
+	u64 map_seq;
+
+	skb = skb_peek(&ssk->sk_receive_queue);
+	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) {
+			/* the TCP stack deliver 0 len FIN pkt to the receive
+			 * queue, that is the only 0len pkts ever expected here,
+			 * and we can admit no mapping only for 0 len pkts
+			 */
+			if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
+				WARN_ONCE(1, "0len seq %d:%d flags %x",
+					  TCP_SKB_CB(skb)->seq,
+					  TCP_SKB_CB(skb)->end_seq,
+					  TCP_SKB_CB(skb)->tcp_flags);
+			sk_eat_skb(ssk, skb);
+			return MAPPING_EMPTY;
+		}
+
+		if (!subflow->map_valid)
+			return MAPPING_INVALID;
+
+		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);
+
+	data_len = mpext->data_len;
+	if (data_len == 0) {
+		MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_INFINITEMAPRX);
+		return MAPPING_INVALID;
+	}
+
+	if (mpext->data_fin == 1) {
+		if (data_len == 1) {
+			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
+				 * has been fully consumed. Continue
+				 * handling the existing mapping.
+				 */
+				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;
+	}
+	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) {
+			skb_ext_del(skb, SKB_EXT_MPTCP);
+			return MAPPING_OK;
+		}
+
+		/* 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)) {
+			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;
+	}
+
+	subflow->map_seq = map_seq;
+	subflow->map_subflow_seq = mpext->subflow_seq;
+	subflow->map_data_len = data_len;
+	subflow->map_valid = 1;
+	subflow->mpc_map = mpext->mpc_map;
+	pr_debug("new map seq=%llu subflow_seq=%u data_len=%u",
+		 subflow->map_seq, subflow->map_subflow_seq,
+		 subflow->map_data_len);
+
+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))
+		return MAPPING_INVALID;
+
+	skb_ext_del(skb, SKB_EXT_MPTCP);
+	return MAPPING_OK;
+}
+
+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;
+	if (incr)
+		tcp_cleanup_rbuf(ssk, incr);
+}
+
+static bool subflow_check_data_avail(struct sock *ssk)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+	enum mapping_status status;
+	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))
+		subflow->data_avail = 0;
+	if (subflow->data_avail)
+		return true;
+
+	msk = mptcp_sk(subflow->conn);
+	for (;;) {
+		u64 ack_seq;
+		u64 old_ack;
+
+		status = get_mapping_status(ssk, msk);
+		pr_debug("msk=%p ssk=%p status=%d", msk, ssk, status);
+		if (status == MAPPING_INVALID) {
+			ssk->sk_err = EBADMSG;
+			goto fatal;
+		}
+		if (status == MAPPING_DUMMY) {
+			__mptcp_do_fallback(msk);
+			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;
+			subflow->data_avail = MPTCP_SUBFLOW_DATA_AVAIL;
+			return true;
+		}
+
+		if (status != MAPPING_OK)
+			return false;
+
+		skb = skb_peek(&ssk->sk_receive_queue);
+		if (WARN_ON_ONCE(!skb))
+			return false;
+
+		/* 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;
+			}
+			WRITE_ONCE(msk->remote_key, subflow->remote_key);
+			WRITE_ONCE(msk->ack_seq, subflow->map_seq);
+			WRITE_ONCE(msk->can_ack, true);
+		}
+
+		old_ack = READ_ONCE(msk->ack_seq);
+		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) {
+			subflow->data_avail = MPTCP_SUBFLOW_DATA_AVAIL;
+			break;
+		} else if (after64(ack_seq, old_ack)) {
+			subflow->data_avail = MPTCP_SUBFLOW_OOO_DATA;
+			break;
+		}
+
+		/* only accept in-sequence mapping. Old values are spurious
+		 * retransmission
+		 */
+		mptcp_subflow_discard_data(ssk, skb, old_ack - ack_seq);
+	}
+	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);
+	subflow->data_avail = 0;
+	return false;
+}
+
+bool mptcp_subflow_data_available(struct sock *sk)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+
+	/* 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;
+
+		pr_debug("Done with mapping: seq=%u data_len=%u",
+			 subflow->map_subflow_seq,
+			 subflow->map_data_len);
+	}
+
+	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 concerened 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 = tcp_space(sk);
+	*full_space = tcp_full_space(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;
+
+	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;
+
+		set_bit(MPTCP_DATA_READY, &msk->flags);
+		parent->sk_data_ready(parent);
+		return;
+	}
+
+	WARN_ON_ONCE(!__mptcp_check_fallback(msk) && !subflow->mp_capable &&
+		     !subflow->mp_join && !(state & TCPF_CLOSE));
+
+	if (mptcp_subflow_data_available(sk))
+		mptcp_data_ready(parent, sk);
+}
+
+static void subflow_write_space(struct sock *sk)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct sock *parent = subflow->conn;
+
+	if (!sk_stream_is_writeable(sk))
+		return;
+
+	if (sk_stream_is_writeable(parent)) {
+		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);
+	}
+}
+
+static const struct inet_connection_sock_af_ops *
+subflow_default_af_ops(struct sock *sk)
+{
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	if (sk->sk_family == AF_INET6)
+		return &subflow_v6_specific;
+#endif
+	return &subflow_specific;
+}
+
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+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);
+	const struct inet_connection_sock_af_ops *target;
+
+	target = mapped ? &subflow_v6m_specific : subflow_default_af_ops(sk);
+
+	pr_debug("subflow=%p family=%d ops=%p target=%p mapped=%d",
+		 subflow, sk->sk_family, icsk->icsk_af_ops, target, mapped);
+
+	if (likely(icsk->icsk_af_ops == target))
+		return;
+
+	subflow->icsk_af_ops = icsk->icsk_af_ops;
+	icsk->icsk_af_ops = target;
+}
+#endif
+
+static void mptcp_info2sockaddr(const struct mptcp_addr_info *info,
+				struct sockaddr_storage *addr)
+{
+	memset(addr, 0, sizeof(*addr));
+	addr->ss_family = info->family;
+	if (addr->ss_family == AF_INET) {
+		struct sockaddr_in *in_addr = (struct sockaddr_in *)addr;
+
+		in_addr->sin_addr = info->addr;
+		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;
+
+		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;
+	struct socket *sf;
+	struct sock *ssk;
+	u32 remote_token;
+	int addrlen;
+	int err;
+
+	if (!mptcp_is_fully_established(sk))
+		return -ENOTCONN;
+
+	err = mptcp_subflow_create_socket(sk, &sf);
+	if (err)
+		return err;
+
+	ssk = sf->sk;
+	subflow = mptcp_subflow_ctx(ssk);
+	do {
+		get_random_bytes(&subflow->local_nonce, sizeof(u32));
+	} while (!subflow->local_nonce);
+
+	if (!local_id) {
+		err = mptcp_pm_get_local_id(msk, (struct sock_common *)ssk);
+		if (err < 0)
+			goto failed;
+
+		local_id = err;
+	}
+
+	subflow->remote_key = msk->remote_key;
+	subflow->local_key = msk->local_key;
+	subflow->token = msk->token;
+	mptcp_info2sockaddr(loc, &addr);
+
+	addrlen = sizeof(struct sockaddr_in);
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	if (loc->family == AF_INET6)
+		addrlen = sizeof(struct sockaddr_in6);
+#endif
+	ssk->sk_bound_dev_if = loc->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->local_id = local_id;
+	subflow->remote_id = remote_id;
+	subflow->request_join = 1;
+	subflow->request_bkup = !!(loc->flags & MPTCP_PM_ADDR_FLAG_BACKUP);
+	mptcp_info2sockaddr(remote, &addr);
+
+	err = kernel_connect(sf, (struct sockaddr *)&addr, addrlen, O_NONBLOCK);
+	if (err && err != -EINPROGRESS)
+		goto failed;
+
+	spin_lock_bh(&msk->join_list_lock);
+	list_add_tail(&subflow->node, &msk->join_list);
+	spin_unlock_bh(&msk->join_list_lock);
+
+	return err;
+
+failed:
+	sock_release(sf);
+	return err;
+}
+
+int mptcp_subflow_create_socket(struct sock *sk, struct socket **new_sock)
+{
+	struct mptcp_subflow_context *subflow;
+	struct net *net = sock_net(sk);
+	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)
+		return err;
+
+	lock_sock(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
+	err = tcp_set_ulp(sf->sk, "mptcp");
+	release_sock(sf->sk);
+
+	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 interaces 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);
+
+	*new_sock = sf;
+	sock_hold(sk);
+	subflow->conn = sk;
+
+	return 0;
+}
+
+static struct mptcp_subflow_context *subflow_create_ctx(struct sock *sk,
+							gfp_t priority)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	struct mptcp_subflow_context *ctx;
+
+	ctx = kzalloc(sizeof(*ctx), priority);
+	if (!ctx)
+		return NULL;
+
+	rcu_assign_pointer(icsk->icsk_ulp_data, ctx);
+	INIT_LIST_HEAD(&ctx->node);
+
+	pr_debug("subflow=%p", ctx);
+
+	ctx->tcp_sock = sk;
+
+	return ctx;
+}
+
+static void __subflow_state_change(struct sock *sk)
+{
+	struct socket_wq *wq;
+
+	rcu_read_lock();
+	wq = rcu_dereference(sk->sk_wq);
+	if (skwq_has_sleeper(wq))
+		wake_up_interruptible_all(&wq->wait);
+	rcu_read_unlock();
+}
+
+static bool subflow_is_done(const struct sock *sk)
+{
+	return sk->sk_shutdown & RCV_SHUTDOWN || sk->sk_state == TCP_CLOSE;
+}
+
+static void subflow_state_change(struct sock *sk)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct sock *parent = subflow->conn;
+
+	__subflow_state_change(sk);
+
+	if (subflow_simultaneous_connect(sk)) {
+		mptcp_do_fallback(sk);
+		mptcp_rcv_space_init(mptcp_sk(parent), sk);
+		pr_fallback(mptcp_sk(parent));
+		subflow->conn_finished = 1;
+		if (inet_sk_state_load(parent) == TCP_SYN_SENT) {
+			inet_sk_state_store(parent, TCP_ESTABLISHED);
+			parent->sk_state_change(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 (mptcp_subflow_data_available(sk))
+		mptcp_data_ready(parent, sk);
+
+	if (__mptcp_check_fallback(mptcp_sk(parent)) &&
+	    !(parent->sk_shutdown & RCV_SHUTDOWN) &&
+	    !subflow->rx_eof && subflow_is_done(sk)) {
+		subflow->rx_eof = 1;
+		mptcp_subflow_eof(parent);
+	}
+}
+
+static int subflow_ulp_init(struct sock *sk)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	struct mptcp_subflow_context *ctx;
+	struct tcp_sock *tp = tcp_sk(sk);
+	int err = 0;
+
+	/* disallow attaching ULP to a socket unless it has been
+	 * created with sock_create_kern()
+	 */
+	if (!sk->sk_kern_sock) {
+		err = -EOPNOTSUPP;
+		goto out;
+	}
+
+	ctx = subflow_create_ctx(sk, GFP_KERNEL);
+	if (!ctx) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	pr_debug("subflow=%p, family=%d", ctx, sk->sk_family);
+
+	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;
+	sk->sk_data_ready = subflow_data_ready;
+	sk->sk_write_space = subflow_write_space;
+	sk->sk_state_change = subflow_state_change;
+out:
+	return err;
+}
+
+static void subflow_ulp_release(struct sock *sk)
+{
+	struct mptcp_subflow_context *ctx = mptcp_subflow_ctx(sk);
+
+	if (!ctx)
+		return;
+
+	if (ctx->conn)
+		sock_put(ctx->conn);
+
+	kfree_rcu(ctx, rcu);
+}
+
+static void subflow_ulp_clone(const struct request_sock *req,
+			      struct sock *newsk,
+			      const gfp_t priority)
+{
+	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(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 && !subflow_req->mp_join)) {
+		subflow_ulp_fallback(newsk, old_ctx);
+		return;
+	}
+
+	new_ctx = subflow_create_ctx(newsk, priority);
+	if (!new_ctx) {
+		subflow_ulp_fallback(newsk, old_ctx);
+		return;
+	}
+
+	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->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;
+	} 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->local_id = subflow_req->local_id;
+		new_ctx->remote_id = subflow_req->remote_id;
+		new_ctx->token = subflow_req->token;
+		new_ctx->thmac = subflow_req->thmac;
+	}
+}
+
+static struct tcp_ulp_ops subflow_ulp_ops __read_mostly = {
+	.name		= "mptcp",
+	.owner		= THIS_MODULE,
+	.init		= subflow_ulp_init,
+	.release	= subflow_ulp_release,
+	.clone		= subflow_ulp_clone,
+};
+
+static int subflow_ops_init(struct request_sock_ops *subflow_ops)
+{
+	subflow_ops->obj_size = sizeof(struct mptcp_subflow_request_sock);
+
+	subflow_ops->slab = kmem_cache_create(subflow_ops->slab_name,
+					      subflow_ops->obj_size, 0,
+					      SLAB_ACCOUNT |
+					      SLAB_TYPESAFE_BY_RCU,
+					      NULL);
+	if (!subflow_ops->slab)
+		return -ENOMEM;
+
+	return 0;
+}
+
+void __init mptcp_subflow_init(void)
+{
+	mptcp_subflow_v4_request_sock_ops = tcp_request_sock_ops;
+	mptcp_subflow_v4_request_sock_ops.slab_name = "request_sock_subflow_v4";
+	mptcp_subflow_v4_request_sock_ops.destructor = subflow_v4_req_destructor;
+
+	if (subflow_ops_init(&mptcp_subflow_v4_request_sock_ops) != 0)
+		panic("MPTCP: failed to init subflow v4 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_specific = ipv4_specific;
+	subflow_specific.conn_request = subflow_v4_conn_request;
+	subflow_specific.syn_recv_sock = subflow_syn_recv_sock;
+	subflow_specific.sk_rx_dst_set = subflow_finish_connect;
+
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	/* In struct mptcp_subflow_request_sock, we assume the TCP request sock
+	 * structures for v4 and v6 have the same size. It should not changed in
+	 * the future but better to make sure to be warned if it is no longer
+	 * the case.
+	 */
+	BUILD_BUG_ON(sizeof(struct tcp_request_sock) != sizeof(struct tcp6_request_sock));
+
+	mptcp_subflow_v6_request_sock_ops = tcp6_request_sock_ops;
+	mptcp_subflow_v6_request_sock_ops.slab_name = "request_sock_subflow_v6";
+	mptcp_subflow_v6_request_sock_ops.destructor = subflow_v6_req_destructor;
+
+	if (subflow_ops_init(&mptcp_subflow_v6_request_sock_ops) != 0)
+		panic("MPTCP: failed to init subflow v6 request sock ops\n");
+
+	subflow_request_sock_ipv6_ops = tcp_request_sock_ipv6_ops;
+	subflow_request_sock_ipv6_ops.init_req = subflow_v6_init_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_v6m_specific = subflow_v6_specific;
+	subflow_v6m_specific.queue_xmit = ipv4_specific.queue_xmit;
+	subflow_v6m_specific.send_check = ipv4_specific.send_check;
+	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;
+#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");
+}