1 files changed, 102 insertions, 17 deletions

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 1b64dfaa5f63..ee916b3686fe 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -24,6 +24,58 @@
 
 #define MPTCP_SAME_STATE TCP_MAX_STATES
 
+static void __mptcp_close(struct sock *sk, long timeout);
+
+static const struct proto_ops * tcp_proto_ops(struct sock *sk)
+{
+#if IS_ENABLED(CONFIG_IPV6)
+	if (sk->sk_family == AF_INET6)
+		return &inet6_stream_ops;
+#endif
+	return &inet_stream_ops;
+}
+
+/* MP_CAPABLE handshake failed, convert msk to plain tcp, replacing
+ * socket->sk and stream ops and destroying msk
+ * return the msk socket, as we can't access msk anymore after this function
+ * completes
+ * Called with msk lock held, releases such lock before returning
+ */
+static struct socket *__mptcp_fallback_to_tcp(struct mptcp_sock *msk,
+					      struct sock *ssk)
+{
+	struct mptcp_subflow_context *subflow;
+	struct socket *sock;
+	struct sock *sk;
+
+	sk = (struct sock *)msk;
+	sock = sk->sk_socket;
+	subflow = mptcp_subflow_ctx(ssk);
+
+	/* detach the msk socket */
+	list_del_init(&subflow->node);
+	sock_orphan(sk);
+	sock->sk = NULL;
+
+	/* socket is now TCP */
+	lock_sock(ssk);
+	sock_graft(ssk, sock);
+	if (subflow->conn) {
+		/* We can't release the ULP data on a live socket,
+		 * restore the tcp callback
+		 */
+		mptcp_subflow_tcp_fallback(ssk, subflow);
+		sock_put(subflow->conn);
+		subflow->conn = NULL;
+	}
+	release_sock(ssk);
+	sock->ops = tcp_proto_ops(ssk);
+
+	/* destroy the left-over msk sock */
+	__mptcp_close(sk, 0);
+	return sock;
+}
+
 /* If msk has an initial subflow socket, and the MP_CAPABLE handshake has not
  * completed yet or has failed, return the subflow socket.
  * Otherwise return NULL.
@@ -36,25 +88,37 @@ static struct socket *__mptcp_nmpc_socket(const struct mptcp_sock *msk)
 	return msk->subflow;
 }
 
-/* if msk has a single subflow, and the mp_capable handshake is failed,
- * return it.
+static bool __mptcp_needs_tcp_fallback(const struct mptcp_sock *msk)
+{
+	return msk->first && !sk_is_mptcp(msk->first);
+}
+
+/* if the mp_capable handshake has failed, it fallbacks msk to plain TCP,
+ * releases the socket lock and returns a reference to the now TCP socket.
  * Otherwise returns NULL
  */
-static struct socket *__mptcp_tcp_fallback(const struct mptcp_sock *msk)
+static struct socket *__mptcp_tcp_fallback(struct mptcp_sock *msk)
 {
-	struct socket *ssock = __mptcp_nmpc_socket(msk);
-
 	sock_owned_by_me((const struct sock *)msk);
 
-	if (!ssock || sk_is_mptcp(ssock->sk))
+	if (likely(!__mptcp_needs_tcp_fallback(msk)))
 		return NULL;
 
-	return ssock;
+	if (msk->subflow) {
+		/* the first subflow is an active connection, discart the
+		 * paired socket
+		 */
+		msk->subflow->sk = NULL;
+		sock_release(msk->subflow);
+		msk->subflow = NULL;
+	}
+
+	return __mptcp_fallback_to_tcp(msk, msk->first);
 }
 
 static bool __mptcp_can_create_subflow(const struct mptcp_sock *msk)
 {
-	return ((struct sock *)msk)->sk_state == TCP_CLOSE;
+	return !msk->first;
 }
 
 static struct socket *__mptcp_socket_create(struct mptcp_sock *msk, int state)
@@ -75,6 +139,7 @@ static struct socket *__mptcp_socket_create(struct mptcp_sock *msk, int state)
 	if (err)
 		return ERR_PTR(err);
 
+	msk->first = ssock->sk;
 	msk->subflow = ssock;
 	subflow = mptcp_subflow_ctx(ssock->sk);
 	list_add(&subflow->node, &msk->conn_list);
@@ -154,6 +219,8 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
 		ret = sk_stream_wait_memory(ssk, timeo);
 		if (ret)
 			return ret;
+		if (unlikely(__mptcp_needs_tcp_fallback(msk)))
+			return 0;
 	}
 
 	/* compute copy limit */
@@ -265,11 +332,11 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 
 	lock_sock(sk);
 	ssock = __mptcp_tcp_fallback(msk);
-	if (ssock) {
+	if (unlikely(ssock)) {
+fallback:
 		pr_debug("fallback passthrough");
 		ret = sock_sendmsg(ssock, msg);
-		release_sock(sk);
-		return ret;
+		return ret >= 0 ? ret + copied : (copied ? copied : ret);
 	}
 
 	timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);
@@ -288,6 +355,11 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 					 &size_goal);
 		if (ret < 0)
 			break;
+		if (ret == 0 && unlikely(__mptcp_needs_tcp_fallback(msk))) {
+			release_sock(ssk);
+			ssock = __mptcp_tcp_fallback(msk);
+			goto fallback;
+		}
 
 		copied += ret;
 	}
@@ -368,11 +440,11 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 
 	lock_sock(sk);
 	ssock = __mptcp_tcp_fallback(msk);
-	if (ssock) {
+	if (unlikely(ssock)) {
+fallback:
 		pr_debug("fallback-read subflow=%p",
 			 mptcp_subflow_ctx(ssock->sk));
 		copied = sock_recvmsg(ssock, msg, flags);
-		release_sock(sk);
 		return copied;
 	}
 
@@ -477,6 +549,8 @@ wait_for_data:
 		pr_debug("block timeout %ld", timeo);
 		wait_data = true;
 		mptcp_wait_data(sk, &timeo);
+		if (unlikely(__mptcp_tcp_fallback(msk)))
+			goto fallback;
 	}
 
 	if (more_data_avail) {
@@ -529,6 +603,8 @@ static int __mptcp_init_sock(struct sock *sk)
 	INIT_LIST_HEAD(&msk->conn_list);
 	__set_bit(MPTCP_SEND_SPACE, &msk->flags);
 
+	msk->first = NULL;
+
 	return 0;
 }
 
@@ -563,7 +639,8 @@ static void mptcp_subflow_shutdown(struct sock *ssk, int how)
 	release_sock(ssk);
 }
 
-static void mptcp_close(struct sock *sk, long timeout)
+/* Called with msk lock held, releases such lock before returning */
+static void __mptcp_close(struct sock *sk, long timeout)
 {
 	struct mptcp_subflow_context *subflow, *tmp;
 	struct mptcp_sock *msk = mptcp_sk(sk);
@@ -571,8 +648,6 @@ static void mptcp_close(struct sock *sk, long timeout)
 	mptcp_token_destroy(msk->token);
 	inet_sk_state_store(sk, TCP_CLOSE);
 
-	lock_sock(sk);
-
 	list_for_each_entry_safe(subflow, tmp, &msk->conn_list, node) {
 		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
 
@@ -585,6 +660,12 @@ static void mptcp_close(struct sock *sk, long timeout)
 	sk_common_release(sk);
 }
 
+static void mptcp_close(struct sock *sk, long timeout)
+{
+	lock_sock(sk);
+	__mptcp_close(sk, timeout);
+}
+
 static void mptcp_copy_inaddrs(struct sock *msk, const struct sock *ssk)
 {
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
@@ -654,6 +735,7 @@ static struct sock *mptcp_accept(struct sock *sk, int flags, int *err,
 		msk->local_key = subflow->local_key;
 		msk->token = subflow->token;
 		msk->subflow = NULL;
+		msk->first = newsk;
 
 		mptcp_token_update_accept(newsk, new_mptcp_sock);
 
@@ -1007,8 +1089,8 @@ unlock_fail:
 static __poll_t mptcp_poll(struct file *file, struct socket *sock,
 			   struct poll_table_struct *wait)
 {
-	const struct mptcp_sock *msk;
 	struct sock *sk = sock->sk;
+	struct mptcp_sock *msk;
 	struct socket *ssock;
 	__poll_t mask = 0;
 
@@ -1024,6 +1106,9 @@ static __poll_t mptcp_poll(struct file *file, struct socket *sock,
 	release_sock(sk);
 	sock_poll_wait(file, sock, wait);
 	lock_sock(sk);
+	ssock = __mptcp_tcp_fallback(msk);
+	if (unlikely(ssock))
+		return ssock->ops->poll(file, ssock, NULL);
 
 	if (test_bit(MPTCP_DATA_READY, &msk->flags))
 		mask = EPOLLIN | EPOLLRDNORM;