Merge branch 'mptcp-locking-fixes'

Mat Martineau says:

====================
mptcp: Locking fixes

Two separate locking fixes for the networking tree:

Patch 1 addresses a MPTCP fastopen error-path deadlock that was found
with syzkaller.

Patch 2 works around a lockdep false-positive between MPTCP listening and
non-listening sockets at socket destruct time.
====================

Link: https://lore.kernel.org/r/20221220195215.238353-1-mathew.j.martineau@linux.intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

net/mptcp/protocol.c

@@ -1662,6 +1662,8 @@ static void mptcp_set_nospace(struct sock *sk)
 	set_bit(MPTCP_NOSPACE, &mptcp_sk(sk)->flags);
 }
 
+static int mptcp_disconnect(struct sock *sk, int flags);
+
 static int mptcp_sendmsg_fastopen(struct sock *sk, struct sock *ssk, struct msghdr *msg,
 				  size_t len, int *copied_syn)
 {
@@ -1672,9 +1674,9 @@ static int mptcp_sendmsg_fastopen(struct sock *sk, struct sock *ssk, struct msgh
 	lock_sock(ssk);
 	msg->msg_flags |= MSG_DONTWAIT;
 	msk->connect_flags = O_NONBLOCK;
-	msk->is_sendmsg = 1;
+	msk->fastopening = 1;
 	ret = tcp_sendmsg_fastopen(ssk, msg, copied_syn, len, NULL);
-	msk->is_sendmsg = 0;
+	msk->fastopening = 0;
 	msg->msg_flags = saved_flags;
 	release_sock(ssk);
 
@@ -1688,6 +1690,8 @@ static int mptcp_sendmsg_fastopen(struct sock *sk, struct sock *ssk, struct msgh
 		 */
 		if (ret && ret != -EINPROGRESS && ret != -ERESTARTSYS && ret != -EINTR)
 			*copied_syn = 0;
+	} else if (ret && ret != -EINPROGRESS) {
+		mptcp_disconnect(sk, 0);
 	}
 
 	return ret;
@@ -2353,7 +2357,7 @@ static void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
 		/* otherwise tcp will dispose of the ssk and subflow ctx */
 		if (ssk->sk_state == TCP_LISTEN) {
 			tcp_set_state(ssk, TCP_CLOSE);
-			mptcp_subflow_queue_clean(ssk);
+			mptcp_subflow_queue_clean(sk, ssk);
 			inet_csk_listen_stop(ssk);
 			mptcp_event_pm_listener(ssk, MPTCP_EVENT_LISTENER_CLOSED);
 		}
@@ -2989,6 +2993,14 @@ static int mptcp_disconnect(struct sock *sk, int flags)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);
 
+	/* We are on the fastopen error path. We can't call straight into the
+	 * subflows cleanup code due to lock nesting (we are already under
+	 * msk->firstsocket lock). Do nothing and leave the cleanup to the
+	 * caller.
+	 */
+	if (msk->fastopening)
+		return 0;
+
 	inet_sk_state_store(sk, TCP_CLOSE);
 
 	mptcp_stop_timer(sk);
@@ -3532,7 +3544,7 @@ static int mptcp_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 	/* if reaching here via the fastopen/sendmsg path, the caller already
 	 * acquired the subflow socket lock, too.
 	 */
-	if (msk->is_sendmsg)
+	if (msk->fastopening)
 		err = __inet_stream_connect(ssock, uaddr, addr_len, msk->connect_flags, 1);
 	else
 		err = inet_stream_connect(ssock, uaddr, addr_len, msk->connect_flags);

net/mptcp/protocol.h

@@ -295,7 +295,7 @@ struct mptcp_sock {
 	u8		recvmsg_inq:1,
 			cork:1,
 			nodelay:1,
-			is_sendmsg:1;
+			fastopening:1;
 	int		connect_flags;
 	struct work_struct work;
 	struct sk_buff  *ooo_last_skb;
@@ -628,7 +628,7 @@ void mptcp_close_ssk(struct sock *sk, struct sock *ssk,
 		     struct mptcp_subflow_context *subflow);
 void __mptcp_subflow_send_ack(struct sock *ssk);
 void mptcp_subflow_reset(struct sock *ssk);
-void mptcp_subflow_queue_clean(struct sock *ssk);
+void mptcp_subflow_queue_clean(struct sock *sk, struct sock *ssk);
 void mptcp_sock_graft(struct sock *sk, struct socket *parent);
 struct socket *__mptcp_nmpc_socket(const struct mptcp_sock *msk);
 bool __mptcp_close(struct sock *sk, long timeout);

net/mptcp/subflow.c

@@ -1791,7 +1791,7 @@ static void subflow_state_change(struct sock *sk)
 	}
 }
 
-void mptcp_subflow_queue_clean(struct sock *listener_ssk)
+void mptcp_subflow_queue_clean(struct sock *listener_sk, struct sock *listener_ssk)
 {
 	struct request_sock_queue *queue = &inet_csk(listener_ssk)->icsk_accept_queue;
 	struct mptcp_sock *msk, *next, *head = NULL;
@@ -1840,8 +1840,23 @@ void mptcp_subflow_queue_clean(struct sock *listener_ssk)
 
 		do_cancel_work = __mptcp_close(sk, 0);
 		release_sock(sk);
-		if (do_cancel_work)
+		if (do_cancel_work) {
+			/* lockdep will report a false positive ABBA deadlock
+			 * between cancel_work_sync and the listener socket.
+			 * The involved locks belong to different sockets WRT
+			 * the existing AB chain.
+			 * Using a per socket key is problematic as key
+			 * deregistration requires process context and must be
+			 * performed at socket disposal time, in atomic
+			 * context.
+			 * Just tell lockdep to consider the listener socket
+			 * released here.
+			 */
+			mutex_release(&listener_sk->sk_lock.dep_map, _RET_IP_);
 			mptcp_cancel_work(sk);
+			mutex_acquire(&listener_sk->sk_lock.dep_map,
+				      SINGLE_DEPTH_NESTING, 0, _RET_IP_);
+		}
 		sock_put(sk);
 	}