vsock: Fix memory leak in vsock_connect()

stable inclusion
from stable-v4.19.256
commit 2fc2a7767f661e6083f69588718cdf6f07cb9330
category: bugfix
bugzilla: 187891, https://gitee.com/src-openeuler/kernel/issues/I5WYLL
CVE: CVE-2022-3629

--------------------------------

commit 7e97cfed9929eaabc41829c395eb0d1350fccb9d upstream.

An O_NONBLOCK vsock_connect() request may try to reschedule
@connect_work.  Imagine the following sequence of vsock_connect()
requests:

  1. The 1st, non-blocking request schedules @connect_work, which will
     expire after 200 jiffies.  Socket state is now SS_CONNECTING;

  2. Later, the 2nd, blocking request gets interrupted by a signal after
     a few jiffies while waiting for the connection to be established.
     Socket state is back to SS_UNCONNECTED, but @connect_work is still
     pending, and will expire after 100 jiffies.

  3. Now, the 3rd, non-blocking request tries to schedule @connect_work
     again.  Since @connect_work is already scheduled,
     schedule_delayed...

net/vmw_vsock/af_vsock.c

@@ -1213,7 +1213,14 @@ static int vsock_stream_connect(struct socket *sock, struct sockaddr *addr,
 			 * timeout fires.
 			 */
 			sock_hold(sk);
-			schedule_delayed_work(&vsk->connect_work, timeout);
+
+			/* If the timeout function is already scheduled,
+			 * reschedule it, then ungrab the socket refcount to
+			 * keep it balanced.
+			 */
+			if (mod_delayed_work(system_wq, &vsk->connect_work,
+					     timeout))
+				sock_put(sk);
 
 			/* Skip ahead to preserve error code set above. */
 			goto out_wait;