net/smc: fix refcounting for non-blocking connect()

If a nonblocking socket is immediately closed after connect(),
the connect worker may not have started. This results in a refcount
problem, since sock_hold() is called from the connect worker.
This patch moves the sock_hold in front of the connect worker
scheduling.

Reported-by: syzbot+4c063e6dea39e4b79f29@syzkaller.appspotmail.com
Fixes: 50717a3 ("net/smc: nonblocking connect rework")
Reviewed-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/smc/af_smc.c

@@ -707,8 +707,6 @@ static int __smc_connect(struct smc_sock *smc)
 	int smc_type;
 	int rc = 0;
 
-	sock_hold(&smc->sk); /* sock put in passive closing */
-
 	if (smc->use_fallback)
 		return smc_connect_fallback(smc, smc->fallback_rsn);
 
@@ -853,6 +851,8 @@ static int smc_connect(struct socket *sock, struct sockaddr *addr,
 	rc = kernel_connect(smc->clcsock, addr, alen, flags);
 	if (rc && rc != -EINPROGRESS)
 		goto out;
+
+	sock_hold(&smc->sk); /* sock put in passive closing */
 	if (flags & O_NONBLOCK) {
 		if (schedule_work(&smc->connect_work))
 			smc->connect_nonblock = 1;