net/smc: restrict non-blocking connect finish

The smc_poll code tries to finish connect() if the socket is in
state SMC_INIT and polling of the internal CLC-socket returns with
EPOLLOUT. This makes sense for a select/poll call following a connect
call, but not without preceding connect().
With this patch smc_poll starts connect logic only, if the CLC-socket
is no longer in its initial state TCP_CLOSE.

In addition, a poll error on the internal CLC-socket is always
propagated to the SMC socket.

With this patch the code path mentioned by syzbot
https://syzkaller.appspot.com/bug?extid=03faa2dc16b8b64be396
is no longer possible.
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Reported-by: syzbot+03faa2dc16b8b64be396@syzkaller.appspotmail.com
Signed-off-by: David S. Miller <davem@davemloft.net>

net/smc/af_smc.c

@@ -1166,13 +1166,15 @@ static __poll_t smc_poll(struct file *file, struct socket *sock,
 		/* delegate to CLC child sock */
 		release_sock(sk);
 		mask = smc->clcsock->ops->poll(file, smc->clcsock, wait);
-		/* if non-blocking connect finished ... */
 		lock_sock(sk);
-		if ((sk->sk_state == SMC_INIT) && (mask & EPOLLOUT)) {
 		sk->sk_err = smc->clcsock->sk->sk_err;
 		if (sk->sk_err) {
 			mask |= EPOLLERR;
 		} else {
+			/* if non-blocking connect finished ... */
+			if (sk->sk_state == SMC_INIT &&
+			    mask & EPOLLOUT &&
+			    smc->clcsock->sk->sk_state != TCP_CLOSE) {
 				rc = smc_connect_rdma(smc);
 				if (rc < 0)
 					mask |= EPOLLERR;