tipc: fix a potental access after delete in tipc_sk_join()

In commit d12d2e12cec2 "tipc: send out join messages as soon as new
member is discovered") we added a call to the function tipc_group_join()
without considering the case that the preceding tipc_sk_publish() might
have failed, and the group item already deleted.

We fix this by returning from tipc_sk_join() directly after the
failed tipc_sk_publish.

Reported-by: syzbot+e3eeae78ea88b8d6d858@syzkaller.appspotmail.com
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/socket.c

@@ -2774,6 +2774,7 @@ static int tipc_sk_join(struct tipc_sock *tsk, struct tipc_group_req *mreq)
 	if (rc) {
 		tipc_group_delete(net, grp);
 		tsk->group = NULL;
+		return rc;
 	}
 	/* Eliminate any risk that a broadcast overtakes sent JOINs */
 	tsk->mc_method.rcast = true;