af_unix: fix shutdown parameter checking

Return -EINVAL rather than 0 given an invalid "mode" parameter.
Signed-off-by: NXi Wang <xi.wang@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/unix/af_unix.c

@@ -2060,10 +2060,14 @@ static int unix_shutdown(struct socket *sock, int mode)
 	struct sock *sk = sock->sk;
 	struct sock *other;
 
-	mode = (mode+1)&(RCV_SHUTDOWN|SEND_SHUTDOWN);
-
-	if (!mode)
-		return 0;
+	if (mode < SHUT_RD || mode > SHUT_RDWR)
+		return -EINVAL;
+	/* This maps:
+	 * SHUT_RD   (0) -> RCV_SHUTDOWN  (1)
+	 * SHUT_WR   (1) -> SEND_SHUTDOWN (2)
+	 * SHUT_RDWR (2) -> SHUTDOWN_MASK (3)
+	 */
+	++mode;
 
 	unix_state_lock(sk);
 	sk->sk_shutdown |= mode;