[SCTP]: Return socket errors only if the receive queue is empty.

This patch fixes an issue where it is possible to get valid data after
a ENOTCONN error. It returns socket errors only after data queued on
socket receive queue is consumed.
Signed-off-by: NNeil Horman <nhorman@tuxdriver.com>
Signed-off-by: NSridhar Samudrala <sri@us.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sctp/socket.c

@@ -4743,11 +4743,6 @@ static struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags,
 	struct sk_buff *skb;
 	long timeo;
 
-	/* Caller is allowed not to check sk->sk_err before calling.  */
-	error = sock_error(sk);
-	if (error)
-		goto no_packet;
-
 	timeo = sock_rcvtimeo(sk, noblock);
 
 	SCTP_DEBUG_PRINTK("Timeout: timeo: %ld, MAX: %ld.\n",
@@ -4774,6 +4769,11 @@ static struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags,
 		if (skb)
 			return skb;
 
+		/* Caller is allowed not to check sk->sk_err before calling. */
+		error = sock_error(sk);
+		if (error)
+			goto no_packet;
+
 		if (sk->sk_shutdown & RCV_SHUTDOWN)
 			break;