network: tcp_connect should return certain errors up the stack

The current tcp_connect code completely ignores errors from sending an skb.
This makes sense in many situations (like -ENOBUFFS) but I want to be able to
immediately fail connections if they are denied by the SELinux netfilter hook.
Netfilter does not normally return ECONNREFUSED when it drops a packet so we
respect that error code as a final and fatal error that can not be recovered.
Based-on-patch-by: NPatrick McHardy <kaber@trash.net>
Signed-off-by: NEric Paris <eparis@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_output.c

@@ -2592,6 +2592,7 @@ int tcp_connect(struct sock *sk)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct sk_buff *buff;
+	int err;
 
 	tcp_connect_init(sk);
 
@@ -2614,7 +2615,9 @@ int tcp_connect(struct sock *sk)
 	sk->sk_wmem_queued += buff->truesize;
 	sk_mem_charge(sk, buff->truesize);
 	tp->packets_out += tcp_skb_pcount(buff);
-	tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
+	err = tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
+	if (err == -ECONNREFUSED)
+		return err;
 
 	/* We change tp->snd_nxt after the tcp_transmit_skb() call
 	 * in order to make this packet get counted in tcpOutSegs.