[TCP]: Honour sk_bound_dev_if in tcp_v4_send_ack

A time_wait socket inherits sk_bound_dev_if from the original socket,
but it is not used when sending ACK packets using ip_send_reply.

Fix by passing the oif to ip_send_reply in struct ip_reply_arg and
use it for output routing.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ip.h

@@ -143,6 +143,7 @@ struct ip_reply_arg {
 	__wsum 	    csum;
 	int	    csumoffset; /* u16 offset of csum in iov[0].iov_base */
 				/* -1 if not needed */ 
+	int	    bound_dev_if;
 }; 
 
 void ip_send_reply(struct sock *sk, struct sk_buff *skb, struct ip_reply_arg *arg,

net/ipv4/ip_output.c

@@ -1352,7 +1352,8 @@ void ip_send_reply(struct sock *sk, struct sk_buff *skb, struct ip_reply_arg *ar
 	}
 
 	{
-		struct flowi fl = { .nl_u = { .ip4_u =
+		struct flowi fl = { .oif = arg->bound_dev_if,
+				    .nl_u = { .ip4_u =
 					      { .daddr = daddr,
 						.saddr = rt->rt_spec_dst,
 						.tos = RT_TOS(ip_hdr(skb)->tos) } },
@@ -1376,6 +1377,7 @@ void ip_send_reply(struct sock *sk, struct sk_buff *skb, struct ip_reply_arg *ar
 	inet->tos = ip_hdr(skb)->tos;
 	sk->sk_priority = skb->priority;
 	sk->sk_protocol = ip_hdr(skb)->protocol;
+	sk->sk_bound_dev_if = arg->bound_dev_if;
 	ip_append_data(sk, ip_reply_glue_bits, arg->iov->iov_base, len, 0,
 		       &ipc, rt, MSG_DONTWAIT);
 	if ((skb = skb_peek(&sk->sk_write_queue)) != NULL) {

net/ipv4/tcp_ipv4.c

@@ -705,6 +705,8 @@ static void tcp_v4_send_ack(struct tcp_timewait_sock *twsk,
 				      ip_hdr(skb)->saddr, /* XXX */
 				      arg.iov[0].iov_len, IPPROTO_TCP, 0);
 	arg.csumoffset = offsetof(struct tcphdr, check) / 2;
+	if (twsk)
+		arg.bound_dev_if = twsk->tw_sk.tw_bound_dev_if;
 
 	ip_send_reply(tcp_socket->sk, skb, &arg, arg.iov[0].iov_len);