[NETNS][IPV6] route6 - pass always a valid socket to ip6_dst_lookup

The ip6_dst_lookup receive a socket as parameter. In some part of the code
it is called with a NULL socket parameter. We want to rely on the socket
to retrieve the network namespace, so we always pass a valid socket in all
cases.

Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>
Signed-off-by: Benjamin Thery <benjamin.thery@bull.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index fd773ac..aacbb76 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1071,8 +1071,11 @@
 	fl.fl_ip_sport = t1->source;
 	security_skb_classify_flow(skb, &fl);
 
-	/* sk = NULL, but it is safe for now. RST socket required. */
-	if (!ip6_dst_lookup(NULL, &buff->dst, &fl)) {
+	/* Pass a socket to ip6_dst_lookup either it is for RST
+	 * Underlying function will use this to retrieve the network
+	 * namespace
+	 */
+	if (!ip6_dst_lookup(tcp6_socket->sk, &buff->dst, &fl)) {
 
 		if (xfrm_lookup(&buff->dst, &fl, NULL, 0) >= 0) {
 			ip6_xmit(tcp6_socket->sk, buff, &fl, NULL, 0);
@@ -1172,7 +1175,7 @@
 	fl.fl_ip_sport = t1->source;
 	security_skb_classify_flow(skb, &fl);
 
-	if (!ip6_dst_lookup(NULL, &buff->dst, &fl)) {
+	if (!ip6_dst_lookup(tcp6_socket->sk, &buff->dst, &fl)) {
 		if (xfrm_lookup(&buff->dst, &fl, NULL, 0) >= 0) {
 			ip6_xmit(tcp6_socket->sk, buff, &fl, NULL, 0);
 			TCP_INC_STATS_BH(TCP_MIB_OUTSEGS);