https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?h=linux-3.18.y&id=a360eb6f74b999a7546f2542c0d6483fdbb73461

Give preference to Linux-Vserver patch over upstream IPv4-mapped-to-IPv6 fix.

The upstream fix is only relevant for IPv6 loopback (ie mapping destination of
:: to ::ffff:127.0.0.1 or ::1 based on whether source is IPv4-mapped IPv6
address), which Linux-Vserver doesn't specifically support (eg
VSERVER_AUTO_LBACK is IPv4-only).

See https://lwn.net/Articles/688462/, section "Address mapping", for more
information on IPv4-mapped IPv6.

If socket has a Linux-Vserver network context, then handle as previous,
otherwise handle as per the upstream fix.

diff -urNp a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
--- a/net/ipv6/tcp_ipv6.c	2017-07-21 09:49:54.073001106 -0500
+++ b/net/ipv6/tcp_ipv6.c	2017-07-21 09:55:43.805534787 -0500
@@ -166,11 +166,17 @@ static int tcp_v6_connect(struct sock *s
 	 */
 
 	if (ipv6_addr_any(&usin->sin6_addr)) {
-		if (ipv6_addr_v4mapped(&sk->sk_v6_rcv_saddr))
-			ipv6_addr_set_v4mapped(htonl(INADDR_LOOPBACK),
-					       &usin->sin6_addr);
+		struct nx_info *nxi =  sk->sk_nx_info;
+
+		if (nxi && nx_info_has_v6(nxi))
+			/* FIXME: remap lback? */
+			usin->sin6_addr = nxi->v6.ip;
 		else
-			usin->sin6_addr = in6addr_loopback;
+			if (ipv6_addr_v4mapped(&sk->sk_v6_rcv_saddr))
+				ipv6_addr_set_v4mapped(htonl(INADDR_LOOPBACK),
+						       &usin->sin6_addr);
+			else
+				usin->sin6_addr = in6addr_loopback;
 	}
 
 	addr_type = ipv6_addr_type(&usin->sin6_addr);