ipvs: Keep skb->sk when allocating headroom on tunnel xmit

ip_vs_prepare_tunneled_skb() ignores ->sk when allocating a new
skb, either unconditionally setting ->sk to NULL or allowing
the uninitialized ->sk from a newly allocated skb to leak through
to the caller.

This patch properly copies ->sk and increments its reference count.

Signed-off-by: Calvin Owens <calvinowens@fb.com>
Acked-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>

net/netfilter/ipvs/ip_vs_xmit.c

diff --git a/net/netfilter/ipvs/ip_vs_xmit.c b/net/netfilter/ipvs/ip_vs_xmit.c
index 437a366..bd90bf8 100644
--- a/net/netfilter/ipvs/ip_vs_xmit.c
+++ b/net/netfilter/ipvs/ip_vs_xmit.c
@@ -846,6 +846,8 @@
 		new_skb = skb_realloc_headroom(skb, max_headroom);
 		if (!new_skb)
 			goto error;
+		if (skb->sk)
+			skb_set_owner_w(new_skb, skb->sk);
 		consume_skb(skb);
 		skb = new_skb;
 	}