netfilter: Pass socket pointer down through okfn().

On the output paths in particular, we have to sometimes deal with two
socket contexts.  First, and usually skb->sk, is the local socket that
generated the frame.

And second, is potentially the socket used to control a tunneling
socket, such as one the encapsulates using UDP.

We do not want to disassociate skb->sk when encapsulating in order
to fix this, because that would break socket memory accounting.

The most extreme case where this can cause huge problems is an
AF_PACKET socket transmitting over a vxlan device.  We hit code
paths doing checks that assume they are dealing with an ipv4
socket, but are actually operating upon the AF_PACKET one.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index 8493a22..74ceb73 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -1986,13 +1986,13 @@
 }
 #endif
 
-static inline int ip6mr_forward2_finish(struct sk_buff *skb)
+static inline int ip6mr_forward2_finish(struct sock *sk, struct sk_buff *skb)
 {
 	IP6_INC_STATS_BH(dev_net(skb_dst(skb)->dev), ip6_dst_idev(skb_dst(skb)),
 			 IPSTATS_MIB_OUTFORWDATAGRAMS);
 	IP6_ADD_STATS_BH(dev_net(skb_dst(skb)->dev), ip6_dst_idev(skb_dst(skb)),
 			 IPSTATS_MIB_OUTOCTETS, skb->len);
-	return dst_output(skb);
+	return dst_output_sk(sk, skb);
 }
 
 /*
@@ -2064,7 +2064,8 @@
 
 	IP6CB(skb)->flags |= IP6SKB_FORWARDED;
 
-	return NF_HOOK(NFPROTO_IPV6, NF_INET_FORWARD, skb, skb->dev, dev,
+	return NF_HOOK(NFPROTO_IPV6, NF_INET_FORWARD, NULL, skb,
+		       skb->dev, dev,
 		       ip6mr_forward2_finish);
 
 out_free: