[PATCH 3.2 214/221] ip_forward: Drop frames with attached skb->sk

[Ben Hutchings]

3.2.69-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Sebastian PÃhn <sebastian.poehn@xxxxxxxxx>

[ Upstream commit 2ab957492d13bb819400ac29ae55911d50a82a13 ]

Initial discussion was:
[FYI] xfrm: Don't lookup sk_policy for timewait sockets

Forwarded frames should not have a socket attached. Especially
tw sockets will lead to panics later-on in the stack.

This was observed with TPROXY assigning a tw socket and broken
policy routing (misconfigured). As a result frame enters
forwarding path instead of input. We cannot solve this in
TPROXY as it cannot know that policy routing is broken.

v2:
Remove useless comment

Signed-off-by: Sebastian Poehn <sebastian.poehn@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/ipv4/ip_forward.c | 3 +++
 1 file changed, 3 insertions(+)

--- a/net/ipv4/ip_forward.c
+++ b/net/ipv4/ip_forward.c
@@ -57,6 +57,9 @@ int ip_forward(struct sk_buff *skb)
 	struct rtable *rt;	/* Route we use */
 	struct ip_options * opt	= &(IPCB(skb)->opt);
 
+	if (unlikely(skb->sk))
+		goto drop;
+
 	if (skb_warn_if_lro(skb))
 		goto drop;
 

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