ip_forward: Drop frames with attached skb->sk

[ 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@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/ipv4/ip_forward.c b/net/ipv4/ip_forward.c
index 29a07b6..bcd78a3 100644 (file)
--- 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;