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[NETFILTER]: bridge: fix double POST_ROUTING invocation 

The bridge code incorrectly causes two POST_ROUTING hook invocations
for DNATed packets that end up on the same bridge device. This
happens because packets with a changed destination address are passed
to dst_output() to make them go through the neighbour output function
again to build a new destination MAC address, before they will continue
through the IP hooks simulated by bridge netfilter.

The resulting hook order is:
 PREROUTING	(bridge netfilter)
 POSTROUTING	(dst_output -> ip_output)
 FORWARD	(bridge netfilter)
 POSTROUTING	(bridge netfilter)

The deferred hooks used to abort the first POST_ROUTING invocation,
but since the only thing bridge netfilter actually really wants is
a new MAC address, we can avoid going through the IP stack completely
by simply calling the neighbour output function directly.

Tested, reported and lots of data provided by: Damien Thebault <damien.thebault@gmail.com>

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Patrick McHardy 2008-01-11 18:02:18 -08:00 committed by David S. Miller
parent 0ff4d77bd9
commit 2948d2ebbb
1 changed files with 12 additions and 6 deletions
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18
net/bridge/br_netfilter.c
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@ -247,8 +247,9 @@ static void __br_dnat_complain(void)
* Let us first consider the case that ip_route_input() succeeds:
*
* If skb->dst->dev equals the logical bridge device the packet
* came in on, we can consider this bridging. We then call
* skb->dst->output() which will make the packet enter br_nf_local_out()
* came in on, we can consider this bridging. The packet is passed
* through the neighbour output function to build a new destination
* MAC address, which will make the packet enter br_nf_local_out()
* not much later. In that function it is assured that the iptables
* FORWARD chain is traversed for the packet.
*
@ -285,12 +286,17 @@ static int br_nf_pre_routing_finish_bridge(struct sk_buff *skb)
skb->nf_bridge->mask ^= BRNF_NF_BRIDGE_PREROUTING;
skb->dev = bridge_parent(skb->dev);
if (!skb->dev)
kfree_skb(skb);
else {
if (skb->dev) {
struct dst_entry *dst = skb->dst;
nf_bridge_pull_encap_header(skb);
skb->dst->output(skb);
if (dst->hh)
return neigh_hh_output(dst->hh, skb);
else if (dst->neighbour)
return dst->neighbour->output(skb);
}
kfree_skb(skb);
return 0;
}