Commit 2948d2eb authored Jan 11, 2008 by Patrick McHardy Committed by David S. Miller Jan 11, 2008

[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>

parent 0ff4d77b

net/bridge/br_netfilter.c

+12 −6

Original line number	Diff line number	Diff line
		@@ -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;
		}

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