[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>

diff --git a/net/bridge/br_netfilter.c b/net/bridge/br_netfilter.c
index c1757c7..5d8b939 100644 (file)
--- a/net/bridge/br_netfilter.c
+++ b/net/bridge/br_netfilter.c
@@ -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;
 }