I have been working on an ebtables module to insert an 802.1Q (VLAN)
tags into network packets leaving the bridge, via the POSTROUTING NAT
chain. To insert the VLAN tag the ethernet header size needs to be
increased by 4 bytes. I noticed that after increasing the size of the
ethernet header that the ethernet header in packets on the wire was
incorrect.
I think it is because the br_dev_queue_push_xmit function does not take
the VLAN header into account when it moves the data pointer in the skb
to the start of the ethernet header. The following patch corrects this.
Does this make sense to do? I plan to do more extensive testing passing
vlan and non-vlan traffic across a bridge, and will report back with the
results.
diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c
index ada7f49..f30dc56 100644
--- a/net/bridge/br_forward.c
+++ b/net/bridge/br_forward.c
@@ -43,6 +43,8 @@ int br_dev_queue_push_xmit(struct sk_buff *skb)
kfree_skb(skb);
else {
skb_push(skb, ETH_HLEN);
+ if(skb->protocol == htons(ETH_P_8021Q))
+ skb_push(skb, VLAN_HLEN);
dev_queue_xmit(skb);
}
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