[Bridge] Sending 802.1Q packets using AF_PACKET socket on filtered bridge forwards with wrong MAC addresses

Brandon Carpenter brandon.carpenter at cypherpath.com
Tue Nov 28 23:37:40 UTC 2017

I tracked down the function responsible for changing the MAC header.
It is skb_vlan_untag() called from __allowed_ingress() in
net/bridge/br_vlan.c. Before skb_vlan_untag() is called, the MAC
headers are perfect and afterward they are altered as previously
described. I'll continue digging into that function, but if any of you
have insight into what skb_vlan_untag() does and why it might alter
the MAC header the way it does in this special case, I would
appreciate the help.




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