linux-kernel - Re: Sending 802.1Q packets using AF_PACKET socket on filtered bridge forwards with wrong MAC addresses

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Message-ID: <CAPpVWGvchrhyBd2MaBG4DhwWSsbNYRwdtVE31TLswHdPODzq3A@mail.gmail.com>
Date:   Tue, 28 Nov 2017 15:37:40 -0800
From:   Brandon Carpenter <brandon.carpenter@...herpath.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        bridge@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Sending 802.1Q packets using AF_PACKET socket on filtered bridge
 forwards with wrong MAC addresses

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.

Thanks,

Brandon

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