netdev - Re: [PATCH v2] vlan: don't deliver frames for unknown vlans to protocols

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Message-ID: <20121008191944.GD25288@florz.florz.dyndns.org>
Date:	Mon, 8 Oct 2012 21:19:44 +0200
From:	Florian Zumbiehl <florz@...rz.de>
To:	David Miller <davem@...emloft.net>
Cc:	kaber@...sh.net, eric.dumazet@...il.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, jpirko@...hat.com
Subject: Re: [PATCH v2] vlan: don't deliver frames for unknown vlans to
 protocols

Hi,

> But I wonder if it breaks things, since you do the assignment so late
> we no longer handle the case where the VLAN device's MAC address
> matches the packet MAC address and the top-level device's does not.
> 
> That's handled by logic in vlan_do_receive() which checks for
> PACKET_OTHERHOST.
> 
> But you're going to unconditionally set PACKET_OTHERHOST, overriding
> any decision that code makes.

I don't think that that's actually the case. If vlan_do_receive() reaches
the MAC address check (that is, there is a vlan device for the tag), it
will either clear skb->vlan_tci and return true (which also causes goto
another_round), or return false with a NULL skb, which causes goto out.

The only way to reach the new check without another_round and with a
non-zero tag is the first return false, which happens if there is no device
for the tag, in which case setting PACKET_OTHERHOST should be the right
thing to do (in particular, a non-existent vlan device won't have the
frame's MAC address). I am assuming that rx_handlers don't modify the
frame unless they return RX_HANDLER_ANOTHER.

> This turns out to be a really non-trivial area and it's going to take
> some time to get this right and audit the change appropriately.

I wouldn't want to disagree with that ;-)

Florian
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