netdev - Re: [PATCH] af_packet: account for VLAN when checking packet size

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Date:	Tue, 12 Oct 2010 19:19:41 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	David Miller <davem@...emloft.net>, eric.dumazet@...il.com,
	netdev@...r.kernel.org, johann.baudy@...-log.net
Subject: Re: [PATCH] af_packet: account for VLAN when checking packet size

On Mon, Oct 11, 2010 at 07:29:32PM +0200, Phil Sutter wrote:
> On Mon, Oct 11, 2010 at 09:01:53AM -0700, David Miller wrote:
> > From: Eric Dumazet <eric.dumazet@...il.com>
> > Date: Mon, 11 Oct 2010 16:03:02 +0200
> > 
> > > If we dont test ETH_P_8021Q protocol here, we allow sending 1504 bytes
> > > frames for MTU=1500
> > > 
> > > Should we really care ?
> > > 
> > > If not, just do
> > > 
> > > reserve = dev->hard_header_len + VLAN_HLEN;
> > 
> > Thats a good point, I think we need to validate the SKB protocol
> > field.
> 
> Which is set to the value of the passed struct sockaddr_ll field
> sll_protocol. At least in the two userspace code samples I have here,
> the later field is set to htons(ETH_P_ALL). So unless one changes the
> API, the only way to find out the packet type is to actually parse the
> given ethernet header.

Yes, like eth_type_trans does I guess.  I think we had a similar
discussion already:

http://lists.openwall.net/netdev/2010/01/06/38

Summary: if we want to make the protocol field have the correct
value for this case we need to make it work for other
transports not just for ethernet.

> Since tpacket_rcv() just interprets the vlan_tci skb field, such
> detailed packet inspection is otherwise not done in af_packet.c.
> 
> Greetings, Phil
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