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

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Message-ID: <20101011172932.GB12342@orbit.nwl.cc>
Date:	Mon, 11 Oct 2010 19:29:32 +0200
From:	Phil Sutter <phil@....cc>
To:	David Miller <davem@...emloft.net>
Cc:	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 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.

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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