netdev - Re: sending VLAN packets via packet

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Message-Id: <20101006.235343.98903661.davem@davemloft.net>
Date:	Wed, 06 Oct 2010 23:53:43 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	phil@....cc
Cc:	netdev@...r.kernel.org, johann.baudy@...-log.net,
	eric.dumazet@...il.com
Subject: Re: sending VLAN packets via packet_mmap

From: Phil Sutter <phil@....cc>
Date: Thu, 30 Sep 2010 21:24:14 +0200

> The actual problem in tpacket_snd() is this:
> 
> | reserve = dev->hard_header_len;
> | [...]
> | if (size_max > dev->mtu + reserve)
> | 	size_max = dev->mtu + reserve;
> 
> I guess the check is there to avoid skb overflows on malicious data
> input. Is this correct? Are there other reasons for it's existence?

We can add a special allowance of 4 extra bytes in this size check
_iff_ the device is ethernet and the NETIF_F_VLAN_CHALLENGED netdev
feature bit is not set.

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