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Date:	Fri, 15 Aug 2014 02:43:58 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	Daniel Borkmann <dborkman@...hat.com>,
	Neil Horman <nhorman@...driver.com>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: [RFC] packet: handle too big packets for PACKET_V3

Hi Eric,

On Fri, Aug 15, 2014, at 02:09, Eric Dumazet wrote:
> It looks like PACKET_V3 has no check that a packet can always fit in a
> block.
> 
> Its trivial with GRO to break the assumption and write into kernel
> memory.
> 
> [...]
>
> Not sure how to fix this.
> 
> This patch only shows where the problem is, but should we :
> 
> 1) drop the too long packet

Someone could use GRO to create packet trains to hide from intrustion
detection systems, which maybe are the main user of TPACKET_V3. I don't
think this is a good idea.

> 2) clamp size to maximal admissible size

Maybe.

> 3) other solution ? (PACKET_V2 can queue a clone of skb in
> receive_queue, but PACKET_V3 has no such capability)

4) Can we still try to skb_gso_segment the packet again? Not nice, but I
guess this will work. Maybe depending on a tunable (default to on)?

Bye,
Hannes
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