netdev - Re: [RFC] packet: handle too big packets for PACKET

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Message-ID: <1408064099.6804.64.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 14 Aug 2014 17:54:59 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Daniel Borkmann <dborkman@...hat.com>,
	Neil Horman <nhorman@...driver.com>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [RFC] packet: handle too big packets for PACKET_V3

On Fri, 2014-08-15 at 02:43 +0200, Hannes Frederic Sowa wrote:

> 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.

Presumably these tools already use a large enough bloc_size, and not a
4KB one ;)

Even without GRO, a jumbo frame (9K) can trigger the bug.

I do not think we need to skb_gso_segment() for the cases user setup a
really small bloc_size. This looks like a lot of consumed cycles (we
even might have to recompute the TCP checksums)



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