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

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Date:	Fri, 15 Aug 2014 04:08:13 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
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, Aug 15, 2014, at 04:01, Eric Dumazet wrote:
> On Fri, 2014-08-15 at 03:04 +0200, Hannes Frederic Sowa wrote:
> 
> > Sure, but if I would have written such a tool without knowledge of GRO I
> > would have queried at least the MTU. ;)
> 
> Would all existing tools react to a mtu change properly ?
> 
> (It would have to reinit its af_packet ring)
> 
> I do not think its a GRO issue, really, but an optimistic PACKET_V3
> implementation. GRO was already there when PACKET_V3 was added.
> 
> Even a non GRO packet might not fit and we need to avoid the
> crash/corruption.
> 
> I believe I am going to implement 2)  (clamp the snaplen)

Ok, cool, I think this is the best way forward for now.

Do you think a a printk_once if the packet gets clamped because of GRO
would be sensible with a hint that GRO could be disabled in such cases?

> An application should catch that tp_len might be bigger than tp_snaplen
> and eventually do something sensible about it.
> 
> BTW, tp_sizeof_priv doesnt look to be checked at all, user input is
> accepted as is.

Hmm...

Bye,
Hannes
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