netdev - Re: [PATCH 2/2] IB/ipoib: fix GRO merge failure for IPoIB originated TCP streams

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Date:	Mon, 30 Jan 2012 09:53:03 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Or Gerlitz <ogerlitz@...lanox.com>,
	Roland Dreier <roland@...nel.org>, davem@...emloft.net,
	linux-rdma <linux-rdma@...r.kernel.org>,
	Shlomo Pongratz <shlomop@...lanox.com>, netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] IB/ipoib: fix GRO merge failure for IPoIB
 originated TCP streams

Le lundi 30 janvier 2012 à 19:18 +1100, Herbert Xu a écrit :
> On Mon, Jan 30, 2012 at 09:04:32AM +0100, Eric Dumazet wrote:
> >
> > Hmm, do we really need to compare ether header, thats the question.
> 
> I think we do.  As otherwise macvlan would break.
> 

Thats the theory yes, but practically ?

Really, GRO can merge two TCP frames given they match everything needed,
exactly as our TCP stack would do in the end.

What could be a normal workload where this mismatch of two different tcp
flows could happen with macvlan or any kind of devices ?

If this is an attack, TCP will merge the frames anyway on the same
socket.

Or should we add checks in TCP stack, in case GRO is off ?

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