linux-kernel - Re: [PATCH 3.2 085/115] veth: don’t modify ip_summed; doing so treats packets with bad checksums as good.

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Message-ID: <1462041181.17662.3.camel@decadent.org.uk>
Date:	Sat, 30 Apr 2016 20:33:01 +0200
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Sabrina Dubroca <sd@...asysnail.net>,
	Ben Greear <greearb@...delatech.com>
Cc:	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	akpm@...ux-foundation.org, "David S. Miller" <davem@...emloft.net>,
	Vijay Pandurangan <vijayp@...ayp.ca>,
	Cong Wang <cwang@...pensource.com>, netdev@...r.kernel.org,
	Evan Jones <ej@...njones.ca>,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	Phil Sutter <phil@....cc>,
	Toshiaki Makita <makita.toshiaki@....ntt.co.jp>,
	xiyou.wangcong@...il.com
Subject: Re: [PATCH 3.2 085/115] veth: don’t modify
 ip_summed; doing so treats packets with bad checksums as good.

On Thu, 2016-04-28 at 12:29 +0200, Sabrina Dubroca wrote:
> Hello,
> 
> 2016-04-27, 17:14:44 -0700, Ben Greear wrote:
> > 
> > On 04/27/2016 05:00 PM, Hannes Frederic Sowa wrote:
> > > 
> > > Hi Ben,
> > > 
> > > On Wed, Apr 27, 2016, at 20:07, Ben Hutchings wrote:
> > > > 
> > > > On Wed, 2016-04-27 at 08:59 -0700, Ben Greear wrote:
> > > > > 
> > > > > On 04/26/2016 04:02 PM, Ben Hutchings wrote:
> > > > > > 
> > > > > > 
> > > > > > 3.2.80-rc1 review patch.  If anyone has any objections, please let me know.
> > > > > I would be careful about this.  It causes regressions when sending
> > > > > PACKET_SOCKET buffers from user-space to veth devices.
> > > > > 
> > > > > There was a proposed upstream fix for the regression, but it has not gone
> > > > > into the tree as far as I know.
> > > > > 
> > > > > http://www.spinics.net/lists/netdev/msg370436.html
> > > > [...]
> > > > 
> > > > OK, I'll drop this for now.
> > > The fall out from not having this patch is in my opinion a bigger
> > > fallout than not having this patch. This patch fixes silent data
> > > corruption vs. the problem Ben Greear is talking about, which might not
> > > be that a common usage.
> > > 
> > > What do others think?
> > > 
> > > Bye,
> > > Hannes
> > > 
> > This patch from Cong Wang seems to fix the regression for me, I think it should be added and
> > tested in the main tree, and then apply them to stable as a pair.
> > 
> > http://dmz2.candelatech.com/?p=linux-4.4.dev.y/.git;a=commitdiff;h=8153e983c0e5eba1aafe1fc296248ed2a553f1ac;hp=454b07405d694dad52e7f41af5816eed0190da8a
> Actually, no, this is not really a regression.
[...]

It really is.  Even though the old behaviour was a bug (raw packets
should not be changed), if there are real applications that depend on
that then we have to keep those applications working somehow.

Ben.

-- 
Ben Hutchings
Tomorrow will be cancelled due to lack of interest.
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