From: Ben Greear <greearb@candelatech.com>
To: Sabrina Dubroca <sd@queasysnail.net>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>,
Ben Hutchings <ben@decadent.org.uk>,
linux-kernel@vger.kernel.org, stable@vger.kernel.org,
akpm@linux-foundation.org,
"David S. Miller" <davem@davemloft.net>,
Vijay Pandurangan <vijayp@vijayp.ca>,
Cong Wang <cwang@twopensource.com>,
netdev@vger.kernel.org, Evan Jones <ej@evanjones.ca>,
Nicolas Dichtel <nicolas.dichtel@6wind.com>,
Phil Sutter <phil@nwl.cc>,
Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>,
xiyou.wangcong@gmail.com
Subject: Re: [PATCH 3.2 085/115] veth: don’t modify ip_summed; doing so treats packets with bad checksums as good.
Date: Thu, 28 Apr 2016 06:45:50 -0700 [thread overview]
Message-ID: <5722140E.80702@candelatech.com> (raw)
In-Reply-To: <20160428102953.GA7656@bistromath.localdomain>
On 04/28/2016 03:29 AM, 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.
>
> If you capture packets on a device with checksum offloading enabled,
> the TCP/UDP checksum isn't filled. veth also behaves that way. What
> the "veth: don't modify ip_summed" patch does is enable proper
> checksum validation on veth. This really was a bug in veth.
>
> Cong's patch would also break cases where we choose to inject packets
> with invalid checksums, and they would now be accepted as correct.
>
> Your use case is invalid, it just happened to work because of a
> bug. If you want the stack to fill checksums so that you want capture
> and reinject packets, you have to disable checksum offloading (or
> compute the checksum yourself in userspace).
Disabling checksum offloading or computing in user-space (and then
recomputing in veth to verify the checksum?) is a huge performance loss.
Maybe we could add a socket option to enable Cong's patch on a per-socket
basis? That way my use-case can still work and you can have this new
behaviour by default?
Thanks,
Ben
--
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc http://www.candelatech.com
next prev parent reply other threads:[~2016-04-28 13:45 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <lsq.1461711744.351546278@decadent.org.uk>
2016-04-26 23:02 ` [PATCH 3.2 085/115] veth: don’t modify ip_summed; doing so treats packets with bad checksums as good Ben Hutchings
2016-04-27 15:59 ` Ben Greear
2016-04-27 18:07 ` Ben Hutchings
2016-04-28 0:00 ` Hannes Frederic Sowa
2016-04-28 0:14 ` Ben Greear
2016-04-28 10:29 ` Sabrina Dubroca
2016-04-28 13:45 ` Ben Greear [this message]
2016-04-30 19:18 ` Ben Hutchings
2016-04-30 18:33 ` Ben Hutchings
2016-04-30 19:40 ` Ben Greear
2016-04-30 19:54 ` Tom Herbert
2016-04-30 20:59 ` Ben Greear
2016-04-30 21:13 ` Vijay Pandurangan
2016-04-30 21:29 ` Ben Greear
2016-04-30 21:36 ` Vijay Pandurangan
2016-04-30 21:52 ` Ben Greear
2016-04-30 22:01 ` Vijay Pandurangan
2016-04-30 22:43 ` Ben Greear
2016-05-01 5:30 ` [PATCH 3.2 085/115] veth: don???t " Willy Tarreau
2016-05-13 16:57 ` Ben Greear
2016-05-13 18:21 ` David Miller
2016-05-13 18:23 ` Ben Greear
2016-04-30 22:42 ` [PATCH 3.2 085/115] veth: don’t " Tom Herbert
2016-04-30 20:15 ` Vijay Pandurangan
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