linux-kernel - Re: [PATCH AUTOSEL 4.19 04/42] netfilter: conntrack: always store window size un-scaled

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Date:   Wed, 14 Aug 2019 13:17:30 +0200 (CEST)
From:   Jakub Jankowski <shasta@...corp.com>
To:     Reindl Harald <h.reindl@...lounge.net>
cc:     Thomas Jarosch <thomas.jarosch@...ra2net.com>,
        Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Florian Westphal <fw@...len.de>,
        Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 4.19 04/42] netfilter: conntrack: always store
 window size un-scaled

On 2019-08-14, Reindl Harald wrote:

> that's still not in 5.2.8

It will make its way into next 5.2.x release, as it is now in the pending 
queue: 
https://git.kernel.org/pub/scm/linux/kernel/git/stable/stable-queue.git/tree/queue-5.2

Regards,
  Jakub.


>
> without the exception and "nf_conntrack_tcp_timeout_max_retrans = 60" a
> vnc-over-ssh session having the VNC view in the background freezes
> within 60 secods
>
> -----------------------------------------------------------------------------------------------
> IPV4 TABLE MANGLE (STATEFUL PRE-NAT/FILTER)
> -----------------------------------------------------------------------------------------------
> Chain PREROUTING (policy ACCEPT 100 packets, 9437 bytes)
> num   pkts bytes target     prot opt in     out     source
> destination
> 1     6526 3892K ACCEPT     all  --  *      *       0.0.0.0/0
> 0.0.0.0/0            ctstate RELATED,ESTABLISHED
> 2      125  6264 ACCEPT     all  --  lo     *       0.0.0.0/0
> 0.0.0.0/0
> 3       64  4952 ACCEPT     all  --  vmnet8 *       0.0.0.0/0
> 0.0.0.0/0
> 4        1    40 DROP       all  --  *      *       0.0.0.0/0
> 0.0.0.0/0            ctstate INVALID
>
> -------- Weitergeleitete Nachricht --------
> Betreff: [PATCH AUTOSEL 5.2 07/76] netfilter: conntrack: always store
> window size un-scaled
>
> Am 08.08.19 um 11:02 schrieb Thomas Jarosch:
>> Hello together,
>>
>> You wrote on Fri, Aug 02, 2019 at 09:22:24AM -0400:
>>> From: Florian Westphal <fw@...len.de>
>>>
>>> [ Upstream commit 959b69ef57db00cb33e9c4777400ae7183ebddd3 ]
>>>
>>> Jakub Jankowski reported following oddity:
>>>
>>> After 3 way handshake completes, timeout of new connection is set to
>>> max_retrans (300s) instead of established (5 days).
>>>
>>> shortened excerpt from pcap provided:
>>> 25.070622 IP (flags [DF], proto TCP (6), length 52)
>>> 10.8.5.4.1025 > 10.8.1.2.80: Flags [S], seq 11, win 64240, [wscale 8]
>>> 26.070462 IP (flags [DF], proto TCP (6), length 48)
>>> 10.8.1.2.80 > 10.8.5.4.1025: Flags [S.], seq 82, ack 12, win 65535, [wscale 3]
>>> 27.070449 IP (flags [DF], proto TCP (6), length 40)
>>> 10.8.5.4.1025 > 10.8.1.2.80: Flags [.], ack 83, win 512, length 0
>>>
>>> Turns out the last_win is of u16 type, but we store the scaled value:
>>> 512 << 8 (== 0x20000) becomes 0 window.
>>>
>>> The Fixes tag is not correct, as the bug has existed forever, but
>>> without that change all that this causes might cause is to mistake a
>>> window update (to-nonzero-from-zero) for a retransmit.
>>>
>>> Fixes: fbcd253d2448b8 ("netfilter: conntrack: lower timeout to RETRANS seconds if window is 0")
>>> Reported-by: Jakub Jankowski <shasta@...corp.com>
>>> Tested-by: Jakub Jankowski <shasta@...corp.com>
>>> Signed-off-by: Florian Westphal <fw@...len.de>
>>> Acked-by: Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>
>>> Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
>>> Signed-off-by: Sasha Levin <sashal@...nel.org>
>>
>> Also:
>> Tested-by: Thomas Jarosch <thomas.jarosch@...ra2net.com>
>>
>> ;)
>>
>> We've hit the issue with the wrong conntrack timeout at two different sites,
>> long-lived connections to a SAP server over IPSec VPN were constantly dropping.
>>
>> For us this was a regression after updating from kernel 3.14 to 4.19.
>> Yesterday I've applied the patch to kernel 4.19.57 and the problem is fixed.
>>
>> The issue was extra hard to debug as we could just boot the new kernel
>> for twenty minutes in the evening on these productive systems.
>>
>> The stable kernel patch from last Friday came right on time. I was just
>> about the replay the TCP connection with tcpreplay, so this saved
>> me from another week of debugging. Thanks everyone!
>

-- 
Jakub Jankowski|shasta@...corp.com|https://toxcorp.com/