netdev - Re: [PATCH v2 1/2] tcp: setup timestamp offset when write

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Message-Id: <20170222.163337.1789197655018339564.davem@davemloft.net>
Date:   Wed, 22 Feb 2017 16:33:37 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     alexey.kodanev@...cle.com
Cc:     netdev@...r.kernel.org, fw@...len.de, edumazet@...gle.com
Subject: Re: [PATCH v2 1/2] tcp: setup timestamp offset when write_seq
 already set

From: Alexey Kodanev <alexey.kodanev@...cle.com>
Date: Wed, 22 Feb 2017 13:23:55 +0300

> Found that when randomized tcp offsets are enabled (by default)
> TCP client can still start new connections without them. Later,
> if server does active close and re-uses sockets in TIME-WAIT
> state, new SYN from client can be rejected on PAWS check inside
> tcp_timewait_state_process(), because either tw_ts_recent or
> rcv_tsval doesn't really have an offset set.
> 
> Here is how to reproduce it with LTP netstress tool:
>     netstress -R 1 &
>     netstress -H 127.0.0.1 -lr 1000000 -a1
> 
>     [...]
>     < S  seq 1956977072 win 43690 TS val 295618 ecr 459956970
>     > .  ack 1956911535 win 342 TS val 459967184 ecr 1547117608
>     < R  seq 1956911535 win 0 length 0
> +1. < S  seq 1956977072 win 43690 TS val 296640 ecr 459956970
>     > S. seq 657450664 ack 1956977073 win 43690 TS val 459968205 ecr 296640
> 
> Fixes: 95a22caee396 ("tcp: randomize tcp timestamp offsets for each connection")
> Signed-off-by: Alexey Kodanev <alexey.kodanev@...cle.com>

Applied.