From: Florian Westphal <fw@strlen.de>
To: Jozsef Kadlecsik <kadlec@netfilter.org>
Cc: Francesco Ruggeri <fruggeri@arista.com>,
open list <linux-kernel@vger.kernel.org>,
netdev <netdev@vger.kernel.org>,
coreteam@netfilter.org, netfilter-devel@vger.kernel.org,
Jakub Kicinski <kuba@kernel.org>,
David Miller <davem@davemloft.net>,
fw@strlen.org, Pablo Neira Ayuso <pablo@netfilter.org>
Subject: Re: [PATCH nf v2] netfilter: conntrack: connection timeout after re-register
Date: Fri, 9 Oct 2020 13:03:23 +0200 [thread overview]
Message-ID: <20201009110323.GC5723@breakpoint.cc> (raw)
In-Reply-To: <alpine.DEB.2.23.453.2010090838430.19307@blackhole.kfki.hu>
Jozsef Kadlecsik <kadlec@netfilter.org> wrote:
> > Any comments?
> > Here is a simple reproducer. The idea is to show that keepalive packets
> > in an idle tcp connection will be dropped (and the connection will time
> > out) if conntrack hooks are de-registered and then re-registered. The
> > reproducer has two files. client_server.py creates both ends of a tcp
> > connection, bounces a few packets back and forth, and then blocks on a
> > recv on the client side. The client's keepalive is configured to time
> > out in 20 seconds. This connection should not time out. test is a bash
> > script that creates a net namespace where it sets iptables rules for the
> > connection, starts client_server.py, and then clears and restores the
> > iptables rules (which causes conntrack hooks to be de-registered and
> > re-registered).
>
> In my opinion an iptables restore should not cause conntrack hooks to be
> de-registered and re-registered, because important TCP initialization
> parameters cannot be "restored" later from the packets. Therefore the
> proper fix would be to prevent it to happen. Otherwise your patch looks OK
> to handle the case when conntrack is intentionally restarted.
The repro clears all rules, waits 4 seconds, then restores the ruleset.
using iptables-restore < FOO; sleep 4; iptables-restore < FOO will
not result in any unregister ops.
We could make kernel defer unregister via some work queue but i don't
see what this would help/accomplish (and its questionable of how long it
should wait).
We could disallow unregister, but that seems silly (forces reboot...).
I think the patch is fine.
next prev parent reply other threads:[~2020-10-09 11:03 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-07 19:32 [PATCH nf v2] netfilter: conntrack: connection timeout after re-register Francesco Ruggeri
2020-10-08 23:41 ` Francesco Ruggeri
2020-10-09 6:52 ` Jozsef Kadlecsik
2020-10-09 11:03 ` Florian Westphal [this message]
2020-10-09 18:48 ` Jozsef Kadlecsik
2020-10-09 18:55 ` Florian Westphal
2020-10-09 19:49 ` Jozsef Kadlecsik
2020-10-09 20:00 ` Francesco Ruggeri
2020-10-09 20:05 ` Florian Westphal
2020-10-14 0:06 ` Pablo Neira Ayuso
2020-10-14 8:11 ` Pablo Neira Ayuso
2020-10-14 8:23 ` Florian Westphal
2020-10-14 18:42 ` Francesco Ruggeri
2020-10-14 19:35 ` Florian Westphal
2020-10-20 15:21 ` Pablo Neira Ayuso
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