netdev - Re: [PATCH] netfilter: conntrack: tcp: do not lower timeout to CLOSE for in-window RSTs

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Date: Sat, 6 Jul 2024 19:04:32 +0200
From: Florian Westphal <fw@...len.de>
To: Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>
Cc: Florian Westphal <fw@...len.de>, yyxRoy <yyxroy22@...il.com>,
	pablo@...filter.org, gregkh@...uxfoundation.org,
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, netfilter-devel@...r.kernel.org,
	coreteam@...filter.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, yyxRoy <979093444@...com>
Subject: Re: [PATCH] netfilter: conntrack: tcp: do not lower timeout to CLOSE
 for in-window RSTs

Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu> wrote:
> I fully agree with Florian: conntrack plays the role of a middle box and 
> cannot absolutely know the right seq/ack numbers of the client/server 
> sides. Add NAT on top of that and there are a couple of ways to attack a 
> given traffic. I don't see a way by which the checkings/parameters could 
> be tightened without blocking real traffic.

I forgot about TCP timestamps, which we do not track at the moment.

But then there is a slight caveat: if one side exits, RST won't
carry timestamp option, so even keeping track of timestamps will help
:-(