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Date:   Fri, 13 Jan 2023 00:45:03 +0100
From:   Florian Westphal <fw@strlen.de>
To:     "Russell King (Oracle)" <linux@armlinux.org.uk>
Cc:     netdev@vger.kernel.org, netfilter-devel@vger.kernel.org,
        coreteam@netfilter.org
Subject: Re: 6.1: possible bug with netfilter conntrack?
Message-ID: <20230112234503.GB19463@breakpoint.cc>
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Russell King (Oracle) <linux@armlinux.org.uk> wrote:
> Given the packet counts as per my example above, it looks like
> conntrack only saw:
> 
> src=180.173.2.183 dst=78.32.30.218	SYN
> src=78.32.30.218 dst=180.173.2.183	SYN+ACK
> src=180.173.2.183 dst=78.32.30.218	ACK
> 
> and I suspect at that point, the connection went silent - until
> Exim timed out and closed the connection, as does seem to be the
> case:
> 
> 2023-01-11 21:32:04 no host name found for IP address 180.173.2.183
> 2023-01-11 21:33:05 SMTP command timeout on connection from [180.173.2.183]:64332 I=[78.32.30.218]:25
> 
> but if Exim closed the connection, why didn't conntrack pick it up?

Yes, thats the question.  Exim closing the connection should have
conntrack at least pick up a fin packet from the mail server (which
should move the entry to the 2 minute fin timeout).