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Date:   Sat, 23 Jul 2022 10:17:28 +0200
From:   Pablo Neira Ayuso <pablo@netfilter.org>
To:     Jan Engelhardt <jengelh@inai.de>
Cc:     Netfilter Developer Mailing List 
        <netfilter-devel@vger.kernel.org>, fw@strlen.de
Subject: Re: iptables 1.8.8 misses -j CT calls
Message-ID: <YtuumBWikVhxj2S+@salvia>
References: <124qoqo1-q45p-133s-o334-4s59r4s43p4@vanv.qr>
 <Ytun6DBdk5Kkx4vX@salvia>
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On Sat, Jul 23, 2022 at 09:48:56AM +0200, Pablo Neira Ayuso wrote:
> On Thu, Jul 21, 2022 at 04:20:32PM +0200, Jan Engelhardt wrote:
> > 
> > Bug report.
> > 
> > Input
> > =====
> > *raw
> > :PREROUTING ACCEPT [0:0]
> > :OUTPUT ACCEPT [0:0]
> > -A PREROUTING -i lo -j CT --notrack
> > -A PREROUTING -i ve-+ -p tcp --dport 21 -j CT --helper ftp
> > COMMIT
> > 
> > 
> > Output
> > ======
> > # Translated by iptables-restore-translate v1.8.8 on Thu Jul 21 16:18:58 2022
> > add table ip raw
> > add chain ip raw PREROUTING { type filter hook prerouting priority -300; policy accept; }
> > add chain ip raw OUTPUT { type filter hook output priority -300; policy accept; }
> > add rule ip raw PREROUTING iifname "lo" counter notrack
> > # -t raw -A PREROUTING -i ve-+ -p tcp --dport 21 -j CT --helper ftp
> > # Completed on Thu Jul 21 16:18:58 2022
> 
> the problem with this translation is that nftables expects the helper
> to be set after the input conntrack hook.

for the sake of clarity:

NF_IP_PRI_CONNTRACK = -200 in the prerouting hook.

which is coming _after_ the NF_IP_PRI_RAW = -300

> IIRC Florian preferred not to use the conntrack template (which is
> used before the conntrack object is attached to the skb). Instead, the
> help is attached once after the conntrack lookup.
> 
> > Expected output
> > ===============
> > An nft rule involving port 21.