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Message-ID: <20240307120054.GK4420@breakpoint.cc>
Date: Thu, 7 Mar 2024 13:00:54 +0100
From: Florian Westphal <fw@...len.de>
To: Jason Xing <kerneljasonxing@...il.com>
Cc: Florian Westphal <fw@...len.de>, edumazet@...gle.com,
pablo@...filter.org, kadlec@...filter.org, kuba@...nel.org,
pabeni@...hat.com, davem@...emloft.net,
netfilter-devel@...r.kernel.org, coreteam@...filter.org,
netdev@...r.kernel.org, Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next] netfilter: conntrack: avoid sending RST to
reply out-of-window skb
Jason Xing <kerneljasonxing@...il.com> wrote:
> > This change disables most of the tcp_in_window() test, this will
> > pretend everything is fine even though tcp_in_window says otherwise.
>
> Thanks for the information. It does make sense.
>
> What I've done is quite similar to nf_conntrack_tcp_be_liberal sysctl
> knob which you also pointed out. It also pretends to ignore those
> out-of-window skbs.
>
> >
> > You could:
> > - drop invalid tcp packets in input hook
>
> How about changing the return value only as below? Only two cases will
> be handled:
>
> diff --git a/net/netfilter/nf_conntrack_proto_tcp.c
> b/net/netfilter/nf_conntrack_proto_tcp.c
> index ae493599a3ef..c88ce4cd041e 100644
> --- a/net/netfilter/nf_conntrack_proto_tcp.c
> +++ b/net/netfilter/nf_conntrack_proto_tcp.c
> @@ -1259,7 +1259,7 @@ int nf_conntrack_tcp_packet(struct nf_conn *ct,
> case NFCT_TCP_INVALID:
> nf_tcp_handle_invalid(ct, dir, index, skb, state);
> spin_unlock_bh(&ct->lock);
> - return -NF_ACCEPT;
> + return -NF_DROP;
Lets not do this. conntrack should never drop packets and defer to ruleset
whereever possible.
> > - set nf_conntrack_tcp_be_liberal=1
>
> Sure, it can workaround this case, but I would like to refuse the
> out-of-window in netfilter or TCP layer as default instead of turning
> on this sysctl knob. If I understand wrong, please correct me.
Thats contradictory, you make a patch to always accept, then another
patch to always drop such packets?
You can get the drop behaviour via '-m conntrack --ctstate DROP' in
prerouting or inut hooks.
You can get the 'accept + do nat processing' via
nf_conntrack_tcp_be_liberal=1.
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