netdev - Re: [net-next] netfiler: conntrack: Add the option to set ct tcp flag

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Date:   Tue, 10 Nov 2020 14:11:41 +0100
From:   Florian Westphal <fw@...len.de>
To:     Numan Siddique <nusiddiq@...hat.com>
Cc:     Florian Westphal <fw@...len.de>, ovs dev <dev@...nvswitch.org>,
        netdev <netdev@...r.kernel.org>,
        Pravin B Shelar <pshelar@....org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        netfilter-devel@...r.kernel.org
Subject: Re: [net-next] netfiler: conntrack: Add the option to set ct tcp
 flag - BE_LIBERAL per-ct basis.

Numan Siddique <nusiddiq@...hat.com> wrote:
> On Tue, Nov 10, 2020 at 5:55 PM Florian Westphal <fw@...len.de> wrote:
> >
> > Numan Siddique <nusiddiq@...hat.com> wrote:
> > > On Tue, Nov 10, 2020 at 3:06 AM Florian Westphal <fw@...len.de> wrote:
> > > Thanks for the comments. I actually tried this approach first, but it
> > > doesn't seem to work.
> > > I noticed that for the committed connections, the ct tcp flag -
> > > IP_CT_TCP_FLAG_BE_LIBERAL is
> > > not set when nf_conntrack_in() calls resolve_normal_ct().
> >
> > Yes, it won't be set during nf_conntrack_in, thats why I suggested
> > to do it before confirming the connection.
> 
> Sorry for the confusion. What I mean is - I tested  your suggestion - i.e called
> nf_ct_set_tcp_be_liberal()  before calling nf_conntrack_confirm().
> 
>  Once the connection is established, for subsequent packets, openvswitch
>  calls nf_conntrack_in() [1] to see if the packet is part of the
> existing connection or not (i.e ct.new or ct.est )
> and if the packet happens to be out-of-window then skb->_nfct is set
> to NULL. And the tcp
> be flags set during confirmation are not reflected when
> nf_conntrack_in() calls resolve_normal_ct().

Can you debug where this happens?  This looks very very wrong.
resolve_normal_ct() has no business to check any of those flags
(and I don't see where it uses them, it should only deal with the
 tuples).

The flags come into play when nf_conntrack_handle_packet() gets called
after resolve_normal_ct has found an entry, since that will end up
calling the tcp conntrack part.

The entry found/returned by resolve_normal_ct should be the same
nf_conn entry that was confirmed earlier, i.e. it should be in "liberal"
mode.