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

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Date:   Tue, 10 Nov 2020 18:28:24 +0530
From:   Numan Siddique <nusiddiq@...hat.com>
To:     Florian Westphal <fw@...len.de>
Cc:     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.

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().

>
> > Would you expect that the tcp ct flags should have been preserved once
> > the connection is committed ?
>
> Yes, they are preserved when you set them after nf_conntrack_in(), else
> we would already have trouble with hw flow offloading which needs to
> turn off window checks as well.

Looks they are not preserved for the openvswitch case. Probably
openvswitch is doing something wrong.
I will debug further and see what is going on.

Please let me know if you have any further comments.

Thanks
Numan

>