netdev - Re: [PATCH net v2 1/1] net/sched: act_ct: Fix flow table lookup failure with no originating ifindex

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Date:   Mon, 21 Feb 2022 19:02:45 +0200
From:   Paul Blakey <paulb@...dia.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>
CC:     <dev@...nvswitch.org>, <netdev@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>, <davem@...emloft.net>,
        Jiri Pirko <jiri@...dia.com>,
        "Cong Wang" <xiyou.wangcong@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        <netfilter-devel@...r.kernel.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Oz Shlomo <ozsh@...dia.com>, Vlad Buslov <vladbu@...dia.com>,
        Roi Dayan <roid@...dia.com>,
        Ariel Levkovich <lariel@...dia.com>, <coreteam@...filter.org>
Subject: Re: [PATCH net v2 1/1] net/sched: act_ct: Fix flow table lookup
 failure with no originating ifindex




On Sun, 20 Feb 2022, Pablo Neira Ayuso wrote:

> Hi Paul,
> 
> On Sun, Feb 20, 2022 at 11:32:26AM +0200, Paul Blakey wrote:
> > After cited commit optimizted hw insertion, flow table entries are
> > populated with ifindex information which was intended to only be used
> > for HW offload. This tuple ifindex is hashed in the flow table key, so
> > it must be filled for lookup to be successful. But tuple ifindex is only
> > relevant for the netfilter flowtables (nft), so it's not filled in
> > act_ct flow table lookup, resulting in lookup failure, and no SW
> > offload and no offload teardown for TCP connection FIN/RST packets.
> > 
> > To fix this, remove ifindex from hash, and allow lookup without
> > the ifindex. Act ct will lookup without the ifindex filled.
> 
> I think it is good to add FLOW_OFFLOAD_XMIT_TC (instead of relying on
> FLOW_OFFLOAD_XMIT_UNSPEC), this allows for more tc specific fields in
> the future.
> 
> See attached patch.
> 
> Thanks.
> 

This patch will fix it, but ifindex which we fill is for the input device 
and not related to XMIT, exactly what tuple->iifidx means. We don't have 
XMIT, so I think it was ok to use  UNSPEC for now. If I use 
tuple->tc.iifidx as you suggest, tuple->iifidx  will remain unused.

I think once we have more fields that are really specific to TC, we 
can do what you sugguest, right now we can share the ifindex.