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

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Date:   Sun, 20 Feb 2022 10:48:47 +0200
From:   Paul Blakey <paulb@...dia.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>
CC:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        <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 1/1] net/sched: act_ct: Fix flow table lookup failure
 with no originating ifindex



On Fri, 18 Feb 2022, Pablo Neira Ayuso wrote:

> On Fri, Feb 18, 2022 at 12:55:07AM +0100, Pablo Neira Ayuso wrote:
> > On Thu, Feb 17, 2022 at 08:27:08PM -0300, Marcelo Ricardo Leitner wrote:
> > > On Thu, Feb 17, 2022 at 02:55:27PM +0100, Pablo Neira Ayuso wrote:
> > > > On Thu, Feb 17, 2022 at 11:34:24AM +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, allow flow tables that don't hash the ifindex.
> > > > > Netfilter flow tables will keep using ifindex for a more specific
> > > > > offload, while act_ct will not.
> > > > 
> > > > Using iif == zero should be enough to specify not set?
> > > 
> > > You mean, when searching, if search input iif == zero, to simply not
> > > check it? That seems dangerous somehow.
> > 
> > dev_new_index() does not allocate ifindex as zero.
> > 
> > Anyway, @Paul: could you add a tc_ifidx field instead in the union
> > right after __hash instead to fix 9795ded7f924?
> 
> I mean this incomplete patch below:
> 
> diff --git a/include/net/netfilter/nf_flow_table.h b/include/net/netfilter/nf_flow_table.h
> index a3647fadf1cc..d4fa4f716f68 100644
> --- a/include/net/netfilter/nf_flow_table.h
> +++ b/include/net/netfilter/nf_flow_table.h
> @@ -142,6 +142,7 @@ struct flow_offload_tuple {
>                         u8              h_source[ETH_ALEN];
>                         u8              h_dest[ETH_ALEN];
>                 } out;
> +               u32                     tc_ifidx;
>         };
>  };
> 
> You will need to update nf_flow_rule_match() to set key->meta.ingress_ifindex to
> use tc_ifidx if it is set to non-zero value.
> 

I  understand how it could fix the original issue, but I don't think this
is better, because it makes tuple less generic. What you suggested with 
using 0 to avoid needing the new flag is good enough for me, and is 
cleaner in my opinion.

I'll send the == 0 one as V2 for chance you agree, and if you want to 
change to this, I won't mind sending it as V3.