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From:   Aaron Conole <aconole@redhat.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Cc:     netdev@vger.kernel.org, Pravin B Shelar <pshelar@ovn.org>,
        "David S . Miller" <davem@davemloft.net>,
        Jamal Hadi Salim <jhs@mojatatu.com>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        Jiri Pirko <jiri@resnulli.us>, dev@openvswitch.org,
        linux-kernel@vger.kernel.org, paulb@mellanox.com
Subject: Re: [PATCH net 2/2] act_ct: support asymmetric conntrack
References: <20191108210714.12426-1-aconole@redhat.com>
        <20191108210714.12426-2-aconole@redhat.com>
        <20191114162949.GB3419@localhost.localdomain>
Date:   Mon, 18 Nov 2019 16:21:39 -0500
In-Reply-To: <20191114162949.GB3419@localhost.localdomain> (Marcelo Ricardo
        Leitner's message of "Thu, 14 Nov 2019 13:29:49 -0300")
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Marcelo Ricardo Leitner <marcelo.leitner@gmail.com> writes:

> On Fri, Nov 08, 2019 at 04:07:14PM -0500, Aaron Conole wrote:
>> The act_ct TC module shares a common conntrack and NAT infrastructure
>> exposed via netfilter.  It's possible that a packet needs both SNAT and
>> DNAT manipulation, due to e.g. tuple collision.  Netfilter can support
>> this because it runs through the NAT table twice - once on ingress and
>> again after egress.  The act_ct action doesn't have such capability.
>>=20
>> Like netfilter hook infrastructure, we should run through NAT twice to
>> keep the symmetry.
>>=20
>> Fixes: b57dc7c13ea9 ("net/sched: Introduce action ct")
>>=20
>> Signed-off-by: Aaron Conole <aconole@redhat.com>
>> ---
>>  net/sched/act_ct.c | 13 ++++++++++++-
>>  1 file changed, 12 insertions(+), 1 deletion(-)
>>=20
>> diff --git a/net/sched/act_ct.c b/net/sched/act_ct.c
>> index fcc46025e790..f3232a00970f 100644
>> --- a/net/sched/act_ct.c
>> +++ b/net/sched/act_ct.c
>> @@ -329,6 +329,7 @@ static int tcf_ct_act_nat(struct sk_buff *skb,
>>  =09=09=09  bool commit)
>>  {
>>  #if IS_ENABLED(CONFIG_NF_NAT)
>> +=09int err;
>>  =09enum nf_nat_manip_type maniptype;
>> =20
>>  =09if (!(ct_action & TCA_CT_ACT_NAT))
>> @@ -359,7 +360,17 @@ static int tcf_ct_act_nat(struct sk_buff *skb,
>>  =09=09return NF_ACCEPT;
>>  =09}
>> =20
>> -=09return ct_nat_execute(skb, ct, ctinfo, range, maniptype);
>> +=09err =3D ct_nat_execute(skb, ct, ctinfo, range, maniptype);
>> +=09if (err =3D=3D NF_ACCEPT &&
>> +=09    ct->status & IPS_SRC_NAT && ct->status & IPS_DST_NAT) {
>> +=09=09if (maniptype =3D=3D NF_NAT_MANIP_SRC)
>> +=09=09=09maniptype =3D NF_NAT_MANIP_DST;
>> +=09=09else
>> +=09=09=09maniptype =3D NF_NAT_MANIP_SRC;
>> +
>> +=09=09err =3D ct_nat_execute(skb, ct, ctinfo, range, maniptype);
>> +=09}
>
> I keep thinking about this and I'm not entirely convinced that this
> shouldn't be simpler. More like:
>
> if (DNAT)
> =09DNAT
> if (SNAT)
> =09SNAT
>
> So it always does DNAT before SNAT, similarly to what iptables would
> do on PRE/POSTROUTING chains.

I can rewrite the whole function, but I wanted to start with the smaller
fix that worked.  I also think it needs more testing then (since it's
something of a rewrite of the function).

I guess it's not too important - do you think it gives any readability
to do it this way?  If so, I can respin the patch changing it like you
describe.

>> +=09return err;
>>  #else
>>  =09return NF_ACCEPT;
>>  #endif
>> --=20
>> 2.21.0
>>=20