Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Aaron Conole <aconole@redhat.com>
To:     Nicolas Dichtel <nicolas.dichtel@6wind.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
Subject: Re: [PATCH net 1/2] openvswitch: support asymmetric conntrack
References: <20191108210714.12426-1-aconole@redhat.com>
        <eb0bdc35-7f29-77c7-c013-e88f74772c24@6wind.com>
Date:   Mon, 18 Nov 2019 16:19:29 -0500
In-Reply-To: <eb0bdc35-7f29-77c7-c013-e88f74772c24@6wind.com> (Nicolas
        Dichtel's message of "Tue, 12 Nov 2019 09:52:45 +0100")
Message-ID: <f7tsgmkyja6.fsf@dhcp-25.97.bos.redhat.com>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Nicolas Dichtel <nicolas.dichtel@6wind.com> writes:

> Le 08/11/2019 =C3=A0 22:07, Aaron Conole a =C3=A9crit=C2=A0:
>> The openvswitch 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 openvswitch module doesn't have such capability=
.
>>=20
>> Like netfilter hook infrastructure, we should run through NAT twice to
>> keep the symmetry.
>>=20
>> Fixes: 05752523e565 ("openvswitch: Interface with NAT.")
>> Signed-off-by: Aaron Conole <aconole@redhat.com>
> In this case, ovs_ct_find_existing() won't be able to find the
> conntrack, right?

vswitchd normally won't allow both actions to get programmed.  Even the
kernel module won't allow it, so this really will only happen when the
connection gets established via the nf_hook path, and then needs to be
processed via openvswitch.  In those cases, the tuple lookup should be
correct, because the nf_nat table should contain the correct tuple data,
and the skbuff should have the correct tuples in the packet data to
begin with.

> Inverting the tuple to find the conntrack doesn't work anymore with doubl=
e NAT.
> Am I wrong?

I think since the packet was double-NAT on the way out (via nf_hook
path), then the incoming reply will have the correct NAT tuples and the
lookup will happen just fine.  Just that during processing, both
transformations aren't applied.

Makes sense?

> Regards,
> Nicolas