[ovs-dev] [PATCH] ovn-northd: Skip icmp4 packets destined for router ports from conntrack

[Numan Siddique]

On Tue, Mar 14, 2017 at 12:57 AM, Russell Bryant <russell at ovn.org> wrote:

> On Fri, Mar 10, 2017 at 4:48 PM, Russell Bryant <russell at ovn.org> wrote:
> > On Fri, Mar 10, 2017 at 2:35 PM, Russell Bryant <russell at ovn.org> wrote:
> >> On Thu, Mar 9, 2017 at 11:52 PM, Numan Siddique <nusiddiq at redhat.com>
> wrote:
> >> I don't think it's a Neutron issue.
> >>
> >> I see the conntrack entry remaining in the UNREPLIED state, even in
> >> the working case where there's not an ACL dropping the reply.
> >>
> >> icmp     1 29 src=10.0.0.10 dst=10.0.0.1 type=8 code=0 id=25857
> >> [UNREPLIED] src=10.0.0.1 dst=10.0.0.10 type=0 code=0 id=25857 mark=0
> >> zone=8 use=1
> >>
> >> If I ping a different address (something past the logical router), I
> >> see a proper conntrack entry that's not in the UNREPLIED state.
> >>
> >> I wonder if there's something about how we are generating the ICMP
> >> response from the logical router that's making conntrack not properly
> >> associate it with the request?
> >
> > I checked into this and there's no meaningful difference in how we
> > form the ICMP reply.
> >
> > I'm guessing this has to do with the request and reply both going
> > through conntrack as a part of processing the same packet in the OVS
> > data path.  That's not behaving how we would expect.  I'll keep
> > looking next week to try to identify the root cause here, but I would
> > appreciate any insight others may have about the behavior we should
> > expect in this scenario.
>
> I'm able to reproduce this outside of OpenStack.
>
> https://gist.github.com/russellb/4ab0a9641f12f8ac66fdd6822ee7789e
>
> This creates an OVN setup with two logical switches connected by a
> logical router.
>
>     switch d47412f9-e64a-4734-be26-80ee71ded805 (sw1)
>         port sw1-port1
>             addresses: ["50:54:00:00:00:03 11.0.0.2"]
>     switch a1730d73-ccab-4f00-b748-3cafb683e9b8 (sw0)
>         port sw0-port2
>             addresses: ["50:54:00:00:00:02 192.168.0.3"]
>         port sw0-port1
>             addresses: ["50:54:00:00:00:01 192.168.0.2"]
>     router 193f68cd-4a93-4a04-ad3b-3ddf7b5c66f3 (lr0)
>
> The ping commands at the end demonstrate the problem.  My expectation
> is that the very last ping command should be successful, but is not
> due to the issue we're seeing here.
>
>

This issue seems to be fixed with the below code diff. From my observation,
I could see that when the router datapath generates the icmp response and
when the reply packet hits the ovs_ct_execute function in datapath
 - the "sw_flow_key - key" param has old conntrack values
 - in the function "__ovs_ct_lookup",  skb_nfct_cached(net, key, info, skb)
returns false.
 - and the state is not set with the flag- OVS_CS_F_ESTABLISHED.


I want to check, if this is the right fix and get your feedback before
sending the upstream patch to net-next.


>************************************************<
diff --git a/datapath/flow.c b/datapath/flow.c
index 2bc1ad0..2c59acd 100644
--- a/datapath/flow.c
+++ b/datapath/flow.c
@@ -845,6 +845,8 @@ int ovs_flow_key_extract_userspace(struct net *net,
const struct nlattr *attr,
        if (err)
                return err;

+       ovs_ct_fill_key(skb, key);
+
        /* Check that we have conntrack original direction tuple metadata
only
         * for packets for which it makes sense.  Otherwise the key may be
         * corrupted due to overlapping key fields.

>************************************************<

Thanks
Numan


​


> --
> Russell Bryant
>