netdev - Re: [ovs-dev] [PATCH net-next] openvswitch: Only set mark and labels when commiting a connection.

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Date:	Tue, 21 Jun 2016 13:57:53 -0700
From:	Joe Stringer <joe@....org>
To:	Jarno Rajahalme <jarno@....org>
Cc:	netdev <netdev@...r.kernel.org>, ovs dev <dev@...nvswitch.org>
Subject: Re: [ovs-dev] [PATCH net-next] openvswitch: Only set mark and labels
 when commiting a connection.

On 20 June 2016 at 17:19, Jarno Rajahalme <jarno@....org> wrote:
> Only allow setting conntrack mark or labels when the commit flag is
> specified.  This makes sure we can not set them before the connection
> has been persisted, as in that case the mark and labels would be lost
> in an event of an userspace upcall.
>
> OVS userspace already requires the commit flag to accept setting
> ct_mark and/or ct_labels.  Validate for this on the kernel API.
>
> Finally, set conntrack mark and labels right before committing so that
> the initial conntrack NEW event has the mark and labels.
>
> Signed-off-by: Jarno Rajahalme <jarno@....org>

The structure of this commit message suggests there are multiple
changes trying to be addressed in one patch. I suggest splitting them
out.

In terms of applying the mark and labels before committing the
connection, that's actually the behaviour I would expect if you were
to execute ct(mark=foo,commit). The NEW event should include these
pieces, and should have all along.

> @@ -1145,6 +1155,20 @@ static int parse_ct(const struct nlattr *attr, struct ovs_conntrack_info *info,
>                 }
>         }
>
> +#ifdef CONFIG_NF_CONNTRACK_MARK
> +       if (!info->commit && info->mark.mask) {
> +               OVS_NLERR(log,
> +                         "Setting conntrack mark requires 'commit' flag.");
> +               return -EINVAL;
> +       }
> +#endif
> +#ifdef CONFIG_NF_CONNTRACK_LABELS
> +       if (!info->commit && labels_nonzero(&info->labels.mask)) {
> +               OVS_NLERR(log,
> +                         "Setting conntrack labels requires 'commit' flag.");
> +               return -EINVAL;
> +       }
> +#endif

I'm of mixed minds about this, but I lean towards agreeing with it. On
one hand, it's applying more restrictions on an otherwise fairly loose
interface and if anyone is relying on this behaviour then it would be
surprising to have this restriction introduced. On the other hand, it
doesn't make a lot of sense to set a label/mark but not to commit the
connection. As you say, the behaviour isn't exactly consistent in that
case today anyway: If there was a flow with
actions=ct(mark=foo),recirc() followed by a userspace upcall, then the
mark would be reflected in the flow key but not saved to any persisted
connection. A subsequent ct(commit) after upcall wouldn't persist it,
either. However if there were two flows already in the datapath to do
this, then it /would/ be persisted. Restricting the mark/labels
modification to only if you have the "commit" flag would address that
consistency issue. The OVS userspace enforcing this constraint also
hints that this was an unintentional omission from kernel validation.