[ovs-dev] [PATCH v2 1/5] ofproto-dpif-xlate: Don't unwildcard tunnel attributes on set.

Ben Pfaff blp at ovn.org
Tue Oct 4 00:38:48 UTC 2016


Does this patch need anything more?  I don't see it on master and it's
still in patchwork.  Same thing for patch 4/5 in this series.

On Thu, Sep 01, 2016 at 01:31:06AM +0000, Daniele Di Proietto wrote:
> 
> On 31/08/2016 11:32, "Jarno Rajahalme" <jarno at ovn.org> wrote:
> 
> >I’d put the registers and metadata field to the ‘false’ and also maybe non-writeable fields (ether type, frags, nw_proto, etc.) in to OVS_NOT_REACHED() case, just in case.
> >
> >  Jarno
> 
> Agreed, done
> 
> Thanks,
> 
> Daniele
> 
> >
> >> On Aug 31, 2016, at 10:38 AM, Jesse Gross <jesse at kernel.org> wrote:
> >> 
> >> On Tue, Aug 30, 2016 at 6:47 PM, Daniele Di Proietto
> >> <diproiettod at vmware.com> wrote:
> >>> When translating a set action we also unwildcard the field in question.
> >>> This is done to correctly translate set actions with the value identical
> >>> to the ingress flow, like in the following example:
> >>> 
> >>> flow table:
> >>> 
> >>> tcp,actions=set_field:80->tcp_dst,output:5
> >>> 
> >>> ingress packet:
> >>> 
> >>> ...,tcp,tcp_dst=80
> >>> 
> >>> datapath flow
> >>> 
> >>> ...,tcp(dst=80) actions:5
> >>> 
> >>> The datapath flow must exact match the target field, because the actions
> >>> do not include a set field. (Otherwise a packet coming in with a
> >>> different tcp_dst would be matched, and its port wouldn't be altered).
> >>> 
> >>> Tunnel attributes behave differently: at the datapath layer, before
> >>> action processing they're cleared (we do the same at the ofproto layer
> >>> in xlate_actions()).  Therefore there's no need to unwildcard them,
> >>> because a set action would always be detected (since we zero them at the
> >>> beginning of xlate_ations()).
> >>> 
> >>> This fixes a problem related to the handling of Geneve options.
> >>> Unwildcarding non existing Geneve options (as done by a
> >>> set_field:X->tun_metadata<n> on a packet coming from a non-tunnel
> >>> interface) would be problematic for the datapaths: the ODP translation
> >>> functions cannot express a match on non existing Geneve options (unlike
> >>> on other attributes), and the userspace datapath wouldn't be able to
> >>> translate them to "userspace datapath format".  In both cases the
> >>> installed flow would be deleted by revalidation at the first
> >>> opportunity.
> >>> 
> >>> Signed-off-by: Daniele Di Proietto <diproiettod at vmware.com>
> >> 
> >> I think there might be some more obscure ways of triggering this
> >> problem that still exist. Basically anything that can use a register
> >> as a target is a potential issue. For example, stack_pop, bundle, and
> >> multipath all look like they have the same masking behavior.
> >> 
> >> I do have a general solution in this patch (look at the bottom of
> >> xlate_actions() where it is adjusting the wildcards):
> >> http://openvswitch.org/pipermail/dev/2016-August/078484.html
> >> 
> >> I didn't realize that it was addressing an existing issue though and
> >> that patch certainly isn't suitable for anything other than master.
> >> 
> >> I'm also not really a big fan of the way I handled it there since it's
> >> a pretty coarse way to do it. I would be happy to drop it if we can
> >> feel comfortable that we got all of the callsites (now and in the
> >> future) using your method. Perhaps we can just create a helper
> >> function with this check builtin and then use it everywhere? That
> >> might be enough to be confident about the future.
> >> _______________________________________________
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> >> dev at openvswitch.org
> >> http://openvswitch.org/mailman/listinfo/dev
> >
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