[ovs-discuss] Small 802.1q-prepended packets not getting through to VM

Ben Pfaff blp at ovn.org
Fri Jun 7 23:27:12 UTC 2019


On Sat, Jun 08, 2019 at 12:55:43AM +0200, Steinar H. Gunderson wrote:
> On Fri, Jun 07, 2019 at 02:57:04PM -0700, Ben Pfaff wrote:
> > This used to work fine.  Has anything changed?
> 
> Are you sure it actually has worked, ever? For this bug to manifest, you need
> two conditions to happen at once:
> 
>   1. The packet must come from some non-physical interface (e.g. OVS internal
>      port -- although Linux' EoGRE code doesn't pad either, and I'm trying to
>      convince them they have to).
>   2. The VM must actually be picky about undersized frames.
> 
> Given that 99% of VMs are stock Windows or Linux (whose virtio drivers don't
> care, I believe[1]), and also run userspace that doesn't care about raw
> Ethernet frames, #2 goes out of the window and the bug doesn't trigger.
> I can easily see how such an issue can fly under the radar for a long time.

I'm not 100% sure.  The last time I maintained any of the OVS datapath
code myself was in the 2.6.x era.


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