[kata-dev] vsock & network namespaces in Kata

Boeuf, Sebastien sebastien.boeuf at intel.com
Thu Dec 12 21:32:18 UTC 2019

Hi Stefano,

On Wed, 2019-12-11 at 18:27 +0100, Stefano Garzarella wrote:
> Hi Sebastien,
> On Thu, Dec 5, 2019 at 9:07 AM Boeuf, Sebastien <
> sebastien.boeuf at intel.com> wrote:
> > On Wed, 2019-12-04 at 17:36 +0000, Montes, Julio wrote:
> > 
> > Stefano,
> > 
> > 
> > > Do you think could be an easy change in the Kata runtime?
> > > I need to look better, but if you already know the answer you'll
> > > save me some time :)
> > 
> > ok, this means all kata components must be in the same network
> > namespace.
> > 
> > fortunately, kata-shim and qemu run in the same network namespace,
> > so the change should be easy, just move kata-proxy and kata-runtime 
> > into the same net namespace
> > 
> > 
> > Well in case of vsock, we don't need kata-proxy, the shim being
> > directly connected to the VM through vsock. And the kata-shim runs
> > in the same netns as the VMM, so we're good from this perspective.
> > 
> > In case of containerd-shimv2, we don't have kata-shim anymore, the
> > shim being a simple thread part of the kata-runtime process, which
> > means kata-runtime needs to enter the netns, and that's where it
> > might be pretty complex. IIRC, Julio did some experiments to run
> > the kata-runtime in a set of namespaces, but I don't think we
> > merged it, did we?
> Looking in the code seems that kata-runtime uses the "vhostfd"
> parameter
> of the vsock device, this means that the vhost device (/dev/vhost-
> vsock)
> is opened by the runtime and then the file descriptor is passed to
> This is great for this case because the netns assigned to the device
> is
> the one of the process that opened the /dev/vhost-vsock.
> I tried containerd-shimv2 with the vhost-vsock modified to support
> netns
> and seems to work well.
> Instead with v1 it doesn't work, maybe because kata-runtime and
> kata-shim run in two different netns. (or maybe I did something
> wrong,
> but it works disabling vsock or using the vhost-vsock without netns)
> Does that make sense?

Yes I think your experiment and the result makes sense.

In case of v1, kata-shim runs in the same netns as QEMU, but kata-
runtime runs in a separate one (the default netns). Later when kata-
shim tries to access the fd, because it runs in a different netns than
kata-runtime, the permission is denied.

In case of v2, there's only one process, the containerd-shimv2, which
again runs on the default netns, but later will be the one trying to
connect to the vhost-vsock fd, which is why it will succeed. In this
case there's no more additional process connecting through vsock, it is
simply a different thread from containerd-shimv2.

At first, I didn't get the fact that the netns authorized to access
vsock had to be the one where the device was opened from. That's why my
analysis was completely reversed :)


> Thanks,
> Stefano
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