Re: [PATCH net-next 1/3] vsock: add network namespace support

Bobby Eshleman
2025-03-05T15:54:38Z

On Wed, Mar 05, 2025 at 10:23:08AM +0100, Stefano Garzarella wrote:
> On Wed, 5 Mar 2025 at 08:32, Michael S. Tsirkin <mst@redhat.com> wrote:
> >

[...]

> >
> >
> > I'm not sure I understand the usecase. Can you explain a bit more,
> > please?
>
> It's been five years, but I'm trying!
> We are tracking this RFE here [1].
>
> I also add Jakub in the thread with who I discussed last year a possible
> restart of this effort, he could add more use cases.
>
> The problem with vsock, host-side, currently is that if you launch a VM
> with a virtio-vsock device (using vhost) inside a container (e.g.,
> Kata), so inside a network namespace, it is reachable from any other
> container, whereas they would like some isolation. Also the CID is
> shared among all, while they would like to reuse the same CID in
> different namespaces.
>
> This has been partially solved with vhost-user-vsock, but it is
> inconvenient to use sometimes because of the hybrid-vsock problem
> (host-side vsock is remapped to AF_UNIX).
>
> Something from the cover letter of the series [2]:
>
> As we partially discussed in the multi-transport proposal, it could
> be nice to support network namespace in vsock to reach the following
> goals:
> - isolate host applications from guest applications using the same ports
> with CID_ANY
> - assign the same CID of VMs running in different network namespaces
> - partition VMs between VMMs or at finer granularity
>
> Thanks,
> Stefano
>

Do you know of any use cases for guest-side vsock netns?

Our use case is also host-side. vsock is used to communicate with a
host-side shim/proxy/debug console. Each vmm and these components share
a namespace and are isolated from other vmm + components. The VM
connects back to the host via vsock after startup and communicates its
port of choice out-of-band (fw_cfg). The main problem is in security:
untrusted VM programs can potentially connect with and exploit the
host-side vsock services meant for other VMs. If vsock respected
namespaces, then these host-side services would be unreachable by other
VMs and protected. Namespaces would also allow the vsock port to be
static across VMs, and avoid the need for the out-of-band mechanism for
communicating the port.

Jakub can jump in to add anything, but I think this is the same use case
/ user he was probably referring to.

Best,
Bobby