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

[Bobby Eshleman]

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@xxxxxxxxxx> 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