Re: [PATCH net v3 2/3] vsock: lock down child_ns_mode as write-once

[Bobby Eshleman <bobbyeshleman@gmail.com>]

On Mon, Feb 23, 2026 at 02:38:33PM -0800, Bobby Eshleman wrote:
> From: Bobby Eshleman <bobbyeshleman@meta.com>
> 
> Two administrator processes may race when setting child_ns_mode as one
> process sets child_ns_mode to "local" and then creates a namespace, but
> another process changes child_ns_mode to "global" between the write and
> the namespace creation. The first process ends up with a namespace in
> "global" mode instead of "local". While this can be detected after the
> fact by reading ns_mode and retrying, it is fragile and error-prone.
> 
> Make child_ns_mode write-once so that a namespace manager can set it
> once and be sure it won't change. Writing a different value after the
> first write returns -EBUSY. This applies to all namespaces, including
> init_net, where an init process can write "local" to lock all future
> namespaces into local mode.
> 
> Fixes: eafb64f40ca4 ("vsock: add netns to vsock core")
> Suggested-by: Daan De Meyer <daan.j.demeyer@gmail.com>
> Suggested-by: Stefano Garzarella <sgarzare@redhat.com>
> Co-developed-by: Stefano Garzarella <sgarzare@redhat.com>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>

Stefano, I wasn't sure if you wanted the Co-developed-by and S-o-b on
this iteration, but I added it just in case. Please let me know, if that
wasn't what you intended.

Best,
Bobby