Re: [PATCH net] tun: revert fix group permission check

[stsp <stsp2@yandex.ru>]

03.02.2025 18:05, Willem de Bruijn пишет:
> From: Willem de Bruijn <willemb@google.com>
>
> This reverts commit 3ca459eaba1bf96a8c7878de84fa8872259a01e3.
>
> The blamed commit caused a regression when neither tun->owner nor
> tun->group is set. This is intended to be allowed, but now requires
> CAP_NET_ADMIN.
>
> Discussion in the referenced thread pointed out that the original
> issue that prompted this patch can be resolved in userspace.

The point of the patch was
not to fix userspace, but this
bug: when you have owner set,
then adding group either changes
nothing at all, or removes all
access. I.e. there is no valid case
for adding group when owner
already set.
During the discussion it became
obvious that simpler fixes may
exist (like eg either-or semantic),
so why not to revert based on
that?

> The relaxed access control may now make a device accessible when it
> previously wasn't, while existing users may depend on it to not be.
>
> Since the fix is not critical and introduces security risk, revert,
Well, I don't agree with that justification.
My patch introduced the usability
problem, but not a security risk.
I don't want to be attributed with
the security risk when this wasn't
the case (to the very least, you
still need the perms to open /dev/net/tun),
so could you please remove that part?
I don't think you need to exaggerate
anything: it introduces the usability
regression, which should be enough
for any instant revert.