stsp wrote:

03.02.2025 18:05, Willem de Bruijn пишет:

quoted

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.

As long as no existing users are affected, no need to relax this after
all these years.

It is up to users to not choose an overly restrictive setting, similar
to how they should not set chmod a-rwx on a file.

A user will immediately find out if they mess up this configuration,
and it takes extra steps (ioctls) to reach it, so is unlikely to be
reached by accident.

During the discussion it became
obvious that simpler fixes may
exist (like eg either-or semantic),
so why not to revert based on
that?

We did not define either-or in detail. Do you mean failing the
TUNSETOWNER or TUNSETGROUP ioctl if the other is already set? That
could break existing users that set both.

quoted

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.

This is not intended to cast blame, of course.

That said, I can adjust the wording.

The access control that we relaxed is when a process is not allowed
to access a device until the administrator adds it to the right group.
Is this used? I doubt it. But we cannot be sure.