Re: [PATCH v6 3/9] landlock: Control pathname UNIX domain socket resolution by path

["Mickaël Salaün" <mic@digikod.net>]

On Wed, Mar 18, 2026 at 12:43:55PM -0400, Justin Suess wrote:
> On Wed, Mar 18, 2026 at 05:26:20PM +0100, Mickaël Salaün wrote:
> > On Wed, Mar 18, 2026 at 04:05:59PM +0100, Sebastian Andrzej Siewior wrote:
> > > On 2026-03-18 10:14:52 [-0400], Justin Suess wrote:
> > > > Sebastian,
> > > Justin,
> > > 
> > > > In short: dom_other is a pointer to a landlock-owned refcounted struct.
> > > …
> > > > 
> > > > But we copy the domain pointer, which points to a landlock allocated
> > > > and controlled object.
> > > 
> > > and this is not going away while we are here and preempted after
> > > dropping the lock? (if the landlock policy is updated/ changed/ …)
> > 
> > I agree with Sebastian, this is a bug, see my original proposal:
> > https://lore.kernel.org/all/20260217.lievaS8eeng8@digikod.net/
> Mickaël,
> 
> Just to make sure we're speaking of the same thing (I spotted a bug
> shortly after replying to Sebastian).
> 
> This is a potential UAF if the dom_other is freed before the access
> check takes place correct?

Yes

> 
> 	dom_other = landlock_cred(other->sk_socket->file->f_cred)->domain;
> 	unix_state_unlock(other);
> 
> 	unmask_scoped_access(subject->domain, dom_other, &layer_masks,
> 			     fs_resolve_unix.fs);
> 
> If the dom_other->usage reaches zero, then the domain could be
> freed after the unix_state_unlock while we're checking access??
> 
> (I guess I assumed the sock_hold on the @other would prevent the task
> @other belongs to from being freed.)
> 
> Would it be better to move the access check under the unix_state_lock or
> to acquire another reference to the ruleset (or something else)?

Because the unmask_scoped_access() only read a bounded array, it's
simpler to unlock just after.

The other alternatives would be to use an RCU lock or a new reference
but I don't think it's worth it.

> 
> (Good catch Sebastian sorry for the confusion.)
> 
> Justin