Re: [PATCH] ima: Handle -ESTALE returned by ima_filter_rule_match()

[Mimi Zohar <zohar@linux.ibm.com>]

On Sat, 2022-08-27 at 17:57 +0800, Guozihua (Scott) wrote:
> On 2022/8/25 21:02, Mimi Zohar wrote:
> > On Wed, 2022-08-24 at 09:56 +0800, Guozihua (Scott) wrote:
> >> On 2022/8/24 9:26, Mimi Zohar wrote:
> >>> On Tue, 2022-08-23 at 21:28 +0800, Guozihua (Scott) wrote:
> >>>> On 2022/8/23 21:21, Mimi Zohar wrote:
> >>>>> On Tue, 2022-08-23 at 16:12 +0800, Guozihua (Scott) wrote:
> >>>>>>> The question is whether we're waiting for the SELinux policy to change
> >>>>>>> from ESTALE or whether it is the number of SELinux based IMA policy
> >>>>>>> rules or some combination of the two.  Retrying three times seems to be
> >>>>>>> random.  If SELinux waited for ESTALE to change, then it would only be
> >>>>>>> dependent on the time it took to update the SELinux based IMA policy
> >>>>>>> rules.
> >>>>>>
> >>>>>> We are waiting for ima_lsm_update_rules() to finish re-initializing all
> >>>>>> the LSM based rules.
> >>>>>
> >>>>> Fine.  Hopefully retrying a maximum of 3 times is sufficient.
> >>>>>
> >>>> Well, at least this should greatly reduce the chance of this issue from
> >>>> happening.
> >>>
> >>> Agreed
> >>>
> >>>> This would be the best we I can think of without locking and
> >>>> busy waiting. Maybe we can also add delays before we retry. Maybe you
> >>>> got any other thought in mind?
> >>>
> >>> Another option would be to re-introduce the equivalent of the "lazy"
> >>> LSM update on -ESTALE, but without updating the policy rule, as the
> >>> notifier callback will eventually get to it.
> >>>
> >>
> >> For this to happen we would need a way to tell when we are able to
> >> continue with the retry though.
> > 
> > Previously with the lazy update, on failure security_filter_rule_init()
> > was called before the retry.  To avoid locking or detecting when to
> > continue, another option would be to call to
> > security_filter_rule_init() with a local copy of the rule.  The retry
> > would be based on a local copy of the rule.
> > 
> > Eventually the registered callback will complete, so we don't need to
> > be concerned about updating the actual rules.
> 
> Is it possible to cause race condition though? With this, the notifier 
> path seems to be unnecessary.

I don't see how there would be a race condition.  The notifier callback
is the normal method of updating the policy rules.  Hopefully -ESTALE
isn't something that happens frequently.
-- 
thanks,

Mimi