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

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

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.
-- 
thanks,

Mimi