[RFC][PATCH 8/8] ima: Detect if digest cache changed since last measurement/appraisal

[Mimi Zohar]

On Mon, 2024-03-11 at 10:11 +0100, Roberto Sassu wrote:
> 
> > > @@ -386,8 +402,6 @@ static int process_measurement(struct file *file,
> > > const
> > > struct cred *cred,
> > >  			if (verif_mask_ptr)
> > >  				allow_mask = policy_mask & *verif_mask_ptr;
> > >  		}
> > > -
> > > -		digest_cache_put(digest_cache);
> > 
> > Keeping a reference to the digest_cache list for each file in the iint cache
> > until the file is re-accessed, might take a while to free.
> 
> Yes, that is the drawback...
> 
> > I'm wondering if it necessary to keep a reference to the digest_cache.  Or
> > is it
> > possible to just compare the existing iint->digest_cache pointer with the
> > current digest_cache pointer?
> 
> If the pointer value is the same, it does not guarantee that it is the
> same digest cache used for the previous verification. It might have
> been freed and reallocated.

Agreed.
> 
> Maybe, if the digest_cache LSM is able to notify to IMA that the digest
> cache changed, so that IMA resets its flags in the integrity metadata,
> we would not need to pin it.

Yes, something similar to the "ima_lsm_policy_notifier".

Mimi