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Message-ID: <d923917cfd387cbf275eece78406f9ad07e6d0d3.camel@linux.ibm.com>
Subject: Re: [RFC][PATCH 8/8] ima: Detect if digest cache changed since last
 measurement/appraisal
From: Mimi Zohar <zohar@linux.ibm.com>
To: Roberto Sassu <roberto.sassu@huaweicloud.com>, corbet@lwn.net,
        dmitry.kasatkin@gmail.com, eric.snowberg@oracle.com,
        paul@paul-moore.com, jmorris@namei.org, serge@hallyn.com
Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org,
        wufan@linux.microsoft.com, pbrobinson@gmail.com, zbyszek@in.waw.pl,
        hch@lst.de, mjg59@srcf.ucam.org, pmatilai@redhat.com, jannh@google.com,
        dhowells@redhat.com, jikos@kernel.org, mkoutny@suse.com,
        ppavlu@suse.com, petr.vorel@gmail.com, petrtesarik@huaweicloud.com,
        mzerqung@0pointer.de, kgold@linux.ibm.com,
        Roberto Sassu <roberto.sassu@huawei.com>
Date: Mon, 11 Mar 2024 08:19:56 -0400
In-Reply-To: <4bac45ced03f82c2f3775684368e22db5dafea11.camel@huaweicloud.com>
References: <20240214143525.2205481-1-roberto.sassu@huaweicloud.com>
	 <20240214143525.2205481-9-roberto.sassu@huaweicloud.com>
	 <ddb1c28356fb8a4dcca9bff6dc206802d7981bb8.camel@linux.ibm.com>
	 <4bac45ced03f82c2f3775684368e22db5dafea11.camel@huaweicloud.com>
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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