linux-kernel - Re: [RFC 08/20] ima: Move measurement list related variables into ima

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Date:   Thu, 02 Dec 2021 11:29:46 -0500
From:   James Bottomley <jejb@...ux.ibm.com>
To:     Stefan Berger <stefanb@...ux.ibm.com>,
        linux-integrity@...r.kernel.org
Cc:     zohar@...ux.ibm.com, serge@...lyn.com,
        christian.brauner@...ntu.com, containers@...ts.linux.dev,
        dmitry.kasatkin@...il.com, ebiederm@...ssion.com,
        krzysztof.struczynski@...wei.com, roberto.sassu@...wei.com,
        mpeters@...hat.com, lhinds@...hat.com, lsturman@...hat.com,
        puiterwi@...hat.com, jamjoom@...ibm.com,
        linux-kernel@...r.kernel.org, paul@...l-moore.com, rgb@...hat.com,
        linux-security-module@...r.kernel.org, jmorris@...ei.org
Subject: Re: [RFC 08/20] ima: Move measurement list related variables into
 ima_namespace

On Thu, 2021-12-02 at 08:41 -0500, Stefan Berger wrote:
> On 12/2/21 07:46, James Bottomley wrote:
> > On Tue, 2021-11-30 at 11:06 -0500, Stefan Berger wrote:
> > > Move measurement list related variables into the ima_namespace.
> > > This
> > > way a
> > > front-end like SecurityFS can show the measurement list inside an
> > > IMA
> > > namespace.
> > > 
> > > Implement ima_free_measurements() to free a list of measurements
> > > and call it when an IMA namespace is deleted.
> > This one worries me quite a lot.  What seems to be happening in
> > this
> > code:
> > 
> > > @@ -107,7 +100,7 @@ static int ima_add_digest_entry(struct
> > > ima_namespace *ns,
> > >          qe->entry = entry;
> > >   
> > >          INIT_LIST_HEAD(&qe->later);
> > > -       list_add_tail_rcu(&qe->later, &ima_measurements);
> > > +       list_add_tail_rcu(&qe->later, &ns->ima_measurements);
> > >   
> > >          atomic_long_inc(&ns->ima_htable.len);
> > >          if (update_htable) {
> > > 
> > is that we now only add the measurements to the namespace list, but
> > that list is freed when the namespace dies.  However, the
> > measurement
> > is still extended through the PCRs meaning we have incomplete
> > information for a replay after the namespace dies?
> 
> *Not at all.* The measurement list of the namespace is independent
> of 
> the host.
> 
> The cover letter states:

I get that the host can set up a policy to log everything in the
namespace, but that wasn't my question.  My question is can the guest
set up a policy to log something that doesn't go into the host log
(because the host hasn't asked for it to be logged) but extends a PCR
anyway, thus destroying the ability of the host to do log replay.

James