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

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Date:   Thu, 02 Dec 2021 15:03:28 -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 13:03 -0500, Stefan Berger wrote:
> On 12/2/21 12:44, James Bottomley wrote:
> > On Thu, 2021-12-02 at 11:45 -0500, Stefan Berger wrote:
> > > On 12/2/21 11:29, James Bottomley wrote:
> > > > 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.
> > > host log goes with host TPM and vice versa
> > > 
> > > guest log goes with (optional) vTPM and vice version
> > But that's what doesn't seem to happen ... ima_pcr_extend isn't
> > virtualized and it's always called from ima_add_template_entry()
> > meaning the physical TPM is always extended even for a namespace
> > only entry.
> 
> You cannot set a measurement rule in the namespace. That is
> prevented per 9/20: ima: Only accept AUDIT rules for IMA non-
> init_ima_ns namespaces for now.

Ah, OK, so the answer is nothing ever traverses this code for the non-
root namespace, so no measurement ever get logged inside a namespace.
Got it.

James