linux-kernel - Re: [PATCH 4/5] LSM: Define SELinux function to measure security state

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Date:   Mon, 15 Jun 2020 13:44:28 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Casey Schaufler <casey@...aufler-ca.com>,
        Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        John Johansen <john.johansen@...onical.com>
Cc:     Stephen Smalley <stephen.smalley@...il.com>,
        James Morris <jmorris@...ei.org>,
        linux-integrity@...r.kernel.org,
        LSM List <linux-security-module@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/5] LSM: Define SELinux function to measure security
 state

(Cc'ing John)

On Mon, 2020-06-15 at 10:33 -0700, Casey Schaufler wrote:
> On 6/15/2020 9:45 AM, Lakshmi Ramasubramanian wrote:
> > On 6/15/20 4:57 AM, Stephen Smalley wrote:
> >
> > Hi Stephen,
> >
> > Thanks for reviewing the patches.
> >
> >>> +void security_state_change(char *lsm_name, void *state, int state_len)
> >>> +{
> >>> +       ima_lsm_state(lsm_name, state, state_len);
> >>> +}
> >>> +
> >>
> >> What's the benefit of this trivial function instead of just calling
> >> ima_lsm_state() directly?
> >
> > One of the feedback Casey Schaufler had given earlier was that calling an IMA function directly from SELinux (or, any of the Security Modules) would be a layering violation.
> 
> Hiding the ima_lsm_state() call doesn't address the layering.
> The point is that SELinux code being called from IMA (or the
> other way around) breaks the subsystem isolation. Unfortunately,
> it isn't obvious to me how you would go about what you're doing
> without integrating the subsystems.

Casey, I'm not sure why you think there is a layering issue here.
 There were multiple iterations of IMA before it was upstreamed.  One
iteration had separate integrity hooks(LIM).  Only when the IMA calls
and the security hooks are co-located, are they combined, as requested
by Linus.

There was some AppArmour discussion about calling IMA directly, but I
haven't heard about it in a while or seen the patch.

Mimi