linux-kernel - Re: [PATCH v3 4/5] LSM: Define SELinux function to measure security state

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Message-ID: <72af0630-dce0-12af-0977-b4e81c2f99ac@linux.microsoft.com>
Date:   Mon, 20 Jul 2020 11:59:51 -0700
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     Stephen Smalley <stephen.smalley.work@...il.com>
Cc:     Mimi Zohar <zohar@...ux.ibm.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        James Morris <jmorris@...ei.org>,
        linux-integrity@...r.kernel.org,
        SElinux list <selinux@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 4/5] LSM: Define SELinux function to measure security
 state

On 7/20/20 11:44 AM, Stephen Smalley wrote:

>>>
>>> Actually, if we used ima-ng template for selinux-policy-hash, then
>>> instead of needing to hash the policy
>>> first and passing the hash to IMA, we could just pass the policy as
>>> the buffer and IMA would take care of the hashing, right?
>>
>> That is correct.
>>
>> The IMA hook I've added to measure LSM structures is a generic one that
>> can be used by any security module (SM). I feel it would be better to
>> not have policy or state or any such SM specific logic in IMA, but leave
>> that to the individual SM to handle.
>>
>> What do you think?
> 
> It is correct to remain security module agnostic.  However, I think
> you can remain LSM-neutral while still avoiding the double hashing of
> the policy here.  Can't you just pass in the policy itself as the
> buffer and let IMA hash it?

Yes - that is an option. If I do that then, as you have stated below, 
we'll need to two funcs -
one that will only add the hash but not the entire data payload in the 
IMA log (i.e., "ima-ng")
and, the other that handles hashing and including date payload (i.e., 
"ima-buf").

   Then you can let the policy author decide
> on the template to be used (ima-buf versus ima-ng).  If you want to
> support the use of different templates for different "kinds" of LSM
> state (e.g. state versus policy) you could either provide two funcs
> (LSM_STATE, LSM_POLICY) or otherwise support selection based on some
> other attribute.
> 

I can do the above.

  -lakshmi