linux-kernel - Re: [PATCH v2 4/5] LSM: Define SELinux function to measure security state

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Message-ID: <37d3d380-f4e2-1bdc-88c8-7bb8ffbee612@linux.microsoft.com>
Date:   Thu, 16 Jul 2020 15:03:32 -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 v2 4/5] LSM: Define SELinux function to measure security
 state

On 7/16/20 12:45 PM, Stephen Smalley wrote:
> On Thu, Jul 16, 2020 at 3:13 PM Lakshmi Ramasubramanian
> <nramas@...ux.microsoft.com> wrote:
>>
>> On 7/16/20 11:54 AM, Stephen Smalley wrote:
>>> Not sure about this error handling approach (silent, proceeding as if
>>> the length was zero and then later failing with ENOMEM on every
>>> attempt?). I'd be more inclined to panic/BUG here but I know Linus
>>> doesn't like that.
>> I am not sure if failing (kernel panic/BUG) to "measure" LSM data under
>> memory pressure conditions is the right thing. But I am open to treating
>> this error as a fatal error. Please let me know.
> 
> Let's at least log an error message since it otherwise silently
> disables all measuring of security state.
Agree - will log error messages as appropriate.

> Also not sure why we bother returning errors from
> selinux_measure_data() since nothing appears to check or use the
> result.
Maybe SELinux can log audit messages on failures, but I guess it may be 
better to do that closer to where the error occurs.

Will change selinux_measure_data() to void function.

> Don't know if integrity/IMA has any equivalent to the audit
> subsystem's concept of audit_failure settings to control whether
> errors that prevent auditing (measuring) are handled silently, with a
> log message, or via a panic.  If not, I guess that can be explored
> separately.
> 

Yes - integrity subsystem logs audit messages for errors\failures.

  -lakshmi