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

From: Casey Schaufler <casey@schaufler-ca.com>
To: Mimi Zohar <zohar@linux.ibm.com>,
	Lakshmi Ramasubramanian <nramas@linux.microsoft.com>,
	Stephen Smalley <stephen.smalley.work@gmail.com>
Cc: Casey Schaufler <casey@schaufler-ca.com>,
	Stephen Smalley <stephen.smalley@gmail.com>,
	James Morris <jmorris@namei.org>,
	linux-integrity@vger.kernel.org,
	LSM List <linux-security-module@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 4/5] LSM: Define SELinux function to measure security state
Date: Mon, 15 Jun 2020 16:18:22 -0700	[thread overview]
Message-ID: <59f3b8bf-1b61-b67e-7318-3ed251bd10bf@schaufler-ca.com> (raw)
In-Reply-To: <1592243068.11061.155.camel@linux.ibm.com>

On 6/15/2020 10:44 AM, Mimi Zohar wrote:
> (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.

I don't think there is, after further review. If the IMA code called
selinux_dosomething() directly I'd be very concerned, but calling
security_dosomething() which then calls selinux_dosomething() is fine.
If YAMA called security_dosomething() I'd be very concerned, but that's
not what's happening 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