Messages in this thread | | | Subject | Re: [PATCH v6 0/4] LSM: Measure security module data | From | Lakshmi Ramasubramanian <> | Date | Wed, 5 Aug 2020 09:21:24 -0700 |
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On 8/5/20 9:14 AM, Tyler Hicks wrote: > On 2020-08-05 09:07:48, Lakshmi Ramasubramanian wrote: >> On 8/5/20 8:45 AM, Tyler Hicks wrote: >>> On 2020-08-05 08:36:40, Casey Schaufler wrote: >>>> On 8/4/2020 6:14 PM, Lakshmi Ramasubramanian wrote: >>>>> On 8/4/20 6:04 PM, Casey Schaufler wrote: >>>>>> On 8/4/2020 5:43 PM, Lakshmi Ramasubramanian wrote: >>>>>>> Critical data structures of security modules are currently not measured. >>>>>>> Therefore an attestation service, for instance, would not be able to >>>>>>> attest whether the security modules are always operating with the policies >>>>>>> and configuration that the system administrator had setup. The policies >>>>>>> and configuration for the security modules could be tampered with by >>>>>>> malware by exploiting kernel vulnerabilities or modified through some >>>>>>> inadvertent actions on the system. Measuring such critical data would >>>>>>> enable an attestation service to better assess the state of the system. >>>>>> >>>>>> I still wonder why you're calling this an LSM change/feature when >>>>>> all the change is in IMA and SELinux. You're not putting anything >>>>>> into the LSM infrastructure, not are you using the LSM infrastructure >>>>>> to achieve your ends. Sure, you *could* support other security modules >>>>>> using this scheme, but you have a configuration dependency on >>>>>> SELinux, so that's at best going to be messy. If you want this to >>>>>> be an LSM "feature" you need to use the LSM hooking mechanism. >>>>> >>>>>> >>>>>> I'm not objecting to the feature. It adds value. But as you've >>>>>> implemented it it is either an IMA extension to SELinux, or an >>>>>> SELiux extension to IMA. Could AppArmor add hooks for this without >>>>>> changing the IMA code? It doesn't look like it to me. >>>>> >>>>> The check in IMA to allow the new IMA hook func LSM_STATE and LSM_POLICY when SELinux is enabled is just because SELinux is the only security module using these hooks now. >>>>> >>>>> To enable AppArmor, for instance, to use the new IMA hooks to measure state and policy would just require adding the check for CONFIG_SECURITY_APPARMOR. Other than that, there are no IMA changes needed to support AppArmor or other such security modules. >>>> >>>> This is exactly what I'm objecting to. What if a system has both SELinux >>>> and AppArmor compiled in? What if it has both enabled? >>> >>> The SELinux state and policy would be measured but the AppArmor >>> state/policy would be silently ignored. This isn't ideal as the IMA >>> policy author would need to read the kernel code to figure out which >>> LSMs are going to be measured. >> >> Tyler - I am not sure why AppArmor state\policy would be ignored when both >> SELinux and AppArmor are enabled. Could you please clarify? > > I think Casey is talking about now (when AppArmor is not supported by > this feature) and you're talking about the future (when AppArmor may be > supported by this feature).
Got it - thanks for clarifying.
But with the current code if SELinux is enabled on the system, but AppArmor is not and the IMA policy contains "measure func=LSM_STATE" then the policy will be rejected as "-EINVAL". So the policy author would get a feedback even now. Correct me if I am wrong.
-lakshmi
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