Re: [PATCH v2 1/2] IMA: Define workqueue for early boot "key" measurements

From: Lakshmi Ramasubramanian
Date: Thu Dec 12 2019 - 16:59:40 EST

On 12/12/19 1:13 PM, Mimi Zohar wrote:

Looking at this again, something seems off or at least the comment
doesn't match the code.

* To avoid holding the mutex while processing queued keys,
* transfer the queued keys with the mutex held to a temp list,
* release the mutex, and then process the queued keys from
* the temp list.
* Since ima_process_keys is set to true above, any new key will
* be processed immediately and not queued.

Setting ima_process_key before taking the lock won't prevent the race.
ÂI think you want to test ima_process_keys before taking the lock and
again immediately afterward taking the lock, before setting it. ÂThen
the comment would match the code.

Shouldn't ima_process_keys be defined as static to limit the scope to
this file?


In IMA hook, ima_process_key is checked without lock. If it is false, ima_queue_key is called. If the key was queued (by ima_queue_key()) then the hook defers measurement. Else, it processes it immediately.

In ima_queue_key() function the check for ima_process_key is done after taking the lock and the key queued if the flag is false.

In ima_process_keys() ima_process_key is set without lock and then the queued keys are moved to a temp list after taking the lock.

I have reviewed the changes myself and also with a few of my colleagues. I don't think there is a race condition. Please let me know if you do see a problem.

I can move the setting of ima_process_key flag inside the lock. But honestly I don't think that is necessary.

I agree that ima_process_keys should be static since it is used in this file one. I'll make that change.

I can also move the setting of ima_process_key flag inside the lock along with the above change.