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

Lakshmi Ramasubramanian
2019-12-12T21:59:39Z

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.
>  I think you want to test ima_process_keys before taking the lock and
> again immediately afterward taking the lock, before setting it.  Then
> the comment would match the code.
>
> Shouldn't ima_process_keys be defined as static to limit the scope to
> this file?
>
> Mimi
>

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.

thanks,
-lakshmi