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

[Lakshmi Ramasubramanian <nramas@linux.microsoft.com>]

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