Re: [PATCH v0 1/2] IMA: Defined queue functions

Lakshmi Ramasubramanian
2019-12-02T18:39:28Z

On 12/2/19 10:00 AM, Mimi Zohar wrote:

>
> ima_update_policy() is called from multiple places.  Initially, it is
> called before a custom policy has been loaded.  The call to
> ima_process_queued_keys_for_measurement() needs to be moved to within
> the test, otherwise it runs the risk of dropping "key" measurements.

static const struct file_operations ima_measure_policy_ops = {
.release = ima_release_policy,
};

ima_update_policy() is called from ima_release_policy() function.

On my test machine I have the IMA policy in /etc/ima/ima-policy file.
When IMA policy is setup from this file, I see ima_release_policy()
called (which in turn calls ima_update_policy()).

How can I have ima_update_policy() called before a custom policy is loaded?

If CONFIG_IMA_WRITE_POLICY is enabled, IMA policy can be updated at
runtime - which would invoke ima_update_policy().

Is there any other way ima_update_policy() can get called?

> All the queued keys need to be processed at the same time.  Afterwards
> the queue should be deleted.  Unfortunately, the current queue locking
> assumes ima_process_queued_keys_for_measurement() is called multiple
> times.

When ima_process_queued_keys_for_measurement() is called the first time,
the flag ima_process_keys_for_measurement is set to true and all queued
keys are processed at that time.

The queue is not used after this point - In the IMA hook the key is
processed immediately when ima_process_keys_for_measurement is set to true.

ima_process_queued_keys_for_measurement() can be called multiple times,
but on 2nd and subsequent calls it will be a NOP.

>
> Perhaps using the RCU method of walking lists would help.  I need to
> think about it some more.
>
> Mimi

Please let me know how using RCU method would help.

thanks,
-lakshmi