Messages in this thread |  | | Subject | Re: [PATCH v4 2/2] IMA: Call workqueue functions to measure queued keys | From | Lakshmi Ramasubramanian <> | Date | Mon, 16 Dec 2019 13:52:26 -0800 |
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On 12/16/2019 1:37 PM, Lakshmi Ramasubramanian wrote: > > On 12/16/2019 1:17 PM, James Bottomley wrote: >> On Mon, 2019-12-16 at 11:20 -0800, Lakshmi Ramasubramanian wrote: >>> => If the flag is false, mutex is taken and the flag is checked >>> again. If the flag changed from false to true between the above two >>> tests, that means another thread had raced to call >>> ima_process_queued_keys() and has processed the queued keys. So >>> again, no further action is required. >> >> This is the problem: in the race case you may still be adding keys to >> the queue after the other thread has processed it. Those keys won't get >> processed because the flag is now false in the post check so the >> current thread won't process them either. >> >> James >>
Please keep in mind that ima_queue_key() returns a boolean indicating whether or not the key was queued. This flag is set inside the lock - please see the code snippet from ima_queue_key() below:
+ mutex_lock(&ima_keys_mutex); + if (!ima_process_keys) { + list_add_tail(&entry->list, &ima_keys); + queued = true; + } + mutex_unlock(&ima_keys_mutex);
If ima_process_keys had changed from false to true, ima_queue_key() will not queue the key and return false to ima_post_key_create_or_update().
Code snippet in ima_post_key_create_or_update():
+ if (!ima_process_keys) + queued = ima_queue_key(keyring, payload, payload_len); + + if (queued) + return;
If the "queued" is false, ima_post_key_create_or_update() will process the key immediately.
-lakshmi
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