On Wed, 2019-12-18 at 08:44 -0800, Lakshmi Ramasubramanian wrote:
> +/*
> + * ima_process_queued_keys() - process keys queued for measurement
> + *
> + * This function sets ima_process_keys to true and processes queued keys.
> + * From here on keys will be processed right away (not queued).
> + */
> +void ima_process_queued_keys(void)
> +{
> + struct ima_key_entry *entry, *tmp;
> + bool process = false;
> +
> + if (ima_process_keys)
> + return;
> +
> + /*
> + * Since ima_process_keys is set to true, any new key will be
> + * processed immediately and not be queued to ima_keys list.
> + * First one setting the ima_process_keys flag to true will
> + * process the queued keys.
> + */
> + mutex_lock(&ima_keys_mutex);
> + if (!ima_process_keys) {
> + ima_process_keys = true;
> + process = true;
> + }
> + mutex_unlock(&ima_keys_mutex);
> +
> + if (!process)
> + return;
> +
> + list_for_each_entry_safe(entry, tmp, &ima_keys, list) {
> + process_buffer_measurement(entry->payload, entry->payload_len,
> + entry->keyring_name, KEY_CHECK, 0,
> + entry->keyring_name);
> + list_del(&entry->list);
> + ima_free_key_entry(entry);
> + }
> +}
> +
Getting rid of the temporary list is definitely a big improvement. As
James suggested, using test_and_set_bit() and test_bit() would improve
this code even more. I think, James correct me if I'm wrong, you
would be able to get rid of both the mutex and "process".
Mimi
> /**
> * ima_post_key_create_or_update - measure asymmetric keys
> * @keyring: keyring to which the key is linked to
On 12/19/19 5:11 AM, Mimi Zohar wrote:
>
> Getting rid of the temporary list is definitely a big improvement. As
> James suggested, using test_and_set_bit() and test_bit() would improve
> this code even more. I think, James correct me if I'm wrong, you
> would be able to get rid of both the mutex and "process".
>
> Mimi
I am not sure if the mutex can be removed.
In ima_queue_key() we need to test the flag and add the key to the list
as an atomic operation:
if (!test_bit())
insert_key_to_list
Suppose the if condition is true, but before we could insert the key to
the list, ima_process_queued_keys() runs and processes queued keys we'll
add the key to the list and never process it.
Is there an API in the kernel to test and add an entry to a list
atomically?
thanks,
-lakshmi
On Thu, 2019-12-19 at 08:55 -0800, Lakshmi Ramasubramanian wrote:
> I am not sure if the mutex can be removed.
>
> In ima_queue_key() we need to test the flag and add the key to the list
> as an atomic operation:
>
> if (!test_bit())
> insert_key_to_list
>
> Suppose the if condition is true, but before we could insert the key to
> the list, ima_process_queued_keys() runs and processes queued keys we'll
> add the key to the list and never process it.
>
> Is there an API in the kernel to test and add an entry to a list
> atomically?
Ok, using test_and_set_bit() and test_bit() only helps, if we can get
rid of the mutex. I'll queue these patches.
thanks,
Mimi