linux-kernel - Re: [PATCH v4 1/2] IMA: Define workqueue for early boot "key" measurements

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Date:   Mon, 16 Dec 2019 07:30:00 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        linux-integrity@...r.kernel.org
Cc:     eric.snowberg@...cle.com, dhowells@...hat.com,
        mathew.j.martineau@...ux.intel.com, matthewgarrett@...gle.com,
        sashal@...nel.org, jamorris@...ux.microsoft.com,
        linux-kernel@...r.kernel.org, keyrings@...r.kernel.org
Subject: Re: [PATCH v4 1/2] IMA: Define workqueue for early boot "key"
 measurements

On Fri, 2019-12-13 at 09:18 -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;
> +	LIST_HEAD(temp_ima_keys);
> +	bool process = false;
> +
> +	if (ima_process_keys)
> +		return;
> +
> +	/*
> +	 * To avoid holding the mutex when 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, any new key will be
> +	 * processed immediately and not be queued.
> +	 */
> +	INIT_LIST_HEAD(&temp_ima_keys);
> +
> +	mutex_lock(&ima_keys_mutex);
> +
> +	if (!ima_process_keys) {
> +		ima_process_keys = true;

Thank you for moving the initialization here.  The comment is now
valid and the following code is now guaranteed to execute just once.

> +
> +		if (!list_empty(&ima_keys)) {
> +			list_for_each_entry_safe(entry, tmp, &ima_keys, list)
> +				list_move_tail(&entry->list, &temp_ima_keys);
> +			process = true;
> +		}
> +	}
> +
> +	mutex_unlock(&ima_keys_mutex);
> +
> +	if (!process)
> +		return;

The new changes - checking if the list is empty and this test - are
unnecessary, as you implied earlier.

Mimi

> +
> +	list_for_each_entry_safe(entry, tmp, &temp_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);
> +	}
> +}
> +
>  /**
>   * ima_post_key_create_or_update - measure asymmetric keys
>   * @keyring: keyring to which the key is linked to