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

[Mimi Zohar]

On Wed, 2019-12-11 at 10:51 -0800, Lakshmi Ramasubramanian wrote:
> Measuring keys requires a custom IMA policy to be loaded.
> Keys created or updated before a custom IMA policy is loaded should
> be queued and the keys should be processed after a custom policy
> is loaded.
> 
> This patch defines workqueue for queuing keys when a custom IMA policy
> has not yet been loaded.
> 
> A flag namely ima_process_keys is used to check if the key should be
> queued or should be processed immediately.
> 
> Signed-off-by: Lakshmi Ramasubramanian <nramas@xxxxxxxxxxxxxxxxxxx>
> ---
>  security/integrity/ima/ima.h                 |  15 +++
>  security/integrity/ima/ima_asymmetric_keys.c | 110 +++++++++++++++++++
>  2 files changed, 125 insertions(+)
> 
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index f06238e41a7c..97f8a4078483 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -205,6 +205,21 @@ extern const char *const func_tokens[];
>  
>  struct modsig;
>  
> +#ifdef CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE
> +/*
> + * To track keys that need to be measured.
> + */
> +struct ima_key_entry {
> +	struct list_head list;
> +	void *payload;
> +	size_t payload_len;
> +	char *keyring_name;
> +};
> +void ima_process_queued_keys(void);
> +#else
> +static inline void ima_process_queued_keys(void) {}
> +#endif /* CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE */
> +
>  /* LIM API function definitions */
>  int ima_get_action(struct inode *inode, const struct cred *cred, u32 secid,
>  		   int mask, enum ima_hooks func, int *pcr,
> diff --git a/security/integrity/ima/ima_asymmetric_keys.c b/security/integrity/ima/ima_asymmetric_keys.c
> index fea2e7dd3b09..ba01e04ec025 100644
> --- a/security/integrity/ima/ima_asymmetric_keys.c
> +++ b/security/integrity/ima/ima_asymmetric_keys.c
> @@ -14,6 +14,116 @@
>  #include <keys/asymmetric-type.h>
>  #include "ima.h"
>  
> +/*
> + * Flag to indicate whether a key can be processed
> + * right away or should be queued for processing later.
> + */
> +bool ima_process_keys;
> +
> +/*
> + * To synchronize access to the list of keys that need to be measured
> + */
> +static DEFINE_MUTEX(ima_keys_mutex);
> +static LIST_HEAD(ima_keys);
> +
> +static void ima_free_key_entry(struct ima_key_entry *entry)
> +{
> +	if (entry) {
> +		kfree(entry->payload);
> +		kfree(entry->keyring_name);
> +		kfree(entry);
> +	}
> +}
> +
> +static struct ima_key_entry *ima_alloc_key_entry(
> +	struct key *keyring,
> +	const void *payload, size_t payload_len)
> +{
> +	int rc = 0;
> +	struct ima_key_entry *entry;
> +
> +	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
> +	if (entry) {
> +		entry->payload = kmemdup(payload, payload_len, GFP_KERNEL);
> +		entry->keyring_name = kstrdup(keyring->description,
> +					      GFP_KERNEL);
> +		entry->payload_len = payload_len;
> +	}
> +
> +	if ((entry == NULL) || (entry->payload == NULL) ||
> +	    (entry->keyring_name == NULL)) {
> +		rc = -ENOMEM;
> +		goto out;
> +	}
> +
> +	INIT_LIST_HEAD(&entry->list);
> +
> +out:
> +	if (rc) {
> +		ima_free_key_entry(entry);
> +		entry = NULL;
> +	}
> +
> +	return entry;
> +}
> +
> +bool ima_queue_key(struct key *keyring, const void *payload,
> +		   size_t payload_len)
> +{
> +	bool queued = false;
> +	struct ima_key_entry *entry;
> +
> +	entry = ima_alloc_key_entry(keyring, payload, payload_len);
> +	if (!entry)
> +		return false;
> +
> +	mutex_lock(&ima_keys_mutex);
> +	if (!ima_process_keys) {
> +		list_add_tail(&entry->list, &ima_keys);
> +		queued = true;
> +	}
> +	mutex_unlock(&ima_keys_mutex);
> +
> +	if (!queued)
> +		ima_free_key_entry(entry);
> +
> +	return queued;
> +}
> +
> +/*
> + * 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);
> +
> +	if (ima_process_keys)
> +		return;
> +
> +	ima_process_keys = true;
> +
> +	INIT_LIST_HEAD(&temp_ima_keys);
> +
> +	mutex_lock(&ima_keys_mutex);
> +
> +	list_for_each_entry_safe(entry, tmp, &ima_keys, list)
> +		list_move_tail(&entry->list, &temp_ima_keys);
> +
> +	mutex_unlock(&ima_keys_mutex);


The v1 comment, which explained the need for using a temporary
keyring, is an example of an informative comment. ÂIf you don't
object, instead of re-posting this patch, I can insert it.

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