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

Mimi Zohar
2019-12-12T08:19:16Z

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@linux.microsoft.com>
> ---
> 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.  If 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