| Message ID | 20191218164434.2877-2-nramas@linux.microsoft.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | IMA: Deferred measurement of keys | expand |
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
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..d520a67180d8 100644 --- a/security/integrity/ima/ima_asymmetric_keys.c +++ b/security/integrity/ima/ima_asymmetric_keys.c @@ -14,6 +14,121 @@ #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. + */ +static 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; + 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); + } +} + /** * ima_post_key_create_or_update - measure asymmetric keys * @keyring: keyring to which the key is linked to
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 | 115 +++++++++++++++++++ 2 files changed, 130 insertions(+)