| Message ID | 20191211185116.2740-2-nramas@linux.microsoft.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | IMA: Deferred measurement of keys | expand |
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
On 12/12/19 12:19 AM, Mimi Zohar wrote: >>> + 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 Sure Mimi. Thanks for including the comment in the patch. thanks, -lakshmi
On Thu, 2019-12-12 at 08:57 -0800, Lakshmi Ramasubramanian wrote: > On 12/12/19 12:19 AM, Mimi Zohar wrote: > > >>> + 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. > > Sure Mimi. Thanks for including the comment in the patch. Looking at this again, something seems off or at least the comment doesn't match the code. /* * To avoid holding the mutex while 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 above, any new key will * be processed immediately and not queued. */ Setting ima_process_key before taking the lock won't prevent the race. I think you want to test ima_process_keys before taking the lock and again immediately afterward taking the lock, before setting it. Then the comment would match the code. Shouldn't ima_process_keys be defined as static to limit the scope to this file? Mimi
On 12/12/19 1:13 PM, Mimi Zohar wrote: > > Looking at this again, something seems off or at least the comment > doesn't match the code. > > /* > * To avoid holding the mutex while 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 above, any new key will > * be processed immediately and not queued. > */ > > Setting ima_process_key before taking the lock won't prevent the race. > I think you want to test ima_process_keys before taking the lock and > again immediately afterward taking the lock, before setting it. Then > the comment would match the code. > > Shouldn't ima_process_keys be defined as static to limit the scope to > this file? > > Mimi > In IMA hook, ima_process_key is checked without lock. If it is false, ima_queue_key is called. If the key was queued (by ima_queue_key()) then the hook defers measurement. Else, it processes it immediately. In ima_queue_key() function the check for ima_process_key is done after taking the lock and the key queued if the flag is false. In ima_process_keys() ima_process_key is set without lock and then the queued keys are moved to a temp list after taking the lock. I have reviewed the changes myself and also with a few of my colleagues. I don't think there is a race condition. Please let me know if you do see a problem. I can move the setting of ima_process_key flag inside the lock. But honestly I don't think that is necessary. I agree that ima_process_keys should be static since it is used in this file one. I'll make that change. I can also move the setting of ima_process_key flag inside the lock along with the above change. thanks, -lakshmi
On Thu, 2019-12-12 at 13:59 -0800, Lakshmi Ramasubramanian wrote: > On 12/12/19 1:13 PM, Mimi Zohar wrote: > > > > > Looking at this again, something seems off or at least the comment > > doesn't match the code. > > > > /* > > * To avoid holding the mutex while 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 above, any new key will > > * be processed immediately and not queued. > > */ > > > > Setting ima_process_key before taking the lock won't prevent the race. > > I think you want to test ima_process_keys before taking the lock and > > again immediately afterward taking the lock, before setting it. Then > > the comment would match the code. > > > > Shouldn't ima_process_keys be defined as static to limit the scope to > > this file? > > > > Mimi > > > > In IMA hook, ima_process_key is checked without lock. If it is false, > ima_queue_key is called. If the key was queued (by ima_queue_key()) then > the hook defers measurement. Else, it processes it immediately. > > In ima_queue_key() function the check for ima_process_key is done after > taking the lock and the key queued if the flag is false. > > In ima_process_keys() ima_process_key is set without lock and then the > queued keys are moved to a temp list after taking the lock. > > I have reviewed the changes myself and also with a few of my colleagues. > I don't think there is a race condition. Please let me know if you do > see a problem. > > I can move the setting of ima_process_key flag inside the lock. But > honestly I don't think that is necessary. > > I agree that ima_process_keys should be static since it is used in this > file one. I'll make that change. > > I can also move the setting of ima_process_key flag inside the lock > along with the above change. My concern is with the last sentence "Since ima_process_keys is set to true above, any new key will be processed immediately and not queued." It's unlikely, but possible, that a second process will wait for the ima_keys_mutex. Either we remove this sentence or move setting ima_process_keys to after taking the lock. Mimi
On 12/12/2019 2:54 PM, Mimi Zohar wrote: >> >> I can also move the setting of ima_process_key flag inside the lock >> along with the above change. > > My concern is with the last sentence "Since ima_process_keys is set to > true above, any new key will be processed immediately and not queued." > It's unlikely, but possible, that a second process will wait for the > ima_keys_mutex. Either we remove this sentence or move setting > ima_process_keys to after taking the lock. > > Mimi Sure - i'll move the setting of ima_process_keys flag inside the lock and define the flag as static. Will keep the comment as is. thanks, -lakshmi
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); + + 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
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(+)