Re: [PATCH v0 1/2] IMA: Defined queue functions

Mimi Zohar
2019-12-03T00:02:18Z

Hi Lakshmi,

On Tue, 2019-11-26 at 18:52 -0800, Lakshmi Ramasubramanian wrote:
> Keys created or updated in the system before IMA is initialized
> should be queued up. And, keys (including any queued ones)
> should be processed when IMA initialization is completed.
>
> This patch defines functions to queue and dequeue keys for
> measurement. A flag namely ima_process_keys_for_measurement
> is used to check if the key should be queued or should be
> processed immediately.
>
> ima_policy_flag cannot be relied upon to make queuing decision
> because ima_policy_flag will be set to 0 when either IMA is
> not initialized or when the IMA policy itself is empty.

Already commented on the patch description.  Some additional minor
comments below.

>
> Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
> ---
> security/integrity/ima/ima.h | 15 +++
> security/integrity/ima/ima_asymmetric_keys.c | 135 ++++++++++++++++++-
> 2 files changed, 146 insertions(+), 4 deletions(-)
>
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index f06238e41a7c..f86371647707 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_measure_key_entry {
> + struct list_head list;
> + void *payload;
> + size_t payload_len;
> + char *keyring_name;
> +};
> +void ima_process_queued_keys_for_measurement(void);
> +#else
> +static inline void ima_process_queued_keys_for_measurement(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 ca895f9a6504..10deb77b22a0 100644
> --- a/security/integrity/ima/ima_asymmetric_keys.c
> +++ b/security/integrity/ima/ima_asymmetric_keys.c
> @@ -14,12 +14,139 @@
> #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_for_measurement;
> +
> +/*
> + * To synchronize access to the list of keys that need to be measured
> + */
> +static DEFINE_MUTEX(ima_measure_keys_mutex);
> +static LIST_HEAD(ima_measure_keys);
> +
> +static void ima_free_measure_key_entry(struct ima_measure_key_entry *entry)
> +{
> + if (entry) {
> + kfree(entry->payload);
> + kfree(entry->keyring_name);
> + kfree(entry);
> + }
> +}
> +
> +static struct ima_measure_key_entry *ima_alloc_measure_key_entry(
> + struct key *keyring,
> + const void *payload, size_t payload_len)
> +{
> + int rc = 0;
> + struct ima_measure_key_entry *entry = NULL;
> +
> + entry = kzalloc(sizeof(*entry), GFP_KERNEL);
> + if (entry) {
> + entry->payload =
> + kmemdup(payload, payload_len, GFP_KERNEL);
> + entry->keyring_name =
> + kstrdup(keyring->description, GFP_KERNEL);

No need to break up the assignments like this.  Neither line when
joined is greater than 80 bytes.

> + entry->payload_len = payload_len;
> + }
> +
> + if ((entry == NULL) || (entry->payload == NULL) ||
> + (entry->keyring_name == NULL)) {
> + rc = -ENOMEM;
> + goto out;
> + }
> +
> + INIT_LIST_HEAD(&entry->list);
> + rc = 0;

"rc" was initialized in the declaration.

> +
> +out:
> + if (rc) {
> + ima_free_measure_key_entry(entry);
> + entry = NULL;
> + }
> +
> + return entry;
> +}
> +
> +bool ima_queue_key_for_measurement(struct key *keyring,
> + const void *payload, size_t payload_len)
> +{
> + bool queued = false;
> + struct ima_measure_key_entry *entry = NULL;

No need to initialize ima_measure_key_entry here, as the first
statement sets it.
> +
> + entry = ima_alloc_measure_key_entry(keyring, payload, payload_len);
> + if (entry) {

If we're ignoring failure to allocate memory, why not just return?

> + /*
> + * ima_measure_keys_mutex should be taken before checking
> + * ima_process_keys_for_measurement flag to avoid the race
> + * condition between the IMA hook checking this flag and
> + * calling ima_queue_key_for_measurement() to queue
> + * the key and ima_process_queued_keys_for_measurement()
> + * setting this flag.
> + */
> + mutex_lock(&ima_measure_keys_mutex);
> + if (!ima_process_keys_for_measurement) {
> + list_add_tail(&entry->list, &ima_measure_keys);
> + queued = true;
> + }
> + mutex_unlock(&ima_measure_keys_mutex);
> +
> + if (!queued)
> + ima_free_measure_key_entry(entry);
> + }
> +
> + return queued;
> +}
> +
> +void ima_process_queued_keys_for_measurement(void)
> +{
> + struct ima_measure_key_entry *entry, *tmp;
> + LIST_HEAD(temp_ima_measure_keys);
> +
> + if (ima_process_keys_for_measurement)
> + return;
> +
> + /*
> + * Any queued keys will be processed now. From here on
> + * keys should be processed right away.
> + */
> + ima_process_keys_for_measurement = true;
> +
> + /*
> + * 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_for_measurement is set to true above,
> + * any new key will be processed immediately and not be queued.
> + */
> + INIT_LIST_HEAD(&temp_ima_measure_keys);
> + mutex_lock(&ima_measure_keys_mutex);
> + list_for_each_entry_safe(entry, tmp, &ima_measure_keys, list) {
> + list_move_tail(&entry->list, &temp_ima_measure_keys);
> + }

Parenthesis not needed.

> + mutex_unlock(&ima_measure_keys_mutex);
> +
> + list_for_each_entry_safe(entry, tmp,
> + &temp_ima_measure_keys, list) {

No need to break up this line either.  The joined line is not greater
than 80 bytes.

> + process_buffer_measurement(entry->payload,
> + entry->payload_len,
> + entry->keyring_name,
> + KEY_CHECK, 0,
> + entry->keyring_name);
> + list_del(&entry->list);
> + ima_free_measure_key_entry(entry);
> + }
> +}
> +