Keys should be queued for measurement if custom IMA policies have
not yet been applied. Keys queued for measurement, if any, need to be
processed when custom IMA policies have been applied.
This patch adds the call to ima_queue_key_for_measurement() in
the IMA hook function if ima_process_keys_for_measurement flag is set
to false. And, the call to ima_process_queued_keys_for_measurement()
when custom IMA policies have been applied in ima_update_policy().
NOTE:
If the kernel is built with CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE
enabled then the IMA policy should be applied as custom IMA policies.
Keys will be queued up until custom policies are applied and processed
when custom policies have been applied.
Signed-off-by: Lakshmi Ramasubramanian <[email protected]>
---
security/integrity/ima/ima_asymmetric_keys.c | 16 ++++++++++++++++
security/integrity/ima/ima_policy.c | 12 ++++++++++++
2 files changed, 28 insertions(+)
diff --git a/security/integrity/ima/ima_asymmetric_keys.c b/security/integrity/ima/ima_asymmetric_keys.c
index 10deb77b22a0..adb7a307190f 100644
--- a/security/integrity/ima/ima_asymmetric_keys.c
+++ b/security/integrity/ima/ima_asymmetric_keys.c
@@ -157,6 +157,8 @@ void ima_post_key_create_or_update(struct key *keyring, struct key *key,
const void *payload, size_t payload_len,
unsigned long flags, bool create)
{
+ bool key_queued = false;
+
/* Only asymmetric keys are handled by this hook. */
if (key->type != &key_type_asymmetric)
return;
@@ -164,6 +166,20 @@ void ima_post_key_create_or_update(struct key *keyring, struct key *key,
if (!payload || (payload_len == 0))
return;
+ if (!ima_process_keys_for_measurement)
+ key_queued = ima_queue_key_for_measurement(keyring,
+ payload,
+ payload_len);
+
+ /*
+ * Need to check again if the key was queued or not because
+ * ima_process_keys_for_measurement could have flipped from
+ * false to true after it was checked above, but before the key
+ * could be queued by ima_queue_key_for_measurement().
+ */
+ if (key_queued)
+ return;
+
/*
* keyring->description points to the name of the keyring
* (such as ".builtin_trusted_keys", ".ima", etc.) to
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 78b25f083fe1..a2e30a90f97d 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -812,6 +812,18 @@ void ima_update_policy(void)
kfree(arch_policy_entry);
}
ima_update_policy_flag();
+
+ /*
+ * Custom IMA policies have been setup.
+ * Process key(s) queued up for measurement now.
+ *
+ * NOTE:
+ * Custom IMA policies always overwrite builtin policies
+ * (policies compiled in code). If one wants measurement
+ * of asymmetric keys then it has to be configured in
+ * custom policies and updated here.
+ */
+ ima_process_queued_keys_for_measurement();
}
/* Keep the enumeration in sync with the policy_tokens! */
--
2.17.1
Hi Lakshmi,
On Tue, 2019-11-26 at 18:52 -0800, Lakshmi Ramasubramanian wrote:
> Keys should be queued for measurement if custom IMA policies have
> not yet been applied. Keys queued for measurement, if any, need to be
> processed when custom IMA policies have been applied.
Please start with the problem description. For example, measuring
keys requires loading a custom IMA policy.
>
> This patch adds the call to ima_queue_key_for_measurement() in
> the IMA hook function if ima_process_keys_for_measurement flag is set
> to false. And, the call to ima_process_queued_keys_for_measurement()
> when custom IMA policies have been applied in ima_update_policy().
This reads like pseudo code. Please summarize the purpose of this
patch.
>
> NOTE:
> If the kernel is built with CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE
> enabled then the IMA policy should be applied as custom IMA policies.
>
> Keys will be queued up until custom policies are applied and processed
> when custom policies have been applied.
>
> Signed-off-by: Lakshmi Ramasubramanian <[email protected]>
> ---
> security/integrity/ima/ima_asymmetric_keys.c | 16 ++++++++++++++++
> security/integrity/ima/ima_policy.c | 12 ++++++++++++
> 2 files changed, 28 insertions(+)
>
> diff --git a/security/integrity/ima/ima_asymmetric_keys.c b/security/integrity/ima/ima_asymmetric_keys.c
> index 10deb77b22a0..adb7a307190f 100644
> --- a/security/integrity/ima/ima_asymmetric_keys.c
> +++ b/security/integrity/ima/ima_asymmetric_keys.c
> @@ -157,6 +157,8 @@ void ima_post_key_create_or_update(struct key *keyring, struct key *key,
> const void *payload, size_t payload_len,
> unsigned long flags, bool create)
> {
> + bool key_queued = false;
> +
> /* Only asymmetric keys are handled by this hook. */
> if (key->type != &key_type_asymmetric)
> return;
> @@ -164,6 +166,20 @@ void ima_post_key_create_or_update(struct key *keyring, struct key *key,
> if (!payload || (payload_len == 0))
> return;
>
> + if (!ima_process_keys_for_measurement)
> + key_queued = ima_queue_key_for_measurement(keyring,
> + payload,
> + payload_len);
> +
> + /*
> + * Need to check again if the key was queued or not because
> + * ima_process_keys_for_measurement could have flipped from
> + * false to true after it was checked above, but before the key
> + * could be queued by ima_queue_key_for_measurement().
> + */
You're describing a race condition.
> + if (key_queued)
> + return;
> +
> /*
> * keyring->description points to the name of the keyring
> * (such as ".builtin_trusted_keys", ".ima", etc.) to
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 78b25f083fe1..a2e30a90f97d 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -812,6 +812,18 @@ void ima_update_policy(void)
> kfree(arch_policy_entry);
> }
> ima_update_policy_flag();
> +
> + /*
> + * Custom IMA policies have been setup.
> + * Process key(s) queued up for measurement now.
> + *
> + * NOTE:
> + * Custom IMA policies always overwrite builtin policies
> + * (policies compiled in code). If one wants measurement
> + * of asymmetric keys then it has to be configured in
> + * custom policies and updated here.
> + */
The "NOTE" is over commenting the code and belongs in the patch
description.
> + ima_process_queued_keys_for_measurement();
Overwriting the initial policy is highly recommended, but not everyone
defines a custom policy. Should there be a time limit or some other
criteria before deleting the key measurement queue?
Mimi
> }
>
> /* Keep the enumeration in sync with the policy_tokens! */
Thanks for reviewing the changes Mimi. I'll address your comments in the
next update.
>
> Overwriting the initial policy is highly recommended, but not everyone
> defines a custom policy. Should there be a time limit or some other
> criteria before deleting the key measurement queue?
>
> Mimi
For the above, I feel checking for the presence of custom policy, if
that is possible, would be a more deterministic approach compared to
having a time limit.
On my machine, systemd loads the custom IMA policy from
/etc/ima/ima-policy if that file is present. Is this the recommended way
to configure custom IMA policy? If yes, can the IMA initialization
function check for the presence of the above file?
Another way to address this issue is to define a new CONFIG parameter to
determine whether or not to support deferred processing of keys. If this
config is chosen, custom IMA policy must be defined.
Least preferred option would be to leave the queued keys as is if custom
policy is not defined - at the cost of, maybe, a non-trivial amount of
kernel memory consumed.
If detection of custom policy is not possible, then define a timer to
drain the key measurement queue.
Please let me know which approach you think is optimal.
thanks,
-lakshmi