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List:       linux-keyrings
Subject:    [PATCH v5 2/2] IMA: Call workqueue functions to measure queued keys
From:       Lakshmi Ramasubramanian <nramas () linux ! microsoft ! com>
Date:       2019-12-18 16:44:34
Message-ID: 20191218164434.2877-3-nramas () linux ! microsoft ! com
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Measuring keys requires a custom IMA policy to be loaded.
Keys should be queued for measurement if a custom IMA policy
is not yet loaded. Keys queued for measurement, if any, should be
processed when a custom IMA policy is loaded.

This patch updates the IMA hook function ima_post_key_create_or_update()
to queue the key if a custom IMA policy has not yet been loaded.
And, ima_update_policy() function, which is called when
a custom IMA policy is loaded, is updated to process queued keys.

Sample "key" measurement rule in the IMA policy:

measure func=KEY_CHECK uid=0 keyrings=.ima|.builtin_trusted_keys template=ima-buf

If the kernel is built with one or more built-in trusted certificates,
IMA measurement should list all the keys imported from those certificates.

Display "key" measurement in the IMA measurement list:

cat /sys/kernel/security/ima/ascii_runtime_measurements

10 faf3...e702 ima-buf \
sha256:27c915b8ddb9fae7214cf0a8a7043cc3eeeaa7539bcb136f8427067b5f6c3b7b \
.builtin_trusted_keys 308202863082...4aee

Verify "key" measurement data for a key added to ".builtin_trusted_keys" keyring:

cat /sys/kernel/security/integrity/ima/ascii_runtime_measurements | grep -m 1 \
"\.builtin_trusted_keys" | cut -d' ' -f 6 | xxd -r -p |tee btk-cert.der | sha256sum | \
cut -d' ' -f 1

The output of the above command should match the template hash
of the first "key" measurement entry in the IMA measurement list for
the key added to ".builtin_trusted_keys" keyring.

The file namely "btk-cert.der" generated by the above command
should be a valid x509 certificate (in DER format) and should match
the one that was used to import the key to the ".builtin_trusted_keys" keyring.
The certificate file can be verified using openssl tool.

Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
---
 security/integrity/ima/ima_asymmetric_keys.c | 8 ++++++++
 security/integrity/ima/ima_policy.c          | 3 +++
 2 files changed, 11 insertions(+)

diff --git a/security/integrity/ima/ima_asymmetric_keys.c \
b/security/integrity/ima/ima_asymmetric_keys.c index d520a67180d8..4124f10ff0c2 \
                100644
--- a/security/integrity/ima/ima_asymmetric_keys.c
+++ b/security/integrity/ima/ima_asymmetric_keys.c
@@ -145,6 +145,8 @@ 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 queued = false;
+
 	/* Only asymmetric keys are handled by this hook. */
 	if (key->type != &key_type_asymmetric)
 		return;
@@ -152,6 +154,12 @@ void ima_post_key_create_or_update(struct key *keyring, struct \
key *key,  if (!payload || (payload_len == 0))
 		return;
 
+	if (!ima_process_keys)
+		queued = ima_queue_key(keyring, payload, payload_len);
+
+	if (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 a4dde9d575b2..04b9c6c555de 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -807,6 +807,9 @@ void ima_update_policy(void)
 		kfree(arch_policy_entry);
 	}
 	ima_update_policy_flag();
+
+	/* Custom IMA policy has been loaded */
+	ima_process_queued_keys();
 }
 
 /* Keep the enumeration in sync with the policy_tokens! */
-- 
2.17.1


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