linux-kernel - [PATCH v4 2/2] IMA: Call workqueue functions to measure queued keys

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Message-Id: <20191213171827.28657-3-nramas@linux.microsoft.com>
Date:   Fri, 13 Dec 2019 09:18:27 -0800
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     zohar@...ux.ibm.com, linux-integrity@...r.kernel.org
Cc:     eric.snowberg@...cle.com, dhowells@...hat.com,
        mathew.j.martineau@...ux.intel.com, matthewgarrett@...gle.com,
        sashal@...nel.org, jamorris@...ux.microsoft.com,
        linux-kernel@...r.kernel.org, keyrings@...r.kernel.org
Subject: [PATCH v4 2/2] IMA: Call workqueue functions to measure queued keys

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@...ux.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 ae6de1bb2e79..8a9d8bc7e10d 100644
--- a/security/integrity/ima/ima_asymmetric_keys.c
+++ b/security/integrity/ima/ima_asymmetric_keys.c
@@ -158,6 +158,8 @@ 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;
@@ -165,6 +167,12 @@ 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