[v7,2/5] IMA: Define an IMA hook to measure keys

Commit Message

Lakshmi Ramasubramanian Nov. 14, 2019, 3:11 a.m. UTC

Measure asymmetric keys used for verifying file signatures,
certificates, etc.

This patch defines a new IMA hook namely ima_post_key_create_or_update()
to measure asymmetric keys.

The IMA hook is defined in a new file namely ima_asymmetric_keys.c
which is built only if CONFIG_KEYS is enabled.

Signed-off-by: Lakshmi Ramasubramanian <[e-mail]>
---
 security/integrity/ima/Makefile              |  1 +
 security/integrity/ima/ima_asymmetric_keys.c | 51 ++++++++++++++++++++
 2 files changed, 52 insertions(+)
 create mode 100644 security/integrity/ima/ima_asymmetric_keys.c

Comments

Lakshmi Ramasubramanian Nov. 14, 2019, 6:30 p.m. UTC | #1

On 11/13/19 7:11 PM, Lakshmi Ramasubramanian wrote:

> The IMA hook is defined in a new file namely ima_asymmetric_keys.c
> which is built only if CONFIG_KEYS is enabled.

I think instead of CONFIG_KEYS I should use 
CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE for ima_asymmetric_keys.c since 
this config is enabled only when both CONFIG_ASYMMETRIC_KEY_TYPE and 
CONFIG_KEYS are enabled.

Please see below taken from "crypto/asymmetric_keys/Kconfig"

# SPDX-License-Identifier: GPL-2.0
menuconfig ASYMMETRIC_KEY_TYPE
         bool "Asymmetric (public-key cryptographic) key type"
         depends on KEYS
         help
           This option provides support for a key type that holds the 
data for
           the asymmetric keys used for public key cryptographic 
operations such
           as encryption, decryption, signature generation and signature
           verification.

if ASYMMETRIC_KEY_TYPE

config ASYMMETRIC_PUBLIC_KEY_SUBTYPE
         tristate "Asymmetric public-key crypto algorithm subtype"

endif # ASYMMETRIC_KEY_TYPE

thanks,
  -lakshmi

Patch

diff --git a/security/integrity/ima/Makefile b/security/integrity/ima/Makefile
index 31d57cdf2421..3c796664be8a 100644
--- a/security/integrity/ima/Makefile
+++ b/security/integrity/ima/Makefile
@@ -12,3 +12,4 @@  ima-$(CONFIG_IMA_APPRAISE) += ima_appraise.o
 ima-$(CONFIG_IMA_APPRAISE_MODSIG) += ima_modsig.o
 ima-$(CONFIG_HAVE_IMA_KEXEC) += ima_kexec.o
 obj-$(CONFIG_IMA_BLACKLIST_KEYRING) += ima_mok.o
+obj-$(CONFIG_KEYS) += ima_asymmetric_keys.o
diff --git a/security/integrity/ima/ima_asymmetric_keys.c b/security/integrity/ima/ima_asymmetric_keys.c
new file mode 100644
index 000000000000..f6884641a622
--- /dev/null
+++ b/security/integrity/ima/ima_asymmetric_keys.c
@@ -0,0 +1,51 @@ 
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2019 Microsoft Corporation
+ *
+ * Author: Lakshmi Ramasubramanian ([e-mail])
+ *
+ * File: ima_asymmetric_keys.c
+ *       Defines an IMA hook to measure asymmetric keys on key
+ *       create or update.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <crypto/public_key.h>
+#include <keys/asymmetric-type.h>
+#include "ima.h"
+
+/**
+ * ima_post_key_create_or_update - measure asymmetric keys
+ * @keyring: keyring to which the key is linked to
+ * @key: created or updated key
+ * @flags: key flags
+ * @create: flag indicating whether the key was created or updated
+ *
+ * Keys can only be measured, not appraised.
+ */
+void ima_post_key_create_or_update(struct key *keyring, struct key *key,
+				   unsigned long flags, bool create)
+{
+	const struct public_key *pk;
+
+	/* Only asymmetric keys are handled by this hook. */
+	if (key->type != &key_type_asymmetric)
+		return;
+
+	/* Get the public_key of the given asymmetric key to measure. */
+	pk = key->payload.data[asym_crypto];
+
+	/*
+	 * keyring->description points to the name of the keyring
+	 * (such as ".builtin_trusted_keys", ".ima", etc.) to
+	 * which the given key is linked to.
+	 *
+	 * The name of the keyring is passed in the "eventname"
+	 * parameter to process_buffer_measurement() and is set
+	 * in the "eventname" field in ima_event_data for
+	 * the key measurement IMA event.
+	 */
+	process_buffer_measurement(pk->key, pk->keylen,
+				   keyring->description, KEY_CHECK, 0);
+}