IMA: Define an IMA hook to measure keys

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 the payload used to create a new asymmetric key or
update an existing asymmetric key.

Asymmetric key structure is defined only when
CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE is defined. Since the IMA hook
measures asymmetric keys, the IMA hook is defined in a new file namely
ima_asymmetric_keys.c which is built only if
CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE is defined.

Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

diff --git a/security/integrity/ima/Makefile b/security/integrity/ima/Makefile
index 31d57cd..207a0a9 100644 (file)
--- 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_ASYMMETRIC_PUBLIC_KEY_SUBTYPE) += 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 (file)
index 0000000..994d89d
--- /dev/null
+++ b/security/integrity/ima/ima_asymmetric_keys.c
@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2019 Microsoft Corporation
+ *
+ * Author: Lakshmi Ramasubramanian (nramas@linux.microsoft.com)
+ *
+ * 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 <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
+ * @payload: The data used to instantiate or update the key.
+ * @payload_len: The length of @payload.
+ * @flags: key flags
+ * @create: flag indicating whether the key was created or updated
+ *
+ * Keys can only be measured, not appraised.
+ * The payload data used to instantiate or update the key is measured.
+ */
+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)
+{
+       /* Only asymmetric keys are handled by this hook. */
+       if (key->type != &key_type_asymmetric)
+               return;
+
+       if (!payload || (payload_len == 0))
+               return;
+
+       /*
+        * 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(payload, payload_len,
+                                  keyring->description, KEY_CHECK, 0);
+}