ima: load x509 certificate from the kernel

Define configuration option to load X509 certificate into the
IMA trusted kernel keyring. It implements ima_load_x509() hook
to load X509 certificate into the .ima trusted kernel keyring
from the root filesystem.

Changes in v3:
* use ima_policy_flag in ima_get_action()
ima_load_x509 temporarily clears ima_policy_flag to disable
appraisal to load key. Use it to skip appraisal rules.
* Key directory path changed to /etc/keys (Mimi)
* Expand IMA_LOAD_X509 Kconfig help

Changes in v2:
* added '__init'
* use ima_policy_flag to disable appraisal to load keys

Signed-off-by: Dmitry Kasatkin <[e-mail]>
Signed-off-by: Mimi Zohar <[e-mail]>

security/integrity/ima/Kconfig

···
 	help
 	   This option requires that all keys added to the .ima
 	   keyring be signed by a key on the system trusted keyring.
+
+config IMA_LOAD_X509
+	bool "Load X509 certificate onto the '.ima' trusted keyring"
+	depends on IMA_TRUSTED_KEYRING
+	default n
+	help
+	   File signature verification is based on the public keys
+	   loaded on the .ima trusted keyring. These public keys are
+	   X509 certificates signed by a trusted key on the
+	   .system keyring.  This option enables X509 certificate
+	   loading from the kernel onto the '.ima' trusted keyring.
+
+config IMA_X509_PATH
+	string "IMA X509 certificate path"
+	depends on IMA_LOAD_X509
+	default "/etc/keys/x509_ima.der"
+	help
+	   This option defines IMA X509 certificate path.

security/integrity/ima/ima_api.c

···
 {
 	int flags = IMA_MEASURE | IMA_AUDIT | IMA_APPRAISE;
 
-	if (!ima_appraise)
-		flags &= ~IMA_APPRAISE;
+	flags &= ima_policy_flag;
 
 	return ima_match_policy(inode, function, mask, flags);
 }

security/integrity/ima/ima_init.c

···
 #include <crypto/hash_info.h>
 #include "ima.h"
 
+#ifdef CONFIG_IMA_X509_PATH
+#define IMA_X509_PATH	CONFIG_IMA_X509_PATH
+#else
+#define IMA_X509_PATH	"/etc/keys/x509_ima.der"
+#endif
+
 /* name for boot aggregate entry */
 static const char *boot_aggregate_name = "boot_aggregate";
 int ima_used_chip;
···
 			    audit_cause, result, 0);
 	return result;
 }
+
+#ifdef CONFIG_IMA_LOAD_X509
+void __init ima_load_x509(void)
+{
+	int unset_flags = ima_policy_flag & IMA_APPRAISE;
+
+	ima_policy_flag &= ~unset_flags;
+	integrity_load_x509(INTEGRITY_KEYRING_IMA, IMA_X509_PATH);
+	ima_policy_flag |= unset_flags;
+}
+#endif
 
 int __init ima_init(void)
 {

security/integrity/integrity.h

···
 }
 #endif
 
+#ifdef CONFIG_IMA_LOAD_X509
+void __init ima_load_x509(void);
+#else
+static inline void ima_load_x509(void)
+{
+}
+#endif
+
 #ifdef CONFIG_INTEGRITY_AUDIT
 /* declarations */
 void integrity_audit_msg(int audit_msgno, struct inode *inode,