[RFC PATCH v4 3/4] ima: define '.ima' as a builtin 'trusted' keyring

[Mimi Zohar <zohar@linux.vnet.ibm.com>]

Require all keys added to the IMA keyring be signed by an
existing trusted key on the system trusted keyring.

Changelog v1:
- don't link IMA trusted keyring to user keyring

Changelog:
- define stub integrity_init_keyring() function (reported-by Fengguang Wu)
- differentiate between regular and trusted keyring names.
- replace printk with pr_info (D. Kasatkin)
- only make the IMA keyring a trusted keyring (reported-by D. Kastatkin)
- define stub integrity_init_keyring() definition based on
  CONFIG_INTEGRITY_SIGNATURE, not CONFIG_INTEGRITY_ASYMMETRIC_KEYS.
  (reported-by Jim Davis)

Signed-off-by: Mimi Zohar<zohar@linux.vnet.ibm.com>
---
 security/integrity/digsig.c           | 26 +++++++++++++++++++++++++-
 security/integrity/ima/Kconfig        |  8 ++++++++
 security/integrity/ima/ima_appraise.c | 11 +++++++++++
 security/integrity/integrity.h        |  5 +++++
 4 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
index b4af4eb..7da5f9c 100644
--- a/security/integrity/digsig.c
+++ b/security/integrity/digsig.c
@@ -13,7 +13,9 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/err.h>
+#include <linux/sched.h>
 #include <linux/rbtree.h>
+#include <linux/cred.h>
 #include <linux/key-type.h>
 #include <linux/digsig.h>
 
@@ -24,7 +26,11 @@ static struct key *keyring[INTEGRITY_KEYRING_MAX];
 static const char *keyring_name[INTEGRITY_KEYRING_MAX] = {
 	"_evm",
 	"_module",
+#ifndef CONFIG_IMA_TRUSTED_KEYRING
 	"_ima",
+#else
+	".ima",
+#endif
 };
 
 int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen,
@@ -35,7 +41,7 @@ int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen,
 
 	if (!keyring[id]) {
 		keyring[id] =
-			request_key(&key_type_keyring, keyring_name[id], NULL);
+		    request_key(&key_type_keyring, keyring_name[id], NULL);
 		if (IS_ERR(keyring[id])) {
 			int err = PTR_ERR(keyring[id]);
 			pr_err("no %s keyring: %d\n", keyring_name[id], err);
@@ -56,3 +62,21 @@ int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen,
 
 	return -EOPNOTSUPP;
 }
+
+int integrity_init_keyring(const unsigned int id)
+{
+	const struct cred *cred = current_cred();
+
+	keyring[id] = keyring_alloc(keyring_name[id], KUIDT_INIT(0),
+				    KGIDT_INIT(0), cred,
+				    ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
+				      KEY_USR_VIEW | KEY_USR_READ |
+				      KEY_USR_WRITE | KEY_USR_SEARCH),
+				    KEY_ALLOC_NOT_IN_QUOTA, NULL);
+	if (!IS_ERR(keyring[id]))
+		set_bit(KEY_FLAG_TRUSTED_ONLY, &keyring[id]->flags);
+	else
+		pr_info("Can't allocate %s keyring (%ld)\n",
+			keyring_name[id], PTR_ERR(keyring[id]));
+	return 0;
+}
diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 81a2797..dad8d4c 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -123,3 +123,11 @@ config IMA_APPRAISE
 	  For more information on integrity appraisal refer to:
 	  <http://linux-ima.sourceforge.net>
 	  If unsure, say N.
+
+config IMA_TRUSTED_KEYRING
+	bool "Require all keys on the _ima keyring be signed"
+	depends on IMA_APPRAISE && SYSTEM_TRUSTED_KEYRING
+	default y
+	help
+	   This option requires that all keys added to the _ima
+	   keyring be signed by a key on the system trusted keyring.
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index d3113d4..003ff46 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -385,3 +385,14 @@ int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 	}
 	return result;
 }
+
+#ifdef CONFIG_IMA_TRUSTED_KEYRING
+static int __init init_ima_keyring(void)
+{
+	int ret;
+
+	ret = integrity_init_keyring(INTEGRITY_KEYRING_IMA);
+	return 0;
+}
+late_initcall(init_ima_keyring);
+#endif
diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
index 33c0a70..09c440d 100644
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -124,6 +124,7 @@ struct integrity_iint_cache *integrity_iint_find(struct inode *inode);
 int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen,
 			    const char *digest, int digestlen);
 
+int integrity_init_keyring(const unsigned int id);
 #else
 
 static inline int integrity_digsig_verify(const unsigned int id,
@@ -133,6 +134,10 @@ static inline int integrity_digsig_verify(const unsigned int id,
 	return -EOPNOTSUPP;
 }
 
+static inline int integrity_init_keyring(const unsigned int id)
+{
+	return 0;
+}
 #endif /* CONFIG_INTEGRITY_SIGNATURE */
 
 #ifdef CONFIG_INTEGRITY_ASYMMETRIC_KEYS
-- 
1.8.1.4