ima: integrity appraisal extension

IMA currently maintains an integrity measurement list used to assert the
integrity of the running system to a third party.  The IMA-appraisal
extension adds local integrity validation and enforcement of the
measurement against a "good" value stored as an extended attribute
'security.ima'.  The initial methods for validating 'security.ima' are
hashed based, which provides file data integrity, and digital signature
based, which in addition to providing file data integrity, provides
authenticity.

This patch creates and maintains the 'security.ima' xattr, containing
the file data hash measurement.  Protection of the xattr is provided by
EVM, if enabled and configured.

Based on policy, IMA calls evm_verifyxattr() to verify a file's metadata
integrity and, assuming success, compares the file's current hash value
with the one stored as an extended attribute in 'security.ima'.

Changelov v4:
- changed iint cache flags to hex values

Changelog v3:
- change appraisal default for filesystems without xattr support to fail

Changelog v2:
- fix audit msg 'res' value
- removed unused 'ima_appraise=' values

Changelog v1:
- removed unused iint mutex (Dmitry Kasatkin)
- setattr hook must not reset appraised (Dmitry Kasatkin)
- evm_verifyxattr() now differentiates between no 'security.evm' xattr
  (INTEGRITY_NOLABEL) and no EVM 'protected' xattrs included in the
  'security.evm' (INTEGRITY_NOXATTRS).
- replace hash_status with ima_status (Dmitry Kasatkin)
- re-initialize slab element ima_status on free (Dmitry Kasatkin)
- include 'security.ima' in EVM if CONFIG_IMA_APPRAISE, not CONFIG_IMA
- merged half "ima: ima_must_appraise_or_measure API change" (Dmitry Kasatkin)
- removed unnecessary error variable in process_measurement() (Dmitry Kasatkin)
- use ima_inode_post_setattr() stub function, if IMA_APPRAISE not configured
  (moved ima_inode_post_setattr() to ima_appraise.c)
- make sure ima_collect_measurement() can read file

Changelog:
- add 'iint' to evm_verifyxattr() call (Dimitry Kasatkin)
- fix the race condition between chmod, which takes the i_mutex and then
  iint->mutex, and ima_file_free() and process_measurement(), which take
  the locks in the reverse order, by eliminating iint->mutex. (Dmitry Kasatkin)
- cleanup of ima_appraise_measurement() (Dmitry Kasatkin)
- changes as a result of the iint not allocated for all regular files, but
  only for those measured/appraised.
- don't try to appraise new/empty files
- expanded ima_appraisal description in ima/Kconfig
- IMA appraise definitions required even if IMA_APPRAISE not enabled
- add return value to ima_must_appraise() stub
- unconditionally set status = INTEGRITY_PASS *after* testing status,
  not before.  (Found by Joe Perches)

Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>

1 files changed, 36 insertions, 14 deletions

diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index 032ff03ad90..41cce84416c 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -9,13 +9,17 @@
  * License.
  *
  * File: ima_api.c
- *	Implements must_measure, collect_measurement, store_measurement,
- *	and store_template.
+ *	Implements must_appraise_or_measure, collect_measurement,
+ *	appraise_measurement, store_measurement and store_template.
  */
 #include <linux/module.h>
 #include <linux/slab.h>
-
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/xattr.h>
+#include <linux/evm.h>
 #include "ima.h"
+
 static const char *IMA_TEMPLATE_NAME = "ima";
 
 /*
@@ -93,7 +97,7 @@ err_out:
 }
 
 /**
- * ima_must_measure - measure decision based on policy.
+ * ima_must_appraise_or_measure - appraise & measure decision based on policy.
  * @inode: pointer to inode to measure
  * @mask: contains the permission mask (MAY_READ, MAY_WRITE, MAY_EXECUTE)
  * @function: calling function (FILE_CHECK, BPRM_CHECK, FILE_MMAP)
@@ -105,15 +109,22 @@ err_out:
  * 	mask: contains the permission mask
  *	fsmagic: hex value
  *
- * Return 0 to measure. For matching a DONT_MEASURE policy, no policy,
- * or other error, return an error code.
-*/
-int ima_must_measure(struct inode *inode, int mask, int function)
+ * Returns IMA_MEASURE, IMA_APPRAISE mask.
+ *
+ */
+int ima_must_appraise_or_measure(struct inode *inode, int mask, int function)
 {
-	int must_measure;
+	int flags = IMA_MEASURE | IMA_APPRAISE;
+
+	if (!ima_appraise)
+		flags &= ~IMA_APPRAISE;
+
+	return ima_match_policy(inode, function, mask, flags);
+}
 
-	must_measure = ima_match_policy(inode, function, mask);
-	return must_measure ? 0 : -EACCES;
+int ima_must_measure(struct inode *inode, int mask, int function)
+{
+	return ima_match_policy(inode, function, mask, IMA_MEASURE);
 }
 
 /*
@@ -129,16 +140,24 @@ int ima_must_measure(struct inode *inode, int mask, int function)
 int ima_collect_measurement(struct integrity_iint_cache *iint,
 			    struct file *file)
 {
-	int result = -EEXIST;
+	struct inode *inode = file->f_dentry->d_inode;
+	const char *filename = file->f_dentry->d_name.name;
+	int result = 0;
 
-	if (!(iint->flags & IMA_MEASURED)) {
+	if (!(iint->flags & IMA_COLLECTED)) {
 		u64 i_version = file->f_dentry->d_inode->i_version;
 
 		memset(iint->digest, 0, IMA_DIGEST_SIZE);
 		result = ima_calc_hash(file, iint->digest);
-		if (!result)
+		if (!result) {
 			iint->version = i_version;
+			iint->flags |= IMA_COLLECTED;
+		}
 	}
+	if (result)
+		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode,
+				    filename, "collect_data", "failed",
+				    result, 0);
 	return result;
 }
 
@@ -167,6 +186,9 @@ void ima_store_measurement(struct integrity_iint_cache *iint,
 	struct ima_template_entry *entry;
 	int violation = 0;
 
+	if (iint->flags & IMA_MEASURED)
+		return;
+
 	entry = kmalloc(sizeof(*entry), GFP_KERNEL);
 	if (!entry) {
 		integrity_audit_msg(AUDIT_INTEGRITY_PCR, inode, filename,