ima: permit fsverity's file digests in the IMA measurement list

Permit fsverity's file digest (a hash of struct fsverity_descriptor) to
be included in the IMA measurement list, based on the new measurement
policy rule 'digest_type=verity' option.

To differentiate between a regular IMA file hash from an fsverity's
file digest, use the new d-ngv2 format field included in the ima-ngv2
template.

The following policy rule requires fsverity file digests and specifies
the new 'ima-ngv2' template, which contains the new 'd-ngv2' field.  The
policy rule may be constrained, for example based on a fsuuid or LSM
label.

measure func=FILE_CHECK digest_type=verity template=ima-ngv2

Acked-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

1 files changed, 44 insertions, 3 deletions

diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index c6805af46211..c1e76282b5ee 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -14,6 +14,7 @@
 #include <linux/xattr.h>
 #include <linux/evm.h>
 #include <linux/iversion.h>
+#include <linux/fsverity.h>
 
 #include "ima.h"
 
@@ -200,6 +201,32 @@ int ima_get_action(struct user_namespace *mnt_userns, struct inode *inode,
 				allowed_algos);
 }
 
+static int ima_get_verity_digest(struct integrity_iint_cache *iint,
+				 struct ima_max_digest_data *hash)
+{
+	enum hash_algo verity_alg;
+	int ret;
+
+	/*
+	 * On failure, 'measure' policy rules will result in a file data
+	 * hash containing 0's.
+	 */
+	ret = fsverity_get_digest(iint->inode, hash->digest, &verity_alg);
+	if (ret)
+		return ret;
+
+	/*
+	 * Unlike in the case of actually calculating the file hash, in
+	 * the fsverity case regardless of the hash algorithm, return
+	 * the verity digest to be included in the measurement list. A
+	 * mismatch between the verity algorithm and the xattr signature
+	 * algorithm, if one exists, will be detected later.
+	 */
+	hash->hdr.algo = verity_alg;
+	hash->hdr.length = hash_digest_size[verity_alg];
+	return 0;
+}
+
 /*
  * ima_collect_measurement - collect file measurement
  *
@@ -242,16 +269,30 @@ int ima_collect_measurement(struct integrity_iint_cache *iint,
 	 */
 	i_version = inode_query_iversion(inode);
 	hash.hdr.algo = algo;
+	hash.hdr.length = hash_digest_size[algo];
 
 	/* Initialize hash digest to 0's in case of failure */
 	memset(&hash.digest, 0, sizeof(hash.digest));
 
-	if (buf)
+	if (iint->flags & IMA_VERITY_REQUIRED) {
+		result = ima_get_verity_digest(iint, &hash);
+		switch (result) {
+		case 0:
+			break;
+		case -ENODATA:
+			audit_cause = "no-verity-digest";
+			break;
+		default:
+			audit_cause = "invalid-verity-digest";
+			break;
+		}
+	} else if (buf) {
 		result = ima_calc_buffer_hash(buf, size, &hash.hdr);
-	else
+	} else {
 		result = ima_calc_file_hash(file, &hash.hdr);
+	}
 
-	if (result && result != -EBADF && result != -EINVAL)
+	if (result == -ENOMEM)
 		goto out;
 
 	length = sizeof(hash.hdr) + hash.hdr.length;