[PATCH 4/4] ima: support fs-verity file digest based signatures

[Mimi Zohar <zohar@xxxxxxxxxxxxx>]

Instead of calculating a file hash and verifying the signature stored
in the security.ima xattr against the calculated file hash, verify the
signature of the fs-verity's file digest.  The fs-verity file digest is
a hash that includes the Merkle tree root hash.

Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
---
 security/integrity/ima/ima_api.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index 179c7f0364c2..ee1701f8c0f3 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -16,6 +16,7 @@
 #include <linux/xattr.h>
 #include <linux/evm.h>
 #include <linux/iversion.h>
+#include <linux/fsverity.h>
 
 #include "ima.h"
 
@@ -205,6 +206,23 @@ int ima_get_action(struct user_namespace *mnt_userns, struct inode *inode,
 				allowed_algos);
 }
 
+static int ima_collect_verity_measurement(struct integrity_iint_cache *iint,
+					  struct ima_digest_data *hash)
+{
+	u8 verity_digest[FS_VERITY_MAX_DIGEST_SIZE];
+	enum hash_algo verity_alg;
+	int rc;
+
+	rc = fsverity_measure(iint->inode, verity_digest, &verity_alg);
+	if (rc)
+		return -EINVAL;
+	if (hash->algo != verity_alg)
+		return -EINVAL;
+	hash->length = hash_digest_size[verity_alg];
+	memcpy(hash->digest, verity_digest, hash->length);
+	return 0;
+}
+
 /*
  * ima_collect_measurement - collect file measurement
  *
@@ -256,6 +274,8 @@ int ima_collect_measurement(struct integrity_iint_cache *iint,
 
 	if (buf)
 		result = ima_calc_buffer_hash(buf, size, &hash.hdr);
+	else if (veritysig)
+		result = ima_collect_verity_measurement(iint, &hash.hdr);
 	else
 		result = ima_calc_file_hash(file, &hash.hdr);
 
-- 
2.27.0