[PATCH 1/4] fs-verity: define a function to return the integrity protected file digest

Mimi Zohar
2021-11-29T17:03:36Z

Define a function named fsverity_measure() to return the verity file digest
and the associated hash algorithm (enum hash_algo).

Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
---
fs/verity/fsverity_private.h | 6 -----
fs/verity/measure.c | 49 ++++++++++++++++++++++++++++++++++++
include/linux/fsverity.h | 17 +++++++++++++
3 files changed, 66 insertions(+), 6 deletions(-)

diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h
index a7920434bae5..54c5f0993541 100644
--- a/fs/verity/fsverity_private.h
+++ b/fs/verity/fsverity_private.h
@@ -26,12 +26,6 @@ struct ahash_request;
*/
#define FS_VERITY_MAX_LEVELS 8

-/*
- * Largest digest size among all hash algorithms supported by fs-verity.
- * Currently assumed to be <= size of fsverity_descriptor::root_hash.
- */
-#define FS_VERITY_MAX_DIGEST_SIZE SHA512_DIGEST_SIZE
-
/* A hash algorithm supported by fs-verity */
struct fsverity_hash_alg {
struct crypto_ahash *tfm; /* hash tfm, allocated on demand */
diff --git a/fs/verity/measure.c b/fs/verity/measure.c
index f0d7b30c62db..98d8f6f2a2be 100644
--- a/fs/verity/measure.c
+++ b/fs/verity/measure.c
@@ -57,3 +57,52 @@ int fsverity_ioctl_measure(struct file *filp, void __user *_uarg)
return 0;
}
EXPORT_SYMBOL_GPL(fsverity_ioctl_measure);
+
+/**
+ * fsverity_measure() - get a verity file's digest
+ * @inode: inode to get digest of
+ * @digest: pointer to the digest
+ * @alg: pointer to the hash algorithm enumeration
+ *
+ * Return the file hash algorithm, digest size, and digest of an fsverity
+ * protected file.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fsverity_measure(struct inode *inode, u8 digest[FS_VERITY_MAX_DIGEST_SIZE],
+ enum hash_algo *alg)
+{
+ const struct fsverity_info *vi;
+ const struct fsverity_hash_alg *hash_alg;
+ int i;
+
+ vi = fsverity_get_info(inode);
+ if (!vi)
+ return -ENODATA; /* not a verity file */
+
+ hash_alg = vi->tree_params.hash_alg;
+ memset(digest, 0, FS_VERITY_MAX_DIGEST_SIZE);
+ *alg = HASH_ALGO__LAST;
+
+ /* convert hash algorithm to hash_algo_name */
+ for (i = 0; i < HASH_ALGO__LAST; i++) {
+ pr_debug("name %s hash_algo_name[%d] %s\n",
+ hash_alg->name, i, hash_algo_name[i]);
+
+ if (!strcmp(hash_alg->name, hash_algo_name[i])) {
+ *alg = i;
+ break;
+ }
+ }
+
+ /* Shouldn't happen */
+ if (*alg == HASH_ALGO__LAST)
+ return -EINVAL;
+
+ memcpy(digest, vi->file_digest, hash_alg->digest_size);
+
+ pr_debug("file digest:%s %*phN\n", hash_algo_name[*alg],
+ hash_digest_size[*alg], digest);
+
+ return 0;
+}
diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
index b568b3c7d095..11006b60713b 100644
--- a/include/linux/fsverity.h
+++ b/include/linux/fsverity.h
@@ -12,8 +12,16 @@
#define _LINUX_FSVERITY_H

#include <linux/fs.h>
+#include <crypto/hash_info.h>
+#include <crypto/sha2.h>
#include <uapi/linux/fsverity.h>

+/*
+ * Largest digest size among all hash algorithms supported by fs-verity.
+ * Currently assumed to be <= size of fsverity_descriptor::root_hash.
+ */
+#define FS_VERITY_MAX_DIGEST_SIZE SHA512_DIGEST_SIZE
+
/* Verity operations for filesystems */
struct fsverity_operations {

@@ -131,6 +139,8 @@ int fsverity_ioctl_enable(struct file *filp, const void __user *arg);
/* measure.c */

int fsverity_ioctl_measure(struct file *filp, void __user *arg);
+int fsverity_measure(struct inode *inode, u8 digest[FS_VERITY_MAX_DIGEST_SIZE],
+ enum hash_algo *alg);

/* open.c */

@@ -170,6 +180,13 @@ static inline int fsverity_ioctl_measure(struct file *filp, void __user *arg)
return -EOPNOTSUPP;
}

+static inline int fsverity_measure(struct inode *inode,
+ u8 digest[FS_VERITY_MAX_DIGEST_SIZE],
+ enum hash_algo *alg)
+{
+ return -EOPNOTSUPP;
+}
+
/* open.c */

static inline int fsverity_file_open(struct inode *inode, struct file *filp)
--
2.27.0