On 2022/3/26 6:38, Mimi Zohar wrote:
Define a function named fsverity_get_digest() to return the verity file
digest and the associated hash algorithm (enum hash_algo).
This assumes that before calling fsverity_get_digest() the file must have
been opened, which is even true for the IMA measure/appraise on file
open policy rule use case (func=FILE_CHECK). do_open() calls vfs_open()
immediately prior to ima_file_check().
Acked-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
---
fs/verity/Kconfig | 1 +
fs/verity/fsverity_private.h | 7 ------
fs/verity/measure.c | 43 ++++++++++++++++++++++++++++++++++++
include/linux/fsverity.h | 18 +++++++++++++++
4 files changed, 62 insertions(+), 7 deletions(-)
diff --git a/fs/verity/Kconfig b/fs/verity/Kconfig
index 24d1b54de807..54598cd80145 100644
--- a/fs/verity/Kconfig
+++ b/fs/verity/Kconfig
@@ -3,6 +3,7 @@
config FS_VERITY
bool "FS Verity (read-only file-based authenticity protection)"
select CRYPTO
+ select CRYPTO_HASH_INFO
# SHA-256 is implied as it's intended to be the default hash algorithm.
# To avoid bloat, other wanted algorithms must be selected explicitly.
# Note that CRYPTO_SHA256 denotes the generic C implementation, but
diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h
index a7920434bae5..c6fb62e0ef1a 100644
--- a/fs/verity/fsverity_private.h
+++ b/fs/verity/fsverity_private.h
@@ -14,7 +14,6 @@
#define pr_fmt(fmt) "fs-verity: " fmt
-#include <crypto/sha2.h>
#include <linux/fsverity.h>
#include <linux/mempool.h>
@@ -26,12 +25,6 @@ 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..e99c00350c28 100644
--- a/fs/verity/measure.c
+++ b/fs/verity/measure.c
@@ -57,3 +57,46 @@ int fsverity_ioctl_measure(struct file *filp, void __user *_uarg)
return 0;
}
EXPORT_SYMBOL_GPL(fsverity_ioctl_measure);
+
+/**
+ * fsverity_get_digest() - get a verity file's digest
+ * @inode: inode to get digest of
+ * @digest: (out) pointer to the digest
+ * @alg: (out) pointer to the hash algorithm enumeration
+ *
+ * Return the file hash algorithm and digest of an fsverity protected file.
+ * Assumption: before calling fsverity_get_digest(), the file must have been
+ * opened.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fsverity_get_digest(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);
Hi Mimi,
I would suggest moving this memset downward right before the memcpy.
+
+ /* convert the verity hash algorithm name to a hash_algo_name enum */
+ i = match_string(hash_algo_name, HASH_ALGO__LAST, hash_alg->name);
+ if (i < 0)
+ return -EINVAL;
+ *alg = i;
+
+ if (WARN_ON_ONCE(hash_alg->digest_size != hash_digest_size[*alg]))
+ 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;
+}
--
Best
GUO Zihua
