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

[Mimi Zohar <zohar@xxxxxxxxxxxxx>]

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@xxxxxxxxxxxxx>
---
 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