[RFC][PATCH 1/5] fsverity: Introduce fsverity_get_file_digest()

Roberto Sassu
2021-11-12T12:44:58Z

Since the fsverity_info structure is defined internally in fsverity, expose
the fsverity file digest through the new function
fsverity_get_file_digest().

Given that an fsverity file is guaranteed to be immutable, also the
retrieved file digest is stable and won't change.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
fs/verity/open.c | 24 ++++++++++++++++++++++++
include/linux/fsverity.h | 10 ++++++++++
2 files changed, 34 insertions(+)

diff --git a/fs/verity/open.c b/fs/verity/open.c
index 92df87f5fa38..9127c77c6539 100644
--- a/fs/verity/open.c
+++ b/fs/verity/open.c
@@ -218,6 +218,30 @@ void fsverity_free_info(struct fsverity_info *vi)
kmem_cache_free(fsverity_info_cachep, vi);
}

+/*
+ * Copy the file digest and associated algorithm taken from the passed
+ * fsverity_info structure to the locations supplied by the caller.
+ *
+ * Return: the digest size on success, a negative value on error
+ */
+ssize_t fsverity_get_file_digest(struct fsverity_info *info, u8 *buf,
+ size_t bufsize, enum hash_algo *algo)
+{
+ enum hash_algo a;
+
+ a = match_string(hash_algo_name, HASH_ALGO__LAST,
+ info->tree_params.hash_alg->name);
+ if (a < 0)
+ return a;
+
+ if (bufsize < hash_digest_size[a])
+ return -ERANGE;
+
+ *algo = a;
+ memcpy(buf, info->file_digest, hash_digest_size[*algo]);
+ return hash_digest_size[*algo];
+}
+
static bool validate_fsverity_descriptor(struct inode *inode,
const struct fsverity_descriptor *desc,
size_t desc_size)
diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
index b568b3c7d095..877a7f609dd9 100644
--- a/include/linux/fsverity.h
+++ b/include/linux/fsverity.h
@@ -13,6 +13,7 @@

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

/* Verity operations for filesystems */
struct fsverity_operations {
@@ -137,6 +138,8 @@ int fsverity_ioctl_measure(struct file *filp, void __user *arg);
int fsverity_file_open(struct inode *inode, struct file *filp);
int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr);
void fsverity_cleanup_inode(struct inode *inode);
+ssize_t fsverity_get_file_digest(struct fsverity_info *info, u8 *buf,
+ size_t bufsize, enum hash_algo *algo);

/* read_metadata.c */

@@ -187,6 +190,13 @@ static inline void fsverity_cleanup_inode(struct inode *inode)
{
}

+static inline ssize_t fsverity_get_file_digest(struct fsverity_info *info,
+ u8 *buf, size_t bufsize,
+ enum hash_algo *algo)
+{
+ return -EOPNOTSUPP;
+}
+
/* read_metadata.c */

static inline int fsverity_ioctl_read_metadata(struct file *filp,
--
2.32.0