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authorEric Biggers <ebiggers@google.com>2023-06-12 12:00:47 -0700
committerEric Biggers <ebiggers@google.com>2023-06-14 10:41:07 -0700
commit74836ecbc5c7565d24a770917644e96af3e98d25 (patch)
tree097ae681bdb906c38d3da394b388fc17de5b71e3 /fs/verity
parent13e2408d02dd12a3b46bf8a29b3ae4f6119fc520 (diff)
fsverity: rework fsverity_get_digest() again
Address several issues with the calling convention and documentation of fsverity_get_digest(): - Make it provide the hash algorithm as either a FS_VERITY_HASH_ALG_* value or HASH_ALGO_* value, at the caller's choice, rather than only a HASH_ALGO_* value as it did before. This allows callers to work with the fsverity native algorithm numbers if they want to. HASH_ALGO_* is what IMA uses, but other users (e.g. overlayfs) should use FS_VERITY_HASH_ALG_* to match fsverity-utils and the fsverity UAPI. - Make it return the digest size so that it doesn't need to be looked up separately. Use the return value for this, since 0 works nicely for the "file doesn't have fsverity enabled" case. This also makes it clear that no other errors are possible. - Rename the 'digest' parameter to 'raw_digest' and clearly document that it is only useful in combination with the algorithm ID. This hopefully clears up a point of confusion. - Export it to modules, since overlayfs will need it for checking the fsverity digests of lowerdata files (https://lore.kernel.org/r/dd294a44e8f401e6b5140029d8355f88748cd8fd.1686565330.git.alexl@redhat.com). Acked-by: Mimi Zohar <zohar@linux.ibm.com> # for the IMA piece Link: https://lore.kernel.org/r/20230612190047.59755-1-ebiggers@kernel.org Signed-off-by: Eric Biggers <ebiggers@google.com>
Diffstat (limited to 'fs/verity')
-rw-r--r--fs/verity/measure.c37
1 files changed, 26 insertions, 11 deletions
diff --git a/fs/verity/measure.c b/fs/verity/measure.c
index 5c79ea1b2468..eec5956141da 100644
--- a/fs/verity/measure.c
+++ b/fs/verity/measure.c
@@ -61,27 +61,42 @@ 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
+ * @raw_digest: (out) the raw file digest
+ * @alg: (out) the digest's algorithm, as a FS_VERITY_HASH_ALG_* value
+ * @halg: (out) the digest's algorithm, as a HASH_ALGO_* value
*
- * Return the file hash algorithm and digest of an fsverity protected file.
- * Assumption: before calling this, the file must have been opened.
+ * Retrieves the fsverity digest of the given file. The file must have been
+ * opened at least once since the inode was last loaded into the inode cache;
+ * otherwise this function will not recognize when fsverity is enabled.
*
- * Return: 0 on success, -errno on failure
+ * The file's fsverity digest consists of @raw_digest in combination with either
+ * @alg or @halg. (The caller can choose which one of @alg or @halg to use.)
+ *
+ * IMPORTANT: Callers *must* make use of one of the two algorithm IDs, since
+ * @raw_digest is meaningless without knowing which algorithm it uses! fsverity
+ * provides no security guarantee for users who ignore the algorithm ID, even if
+ * they use the digest size (since algorithms can share the same digest size).
+ *
+ * Return: The size of the raw digest in bytes, or 0 if the file doesn't have
+ * fsverity enabled.
*/
int fsverity_get_digest(struct inode *inode,
- u8 digest[FS_VERITY_MAX_DIGEST_SIZE],
- enum hash_algo *alg)
+ u8 raw_digest[FS_VERITY_MAX_DIGEST_SIZE],
+ u8 *alg, enum hash_algo *halg)
{
const struct fsverity_info *vi;
const struct fsverity_hash_alg *hash_alg;
vi = fsverity_get_info(inode);
if (!vi)
- return -ENODATA; /* not a verity file */
+ return 0; /* not a verity file */
hash_alg = vi->tree_params.hash_alg;
- memcpy(digest, vi->file_digest, hash_alg->digest_size);
- *alg = hash_alg->algo_id;
- return 0;
+ memcpy(raw_digest, vi->file_digest, hash_alg->digest_size);
+ if (alg)
+ *alg = hash_alg - fsverity_hash_algs;
+ if (halg)
+ *halg = hash_alg->algo_id;
+ return hash_alg->digest_size;
}
+EXPORT_SYMBOL_GPL(fsverity_get_digest);