fsverity: simplify fsverity_get_digest()

Instead of looking up the algorithm by name in hash_algo_name[] to get
its hash_algo ID, just store the hash_algo ID in the fsverity_hash_alg
struct.  Verify at boot time that every fsverity_hash_alg has a valid
hash_algo ID with matching digest size.

Remove an unnecessary memset() of the whole digest array to 0 before the
digest is copied into it.

Finally, remove the pr_debug statement.  There is already a pr_debug for
the fsverity digest when the file is opened.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Link: https://lore.kernel.org/r/20221129045139.69803-1-ebiggers@kernel.org

diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h
index dbe1ce5..c7fcb85 100644 (file)
--- a/fs/verity/fsverity_private.h
+++ b/fs/verity/fsverity_private.h
@@ -32,6 +32,11 @@ struct fsverity_hash_alg {
        unsigned int digest_size; /* digest size in bytes, e.g. 32 for SHA-256 */
        unsigned int block_size;  /* block size in bytes, e.g. 64 for SHA-256 */
        mempool_t req_pool;       /* mempool with a preallocated hash request */
+       /*
+        * The HASH_ALGO_* constant for this algorithm.  This is different from
+        * FS_VERITY_HASH_ALG_*, which uses a different numbering scheme.
+        */
+       enum hash_algo algo_id;
 };
 
 /* Merkle tree parameters: hash algorithm, initial hash state, and topology */

diff --git a/fs/verity/hash_algs.c b/fs/verity/hash_algs.c
index 71d0fcc..6f8170c 100644 (file)
--- a/fs/verity/hash_algs.c
+++ b/fs/verity/hash_algs.c
@@ -16,11 +16,13 @@ struct fsverity_hash_alg fsverity_hash_algs[] = {
                .name = "sha256",
                .digest_size = SHA256_DIGEST_SIZE,
                .block_size = SHA256_BLOCK_SIZE,
+               .algo_id = HASH_ALGO_SHA256,
        },
        [FS_VERITY_HASH_ALG_SHA512] = {
                .name = "sha512",
                .digest_size = SHA512_DIGEST_SIZE,
                .block_size = SHA512_BLOCK_SIZE,
+               .algo_id = HASH_ALGO_SHA512,
        },
 };
 
@@ -324,5 +326,9 @@ void __init fsverity_check_hash_algs(void)
                 */
                BUG_ON(!is_power_of_2(alg->digest_size));
                BUG_ON(!is_power_of_2(alg->block_size));
+
+               /* Verify that there is a valid mapping to HASH_ALGO_*. */
+               BUG_ON(alg->algo_id == 0);
+               BUG_ON(alg->digest_size != hash_digest_size[alg->algo_id]);
        }
 }

diff --git a/fs/verity/measure.c b/fs/verity/measure.c
index e99c003..5c79ea1 100644 (file)
--- a/fs/verity/measure.c
+++ b/fs/verity/measure.c
@@ -65,8 +65,7 @@ EXPORT_SYMBOL_GPL(fsverity_ioctl_measure);
  * @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.
+ * Assumption: before calling this, the file must have been opened.
  *
  * Return: 0 on success, -errno on failure
  */
@@ -76,27 +75,13 @@ int fsverity_get_digest(struct inode *inode,
 {
        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);
-
-       /* 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);
-
+       *alg = hash_alg->algo_id;
        return 0;
 }