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

1 files changed, 6 insertions, 0 deletions

diff --git a/fs/verity/hash_algs.c b/fs/verity/hash_algs.c
index 71d0fccb6d4c..6f8170cf4ae7 100644
--- 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]);
 	}
 }