Commit a4bbf53d authored by Eric Biggers's avatar Eric Biggers
Browse files

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: default avatarEric Biggers <ebiggers@google.com>
Reviewed-by: default avatarMimi Zohar <zohar@linux.ibm.com>
Link: https://lore.kernel.org/r/20221129045139.69803-1-ebiggers@kernel.org
parent 98dc08ba

fs/verity/fsverity_private.h

+5 −0
Original line number Diff line number Diff line
@@ -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 */

fs/verity/hash_algs.c

+6 −0
Original line number Diff line number Diff line
@@ -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]);

	}

}

fs/verity/measure.c

+2 −17
Original line number Diff line number Diff line
@@ -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;

}