linux-kernel - Re: [PATCH v3 3/8] fs-verity: define a function to return the integrity protected file digest

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Message-ID: <YfiCc9XXzbQz9rqy@sol.localdomain>
Date:   Mon, 31 Jan 2022 16:44:35 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     linux-integrity@...r.kernel.org,
        Stefan Berger <stefanb@...ux.ibm.com>,
        linux-fscrypt@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/8] fs-verity: define a function to return the
 integrity protected file digest

On Tue, Jan 25, 2022 at 07:06:53PM -0500, Mimi Zohar wrote:
> +	hash_alg = vi->tree_params.hash_alg;
> +	memset(digest, 0, FS_VERITY_MAX_DIGEST_SIZE);
> +
> +	/* convert hash algorithm to hash_algo_name */
> +	i = match_string(hash_algo_name, HASH_ALGO__LAST, hash_alg->name);
> +	if (i < 0)
> +		return -EINVAL;
> +	*alg = i;

The above comment is backwards.  This code is converting a hash algorithm name
to an ID.  The comment is unclear, but it sounds like it's saying the opposite.

> +
> +	memcpy(digest, vi->file_digest, hash_alg->digest_size);

Here there are two "sources of truth" for the digest size.  How about checking
that they are the same:

	if (WARN_ON_ONCE(hash_alg->digest_size != hash_digest_size[*alg]))
		return -EINVAL;

- Eric