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Date: Wed, 26 Apr 2023 14:47:43 -0700
From: Eric Biggers <ebiggers@kernel.org>
To: Alexander Larsson <alexl@redhat.com>
Cc: miklos@szeredi.hu, linux-unionfs@vger.kernel.org, amir73il@gmail.com,
	tytso@mit.edu, fsverity@lists.linux.dev
Subject: Re: [PATCH 5/6] ovl: Validate verity xattr when resolving lowerdata
Message-ID: <20230426214743.GA58528@sol.localdomain>
References: <cover.1681917551.git.alexl@redhat.com>
 <df41e9dc96ddad9f9e1e684e39c28f4e097e9d9b.1681917551.git.alexl@redhat.com>
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In-Reply-To: <df41e9dc96ddad9f9e1e684e39c28f4e097e9d9b.1681917551.git.alexl@redhat.com>

On Thu, Apr 20, 2023 at 09:44:04AM +0200, Alexander Larsson wrote:
> +	err = fsverity_get_digest(d_inode(datapath->dentry), actual_digest, &verity_algo);
> +	if (err < 0) {
> +		pr_warn_ratelimited("lower file '%pd' has no fs-verity digest\n", datapath->dentry);
> +		return -EIO;
> +	}
> +
> +	if (digest_len != hash_digest_size[verity_algo] ||
> +	    memcmp(required_digest, actual_digest, digest_len) != 0) {
> +		pr_warn_ratelimited("lower file '%pd' has the wrong fs-verity digest\n",
> +				    datapath->dentry);
> +		return -EIO;
> +	}
> +
> +	return 0;

This is incorrect because the digest algorithm is not being compared.

- Eric