Re: [PATCH v5 21/24] xfs: add fs-verity support

[Eric Biggers <ebiggers@kernel.org>]

On Mon, Mar 04, 2024 at 08:10:44PM +0100, Andrey Albershteyn wrote:
> +static void
> +xfs_verity_put_listent(
> +	struct xfs_attr_list_context	*context,
> +	int				flags,
> +	unsigned char			*name,
> +	int				namelen,
> +	int				valuelen)
> +{
> +	struct fsverity_blockbuf	block = {
> +		.offset = xfs_fsverity_name_to_block_offset(name),
> +		.size = valuelen,
> +	};
> +	/*
> +	 * Verity descriptor is smaller than 1024; verity block min size is
> +	 * 1024. Exclude verity descriptor
> +	 */
> +	if (valuelen < 1024)
> +		return;
> +

Is there no way to directly check whether it's the verity descriptor?  The
'valuelen < 1024' check is fragile because it will break if support for smaller
Merkle tree block sizes is ever added.  (Silently, because this is doing
invalidation which is hard to test and we need to be super careful with.)

If you really must introduce the assumption that the Merkle tree block size is
at least 1024, this needs to be documented in the comment in
fsverity_init_merkle_tree_params() that explains the reasoning behind the
current restrictions on the Merkle tree block size.

- Eric