Re: [PATCH v6 2/4] generic/574: corrupt btrfs merkle tree data

[Eric Biggers <ebiggers@kernel.org>]

On Mon, Feb 14, 2022 at 04:09:56PM -0800, Boris Burkov wrote:
> generic/574 has tests for corrupting the merkle tree data stored by the
> filesystem. Since btrfs uses a different scheme for storing this data,
> the existing logic for corrupting it doesn't work out of the box. Adapt
> it to properly corrupt btrfs merkle items.
> 
> This test relies on the btrfs implementation of fsverity in the patch:
> btrfs: initial fsverity support
> 
> and on btrfs-corrupt-block for corruption in the patches titled:
> btrfs-progs: corrupt generic item data with btrfs-corrupt-block
> btrfs-progs: expand corrupt_file_extent in btrfs-corrupt-block
> 
> Signed-off-by: Boris Burkov <boris@bur.io>
> ---
>  common/verity     | 18 ++++++++++++++++++
>  tests/generic/574 |  1 +
>  2 files changed, 19 insertions(+)
> 
> diff --git a/common/verity b/common/verity
> index eec8ae72..07d9d3fe 100644
> --- a/common/verity
> +++ b/common/verity
> @@ -322,6 +322,24 @@ _fsv_scratch_corrupt_merkle_tree()
>  		(( offset += ($(_get_filesize $file) + 65535) & ~65535 ))
>  		_fsv_scratch_corrupt_bytes $file $offset
>  		;;
> +	btrfs)
> +		local ino=$(stat -c '%i' $file)
> +		_scratch_unmount
> +		local byte=""
> +		while read -n 1 byte; do
> +			if [ -z $byte ]; then
> +				break
> +			fi

'[ -z $byte ]' could use quotes around $byte.  But isn't that check unneeded at
all, given that 'read' will fail when EOF is reached?

- Eric