Re: [PATCH v2] fstests: generic: add a test case to check fsverity reads

[Dhruva G <goledhruva@gmail.com>]

On 10-10-2026 14:34, Qu Wenruo wrote:
> There is a bug report that with the recently enabled large folios

Do you want to perhaps add a link to this bug report? Just for more context,
no hard requirement as such.

> support, fsverity enabled files on btrfs can trigger reproducible
> warnings about file corruption, but in the end no error is returned to
> user space.
> 
> It turns out to be a bug in the btrfs fsverity integration, where blocks
> not included in the read range are passed to be verified.
> 
> This is a long-standing bug where btrfs fsverity always assumed that one
> folio contains exactly one fs block, ignoring the fact that btrfs had
> block size < page size support before fsverity support was added.
> 
> Add a new regression test case for it. The workload is pretty simple:
> 
> - Create a 32M file
> 
> - Punch a 64K hole for every 128K
>   This will limit the read bio size to 64K, which is smaller than
>   a lot of large folios, and thus can trigger the btrfs bug.
> 
> - Enable fsverity digest and drop page cache
> 
> - Read that file
> 
> - Verify there is no "FILE CORRUPTED!" warning
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
> Changelog
> v2:
> - Do not use btrfs specific mount options to limit read bio size
>   Use holes to limit the size of read bios instead, now the test case
>   can be generic other than btrfs specific.
> 
> - Add the missing _require_check_dmesg call
> 
> v1:
> https://lore.kernel.org/linux-btrfs/20261010032508.36935-1-wqu@suse.com/
> ---
>  tests/generic/807     | 56 +++++++++++++++++++++++++++++++++++++++++++
>  tests/generic/807.out |  2 ++
>  2 files changed, 58 insertions(+)
>  create mode 100755 tests/generic/807
>  create mode 100644 tests/generic/807.out
> 
> diff --git a/tests/generic/807 b/tests/generic/807
> new file mode 100755
> index 00000000..24e22e8c
> --- /dev/null
> +++ b/tests/generic/807
> @@ -0,0 +1,56 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2026 SUSE S.A.  All Rights Reserved.
> +#
> +# FS QA Test 807
> +#
> +# Verify that reading a large file with holes won't trigger fsverity warnings
> +#
> +. ./common/preamble
> +_begin_fstest auto quick verity
> +
> +_fixed_by_fs_commit btrfs xxxxxxxxxxxx \
> +	"btrfs: fix the fsverity callback where unexpected range is verified"
> +
> +. ./common/verity
> +
> +_require_xfs_io_command "fpunch"
> +_require_check_dmesg
> +_require_scratch_verity
> +
> +filesize=$(( 32 * 1024 * 1024 ))
> +interval=$(( 128 * 1024 ))
> +holesize=$(( 64 * 1024 ))
> +
> +_scratch_mkfs_verity >> $seqres.full
> +_scratch_mount
> +
> +# Create a large enough file so that readahead is triggered, and
> +# large folios are allocated during readahead.
> +_pwrite_byte "0xcd" 0 "$filesize" "$SCRATCH_MNT/foobar" > /dev/null
> +
> +# Create a hole for every $interval bytes. This should limit the read to
> +# $(( $interval - $holesize)), which should be much smaller than the maximum
> +# folio size (2M for x86_64).
> +for (( i = 0; i < $(( $filesize / $interval )); i++ )); do
> +	$XFS_IO_PROG -c "fpunch $(( $i * $interval )) $holesize" \
> +		"$SCRATCH_MNT/foobar" > /dev/null
> +done
> +
> +_fsv_enable "$SCRATCH_MNT/foobar"

Could this disable signature enforcement with _disable_fsverity_signatures
and restore it from _cleanup(), as generic/572 and generic/788 do?

With fs.verity.require_signatures=1, _require_scratch_verity() succeeds:
_fsv_can_enable() temporarily disables signature enforcement and then
restores it. The later _fsv_enable() therefore fails with EPERM because
foobar is unsigned. I reproduced the output mismatch in the local Btrfs
VM; the same test passed with require_signatures=0

> +
> +# Cycle mount to drop page cache
> +_scratch_cycle_mount
> +
> +# Read the file, unpatched btrfs will verify blocks outside the read range and
> +# trigger fs-verity warnings.
> +# But the read itself should still be fine, as the failed part will be retried.
> +cat "$SCRATCH_MNT/foobar" > /dev/null
> +
> +# Check for any kernel warnings from fs-verity on file corruption.
> +if _check_dmesg_for "FILE CORRUPTED!"; then
> +	echo "fs-verity detected corruption"
> +fi
> +echo "Silence is golden"
> +
> +_exit 0
> diff --git a/tests/generic/807.out b/tests/generic/807.out
> new file mode 100644
> index 00000000..3752a5f7
> --- /dev/null
> +++ b/tests/generic/807.out
> @@ -0,0 +1,2 @@
> +QA output created by 807
> +Silence is golden