On Fri, Nov 12, 2021 at 2:36 AM Qu Wenruo <wqu@xxxxxxxx> wrote:
>
> Since kernel commit d4088803f511 ("btrfs: subpage: make lzo_compress_pages()
> compatible"), lzo compression no longer respects the max compressed page
> limit, and can cause kernel crash.
>
> The fix is titled "btrfs: fix a out-of-boundary access for
> copy_compressed_data_to_page()".
>
> This patch will add such regression test for compress-force=lzo mount
> option against incompressible data.
>
> Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
> ---
> tests/btrfs/049 | 41 +++++++++++++++++++++++++++++++++++++++++
> tests/btrfs/049.out | 1 +
> 2 files changed, 42 insertions(+)
> create mode 100755 tests/btrfs/049
>
> diff --git a/tests/btrfs/049 b/tests/btrfs/049
> new file mode 100755
> index 00000000..5a73f738
> --- /dev/null
> +++ b/tests/btrfs/049
> @@ -0,0 +1,41 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (C) 2021 SUSE Linux Products GmbH. All Rights Reserved.
> +#
> +# FS QA Test 049
> +#
> +# Test if btrfs will crash when compress-force=lzo hits incompressible data
> +#
> +. ./common/preamble
> +_begin_fstest auto quick compress dangerous
> +
> +# Override the default cleanup function.
> +# _cleanup()
> +# {
> +# cd /
> +# rm -r -f $tmp.*
> +# }
> +
> +# Import common functions.
> +# . ./common/filter
> +
> +# real QA test starts here
> +
> +# Modify as appropriate.
> +_supported_fs btrfs
> +_require_scratch
> +
> +_scratch_mkfs >> $seqres.full
> +_scratch_mount -o compress-force=lzo
> +
> +$XFS_IO_PROG -f -c "pwrite -i /dev/urandom 0 4k" $SCRATCH_MNT/file > /dev/null
While at it, instead of just having the minimum to trigger that
specific bug, it would also be good to:
1) Try with zlib and zstd, instead of only lzo. This way it will help
more easily catch any future regression with those algorithms;
2) Instead of redirecting to /dev/null and ignoring if we are actually
writing what we are supposed to do, can we verify that we write all
the bytes - i.e. that there's no short write?
3) After unmount, we could also mount the fs again and check if we are
able to read exactly what we tried to write - that the write was
persisted and we're not reading from the page cache.
Thanks.
> +
> +# With kernel commit d4088803f511 ("btrfs: subpage: make lzo_compress_pages()
> +# compatible"), the kernel would crash when writing back above data.
> +_scratch_unmount
> +
> +echo "Silence is golden"
> +
> +# success, all done
> +status=0
> +exit
> diff --git a/tests/btrfs/049.out b/tests/btrfs/049.out
> index cb0061b3..c69568ad 100644
> --- a/tests/btrfs/049.out
> +++ b/tests/btrfs/049.out
> @@ -1 +1,2 @@
> QA output created by 049
> +Silence is golden
> --
> 2.33.0
>
--
Filipe David Manana,
“Whether you think you can, or you think you can't — you're right.”
