CVE-2026-53040: ocfs2: validate bg_bits during freefrag scan

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

ocfs2: validate bg_bits during freefrag scan

[BUG]
A crafted filesystem can trigger an out-of-bounds bitmap walk when
OCFS2_IOC_INFO is issued with OCFS2_INFO_FL_NON_COHERENT.

BUG: KASAN: use-after-free in instrument_atomic_read include/linux/instrumented.h:68 [inline]
BUG: KASAN: use-after-free in _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
BUG: KASAN: use-after-free in test_bit_le include/asm-generic/bitops/le.h:21 [inline]
BUG: KASAN: use-after-free in ocfs2_info_freefrag_scan_chain fs/ocfs2/ioctl.c:495 [inline]
BUG: KASAN: use-after-free in ocfs2_info_freefrag_scan_bitmap fs/ocfs2/ioctl.c:588 [inline]
BUG: KASAN: use-after-free in ocfs2_info_handle_freefrag fs/ocfs2/ioctl.c:662 [inline]
BUG: KASAN: use-after-free in ocfs2_info_handle_request+0x1c66/0x3370 fs/ocfs2/ioctl.c:754
Read of size 8 at addr ffff888031bce000 by task syz.0.636/1435
Call Trace:
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0xbe/0x130 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xd1/0x650 mm/kasan/report.c:482
 kasan_report+0xfb/0x140 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:186 [inline]
 kasan_check_range+0x11c/0x200 mm/kasan/generic.c:200
 __kasan_check_read+0x11/0x20 mm/kasan/shadow.c:31
 instrument_atomic_read include/linux/instrumented.h:68 [inline]
 _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
 test_bit_le include/asm-generic/bitops/le.h:21 [inline]
 ocfs2_info_freefrag_scan_chain fs/ocfs2/ioctl.c:495 [inline]
 ocfs2_info_freefrag_scan_bitmap fs/ocfs2/ioctl.c:588 [inline]
 ocfs2_info_handle_freefrag fs/ocfs2/ioctl.c:662 [inline]
 ocfs2_info_handle_request+0x1c66/0x3370 fs/ocfs2/ioctl.c:754
 ocfs2_info_handle+0x18d/0x2a0 fs/ocfs2/ioctl.c:828
 ocfs2_ioctl+0x632/0x6e0 fs/ocfs2/ioctl.c:913
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x197/0x1e0 fs/ioctl.c:583
 ...

[CAUSE]
ocfs2_info_freefrag_scan_chain() uses on-disk bg_bits directly as the
bitmap scan limit. The coherent path reads group descriptors through
ocfs2_read_group_descriptor(), which validates the descriptor before
use. The non-coherent path uses ocfs2_read_blocks_sync() instead and
skips that validation, so an impossible bg_bits value can drive the
bitmap walk past the end of the block.

[FIX]
Compute the bitmap capacity from the filesystem format with
ocfs2_group_bitmap_size(), report descriptors whose bg_bits exceeds
that limit, and clamp the scan to the computed capacity. This keeps the
freefrag report going while avoiding reads beyond the buffer.

The Linux kernel CVE team has assigned CVE-2026-53040 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 3.0 with commit d24a10b9f8ed548981696cd36e2b4f16e6f360b1 and fixed in 5.10.258 with commit bb2906a1065ec28de021bac2ed03f2624edd7d07
	Issue introduced in 3.0 with commit d24a10b9f8ed548981696cd36e2b4f16e6f360b1 and fixed in 5.15.209 with commit 3e167e230d19cd273108bab2e4c61800fc335ae8
	Issue introduced in 3.0 with commit d24a10b9f8ed548981696cd36e2b4f16e6f360b1 and fixed in 6.1.175 with commit 0998674eec138c55e9e349b9cbd9dbc5129a9cc8
	Issue introduced in 3.0 with commit d24a10b9f8ed548981696cd36e2b4f16e6f360b1 and fixed in 6.6.141 with commit bb3c54d1e71578521111f1a1ee7d5f4761a242b8
	Issue introduced in 3.0 with commit d24a10b9f8ed548981696cd36e2b4f16e6f360b1 and fixed in 6.12.91 with commit 05d0cbea41167b6b061c6ba5b70ee5a9a7a24c9e
	Issue introduced in 3.0 with commit d24a10b9f8ed548981696cd36e2b4f16e6f360b1 and fixed in 6.18.33 with commit 4c2d62ddde8928db12f4608950b67a20e67deab2
	Issue introduced in 3.0 with commit d24a10b9f8ed548981696cd36e2b4f16e6f360b1 and fixed in 7.0.10 with commit e0dcf12665d6dde37facf790803cdad44d5c328c
	Issue introduced in 3.0 with commit d24a10b9f8ed548981696cd36e2b4f16e6f360b1 and fixed in 7.1 with commit 8f687eeed3da3012152b0f9473f578869de0cd7b

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-53040
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/ocfs2/ioctl.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/bb2906a1065ec28de021bac2ed03f2624edd7d07
	https://git.kernel.org/stable/c/3e167e230d19cd273108bab2e4c61800fc335ae8
	https://git.kernel.org/stable/c/0998674eec138c55e9e349b9cbd9dbc5129a9cc8
	https://git.kernel.org/stable/c/bb3c54d1e71578521111f1a1ee7d5f4761a242b8
	https://git.kernel.org/stable/c/05d0cbea41167b6b061c6ba5b70ee5a9a7a24c9e
	https://git.kernel.org/stable/c/4c2d62ddde8928db12f4608950b67a20e67deab2
	https://git.kernel.org/stable/c/e0dcf12665d6dde37facf790803cdad44d5c328c
	https://git.kernel.org/stable/c/8f687eeed3da3012152b0f9473f578869de0cd7b