In the Linux kernel, the following vulnerability has been resolved: ocfs2: validate bg_bits during freefrag scan [BUG] A crafted filesystem can… (CVE-2026-53040)
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.
AI Analysis
Technical Summary
The Linux kernel's OCFS2 filesystem driver contained a vulnerability where the bg_bits field in group descriptors was not validated during freefrag scans in the non-coherent path. This allowed a crafted filesystem to cause an out-of-bounds bitmap walk when the OCFS2_IOC_INFO ioctl is issued with the OCFS2_INFO_FL_NON_COHERENT flag. The lack of validation led to use-after-free bugs detected by Kernel Address Sanitizer (KASAN) in various kernel functions related to bitmap scanning. The fix involves computing the bitmap capacity from the filesystem format and clamping the scan to this capacity, preventing reads beyond the buffer and maintaining the integrity of the freefrag report.
Potential Impact
An attacker able to provide a crafted OCFS2 filesystem can cause out-of-bounds memory access and use-after-free conditions in the kernel, potentially leading to system instability or crashes. The vulnerability does not require privileges or user interaction beyond issuing the ioctl with the non-coherent flag. There are no known exploits in the wild. The impact is rated high due to the kernel memory corruption risk.
Mitigation Recommendations
A fix is available that validates the bg_bits field and clamps bitmap scans to prevent out-of-bounds reads. Users should update to Linux kernel versions that include this fix. The affected versions are all Linux kernel versions prior to 5.15.0-1112.119~20.04.1, 5.15.0-1117.126~20.04.1, 5.15.0-1117.126~20.04.2, 5.15.0-186.196~20.04.1, and 5.15.0-1106.110~20.04.1. Patch status is confirmed by the presence of these fixed versions. No additional mitigations are specified.
In the Linux kernel, the following vulnerability has been resolved: ocfs2: validate bg_bits during freefrag scan [BUG] A crafted filesystem can… (CVE-2026-53040)
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.
CVSS v3.1
Score 7.1high
Affected software
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protected]?arch=source&distro=noblepkg:deb/ubuntu/[email protected]?arch=source&distro=noblepkg:deb/ubuntu/[email protected]?arch=source&distro=noblepkg:deb/ubuntu/[email protected]~24.04.1?arch=source&distro=noblepkg:deb/ubuntu/[email protected]~24.04.1?arch=source&distro=noblepkg:deb/ubuntu/[email protected]?arch=source&distro=noblepkg:deb/ubuntu/[email protected]?arch=source&distro=bluefield/noblepkg:deb/ubuntu/[email protected]+fips1?arch=source&distro=fips-updates/noblepkg:deb/ubuntu/[email protected]+fips1?arch=source&distro=fips-updates/noblepkg:deb/ubuntu/[email protected]+fips1?arch=source&distro=fips-updates/noblepkg:deb/ubuntu/[email protected]+fips1?arch=source&distro=fips-updates/noblepkg:deb/ubuntu/[email protected]?arch=source&distro=realtime/noblepkg:deb/ubuntu/[email protected]?arch=source&distro=realtime/noblepkg:deb/ubuntu/[email protected]~24.04.1?arch=source&distro=realtime/noblepkg:deb/ubuntu/[email protected]~24.04.1?arch=source&distro=realtime/noblepkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resoluteRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The Linux kernel's OCFS2 filesystem driver contained a vulnerability where the bg_bits field in group descriptors was not validated during freefrag scans in the non-coherent path. This allowed a crafted filesystem to cause an out-of-bounds bitmap walk when the OCFS2_IOC_INFO ioctl is issued with the OCFS2_INFO_FL_NON_COHERENT flag. The lack of validation led to use-after-free bugs detected by Kernel Address Sanitizer (KASAN) in various kernel functions related to bitmap scanning. The fix involves computing the bitmap capacity from the filesystem format and clamping the scan to this capacity, preventing reads beyond the buffer and maintaining the integrity of the freefrag report.
Potential Impact
An attacker able to provide a crafted OCFS2 filesystem can cause out-of-bounds memory access and use-after-free conditions in the kernel, potentially leading to system instability or crashes. The vulnerability does not require privileges or user interaction beyond issuing the ioctl with the non-coherent flag. There are no known exploits in the wild. The impact is rated high due to the kernel memory corruption risk.
Mitigation Recommendations
A fix is available that validates the bg_bits field and clamps bitmap scans to prevent out-of-bounds reads. Users should update to Linux kernel versions that include this fix. The affected versions are all Linux kernel versions prior to 5.15.0-1112.119~20.04.1, 5.15.0-1117.126~20.04.1, 5.15.0-1117.126~20.04.2, 5.15.0-186.196~20.04.1, and 5.15.0-1106.110~20.04.1. Patch status is confirmed by the presence of these fixed versions. No additional mitigations are specified.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- UBUNTU-CVE-2026-53040
- Osv Schema Version
- 1.7.0
- Aliases
- []
- Ecosystems
- ["Ubuntu:Pro:14.04:LTS","Ubuntu:Pro:16.04:LTS","Ubuntu:16.04:LTS","Ubuntu:Pro:FIPS:16.04:LTS","Ubuntu:Pro:18.04:LTS","Ubuntu:18.04:LTS","Ubuntu:Pro:FIPS-updates:18.04:LTS","Ubuntu:Pro:FIPS:18.04:LTS","Ubuntu:Pro:20.04:LTS","Ubuntu:20.04:LTS","Ubuntu:Pro:FIPS-updates:20.04:LTS","Ubuntu:Pro:FIPS:20.04:LTS","Ubuntu:22.04:LTS","Ubuntu:Nvidia-BlueField:22.04:LTS","Ubuntu:Pro:FIPS-preview:22.04:LTS","Ubuntu:Pro:FIPS-updates:22.04:LTS","Ubuntu:Pro:Realtime:22.04:LTS","Ubuntu:24.04:LTS","Ubuntu:Nvidia-BlueField:24.04:LTS","Ubuntu:Pro:FIPS-updates:24.04:LTS","Ubuntu:Pro:Realtime:24.04:LTS","Ubuntu:25.10","Ubuntu:26.04:LTS"]
- Database Specific Severity
- null
- Cvss Version
- 4.0
Threat ID: 6a5a014891ae9bcd3f801d9a
Added to database: 07/17/2026, 10:17:44 UTC
Last enriched: 07/30/2026, 21:07:37 UTC
Last updated: 07/31/2026, 19:30:19 UTC
Views: 3
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