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Fencer Vulns
high 7.8

CVE-2026-45942 json

ext4: fix e4b bitmap inconsistency reports

published 2026-05-27 5 mo ago modified 2026-10-30 10 d ago also EUVD-2026-32226

cvss
7.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.1%
EPSS 0.1% chance of exploitation in 30 days, percentile 2%
public exploits
0
none known

Summary

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

ext4: fix e4b bitmap inconsistency reports

A bitmap inconsistency issue was observed during stress tests under mixed huge-page workloads. Ext4 reported multiple e4b bitmap check failures like:

ext4_mb_complex_scan_group:2508: group 350, 8179 free clusters as per group info. But got 8192 blocks

Analysis and experimentation confirmed that the issue is caused by a race condition between page migration and bitmap modification. Although this timing window is extremely narrow, it is still hit in practice:

folio_lock ext4_mb_load_buddy __migrate_folio check ref count folio_mc_copy __filemap_get_folio folio_try_get(folio) ...... mb_mark_used ext4_mb_unload_buddy __folio_migrate_mapping folio_ref_freeze folio_unlock

The root cause of this issue is that the fast path of load_buddy only increments the folio's reference count, which is insufficient to prevent concurrent folio migration. We observed that the folio migration process acquires the folio lock. Therefore, we can determine whether to take the fast path in load_buddy by checking the lock status. If the folio is locked, we opt for the slow path (which acquires the lock) to close this concurrency window.

Additionally, this change addresses the following issues:

When the DOUBLE_CHECK macro is enabled to inspect bitmap-related issues, the following error may be triggered:

corruption in group 324 at byte 784(6272): f in copy != ff on disk/prealloc

Analysis reveals that this is a false positive. There is a specific race window where the bitmap and the group descriptor become momentarily inconsistent, leading to this error report:

ext4_mb_load_buddy ext4_mb_load_buddy __filemap_get_folio(create|lock) folio_lock ext4_mb_init_cache folio_mark_uptodate __filemap_get_folio(no lock) ...... mb_mark_used mb_mark_used_double mb_cmp_bitmaps mb_set_bits(e4b->bd_bitmap) folio_unlock

The original logic assumed that since mb_cmp_bitmaps is called when the bitmap is newly loaded from disk, the folio lock would be sufficient to prevent concurrent access. However, this overlooks a specific race condition: if another process attempts to load buddy and finds the folio is already in an uptodate state, it will immediately begin using it without holding folio lock.

Patch / fix

  • Linux Linux 6.1.191, 6.6.130, 6.12.75, 6.18.14, 6.19.4, 7.0
  • linux Debian 13 6.12.85-1
  • linux Debian 14 6.18.14-1

debian advisories DEBIAN-CVE-2026-45942

  • linux Ubuntu 24.04 LTS 6.8.0-136.136
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1061.64
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1064.72
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1059.67
  • linux-ibm Ubuntu 24.04 LTS 6.8.0-1061.62
  • linux-azure Ubuntu 24.04 LTS 6.8.0-1063.71
  • linux-gkeop Ubuntu 24.04 LTS 6.8.0-1046.50
  • linux-raspi Ubuntu 24.04 LTS 6.8.0-1061.65

ubuntu advisories UBUNTU-CVE-2026-45942

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel RHEL 10.2 6.12.0-211.61.1.el10_2
  • rv RHEL 10.2 6.12.0-211.61.1.el10_2
  • perf RHEL 10.2 6.12.0-211.61.1.el10_2
  • rtla RHEL 10.2 6.12.0-211.61.1.el10_2
  • libperf RHEL 10.2 6.12.0-211.61.1.el10_2
  • kernel-rt RHEL 10.2 6.12.0-211.61.1.el10_2
  • kernel-64k RHEL 10.2 6.12.0-211.61.1.el10_2
  • kernel-core RHEL 10.2 6.12.0-211.61.1.el10_2

red hat advisories RHSA-2026:72624RHSA-2026:72623RHSA-2026:72467RHSA-2026:72468

  • kernel-rt Linux Micro 6.2 6.12.0-160000.35.1
  • kernel-64kb SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.35.1
  • kernel-source SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.35.1
  • kernel-default SLES 16.0, SLE High Availability Extension 16.0, Linux Micro 6.2 +1 more 6.12.0-160000.35.1
  • kernel-default-base SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.35.1.160000.2.16
  • kernel-syms SLES 16.0, Linux Micro Extras 6.2, SLES for SAP applications 16.0 6.12.0-160000.35.1
  • kernel-azure SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.35.1
  • kernel-obs-qa SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.35.1

suse advisories SUSE-SU-2026:22112-1SUSE-SU-2026:22127-1SUSE-SU-2026:22117-1SUSE-SU-2026:22099-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.35.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.35.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.35.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.35.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.35.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.35.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.35.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.35.1

opensuse advisories openSUSE-SU-2026:20965-1

  • kernel-rt AlmaLinux 8 4.18.0-553.169.1.rt7.510.el8_10
  • kernel-rt-core AlmaLinux 8 4.18.0-553.169.1.rt7.510.el8_10
  • kernel-rt-modules AlmaLinux 8 4.18.0-553.169.1.rt7.510.el8_10
  • kernel-rt-debug-core AlmaLinux 8 4.18.0-553.169.1.rt7.510.el8_10
  • kernel-rt-debug-modules AlmaLinux 8 4.18.0-553.169.1.rt7.510.el8_10
  • kernel-rt-modules-extra AlmaLinux 8 4.18.0-553.169.1.rt7.510.el8_10
  • kernel-rt-debug-modules-extra AlmaLinux 8 4.18.0-553.169.1.rt7.510.el8_10
  • kernel AlmaLinux 8 4.18.0-553.169.1.el8_10

almalinux advisories ALSA-2026:72467ALSA-2026:72468ALSA-2026:72623ALSA-2026:72624

  • kernel Rocky Linux 10 6.12.0-211.61.1.el10_2
  • kernel Rocky Linux 9 5.14.0-687.53.1.el9_8
  • kernel-rt Rocky Linux 8 4.18.0-553.169.1.rt7.510.el8_10
  • kernel Rocky Linux 8 4.18.0-553.169.1.el8_10

rocky linux advisories RLSA-2026:72624RLSA-2026:72623RLSA-2026:72467RLSA-2026:72468

  • kernel Azure Linux 3.0 6.6.139.1-1

azure linux advisories AZL-88469

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-45942 updated cvss 4.7

kernel: ext4: fix e4b bitmap inconsistency reports

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 9 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +12 more
    affected: workaround, no fix available
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-687.53.1.el9_8, perf 5.14.0-687.53.1.el9_8, rtla 5.14.0-687.53.1.el9_8, python3-perf 5.14.0-687.53.1.el9_8, kernel-devel-matched 5.14.0-687.53.1.el9_8, kernel-64k-devel-matched 5.14.0-687.53.1.el9_8, +7 more
    fixed: vendor fix RHSA-2026:72623
  • Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-211.61.1.el10_2, perf 6.12.0-211.61.1.el10_2, rtla 6.12.0-211.61.1.el10_2, python3-perf 6.12.0-211.61.1.el10_2, kernel-devel-matched 6.12.0-211.61.1.el10_2, kernel-64k-devel-matched 6.12.0-211.61.1.el10_2, +7 more
    fixed: vendor fix RHSA-2026:72624
  • Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-553.169.1.el8_10, kernel 4.18.0-553.169.1.el8_10, bpftool 4.18.0-553.169.1.el8_10, kernel-core 4.18.0-553.169.1.el8_10, kernel-tools 4.18.0-553.169.1.el8_10, python3-perf 4.18.0-553.169.1.el8_10, +15 more
    fixed: vendor fix RHSA-2026:72468
  • Red Hat Enterprise Linux BaseOS (v. 9) kernel 5.14.0-687.53.1.el9_8, kernel-64k 5.14.0-687.53.1.el9_8, kernel-core 5.14.0-687.53.1.el9_8, kernel-tools 5.14.0-687.53.1.el9_8, kernel-modules 5.14.0-687.53.1.el9_8, kernel-64k-core 5.14.0-687.53.1.el9_8, +27 more
    fixed: vendor fix RHSA-2026:72623
  • Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-211.61.1.el10_2, kernel-64k 6.12.0-211.61.1.el10_2, kernel-core 6.12.0-211.61.1.el10_2, kernel-tools 6.12.0-211.61.1.el10_2, kernel-modules 6.12.0-211.61.1.el10_2, kernel-64k-core 6.12.0-211.61.1.el10_2, +28 more
    fixed: vendor fix RHSA-2026:72624
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) libperf 5.14.0-687.53.1.el9_8, kernel-debuginfo-common-s390x 5.14.0-687.53.1.el9_8, kernel-debuginfo-common-x86_64 5.14.0-687.53.1.el9_8, kernel-debuginfo-common-aarch64 5.14.0-687.53.1.el9_8, kernel-debuginfo-common-ppc64le 5.14.0-687.53.1.el9_8
    fixed: vendor fix RHSA-2026:72623
show 8 more
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-211.61.1.el10_2, kernel-debuginfo-common-s390x 6.12.0-211.61.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.61.1.el10_2, kernel-debuginfo-common-aarch64 6.12.0-211.61.1.el10_2, kernel-debuginfo-common-ppc64le 6.12.0-211.61.1.el10_2
    fixed: vendor fix RHSA-2026:72624
  • Red Hat Enterprise Linux CRB (v. 8) kernel-debuginfo-common-x86_64 4.18.0-553.169.1.el8_10, kernel-debuginfo-common-aarch64 4.18.0-553.169.1.el8_10, kernel-debuginfo-common-ppc64le 4.18.0-553.169.1.el8_10
    fixed: vendor fix RHSA-2026:72468
  • Red Hat Enterprise Linux NFV (v. 8) kernel-rt 4.18.0-553.169.1.rt7.510.el8_10, kernel-rt-kvm 4.18.0-553.169.1.rt7.510.el8_10, kernel-rt-core 4.18.0-553.169.1.rt7.510.el8_10, kernel-rt-modules 4.18.0-553.169.1.rt7.510.el8_10, kernel-rt-debug-kvm 4.18.0-553.169.1.rt7.510.el8_10, kernel-rt-debug-core 4.18.0-553.169.1.rt7.510.el8_10, +4 more
    fixed: vendor fix RHSA-2026:72467
  • Red Hat Enterprise Linux Real Time (v. 9) kernel-rt 5.14.0-687.53.1.el9_8, kernel-rt-64k 5.14.0-687.53.1.el9_8, kernel-rt-core 5.14.0-687.53.1.el9_8, kernel-rt-modules 5.14.0-687.53.1.el9_8, kernel-rt-64k-core 5.14.0-687.53.1.el9_8, kernel-rt-debug-core 5.14.0-687.53.1.el9_8, +14 more
    fixed: vendor fix RHSA-2026:72623
  • Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-211.61.1.el10_2, kernel-rt-64k 6.12.0-211.61.1.el10_2, kernel-rt-core 6.12.0-211.61.1.el10_2, kernel-rt-modules 6.12.0-211.61.1.el10_2, kernel-rt-64k-core 6.12.0-211.61.1.el10_2, kernel-rt-debug-core 6.12.0-211.61.1.el10_2, +14 more
    fixed: vendor fix RHSA-2026:72624
  • Red Hat Enterprise Linux Real Time for NFV (v. 9) kernel-rt 5.14.0-687.53.1.el9_8, kernel-rt-core 5.14.0-687.53.1.el9_8, kernel-rt-modules 5.14.0-687.53.1.el9_8, kernel-rt-debug-core 5.14.0-687.53.1.el9_8, kernel-rt-modules-core 5.14.0-687.53.1.el9_8, kernel-rt-debug-modules 5.14.0-687.53.1.el9_8, +4 more
    fixed: vendor fix RHSA-2026:72623
  • Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-211.61.1.el10_2, kernel-rt-core 6.12.0-211.61.1.el10_2, kernel-rt-modules 6.12.0-211.61.1.el10_2, kernel-rt-debug-core 6.12.0-211.61.1.el10_2, kernel-rt-modules-core 6.12.0-211.61.1.el10_2, kernel-rt-debug-modules 6.12.0-211.61.1.el10_2, +4 more
    fixed: vendor fix RHSA-2026:72624
  • Red Hat Enterprise Linux RT (v. 8) kernel-rt 4.18.0-553.169.1.rt7.510.el8_10, kernel-rt-core 4.18.0-553.169.1.rt7.510.el8_10, kernel-rt-modules 4.18.0-553.169.1.rt7.510.el8_10, kernel-rt-debug-core 4.18.0-553.169.1.rt7.510.el8_10, kernel-rt-debug-modules 4.18.0-553.169.1.rt7.510.el8_10, kernel-rt-modules-extra 4.18.0-553.169.1.rt7.510.el8_10, +2 more
    fixed: vendor fix RHSA-2026:72467

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
23 d ago

Exploit prediction

0.13% chance of exploitation in the next 30 days, higher than 2% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Linux Linux

Classification

Weakness
  • CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.