[CVE-2026-46095][MODERATE REGULAR] md/md-llbitmap: raise barrier before state machine transition

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-46095
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: md/md-llbitmap: raise barrier before state machine transition
Commit: 9142f00a9287ca38152717e3e88a033a27774e7f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9142f00a9287ca38152717e3e88a033a27774e7f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46095
Analysis date: Wed, 27 May 2026 12:54:21 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A race in md llbitmap write and discard handling can allow state machine transitions to complete before bitmap barriers are raised, creating a local storage consistency and recovery accounting risk on affected md configurations.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-46095 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46095

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE REGULAR
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-46095	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H';CWE-362;CWE-667;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '6.3';DESCR 'A race in md llbitmap write and discard handling can occur because the state machine transition was executed before the bitmap page barriers were raised. A concurrent operation could observe or complete state changes before the intended barrier protection is in place, which may affect RAID bitmap consistency and recovery accounting. For the CVSS the PR:L is used because a local user may be able to trigger writes or discards through a writable filesystem backed by an affected md device, although reliable triggering depends on md llbitmap configuration and timing. The issue is not network reachable. Impact is mainly storage integrity and availability risk rather than code execution. No UAF, double free, arbitrary write, or direct privilege escalation primitive is shown by this patch.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 4)  SKIP CVE-2026-46095  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	WRITE OOB DANGER DISK SIMPLEFIX RACE IMPROVEONLY LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  A local user may indirectly trigger write or discard activity through a filesystem or block workload backed by an affected md device.

* Filesystem/storage metadata corruption reachable by local user: +1
  The affected code is md lockless bitmap state tracking. Incorrect ordering can affect bitmap state transitions and recovery accounting.

* Important filesystem/storage path: +1
  md bitmap metadata is relevant to RAID consistency, resync behavior, and recovery correctness.

* Integrity impact plausible: +1 paranoid
  A race in bitmap state handling could plausibly cause incorrect dirty or discard tracking, with possible data consistency or recovery implications.

* Availability impact plausible: +1 paranoid
  Incorrect bitmap accounting may cause recovery problems, unnecessary resync, degraded array behavior, or operational DoS.

* Hard or timing dependent race: -1
  The issue depends on ordering between barrier raising and state machine completion. Reliable triggering likely requires timing and a suitable md llbitmap workload.

* No memory corruption primitive: +0
  The patch does not show UAF, double free, OOB write, arbitrary write, page cache corruption, or direct privilege escalation.

* No remote reachability: +0
  This is local storage I/O behavior, not network-triggerable.

## 3. Reachability analysis

The likely trigger is local I/O to an md array using the lockless bitmap implementation. A normal user may generate writes or discards through a writable filesystem on top of the md device, but reliable triggering depends on md configuration, llbitmap being used, workload timing, and concurrent state transitions. Containers generally do not increase reachability unless they can issue I/O to a filesystem backed by the affected md device. The path is not remotely reachable by itself.

## 4. Severity interpretation

This behaves like a storage consistency race rather than memory corruption. The realistic concern is incorrect bitmap or recovery accounting, with possible integrity and availability impact. There is no demonstrated kernel crash, UAF, arbitrary write, information leak, or privilege escalation. It is therefore not an Important memory corruption candidate, but it should receive manual review because storage metadata races can have persistent operational impact.

## 5. One-sentence report phrase

A race in md llbitmap write and discard handling can allow state machine transitions to complete before bitmap barriers are raised, creating a local storage consistency and recovery accounting risk on affected md configurations.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED.

Manual review is recommended because this affects RAID bitmap ordering and storage integrity semantics, but current evidence supports a timing-dependent storage consistency issue rather than memory corruption or privilege escalation.

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UPSTREAM PATCH SUMMARY
======================================================================

Patch: md/md-llbitmap: raise barrier before state machine transition
Commit: 9142f00a9287ca38152717e3e88a033a27774e7f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9142f00a9287ca38152717e3e88a033a27774e7f

Commit description:

Move the barrier raise operation before calling llbitmap_state_machine()
in both llbitmap_start_write() and llbitmap_start_discard(). This
ensures the barrier is in place before any state transitions occur,
preventing potential race conditions where the state machine could
complete before the barrier is properly raised.

Cc: stable@vger.kernel.org
Fixes: 5ab829f ("md/md-llbitmap: introduce new lockless bitmap")
Link: https://lore.kernel.org/linux-raid/20260223024038.3084853-3-yukuai@fnnas.com
Signed-off-by: Yu Kuai <yukuai@fnnas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/md/md-llbitmap.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9142f00a9287ca38152717e3e88a033a27774e7f

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-46095 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46095

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H
  The Best / paranoid CVSS score: 6.3

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 3
  Paranoid ActionableScore: 4

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).