[CVE-2026-45955][LOW] md/md-llbitmap: fix percpu_ref not resurrected on suspend timeout [ Upstream

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

CVE: CVE-2026-45955
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: md/md-llbitmap: fix percpu_ref not resurrected on suspend timeout [ Upstream
Commit: 095417d6b669c2dec39a5842ccb94df915f97f54
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=095417d6b669c2dec39a5842ccb94df915f97f54
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45955
Analysis date: Wed, 27 May 2026 19:35:16 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-45955 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45955

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: LOW
Manual review required: NO

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

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-45955	LOW	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:N/A:H';*CWE-664;CWE-703;CWE-404;**CWE-400;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'md llbitmap can kill a per page percpu_ref during suspend and return ETIMEDOUT without resurrecting it. The bitmap daemon can then skip resume for that page, leaving the page control in a permanently killed state and causing later bitmap operations to fail, stall, or degrade md availability. For the CVSS the PR:L is used in the paranoid score because a local workload may influence I/O and reference lifetime on an already configured md array, although creating and managing the array normally requires administrator control. The issue is not network reachable and does not provide a memory corruption primitive. Impact is availability only through broken bitmap page control after timeout.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)  SKIP CVE-2026-45955  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	DISK SIMPLEFIX  DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=2

1. ActionableScore
* Conservative score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

2. Signal breakdown
* Availability impact realistic: +1. A bitmap page control structure can remain permanently unusable after a suspend timeout.
* Important filesystem/storage path: +1. The issue affects md RAID lockless bitmap handling.
* Requires admin/root in typical deployments: -2. Creating, configuring, and managing md arrays normally requires administrative control.
* Paranoid local workload influence: +1. A local workload on an already configured array may influence I/O and reference lifetime enough to contribute to timeout conditions.
* Hard condition / timeout dependent: -1. Triggering requires `llbitmap_suspend_timeout()` to time out while references remain active.
* No memory corruption signal. This is state restoration/resource lifetime logic, not UAF, OOB write, arbitrary write, or info leak.

3. Reachability analysis
The issue is reachable in md RAID configurations using md-llbitmap when suspend of a bitmap page times out. Direct setup and management are typically privileged. A normal local workload might contribute to I/O pressure or reference lifetime on an already configured array, but reliable triggering is indirect and timing dependent. It is not network reachable.

4. Severity interpretation
This behaves like a Low-like or ordinary Moderate storage availability bug. The realistic impact is failed or degraded bitmap operation after a timeout. There is no evidence of data disclosure, privilege escalation, memory corruption, or persistent metadata corruption beyond the affected page-control state.

5. One-sentence report phrase
md-llbitmap can leave a per-page `percpu_ref` permanently killed after a suspend timeout, causing later bitmap operations to fail or degrade md availability.

6. Manual review recommendation
NO MANUAL CHECK NEEDED. This is availability-only state restoration logic in md bitmap handling with no memory corruption, info leak, or LPE primitive.

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

Patch: md/md-llbitmap: fix percpu_ref not resurrected on suspend timeout [ Upstream
Commit: 095417d6b669c2dec39a5842ccb94df915f97f54
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=095417d6b669c2dec39a5842ccb94df915f97f54

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=095417d6b669c2dec39a5842ccb94df915f97f54

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

The original Linux kernel CVE announcement for CVE-2026-45955 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45955

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:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: unknown
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).