[CVE-2026-90279][MODERATE REGULAR] md/raid5: round bitmap stripes with sector division [ Upstream

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

CVE: CVE-2026-90279
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: md/raid5: round bitmap stripes with sector division [ Upstream
Commit: 9d7490007707f90691911385365bd1d691d99225
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9d7490007707f90691911385365bd1d691d99225
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90279
Analysis date: Thu, 17 Sep 2026 19:03:42 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90279 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90279

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
======================================================================

CVE-2026-90279	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90279 CHECK WITH IMPACT FROM ORIG NN MODERATE	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:L';CWE-682;CWE-193;CWE-693;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.3';DESCR 'RAID5 bitmap sector mapping can be calculated incorrectly when the full stripe width is not a power of two, because the old rounding logic used mask style round_down and round_up before converting array sectors to component sectors. This can mark or reference the wrong bitmap component range for writes on specific RAID5 geometries, which may affect recovery correctness and data integrity after failures or rebuild related operations. For the CVSS the PR:L is used because reliable triggering may be possible by a local user or process that can write data on an already configured affected RAID5 volume, while creating or reconfiguring the array itself is usually administrative. The issue is not network reachable and does not indicate a kernel memory corruption primitive. Impact is primarily storage integrity risk and possible localized availability impact from incorrect recovery metadata rather than privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	YES	DISK SIMPLEFIX LINUS 	YES	NO	checked

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

ActionableScore=4
ActionableScoreLower=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3. No floor or cap applied.
* Raw paranoid score: 4
* Paranoid score: 4. No floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Conservative signals:

* +1 Filesystem/storage metadata corruption reachable through ordinary write activity. The wrong RAID5 bitmap sector mapping can mark or reference the wrong component bitmap range.
* +1 Important filesystem/storage path. The affected code is in md/raid5 bitmap mapping, which can influence recovery or rebuild correctness.
* +1 Integrity plausible. The established consequence is not kernel memory corruption, but incorrect storage recovery metadata can plausibly affect data integrity after failures or rebuild operations.

Paranoid additional signal:

* +1 Local below-host-admin trigger plausibility. On an already configured affected RAID5 volume, a local user or process with write access to data on the volume may cause writes that reach this mapping path, although full RAID creation or reconfiguration is administrative.

Non-awarded signals:

* +0 Real UAF not awarded. No stale object or post-lifetime use is established.
* +0 Memory corruption not awarded. The patch fixes arithmetic and mapping logic, not heap, stack, pointer, refcount, or lifetime corruption.
* +0 Strong LPE or weak LPE not awarded. No privilege-escalation primitive is established.
* +0 Remote reachability not awarded. The trigger is local storage I/O, not network packet processing.
* +0 Reliable kernel crash not awarded. The supplied evidence describes wrong mapping, not panic or fatal fault.
* +0 Extra availability not awarded. Possible recovery problems are already reflected as storage integrity concern, and no distinct host-wide DoS is demonstrated.
* +0 Dirty-Pipe-like ownership/COW violation not awarded. There is no evidence that a write authorized for one file modifies independently permissioned storage belonging to another file.
* No negative privilege penalty applied. Host-admin is required to create or configure the RAID array, but the vulnerable runtime write path may be reachable by non-admin local writers once the array exists.

3. Reachability analysis

The evaluated attacker is a local user or local process that can write to data stored on an already configured affected RAID5 device. Creating the RAID5 array, choosing the chunk size, enabling bitmap behavior, and configuring recovery policy are normally administrative setup steps, but those are deployment prerequisites rather than necessarily part of the runtime trigger.

The complete practical consequence depends on configuration: RAID5 with a full-stripe width that is not a power of two, bitmap usage, writes at affected offsets, and later recovery or rebuild behavior. The supplied patch does not establish a network path. Namespace-scoped privilege is not relevant or not resolved from the evidence. No special rare hardware is required beyond md RAID5 usage, but the exact vulnerable geometry is configuration-dependent.

Race repeatability is not an issue because this is deterministic arithmetic/mapping behavior, not a timing race.

4. Primitive and severity interpretation

The primitive is a deterministic arithmetic and mapping error in `raid5_bitmap_sector()`. The old `round_down()` and `round_up()` logic assumes power-of-two alignment, but RAID5 full-stripe width is `chunk_sectors * data_disks` and can be non-power-of-two. This can produce an incorrect component bitmap range.

This is not an active structured UAF, fixed stale storage UAF, double release, refcount misuse, OOB access, or authorization bypass. It is best treated as Class C invalid-state or bookkeeping corruption affecting storage metadata semantics.

Demonstrated consequence: incorrect RAID5 bitmap range calculation.

Speculative consequence: incorrect bitmap tracking could affect recovery correctness or data integrity after a failure or rebuild. The supplied evidence does not prove cross-file permission bypass, kernel memory corruption, or privilege escalation.

ImportantCandidate=NO because no Class A primitive or strong unresolved Class B corruption/lifetime primitive is established. ManualReview=RECOMMENDED because storage integrity impact is environment-dependent and may be operationally significant. AutoDowngradeAllowed=YES because there is no UAF, security boundary bypass, controlled corruption, or unresolved Important-grade primitive.

Likely operational severity: borderline Moderate. It is more than a harmless correctness issue due to possible RAID recovery integrity impact, but it does not look like an Important-class kernel security vulnerability from the supplied evidence.

5. One-sentence report phrase

RAID5 bitmap sector mapping used power-of-two rounding for a stripe width that may not be a power of two, causing incorrect bitmap component ranges and possible storage recovery integrity impact on affected RAID5 geometries.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the bug is not memory corruption or privilege escalation, but RAID5 bitmap mis-mapping can have environment-specific data integrity consequences during recovery or rebuild, so it should not be dismissed without checking affected RAID geometry and bitmap usage.

7. Call-site confidence

Call-site confidence: medium

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

Patch: md/raid5: round bitmap stripes with sector division [ Upstream
Commit: 9d7490007707f90691911385365bd1d691d99225
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9d7490007707f90691911385365bd1d691d99225

Changed files:
  drivers/md/raid5.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=9d7490007707f90691911385365bd1d691d99225

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

The original Linux kernel CVE announcement for CVE-2026-90279 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90279

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:L
  The Best / paranoid CVSS score: 5.3

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).