[CVE-2026-90401][MODERATE 7.0] md: remove REQ_NOWAIT support from raid1/10/456 [ Upstream

[CVE-2026-90401][MODERATE 7.0] md: remove REQ_NOWAIT support from raid1/10/456 [ Upstream

[AL-KERNEL]

CVE: CVE-2026-90401
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: md: remove REQ_NOWAIT support from raid1/10/456 [ Upstream
Commit: 9bb9504e2d8f3d22ef12d51c333dd499f402dc8f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9bb9504e2d8f3d22ef12d51c333dd499f402dc8f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90401
Analysis date: Fri, 18 Sep 2026 04:49:46 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90401 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90401

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 7.0
Manual review required: YES

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

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

CVE-2026-90401	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90401 CHECK WITH IMPACT FROM ORIG NN LOW	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-754;CWE-703;CWE-440;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:L';BEST CVSS score: '6.3';DESCR 'REQ_NOWAIT support in md RAID1 RAID10 and RAID456 can produce mirror divergence because a nowait write may partially succeed on one member while another member returns EAGAIN. In that state md cannot safely classify the result as transient queue pressure or real device failure, so it may neither mark a bad block nor retry the write in a safe blocking mode. The realistic impact is local data integrity corruption on affected md arrays, with possible availability impact from inconsistent array contents or recovery behavior. For the CVSS the PR:L is used because a local user or process that can submit nowait writes to a filesystem or block path backed by the md array may be enough in some deployments, while direct raw array control may require higher privileges. The issue is not network reachable and there is no evidence of memory corruption or direct privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5)	YES	LOCK DANGER DISK ERRORPATH HARDWARE LINUS KPANIC 	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4. No floor or cap applied.
* Raw paranoid score: 5
* Paranoid score: 5. No floor or cap applied.
* Final recommended bucket: **Actionable Moderate**::

2. Signal breakdown

Positive signals:

* +1 Local unprivileged trigger. A local process with write access to a filesystem or block path backed by an affected md RAID array can plausibly submit NOWAIT write requests without host-admin privileges.
* +1 Persistent storage integrity impact. The commit explicitly states that one mirror may complete a write while another returns EAGAIN, leaving mirrors with divergent data.
* +1 Important storage path. md RAID1, RAID10, and RAID456 are important storage integrity paths where inconsistent writes can affect persistent data and recovery semantics.
* +1 Practical consequence chain. The chain is directly described: REQ_NOWAIT write, partial mirror success, EAGAIN on another member, md cannot classify or safely retry, persistent divergence.
* Paranoid +1 Availability concern. Persistent mirror or parity divergence can plausibly cause later read inconsistency, repair ambiguity, rebuild problems, or operational storage degradation beyond a single failed IO.

Non-awarded signals:

* No Real UAF. The patch does not establish stale object use, double release, refcount misuse, or post-lifetime access.
* No kernel memory corruption. The issue is storage semantic integrity, not heap, stack, page, or object corruption in kernel memory.
* No controlled reclaim or arbitrary write primitive is demonstrated.
* No confidentiality signal is awarded. The supplied evidence does not show disclosure of protected data.
* No authorization bypass is established.
* No remote reachability is established. This is triggered through local IO submission, not packets.
* No race penalty is applied. The issue depends on partial NOWAIT completion and queue behavior, but the supplied evidence does not establish a narrow uncontrollable timing race.
* No host-admin penalty is applied. Host administration may be needed to create the md array, but submitting IO to an already configured filesystem or block path can be below host-admin.

3. Reachability analysis

The relevant attacker is a local user or local process able to submit write IO to storage backed by an affected md RAID1, RAID10, or RAID456 array. Direct raw block-device access may require elevated privileges, but the complete practical path can exist through a writable filesystem on top of the md device, so HostAdminRequired=NO is appropriate for triage.

The issue is not namespace-scoped. No network namespace, user namespace, or namespaced capability path is involved in the supplied evidence.

There is prior administrative deployment of the md array, but that is an environmental precondition, not necessarily an attacker privilege requirement for triggering IO once the storage is mounted and writable. No special hardware requirement is established beyond use of md RAID levels with the affected REQ_NOWAIT support.

The bug is not directly network reachable. A remote attacker would need an additional service that writes attacker-controlled data to the affected filesystem with NOWAIT behavior, which is not established by the patch.

4. Primitive and severity interpretation

The primitive is a persistent storage consistency violation. REQ_NOWAIT was advertised for md personalities that can block internally and cannot safely handle partial write completion across mirrors or parity members. If one member accepts a write and another returns EAGAIN, md cannot reliably distinguish queue pressure from device failure and cannot safely record a bad block or retry the operation in blocking mode. This can leave mirrors or parity state divergent.

This is not an ordinary crash-only bug and not a kernel memory-safety bug. It is also not CLASS_A because no authorization bypass, arbitrary kernel write, COW ownership violation, controlled memory corruption, or demonstrated privilege escalation is established. It is CLASS_B because the patch establishes a concrete persistent storage integrity primitive whose operational and security impact depends on deployment and should not be automatically downgraded.

ImportantCandidate=NO because the evidence does not show privilege escalation, protected-resource theft, memory corruption, or a security-boundary bypass. AutoDowngradeAllowed=NO because persistent RAID data divergence is a meaningful integrity issue and automatic closure as a low or ordinary DoS-only issue would risk missing real operational impact.

Likely operational severity is Actionable Moderate. Manual review is needed to determine whether the affected product exposes NOWAIT writes from untrusted local users and whether the md arrays store security-sensitive or multi-user data.

5. One-sentence report phrase

Incomplete REQ_NOWAIT handling in md RAID1 RAID10 and RAID456 can allow a local writer to create partial mirror or parity updates, causing persistent storage divergence and requiring manual review of affected deployments.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the bug is not memory corruption, but it directly affects persistent storage integrity and can leave RAID mirrors or parity data inconsistent under plausible local IO conditions.

7. Call-site confidence

Call-site confidence: medium

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

Patch: md: remove REQ_NOWAIT support from raid1/10/456 [ Upstream
Commit: 9bb9504e2d8f3d22ef12d51c333dd499f402dc8f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9bb9504e2d8f3d22ef12d51c333dd499f402dc8f

Changed files:
  drivers/md/md-bitmap.c
  drivers/md/md-bitmap.h
  drivers/md/md-linear.c
  drivers/md/md-llbitmap.c
  drivers/md/md.c
  drivers/md/raid0.c
  drivers/md/raid1-10.c
  drivers/md/raid1.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=9bb9504e2d8f3d22ef12d51c333dd499f402dc8f

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

The original Linux kernel CVE announcement for CVE-2026-90401 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90401

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:H/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: 4
  Paranoid ActionableScore: 5

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).