[CVE-2026-90185][MODERATE 7.0] null_blk: serialize configfs attribute stores with the lock [ Upstream

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

CVE: CVE-2026-90185
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: null_blk: serialize configfs attribute stores with the lock [ Upstream
Commit: 8e839ed5210399a0330a8a6c5885c1d40a537c6d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8e839ed5210399a0330a8a6c5885c1d40a537c6d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90185
Analysis date: Thu, 17 Sep 2026 20:39:59 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90185 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90185

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-2026-90185	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90185 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:L/I:L/A:H';CWE-362;CWE-667;*CWE-787;CWE-119;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A race in null_blk configfs attribute stores can allow concurrent writes on separate file descriptors to update device fields while another store is applying queue changes or while power_store is building the device. This can leave software state out of sync with the live queue configuration and can also let zone_nr_conv exceed nr_zones after validation, leading to out of bounds dev zones access. For the CVSS the PR:L is used for the paranoid score because delegated configfs write access or reduced capability admin roles may be enough to race attribute stores, although default host setups usually restrict this interface to administrators. The issue is not network reachable and is triggered through local control plane configuration writes. Impact is at least denial of service via WARN, invalid state, or kernel crash, and worst case may allow limited confidentiality or integrity impact due to a plausible out of bounds memory access candidate.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	YES	WRITE OOB LOCK RACE HARDWARE TEST  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	NO	NO	checked

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

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

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 4
* Applied conservative floor/cap: concrete kernel OOB access candidate with unresolved crash/corruption impact raises 3 -> 4
* Raw paranoid score: 4
* Paranoid score: 5
* Applied paranoid floor/cap: explicit attacker-influenced OOB dev->zones[] access candidate raises 4 -> 5 for manual-review sensitivity
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Positive conservative signals:

* +1 weak or indirect corruption candidate: concurrent configfs stores can make zone_nr_conv exceed nr_zones after validation, leading to out-of-bounds dev->zones[] access.
* +1 reliable kernel crash / strong DoS: commit documents WARN_ON_ONCE in null_map_queues and an OOB access path that can plausibly fault or destabilize the kernel.
* +1 memory/configuration invariant break: validated device configuration can become inconsistent with the live queue count or allocated zone array because field writes occur outside the shared lock.

Positive paranoid signals:

* +1 same weak or indirect corruption candidate.
* +1 same reliable DoS.
* +1 same memory/configuration invariant break.
* +1 weak exploitation concern: the OOB access is tied to attacker-influenced configuration values and active null_blk device state, so limited C/I impact cannot be ruled out without reviewing the later dev->zones[] access sites.

Non-awarded or withheld signals:

* RealUAF not awarded: no use-after-free or stale post-lifetime object use is established by the patch.
* Concrete repeated release/refcount not awarded: no first release, surviving dangling reference, and second lifetime mutation exists.
* Strong exploitation leverage +2 not awarded: no controlled reclaim, arbitrary write, directed write, callback control, refcount takeover, or demonstrated LPE is shown.
* Remote reachability not awarded: trigger is local configfs control-plane writes, not packet or network data-plane input.
* Local unprivileged trigger not awarded: ordinary unprivileged reachability to null_blk configfs stores is not established.
* Host-admin penalty not applied: default access is likely admin-controlled, but the supplied evidence does not positively prove host-admin-equivalent privilege is required in all relevant deployments.
* Race penalty not applied: the race is driven by concurrent stores on separate file descriptors and appears repeatable by an actor with write access.
* Extra availability not awarded: WARN, invalid state, OOB fault, and crash are the same availability consequence.
* C/I bonuses not awarded conservatively: the patch establishes OOB access, but not a concrete disclosure or unauthorized write primitive.

3. Reachability analysis

The vulnerable interface is null_blk configfs attribute storage. An attacker needs the ability to write null_blk device attributes concurrently through separate file descriptors. In default host setups this is normally restricted to administrative users or privileged management services, but the prompt evidence does not prove that host-admin-equivalent privilege is always required.

The complete trigger is not namespace-scoped based on the supplied evidence. configfs and null_blk device configuration are local control-plane mechanisms, not network namespaces or packet traffic. No prior special hardware is required because null_blk is a software block driver, but the vulnerable path depends on null_blk being enabled and its configfs interface being available.

The race is not treated as a hard timing-only race. The commit explicitly states that configfs only serializes stores per open file, so concurrent stores on separate file descriptors can race. An actor with attribute write access can likely repeat attempts cheaply.

4. Primitive and severity interpretation

The exact primitive is a race in null_blk configfs attribute stores that allows device fields to be changed while another store is applying queue changes or while power_store is building the device. This can desynchronize dev->submit_queues from the live queue count and can allow zone_nr_conv to exceed nr_zones after validation.

This is not an ordinary UAF case. It is a Class B kernel corruption candidate because the commit explicitly identifies an out-of-bounds dev->zones[] access caused by attacker-influenced configuration state. The demonstrated consequences are WARN, invalid device state, potential OOB access, and kernel DoS. The speculative consequence is limited confidentiality or integrity impact if the later zone-array access provides a useful read or write effect, but that is not proven from the supplied patch.

ImportantCandidate is YES because an explicit OOB kernel access candidate remains unresolved and should not be auto-closed as a simple warning or configuration bug. AutoDowngradeAllowed is NO because the patch establishes a concrete race-driven OOB access candidate, not merely a harmless bookkeeping mismatch.

Operationally this is best treated as actionable Moderate with mandatory manual review, not as proven Important and not as ordinary Low.

5. One-sentence report phrase

A race in null_blk configfs attribute stores can desynchronize validated device state and lead to out-of-bounds dev->zones[] access, requiring local configfs write capability and causing at least DoS with unresolved limited corruption impact.

6. Manual review recommendation

MANUAL CHECK REQUIRED

The issue includes an explicit out-of-bounds kernel array access candidate controlled through racing configuration writes, and the later dev->zones[] access behavior should be reviewed before downgrading.

7. Call-site confidence

Call-site confidence: medium

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

Patch: null_blk: serialize configfs attribute stores with the lock [ Upstream
Commit: 8e839ed5210399a0330a8a6c5885c1d40a537c6d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8e839ed5210399a0330a8a6c5885c1d40a537c6d

Changed files:
  drivers/block/null_blk/main.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=8e839ed5210399a0330a8a6c5885c1d40a537c6d

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

The original Linux kernel CVE announcement for CVE-2026-90185 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90185

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:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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).