[CVE-2026-90187][LOW] null_blk: free zones array on device power-off [ Upstream

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

CVE: CVE-2026-90187
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: null_blk: free zones array on device power-off [ Upstream
Commit: 056be41932c95aabdb3c2967d1ef4978f17a0225
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=056be41932c95aabdb3c2967d1ef4978f17a0225
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90187
Analysis date: Fri, 18 Sep 2026 03:09:54 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90187 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90187

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-2026-90187	LOW	https://www.kernelcve.org/list/?q=CVE-2026-90187 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A memory leak in null_blk zoned device handling occurs because dev zones is allocated when the device is powered on but was not freed when the device is powered off. Repeated power off and power on cycles can overwrite the old dev zones pointer and accumulate leaked kernel memory, which may eventually cause resource exhaustion and denial of service. For the CVSS the PR:L is used for the paranoid score because some environments may delegate null_blk or configfs control to a reduced privilege service account or container management context, although typical systems require administrator privileges. The issue is not network reachable and requires local control of null_blk configuration or device power state. Impact is denial of service only. There is no supported evidence of use after free, out of bounds access, information disclosure, or privilege escalation in the vulnerable pre patch behavior.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	YES	LOCK INIT LEAK ERRORPATH UAF HARDWARE  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: -1
* Conservative score: 0
* Raw paranoid score: 0
* Paranoid score: 0
* Final recommended bucket: **Ordinary Moderate**::

Conservative score was clamped from -1 to 0 because the actionable scale lower bound is 0. No floor applies because there is no UAF, no memory corruption, no authorization bypass, and no security-boundary primitive.

2. Signal breakdown

Positive signals:

* +1 Concrete persistent kernel resource/reference leak. `dev->zones` is allocated on zoned device power-on and the old pointer can be overwritten on later power-on without freeing the previous allocation.
* +1 Paranoid resource exhaustion concern. Repeated power-off and power-on cycles can accumulate leaked kernel memory and may eventually cause resource exhaustion.

Negative signals:

* -2 Host-admin-equivalent control required. The vulnerable operation is through null_blk configfs device management and device power-state control, which is normally host administrator controlled.

Important non-awarded signals:

* RealUAF not awarded. The patch description explicitly says the previous behavior did not create the zone_cond_store access problem because `dev->zones` was only freed during configfs removal or module exit.
* Memory corruption not awarded. The established vulnerable behavior is lost allocation ownership, not use-after-free, OOB access, double free, or stale object reuse.
* Reliable kernel crash not awarded. Host-wide failure is only an eventual resource-exhaustion consequence after repeated cycles, not an immediate crash primitive.
* Confidentiality and integrity not awarded. No disclosure, unauthorized write, shared-page corruption, or security-boundary bypass is established.
* Remote reachability not awarded. The trigger is local null_blk control-plane configuration, not packet or remote storage input.
* Extra availability not awarded separately in conservative scoring because the leak itself is the established primitive and immediate host-wide DoS is not shown.
* Manual-review preservation not applied because this is a constrained resource leak with host-admin control and no unresolved corruption primitive.

3. Reachability analysis

The trigger requires local control over null_blk zoned-device configuration and power cycling through configfs. That is normally restricted to host root or host-admin-equivalent privileges. No evidence shows that an ordinary local user can create and power-cycle the relevant null_blk configfs device.

Namespace-scoped privilege is not established. The supplied patch does not show that the complete null_blk configfs operation can be performed inside attacker-created namespaces with only namespace-local capabilities.

No network trigger is present. No special physical hardware is required because null_blk is a software block driver, but the relevant configuration interface is administrative. The issue is not a timing race. Repeated triggering is possible only for an actor that can repeatedly power off and power on the null_blk zoned device.

4. Primitive and severity interpretation

The exact primitive is a persistent kernel memory leak of the zoned-device `dev->zones` array. The old allocation becomes unreachable when a later `null_init_zoned_dev()` allocation overwrites the pointer after a power cycle.

This is not active structured UAF and not fixed stale storage UAF. It is a resource ownership leak. The added locking around `zone_cond_store()` is a correctness measure after moving the free operation earlier into `null_del_dev()`, not evidence that the pre-patch bug allowed post-free access.

There is no concrete repeated release/refcount operation. There is no first release that can end object lifetime followed by a second lifetime mutation through the same dangling reference.

PrimitiveClass is NONE because no memory corruption, lifetime corruption, authorization bypass, COW violation, or security-boundary primitive is established. The demonstrated consequence is potential DoS through accumulated kernel memory leakage. The likely operational severity is Low-like or ordinary Moderate, especially because the trigger is host-admin controlled.

ImportantCandidate is NO because there is no meaningful unresolved exploitation leverage beyond resource exhaustion. AutoDowngradeAllowed is YES because automatic downgrade would not discard a concrete corruption or security-boundary primitive.

5. One-sentence report phrase

A null_blk zoned-device memory leak can occur because dev zones is reallocated on device power-on without freeing the previous array on power-off, allowing repeated administrative power cycles to consume kernel memory and potentially cause DoS.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: this is a host-admin-gated resource leak with no UAF, no memory corruption, no authorization bypass, no remote path, and no plausible privilege-escalation primitive established by the patch.

7. Call-site confidence

Call-site confidence: high

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

Patch: null_blk: free zones array on device power-off [ Upstream
Commit: 056be41932c95aabdb3c2967d1ef4978f17a0225
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=056be41932c95aabdb3c2967d1ef4978f17a0225

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=056be41932c95aabdb3c2967d1ef4978f17a0225

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

The original Linux kernel CVE announcement for CVE-2026-90187 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90187

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:L/PR:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 0

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).