[CVE-2026-90188][LOW] null_blk: free global tag_set on init error path [ Upstream

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

CVE: CVE-2026-90188
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: null_blk: free global tag_set on init error path [ Upstream
Commit: 0b2faa330184340d9418ad2c627c2ae881772e33
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0b2faa330184340d9418ad2c627c2ae881772e33
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90188
Analysis date: Thu, 17 Sep 2026 18:02:15 -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-2026-90188 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90188

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-2026-90188	LOW	https://www.kernelcve.org/list/?q=CVE-2026-90188 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:H/UI:N/S:U/C:N/I:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.4';DESCR 'A resource leak in null_blk can occur on the module init error path when shared_tags is enabled and device creation fails after the global tag_set has been allocated. Since module init returns an error, null_exit is not invoked and the tag_set tags and maps can remain allocated. For the CVSS the PR:H is used because triggering normally requires administrative control over null_blk module initialization or equivalent block device setup. The issue is not network reachable and does not provide a memory corruption primitive. Impact is denial of service only through possible memory exhaustion after repeated failed initialization attempts.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	YES	INIT SIMPLEFIX LEAK ERRORPATH HARDWARE 	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**::

Applied conservative minimum clamp: -1 -> 0. No Important-preserving floor applies.

2. Signal breakdown

Positive signals:

* +1 Concrete persistent kernel resource/reference leak. The global null_blk tag_set is allocated when shared_tags is enabled and is not freed if later device creation fails during module init.
* +1 Paranoid-only sustained resource exhaustion concern. Repeated failed initialization attempts could plausibly accumulate permanent tag_set leaks, but this remains host-admin-controlled resource exhaustion.

Negative signals:

* -2 Host-admin-equivalent privilege required. Triggering the relevant path requires null_blk module initialization or equivalent block-driver setup control.

Not awarded:

* No UAF or stale post-lifetime object use is established.
* No repeated release/refcount mutation is established.
* No arbitrary write, controlled reclaim, OOB access, or type confusion is established.
* No confidentiality or integrity impact is supported.
* No network reachability is established.
* No extra availability point is awarded beyond the resource-leak concern.
* No filesystem ownership, COW, authorization, namespace, or security-boundary bypass is established.

3. Reachability analysis

The vulnerable path is the null_blk module init error path. A realistic trigger requires enabling shared_tags and causing device creation to fail after the global tag_set allocation. This is normally reachable only by a host administrator or an equivalent actor able to load and configure the null_blk driver.

Namespace-scoped privilege is not established. This is not a network-triggered issue. No special physical hardware is required, but null_blk is a test block driver and the vulnerable sequence is an initialization failure path rather than ordinary unprivileged runtime activity. There is no race requirement.

4. Primitive and severity interpretation

The exact primitive is a persistent kernel resource leak: the global blk-mq tag_set is allocated but not released when module initialization fails before null_exit can run.

PrimitiveClass=NONE because the patch establishes a leak, not memory corruption, UAF, authorization bypass, semantic reinterpretation, or ownership violation. The demonstrated consequence is potential resource exhaustion after repeated failed init attempts. The speculative consequence is broader DoS by memory pressure, but only under host-admin-controlled repeated triggering.

ImportantCandidate=NO because there is no meaningful unresolved corruption or boundary-bypass primitive. AutoDowngradeAllowed=YES because this is a host-admin-gated resource leak with no memory corruption or privilege escalation evidence.

5. One-sentence report phrase

A null_blk init error path can permanently leak the global shared tag_set after a failed device creation, but exploitation requires host administrative control and the impact is limited to possible resource exhaustion.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: resource leak only, host-admin-gated trigger, no UAF, no corruption primitive, no network exposure, and no security-boundary bypass.

7. Call-site confidence

Call-site confidence: high

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

Patch: null_blk: free global tag_set on init error path [ Upstream
Commit: 0b2faa330184340d9418ad2c627c2ae881772e33
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0b2faa330184340d9418ad2c627c2ae881772e33

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=0b2faa330184340d9418ad2c627c2ae881772e33

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

The original Linux kernel CVE announcement for CVE-2026-90188 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90188

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:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.4

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).