[CVE-2026-53126][LOW] blk-cgroup: fix disk reference leak in blkcg_maybe_throttle_current() [ Upstream

[CVE-2026-53126][LOW] blk-cgroup: fix disk reference leak in blkcg_maybe_throttle_current() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53126
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: blk-cgroup: fix disk reference leak in blkcg_maybe_throttle_current() [ Upstream
Commit: 4048ed98860d3785645ebbd34f69566a6c7320c3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4048ed98860d3785645ebbd34f69566a6c7320c3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53126
Analysis date: Wed, 24 Jun 2026 15:10:37 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A missing put_disk() in blkcg_maybe_throttle_current() can leak a gendisk reference on blkcg or blkg lookup failure, potentially preventing disk cleanup or hot unplug, but the issue is local, configuration dependent, and does not indicate memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-53126 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53126

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-2026-53126	LOW	CHECK	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:N/A:H';*CWE-772;*CWE-401;CWE-404;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'blk cgroup can leak a gendisk reference in blkcg_maybe_throttle_current() when the blkcg or blkg lookup path fails after a disk reference was acquired. The leaked reference can keep the disk object alive after it should have been released, causing a resource leak and possible cleanup or hot unplug problems. For the CVSS the PR:L is used for the paranoid score because an untrusted local process may be able to generate I/O in a configured block cgroup while the failure path is reached during cgroup or disk teardown. The issue is not network reachable and does not indicate UAF, OOB access, or an arbitrary write primitive. Impact is denial of service via resource retention rather than privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) 	MAYBE	SIMPLEFIX LEAK ERRORPATH 	-	-	checked

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

ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Conservative signals:

* Important filesystem/storage path: +1. The bug is in blk-cgroup / block-layer throttling and affects gendisk lifetime management.
* Requires admin/root/CAP_* in typical deployments: -2. Reliable triggering likely requires block cgroup configuration, device teardown, or cgroup management.
* Availability impact realistic: +1. A leaked gendisk reference can prevent disk object cleanup or hot-unplug completion, but this is resource retention rather than immediate corruption.

Conservative total is effectively 1 after bounding at low practical severity.

Paranoid additional interpretation:

* Local unprivileged trigger: +1. A local process doing I/O inside an already configured block cgroup might participate in the failure path while teardown is performed elsewhere.
* Real lifetime corruption: +1. This is a reference lifetime bug, but it is a leak/over-retention, not UAF or double free.
* Hard or unreliable timing / special condition: -1. The error path requires blkcg/blkg lookup or blkg_tryget failure after a disk reference was acquired.

Paranoid total: 2.

No generic memory corruption, no UAF, no OOB write, no arbitrary write, no page-cache corruption, no privilege escalation primitive, and no network reachability are supported by the patch.

## 3. Reachability analysis

The affected path is local block I/O throttling through blk-cgroup. In normal deployments, reliable setup and teardown of the relevant cgroup and disk state is administrative, so the conservative privilege assumption is privileged local control. A weaker paranoid interpretation is that an unprivileged process may generate I/O inside a preconfigured cgroup while an administrator or orchestrator performs teardown, but the unprivileged process does not directly control the full failure condition.

The path is not network reachable. Containers or delegated cgroup management may lower practical triggering requirements, but the impact remains a reference leak rather than memory corruption.

## 4. Severity interpretation

This behaves like an ordinary Moderate / Low-like resource-lifetime bug. The leaked gendisk reference can keep a disk object alive and cause cleanup or hotplug problems, but it does not create a stale pointer, UAF reclaim primitive, attacker-controlled overwrite, or information disclosure path. The realistic impact is limited availability degradation through resource retention.

## 5. One-sentence report phrase

A missing put_disk() in blkcg_maybe_throttle_current() can leak a gendisk reference on blkcg or blkg lookup failure, potentially preventing disk cleanup or hot unplug, but the issue is local, configuration dependent, and does not indicate memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed for urgent triage purposes unless the environment has unusual delegated block-cgroup management or hotplug-heavy storage workflows.

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

Patch: blk-cgroup: fix disk reference leak in blkcg_maybe_throttle_current() [ Upstream
Commit: 4048ed98860d3785645ebbd34f69566a6c7320c3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4048ed98860d3785645ebbd34f69566a6c7320c3

Changed files:
  block/blk-cgroup.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=4048ed98860d3785645ebbd34f69566a6c7320c3

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

The original Linux kernel CVE announcement for CVE-2026-53126 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53126

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:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 1
  Paranoid ActionableScore: 2

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).