[CVE-2026-45861][MODERATE 7.0] gfs2: Fix slab-use-after-free in qd_put [ Upstream

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

CVE: CVE-2026-45861
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: gfs2: Fix slab-use-after-free in qd_put [ Upstream
Commit: ca7c67bdd293089b3483f18886d6b2d0037d2ad9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ca7c67bdd293089b3483f18886d6b2d0037d2ad9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45861
Analysis date: Thu, 28 May 2026 00:17:19 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
GFS2 quota data objects could be freed during filesystem shutdown while still linked on the quota LRU list, allowing a later shrinker traversal to dereference freed slab memory and trigger a kernel use-after-free with at least local DoS impact and possible memory-corruption risk.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-45861 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45861

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-45861	MODERATE	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:H/I:H/A:H';*CWE-416;*CWE-672;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'GFS2 quota data objects could be freed during filesystem shutdown while still linked on the quota LRU list. A later gfs2_qd_shrink_scan traversal may dereference the stale LRU entry and access freed slab memory, resulting in a kernel use-after-free. The realistic base case is a local privileged denial of service because reliable triggering usually needs control over GFS2 mount or shutdown paths. For the CVSS the PR:L is used for the paranoid score because a local user with access to a mounted GFS2 filesystem may influence quota object lifetime and memory pressure even if full mount control is not directly available. Impact is at least a local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel memory corruption, so manual review is required.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6) 	MAYBE	DANGER DISK UAF LINUS SYZBOT KPANIC 	-	-	guess

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Generic memory corruption: +2. The patch fixes a real slab use-after-free caused by freed GFS2 quota objects remaining on an LRU list.
* Real lifetime corruption: +1. This is a stale pointer after free / LRU lifetime bug.
* Reliable kernel crash / strong DoS: +1. The shrinker can later traverse the stale LRU entry and dereference freed memory.
* Availability impact realistic: +1. Kernel crash or filesystem instability is realistic.
* Important filesystem/storage path: +1. The bug is in GFS2 quota object lifetime and shrinker handling.
* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2. Reliable triggering likely requires GFS2 mount or shutdown control in normal systems.

Paranoid additional interpretation:

* Local unprivileged trigger: +1. If a local user can access an already mounted GFS2 filesystem, they may influence quota object creation and memory pressure, even without full mount control.
* Weak LPE concern: +1. The stale LRU entry creates a kernel UAF, but there is no demonstrated reclaim or controlled overwrite primitive in the patch context.
* No remote/network signal. This is not network reachable from the patch context.
* No Dirty-Pipe-like or page-cache corruption signal. The bug is an object lifetime UAF, not shared page ownership corruption.

## 3. Reachability analysis

The realistic trigger is local and depends on GFS2 being mounted with quota activity and then entering filesystem shutdown while quota data objects still exist. In typical deployments, mounting and shutting down GFS2 requires administrative privileges, so the conservative score treats this as privileged local DoS.

The paranoid interpretation is higher because unprivileged users on an already mounted GFS2 filesystem may be able to influence quota object lifetime and memory pressure, while the final free/shrinker timing is handled by kernel paths. Containers usually do not get direct GFS2 mount or shutdown control unless CAP_SYS_ADMIN or equivalent storage management privileges are delegated.

GFS2 is not a default filesystem for most general-purpose systems, but it is a real clustered filesystem deployment target. The bug is not remotely reachable by packet traffic.

## 4. Severity interpretation

This is not an ordinary low-risk cleanup because the primitive is a real kernel use-after-free from a stale LRU list entry. The conservative view is borderline/manual-review Moderate because reliable triggering likely needs privileged filesystem lifecycle control. The paranoid view is a Strong Important candidate because UAF in reclaim/shrinker paths can sometimes become more than DoS if object reuse is influenceable.

Realistic evidence supports kernel crash and filesystem availability impact. Privilege escalation is plausible enough for manual review, but not proven by the patch alone.

## 5. One-sentence report phrase

GFS2 quota data objects could be freed during filesystem shutdown while still linked on the quota LRU list, allowing a later shrinker traversal to dereference freed slab memory and trigger a kernel use-after-free with at least local DoS impact and possible memory-corruption risk.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This is a real kernel UAF in a filesystem shrinker/LRU lifetime path, and the paranoid score depends on whether local users can shape quota object lifetime and slab reuse on mounted GFS2 filesystems.

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UPSTREAM PATCH SUMMARY
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Patch: gfs2: Fix slab-use-after-free in qd_put [ Upstream
Commit: ca7c67bdd293089b3483f18886d6b2d0037d2ad9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ca7c67bdd293089b3483f18886d6b2d0037d2ad9

Changed files:
  fs/gfs2/quota.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=ca7c67bdd293089b3483f18886d6b2d0037d2ad9

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

The original Linux kernel CVE announcement for CVE-2026-45861 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45861

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:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 4
  Paranoid ActionableScore: 7

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).