[CVE-2026-45895][LOW] quota: fix livelock between quotactl and freeze_super [ Upstream

[CVE-2026-45895][LOW] quota: fix livelock between quotactl and freeze_super [ Upstream

[AL-KERNEL]

CVE: CVE-2026-45895
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: quota: fix livelock between quotactl and freeze_super [ Upstream
Commit: 37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45895
Analysis date: Wed, 27 May 2026 22:42:56 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A quota retry loop can livelock with filesystem freeze on non-preemptible kernels, preventing RCU progress and causing a local filesystem administration DoS.

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

The original Linux kernel CVE announcement for CVE-2026-45895 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45895

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-2026-45895	LOW	CHECK	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-835;**CWE-400;CWE-667;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A quota livelock can occur when quotactl_block() spins in a retry loop while freeze_super() waits for RCU progress through percpu_down_write(). On non preemptible kernels the quota loop may not yield the CPU, preventing an RCU quiescent state and leaving the freezer stuck. For the CVSS the PR:L is used in the paranoid score because delegated filesystem administration or service accounts may be able to run quota and freeze operations below full host root, while typical host triggering requires CAP_SYS_ADMIN. The issue is not network reachable. Impact is denial of service through filesystem freeze hang and 100 percent CPU usage. No supported evidence indicates information disclosure, integrity impact, kernel memory corruption, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) 	MAYBE	WRITE OOB DISK HARDWARE LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	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

* Reliable DoS / livelock: +1
  The issue can livelock `quotactl_block()` against `freeze_super()`, causing the freezer to hang and the quota process to consume 100 percent CPU.

* Availability impact realistic: +1
  The realistic impact is local filesystem administration DoS through stuck freeze or quota operations.

* Local delegated filesystem administration: +1 in paranoid scoring
  Some environments may delegate quota or filesystem administration to service accounts or containerized management components.

* Requires CAP_SYS_ADMIN in typical deployments: -2 conservative
  Reliable triggering normally requires filesystem freeze and quota on/off operations, which are privileged host administration actions.

* Special configuration / scheduling condition: -1 in conservative interpretation
  The livelock is most relevant on non-preemptible kernels or when both loops are pinned to the same CPU. The reproducer is reliable, but the conditions are still administrative and environment-specific.

* No memory corruption: +0
  This is a scheduling/RCU progress livelock, not UAF, OOB write, arbitrary write, or object lifetime corruption.

* No confidentiality or integrity impact: +0
  The patch does not indicate data disclosure, filesystem metadata corruption, or privilege escalation.

## 3. Reachability analysis

The bug is reachable by running filesystem freeze/unfreeze concurrently with quota on/off against a quota-enabled filesystem. In ordinary deployments this requires privileged filesystem administration, typically `CAP_SYS_ADMIN`. Namespaces or containers only matter if quota/freeze operations are delegated to less trusted service accounts or container root.

The issue is not network reachable. Realistic exploitation is local DoS only.

## 4. Severity interpretation

This behaves like ordinary Moderate / Low-like availability impact. It can cause a real hang and CPU spin, but it requires privileged filesystem-management operations and does not involve memory corruption or privilege escalation. The paranoid score only accounts for delegated administration environments.

## 5. One-sentence report phrase

A quota retry loop can livelock with filesystem freeze on non-preemptible kernels, preventing RCU progress and causing a local filesystem administration DoS.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

The issue is a local privileged livelock with no memory corruption, no remote reachability, and no privilege escalation primitive.

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

Patch: quota: fix livelock between quotactl and freeze_super [ Upstream
Commit: 37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82

Changed files:
  fs/quota/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=37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82

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

The original Linux kernel CVE announcement for CVE-2026-45895 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45895

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:H
  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: 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).