[CVE-2026-53050][MODERATE 7.0] quota: Fix race of dquot_scan_active() with quota deactivation [ Upstream

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

CVE: CVE-2026-53050
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: quota: Fix race of dquot_scan_active() with quota deactivation [ Upstream
Commit: 2bdc80f4619411e5bd4a3ef23f51e14021ed457c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2bdc80f4619411e5bd4a3ef23f51e14021ed457c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53050
Analysis date: Thu, 25 Jun 2026 08:50:47 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race between `dquot_scan_active()` and quota deactivation can let quota scanning acquire a reference to a zero-reference `dquot` that remains on the releasing list, leading under memory pressure to use-after-free and at least local kernel crash risk, with theoretical privilege-escalation concern requiring manual review.

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

The original Linux kernel CVE announcement for CVE-2026-53050 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53050

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-2026-53050	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-362;*CWE-416;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in quota dquot handling can occur when dquot_scan_active runs concurrently with quota deactivation in quota_release_workfn. A dquot with dq_count 0 can still have DQ_ACTIVE_B set and can be found by the active scan, which may take a reference without removing it from the releasing list. Under memory pressure this can let the scan path operate on a freed dquot, creating a use after free condition. For the CVSS the PR:L is used for the paranoid score because a local user can influence quota objects and memory pressure while quota deactivation or filesystem management is occurring, although reliable standalone triggering may require privileged quota management. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to use after free memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 4)  SKIP CVE-2026-53050  SKIP The Fixes patch not applied yet, so unlikely that actual: 869b6ea1609f655a43251bf41757aa44e5350a8f YES  NO NO unknown 	MAYBE	LOCK DISK INIT RACE UAF HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative scoring:

* Generic memory corruption: +2. The commit explicitly says the caller of `dquot_scan_active()` can work on a freed `dquot`, which is a UAF class issue.
* Real lifetime corruption: +1. The bug is a reference and list lifetime race involving `dq_count`, `releasing_dquots`, and delayed quota release.
* Reliable kernel crash / strong DoS: +1. A freed `dquot` can be used under memory pressure, making kernel crash plausible.
* Important filesystem/storage path: +1. Quota handling is part of filesystem accounting and storage metadata management.
* Hard or unreliable race / special timing required: -1. The issue depends on a race between quota deactivation and active dquot scanning.
* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2. Reliable quota deactivation normally requires privileged filesystem administration.

Conservative total: 3

Paranoid scoring:

* Generic memory corruption: +2. UAF is directly supported by the commit text.
* Real lifetime corruption: +1. The fix changes reference acquisition semantics to remove zero-reference dquots from releasing/free lists before incrementing `dq_count`.
* Weak LPE concern: +1. UAF in kernel quota objects could theoretically become more than DoS, but no controlled reclaim or overwrite primitive is demonstrated.
* Reliable kernel crash / strong DoS: +1. Use of freed quota objects under memory pressure is a credible crash path.
* Important filesystem/storage path: +1. The bug is in quota lifecycle handling for filesystems.
* Local unprivileged influence: +1. A local user may influence quota object creation, quota activity, and memory pressure, even if quota deactivation itself is usually privileged.
* Hard or unreliable race / special timing required: -1. The race window and deactivation timing make exploitation non-trivial.
* Privileged operation dependency: -1. Paranoid scoring does not apply the full -2 because unprivileged users may influence one side of the race, but privileged quota management is still usually needed for reliable triggering.

Paranoid total: 5

## 3. Reachability analysis

The bug is local and not network reachable. The most direct trigger requires quota deactivation or filesystem quota management, which is normally restricted to root or CAP_SYS_ADMIN. However, local users can often create quota-relevant activity, allocate files, churn dquots, and create memory pressure. That makes the UAF worth manual review even if the reliable end-to-end trigger likely involves a privileged quotaoff or filesystem-management operation.

Namespaces and containers do not obviously make this broadly unprivileged by default. If a container or delegated environment allows quota management or mount/filesystem administration, the practical PR may be lower than full host root. The affected code is not a rare driver path, but quotas must be enabled and exercised.

## 4. Severity interpretation

This is not an ordinary cosmetic WARN. The patch and commit message explicitly identify a race that can lead to use-after-free of a `dquot` under memory pressure. Realistic demonstrated impact is local DoS via kernel crash. Privilege escalation is not proven, because the patch does not show a controlled reclaim, arbitrary write, or attacker-controlled overwrite primitive. Still, because this is a kernel UAF in a filesystem lifetime path, it should be treated as Actionable Moderate at minimum and as a Strong Important candidate for paranoid/manual triage.

## 5. One-sentence report phrase

A race between `dquot_scan_active()` and quota deactivation can let quota scanning acquire a reference to a zero-reference `dquot` that remains on the releasing list, leading under memory pressure to use-after-free and at least local kernel crash risk, with theoretical privilege-escalation concern requiring manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the issue is explicitly a UAF/lifetime race in kernel filesystem quota code. Even though reliable triggering likely depends on privileged quota deactivation and a hard timing window, UAF bugs should not be auto-closed without checking reclaimability, reachable call paths, and whether unprivileged quota activity can shape the freed object lifetime.

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

Patch: quota: Fix race of dquot_scan_active() with quota deactivation [ Upstream
Commit: 2bdc80f4619411e5bd4a3ef23f51e14021ed457c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2bdc80f4619411e5bd4a3ef23f51e14021ed457c

Changed files:
  fs/quota/dquot.c
  include/linux/quotaops.h

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=2bdc80f4619411e5bd4a3ef23f51e14021ed457c

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

The original Linux kernel CVE announcement for CVE-2026-53050 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53050

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: 3
  Paranoid ActionableScore: 5

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: NO
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).