[CVE-2026-89752][LOW] mm: memcg: stop reclaim when a limit update is superseded

[CVE-2026-89752][LOW] mm: memcg: stop reclaim when a limit update is superseded

[AL-KERNEL]

CVE: CVE-2026-89752
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: mm: memcg: stop reclaim when a limit update is superseded
Commit: 39ec1e4183a718f448b2e9de681dcbdda18fce42
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=39ec1e4183a718f448b2e9de681dcbdda18fce42
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89752
Analysis date: Sat, 12 Sep 2026 01:18:03 -0400
ActionableScore: 2
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-2026-89752 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89752

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-2026-89752	LOW	https://www.kernelcve.org/list/?q=CVE-2026-89752 CHECK WITH IMPACT FROM ORIG NN MODERATE	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-362;CWE-667;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A race in memcg limit updates can make memory.high or memory.max reclaim use a stale writer target after another open file raises or removes the current limit. For memory.max this can leave the first writer blocked in the reclaim and OOM retry path while the current limit already has enough margin, causing repeated OOM event accounting and a local denial of service for the writer or management process. For the CVSS the PR:L is used for the paranoid score because a local process with delegated write access to cgroup memory control files can trigger the condition without full host administrator privileges. The issue is not network reachable and does not show a memory corruption primitive. Impact is availability only, mainly a stuck write operation and resource management disruption.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	LINUS TEST MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap was applied.

2. Signal breakdown

Positive signals:

* +1: Demonstrated local availability impact. A writer to memory.max can remain blocked indefinitely in the reclaim and OOM retry path after another writer supersedes the limit.
* +1: Resource-management control-plane disruption. The stale target can cause repeated OOM event accounting and a stuck cgroup memory limit update.

Negative or non-awarded signals:

* Real UAF not awarded. The patch shows stale scalar limit usage, not stale object lifetime use.
* Concrete repeated release or refcount mutation not awarded. There is no put, release, free, or refcount operation on a dangling object.
* Memory corruption not awarded. No OOB access, UAF, arbitrary write, type confusion, or stale pointer dereference is established.
* Confidentiality and integrity not awarded. The effect is availability only.
* Remote reachability not awarded. Triggering requires local writes to cgroup memory control files.
* Strong DoS crash point not awarded. The demonstrated result is a stuck writer and repeated OOM events, not a kernel panic.
* Race timing penalty not applied. Although concurrent writers are required, the sequence is reproducible through separate open files and is not shown to require a narrow uncontrollable race.
* Host-admin penalty not applied. Host-admin-equivalent privilege is not positively required because cgroup control files may be delegated to non-root management processes or service accounts.

3. Reachability analysis

The trigger requires two concurrent writers to the same memory.high or memory.max file through separate kernfs open files. The attacker or triggering process must be able to write the relevant cgroup memory control files. On many systems this is performed by host root or a privileged cgroup manager, but the operation can also be delegated to a service account or container management context with write access to that cgroup.

This is not a network-reachable issue. It is also not established as namespace-scoped by capability checks. Cgroup namespace presence alone would not be enough, and the supplied evidence does not show an attacker-created namespace granting the complete required operation.

Prior privileged setup may exist if a non-root actor obtains delegated cgroup write access from a manager such as systemd or an orchestrator. No special hardware, boot option, or rare configuration is required beyond use of memcg memory.high or memory.max controls.

4. Primitive and severity interpretation

The primitive is an invalid concurrent state handling bug in memcg limit updates. The writer stores a target limit and continues reclaiming toward that stale local target even after another writer changes the current limit. For memory.max, this can leave the first writer looping in the reclaim and OOM retry path while the active limit no longer requires reclaim.

This is CLASS_C because the demonstrated behavior is DoS or invalid-state behavior without an independently useful corruption primitive. There is no active structured stale object, no fixed stale storage UAF, no cleanup destructor UAF, and no second lifetime mutation through a dangling reference.

The demonstrated consequence is local availability impact against the writer or cgroup management operation. A broader service-management DoS is plausible if the blocked writer is a critical manager, but the patch does not establish kernel memory corruption, privilege escalation, information disclosure, or a security-boundary bypass.

ImportantCandidate=NO because the bug is availability-only and no memory corruption or authorization primitive remains unresolved. AutoDowngradeAllowed=YES because the issue can be treated as ordinary Moderate or Low-like operational DoS without losing a meaningful kernel exploitation primitive.

5. One-sentence report phrase

A race in memcg memory.high or memory.max updates can make reclaim continue toward a stale superseded limit, leaving a local writer blocked and causing repeated OOM event accounting without memory corruption or privilege escalation.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: the patch establishes a local cgroup control-plane DoS only, with no UAF, refcount corruption, arbitrary write, information disclosure, privilege escalation path, or security-boundary bypass.

7. Call-site confidence

Call-site confidence: high

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

Patch: mm: memcg: stop reclaim when a limit update is superseded
Commit: 39ec1e4183a718f448b2e9de681dcbdda18fce42
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=39ec1e4183a718f448b2e9de681dcbdda18fce42

Commit description:

kernfs serializes file operations only per open file, so separate open
files can update the same memory.high or memory.max file concurrently.
Both handlers store the new limit before synchronous reclaim, but continue
to use the writer's local target in the reclaim loop.  If another writer
raises or removes the limit, the first writer can continue reclaiming
toward a stale target.

For memory.max, this can leave the writer looping indefinitely once
reclaim retries are exhausted.  The OOM path sees sufficient margin under
the current limit and returns true without killing, while the writer still
compares usage against its stale target and records another OOM event.

Check the current limit at the start of each reclaim iteration and stop if
it no longer matches the writer's target.

Reproducer:

Populate a cgroup with anonymous memory and disable swapping.  Lower
memory.max from one open file, then restore it to "max" through another
open file after the new limit becomes visible.

Without the patch, the first writer remains blocked and repeatedly
increments the OOM event counter.  With the patch, it returns normally.

This was not motivated by a reported production workload.  We found it
through automated randomized testing for our cgroup observability work
and reduced it to the reproducer above.

Link: https://lore.kernel.org/20260724021805.1234583-1-guopeng.zhang@linux.dev
Fixes: 8c8c383 ("mm: memcontrol: try harder to set a new memory.high")
Fixes: b6e6edc ("mm: memcontrol: reclaim and OOM kill when shrinking memory.max below usage")
Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
Acked-by: Tao Cui <cuitao@kylinos.cn>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  mm/memcontrol.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=39ec1e4183a718f448b2e9de681dcbdda18fce42

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

The original Linux kernel CVE announcement for CVE-2026-89752 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89752

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:L/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: unknown
  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).