[CVE-2026-93197][LOW] memcg: move LRU size accounting on reparenting instead of copying it [ Upstream

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

CVE: CVE-2026-93197
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: memcg: move LRU size accounting on reparenting instead of copying it [ Upstream
Commit: 007bc1842317bb99f5f6205afede940f951674c2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=007bc1842317bb99f5f6205afede940f951674c2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93197
Analysis date: Fri, 18 Sep 2026 04:38:05 -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-2026-93197 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93197

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-2026-93197	LOW	https://www.kernelcve.org/list/?q=CVE-2026-93197 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-682;**CWE-400;*CWE-664;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'memcg LRU reparenting copied LRU size counters from an offlined child cgroup to its parent instead of moving them. The parent accounting remained correct, but the dying child cgroup could keep stale phantom LRU counters even though the folios were no longer on its lists. Reclaim can still walk dying cgroups, so shrink_lruvec may repeatedly budget scans for empty lists and waste CPU for as long as the dead cgroup remains visible. For MGLRU, the same stale accounting can also over budget shadow node limits. For the CVSS the PR:L in the paranoid score reflects environments with delegated cgroup management, container root, or a service account that can create and remove memory cgroups. The issue is not network reachable and does not indicate UAF, OOB access, or arbitrary write. Impact is denial of service through CPU waste and reclaim degradation, not direct privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)  SKIP CVE-2026-93197 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	OOB UAF LINUS MEMORY  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=2
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2. No floor or cap applied.
* Raw paranoid score: 2
* Paranoid score: 2. No floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Concrete persistent accounting defect. LRU size counters are copied from an offlined child memcg to the parent instead of being moved, leaving stale phantom counters on dying cgroups.
* +1 Availability impact through reclaim degradation. shrink_lruvec and MGLRU accounting can spend CPU budget on empty lists or over budget shadow node limits while dying cgroups remain visible.
* 0 No RealUAF. The patch does not establish a freed object being dereferenced or a stale post lifetime object use.
* 0 No concrete repeated release or refcount operation. The fix changes accounting updates, not object put or release sequencing.
* 0 No controlled reclaim, arbitrary write, OOB access, callback control, or type confusion is demonstrated.
* 0 No confidentiality or integrity impact is awarded. The issue is stale accounting and CPU waste, not disclosure or unauthorized data modification.
* 0 No remote reachability. Triggering is through memcg lifecycle and reclaim behavior, not network input.
* 0 No local unprivileged trigger is established. Delegated cgroup management is possible in some environments, but the supplied evidence does not prove the complete trigger is available to an ordinary local user.
* 0 No extra availability point. The same reclaim CPU waste is already counted once and there is no distinct crash, persistent filesystem shutdown, or data loss.

3. Reachability analysis

The likely trigger requires creating, populating, and offlining memory cgroups so that LRU folios are reparented while stale per-zone LRU counters remain on the dying child. This operation is normally controlled by host cgroup management, systemd, container runtimes, or delegated cgroup subtrees.

Host-admin-equivalent privilege is not positively established from the supplied patch alone, because cgroup delegation may allow a non-root service account or container-management context to create and remove cgroups. However, below-host-admin reachability is also not fully proven. Therefore HostAdminRequired is UNKNOWN.

NamespaceScopedPrivilege is UNKNOWN. The patch is about memcg reparenting rather than a clearly namespace-local capability check, and the complete create, populate, offline, and reclaim trigger chain is not proven to be fully namespace-scoped.

No special hardware, network exposure, firmware mediation, or narrow race is required. The issue is state/accounting persistence after cgroup offlining rather than a timing race.

4. Primitive and severity interpretation

The exact primitive is stale LRU size accounting on dying memcgs after folio reparenting. The parent receives correct accounting, but the child retains counters for folios it no longer owns. Later reclaim still walks dying cgroups and may waste CPU scanning empty LRU lists or over-budgeting MGLRU shadow nodes.

This is not active structured UAF, fixed stale storage UAF, double free, repeated refcount mutation, OOB access, arbitrary write, or authorization bypass. It is a resource/accounting consistency bug with availability consequences.

Demonstrated consequence is reclaim CPU waste and possible system responsiveness degradation under memory pressure or repeated cgroup churn. Speculative privilege escalation is not supported. There is no meaningful exploitation leverage beyond DoS/reclaim degradation.

PrimitiveClass is NONE because no corruption, lifetime, ownership, authorization, or security-boundary primitive is established beyond stale accounting. ImportantCandidate is NO because the issue remains resource/accounting DoS without memory corruption or boundary bypass. AutoDowngradeAllowed is YES because no unresolved Important-grade primitive would be lost by treating this as ordinary Moderate/Low-like.

Likely operational severity is ordinary Moderate or Low-like depending on how much cgroup churn and memory pressure an attacker can induce.

5. One-sentence report phrase

memcg LRU reparenting copied rather than moved LRU size counters, leaving phantom counters on dying cgroups and causing reclaim to waste CPU on empty lists, with impact limited to denial of service through reclaim degradation.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: the patch establishes stale accounting and resource waste only, with no UAF, repeated release, memory corruption, authorization bypass, confidentiality impact, or integrity impact.

7. Call-site confidence

Call-site confidence: high

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

Patch: memcg: move LRU size accounting on reparenting instead of copying it [ Upstream
Commit: 007bc1842317bb99f5f6205afede940f951674c2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=007bc1842317bb99f5f6205afede940f951674c2

Changed files:
  mm/swap.c
  mm/vmscan.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=007bc1842317bb99f5f6205afede940f951674c2

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

The original Linux kernel CVE announcement for CVE-2026-93197 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93197

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:L
  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: 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).