[CVE-2026-93240][LOW] memcg: make the v1 soft limit knob inert

[CVE-2026-93240][LOW] memcg: make the v1 soft limit knob inert

[AL-KERNEL]

CVE: CVE-2026-93240
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: memcg: make the v1 soft limit knob inert
Commit: 72fb67f6e0e5d78e4f34cf9929d1afdb0fd54203
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=72fb67f6e0e5d78e4f34cf9929d1afdb0fd54203
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93240
Analysis date: Thu, 24 Sep 2026 13:46:30 -0400
ActionableScore: 0
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-2026-93240 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93240

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-2026-93240	LOW	https://www.kernelcve.org/list/?q=CVE-2026-93240 CHECK WITH IMPACT FROM ORIG NN LOW	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:N';CWE-670;CWE-754;BEST CVSS score: '0';DESCR 'The deprecated cgroup v1 memory.soft_limit_in_bytes interface can enable soft limit reclaim, which is the only path that invokes shrink_lruvec for a specific memcg from kswapd and reaches a warning in set_mm_walk. The reported behavior is a kernel warning caused by an unsupported execution context. The patch context does not demonstrate a crash, memory corruption, information disclosure, privilege escalation, or realistic resource exhaustion primitive. For the CVSS the PR:L reflects that a local process needs access to the cgroup interface, but C:N I:N A:N applies because no security impact is demonstrated. The issue is not network reachable.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	YES	LEAK LINUS SYZBOT MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 0
* Paranoid score: 0
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +0: The patch establishes a deprecated cgroup v1 soft-limit reclaim path that can reach a WARN in set_mm_walk when invoked from kswapd.
* +0: WARN-only behavior is not evidence of a kernel crash, memory corruption, information disclosure, integrity violation, privilege escalation, or persistent resource exhaustion.
* +0: No UAF, refcount misuse, double release, stale object, out-of-bounds access, ownership violation, or authorization bypass is shown.
* +0: No remote reachability is established. The interface is a local cgroup v1 control file.
* +0: No reliable availability impact is established. The supplied evidence identifies a warning, not a panic, Oops, deadlock, or host-wide stall.
* No negative privilege penalty was applied. Access control for a particular cgroup hierarchy may be delegated, but the complete applicable privilege boundary is not shown and is irrelevant because no security primitive is established.
* No configuration or legacy-mode penalty was applied. Although cgroup v1 soft limits are deprecated, this does not reduce an already zero security-impact score.

3. Reachability analysis

The affected interface is the local cgroup v1 memory.soft_limit_in_bytes file. A process must be able to write to the relevant cgroup control file, but the supplied patch does not establish whether this requires host-admin-equivalent authority, delegated cgroup management rights, or ownership of an attacker-controlled cgroup.

Namespace-scoped reachability is unresolved. Cgroup delegation can exist, but the input does not establish that an ordinary unprivileged user can create the relevant cgroup, write the knob, induce the reclaim path, and obtain a security-relevant result.

No network path, special hardware prerequisite, boot option, sysctl prerequisite, race condition, attacker-controlled payload, or persistent resource-consumption mechanism is established.

4. Primitive and severity interpretation

The patch removes the operational effect of the deprecated cgroup v1 soft-limit interface. Previously, a valid write could set memcg soft-limit state and enable soft-limit reclaim behavior. That reclaim path could call shrink_lruvec from kswapd for a specific memcg and eventually reach set_mm_walk, which emits a warning for that execution context.

The demonstrated issue is an invalid-state or unsupported-context warning. It is not an active-object lifetime violation, UAF, stale-reference use, double release, refcount mutation, controlled overwrite, semantic security-boundary bypass, or ownership/COW violation.

PrimitiveClass is NONE because no meaningful corruption, lifetime, authorization, disclosure, or integrity primitive is established. RealUAF is NO. There is no demonstrated consequence beyond a warning, and no technically grounded paranoid escalation is available. ImportantCandidate is NO and AutoDowngradeAllowed is YES because automatic closure would not discard an unresolved security primitive.

Likely operational severity is non-security maintenance or diagnostics. It may be relevant for warning reduction and removal of deprecated functionality, but it is not actionable as a kernel security vulnerability from the supplied evidence.

5. One-sentence report phrase

The deprecated cgroup v1 memory.soft_limit_in_bytes interface could reach a WARN path when soft-limit reclaim invokes memory walking from kswapd, but the supplied patch establishes no crash, memory corruption, disclosure, privilege escalation, or security-boundary impact.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch and supplied context establish a WARN-only deprecated-feature cleanup without a concrete security primitive or plausible unsupported high-impact consequence.

7. Call-site confidence

Call-site confidence: high

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

Patch: memcg: make the v1 soft limit knob inert
Commit: 72fb67f6e0e5d78e4f34cf9929d1afdb0fd54203
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=72fb67f6e0e5d78e4f34cf9929d1afdb0fd54203

Commit description:

The v1 soft limit has been deprecated since v6.12 and nobody has reported
depending on it.  Start the removal by decoupling the interface from the
implementation: keep memory.soft_limit_in_bytes, but ignore writes to it
and always report the maximum value on read similar to what
memory.kmem.limit_in_bytes already does.

Writes are still parsed, so malformed input keeps returning -EINVAL.  The
knob now also behaves the same everywhere: it used to return -EOPNOTSUPP
on PREEMPT_RT, where soft limit reclaim has always been disabled.

This also fixes the syzbot report linked below.  Soft limit reclaim is the
only caller that runs shrink_lruvec() from kswapd against a specific
memcg, so it is the only way to reach lru_gen_shrink_lruvec() and in turn
set_mm_walk(), which warns when called from kswapd.

Link: https://lore.kernel.org/20260811203203.3456029-2-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Reported-by: syzbot+12ee2725d5fde63a9c96@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/6a7a6929.b50370da.49fe0.005e.GAE@google.com/
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@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-v1.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=72fb67f6e0e5d78e4f34cf9929d1afdb0fd54203

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

The original Linux kernel CVE announcement for CVE-2026-93240 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93240

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:N
  The Best / paranoid CVSS score: 0

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: 0

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).