[CVE-2026-72010][LOW] cgroup/cpuset: rebind mm mempolicy to effective_mems, not mems_allowed

[CVE-2026-72010][LOW] cgroup/cpuset: rebind mm mempolicy to effective_mems, not mems_allowed

[AL-KERNEL]

CVE: CVE-2026-72010
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: cgroup/cpuset: rebind mm mempolicy to effective_mems, not mems_allowed
Commit: b7adeba2a21c98c7b20f18e27e3ead86bdb5e08d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b7adeba2a21c98c7b20f18e27e3ead86bdb5e08d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72010
Analysis date: Sat, 15 Aug 2026 23:11:57 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A local cpuset and mempolicy configuration combined with CPU hotplug can pass an empty nodemask into mempolicy rebind, causing a divide by zero and kernel DoS, but no memory corruption or privilege escalation primitive is evident.

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

The original Linux kernel CVE announcement for CVE-2026-72010 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72010

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-2026-72010	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	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-369;CWE-682;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'A divide by zero can occur in the cpuset and mempolicy rebind path when a child cpuset has cpuset.mems unset and a task with an MPOL_F_RELATIVE_NODES VMA policy is moved into it. During a CPU hotplug driven nodemask update, cpuset_update_tasks_nodemask can pass an empty mems_allowed mask to mpol_rebind_mm, and the later relative nodemask fold can divide by zero. For the CVSS the PR:L is used for the paranoid score because some deployments may delegate cgroup cpuset control to less privileged local users or service accounts, but reliable triggering still usually requires local code execution and a CPU hotplug or equivalent administrative event. The issue is not network reachable and the observed impact is denial of service via kernel crash. There is no concrete evidence of UAF, OOB access, information disclosure, or privilege escalation from this patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	SIMPLEFIX HARDWARE 	NO	NO	checked

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

ActionableScore=2
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: **0**
* Paranoid score: **2**
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: **+1**
  The commit describes a deterministic divide by zero in `mpol_relative_nodemask()` / `__nodes_fold()` during mempolicy rebind.

* Requires admin/root/CAP_SYS_ADMIN-like control in typical deployments: **-2**
  Reliable triggering requires cpuset manipulation plus CPU hotplug. CPU online/offline operations are normally root/admin controlled.

* Broad/default/common subsystem: **+1**
  cgroups/cpuset and mempolicy are common kernel facilities, but the exact trigger path is configuration-dependent.

Conservative total: **0**

Paranoid additional interpretation:

* Local unprivileged or reduced-privilege trigger concern: **+1**
  Some environments delegate cgroup/cpuset control to containers, service managers, or less privileged local actors. This does not make the bug broadly unprivileged, but it weakens a strict PR:H assumption.

* Availability impact realistic: **+1**
  If the preconditions are met, the divide by zero can crash the kernel rather than merely fail an operation.

Paranoid total: **2**

Not awarded:

* No generic memory corruption. The patch fixes an empty nodemask passed to mempolicy rebind, not UAF, OOB, double-free, refcount misuse, or type confusion.
* No privilege escalation plausible signal. There is no supported LPE primitive.
* No confidentiality or integrity impact. The described primitive is divide by zero leading to DoS.
* No remote/network trigger.
* No security-boundary bypass.

Call-site confidence: **high**. The affected caller and the downstream failure condition are described directly in the commit and patch.

## 3. Reachability analysis

The bug is triggered locally through cpuset configuration, task placement, a VMA mempolicy using `MPOL_F_RELATIVE_NODES`, and a CPU hotplug event. In ordinary deployments, creating and managing relevant cpuset state and toggling CPU online status are administrative operations, so the conservative model treats this as privileged local DoS.

Namespaces and delegation can lower practical privilege in some managed environments, especially where cgroup control is delegated to containers or service accounts. However, reliable triggering still depends on CPU hotplug or an equivalent administrative event, so this does not become a normal unprivileged local attack.

The path is not network reachable. The affected subsystem is common, but the exact preconditions are narrow.

## 4. Severity interpretation

This behaves like an **ordinary Moderate / Low-like local DoS**, not an Important-class vulnerability. The failure mode is a divide by zero caused by passing an empty `mems_allowed` mask instead of guaranteed non-empty `effective_mems`.

Theoretical impact is limited to kernel crash. Realistic exploitation evidence does not support memory corruption, information disclosure, integrity impact, or privilege escalation.

## 5. One-sentence report phrase

A local cpuset and mempolicy configuration combined with CPU hotplug can pass an empty nodemask into mempolicy rebind, causing a divide by zero and kernel DoS, but no memory corruption or privilege escalation primitive is evident.

## 6. Manual review recommendation

**NO MANUAL CHECK NEEDED**

This is a local DoS-only divide-by-zero issue with administrative or delegated-management preconditions, no network exposure, and no concrete memory corruption or LPE primitive.

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

Patch: cgroup/cpuset: rebind mm mempolicy to effective_mems, not mems_allowed
Commit: b7adeba2a21c98c7b20f18e27e3ead86bdb5e08d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b7adeba2a21c98c7b20f18e27e3ead86bdb5e08d

Commit description:

Creating a child cpuset where cpuset.mems is never set leads to a div/0
when a VMA mempolicy with MPOL_F_RELATIVE_NODES rebinds in response to a
CPU hotplug event.

Reproduction steps:
 1) Create a cgroup w/ cpuset controls (do not set cpuset.mems)
 2) Move the task into the child cpuset
 3) Create a VMA mempolicy for that task with MPOL_F_RELATIVE_NODES
 4) unplug and hotplug a cpu
      echo 0 > /sys/devices/system/cpu/cpu1/online
      echo 1 > /sys/devices/system/cpu/cpu1/online
 5) mempolicy rebind does a div/0 in mpol_relative_nodemask on the
    call to __nodes_fold()

The cpuset code passes (cs->mems_allowed) which is not guaranteed to have
nodes to the rebind routine.  Use cs->effective_mems instead, which is
guaranteed to have a non-empty nodemask once we reach that code path.

Link: https://lore.kernel.org/all/CA+0ovCiEz6SP_sn3kN4Tb+_oC=eHMXy_Ffj=usV3wREdQrUtww@mail.gmail.com/
Fixes: ae1c802 ("cpuset: apply cs->effective_{cpus,mems}")
Closes: https://lore.kernel.org/linux-mm/CA+0ovCgxbZkXa+OU8w3s84R3KNPNxxRfmsNR-udh+afQBbGNmw@mail.gmail.com/
Suggested-by: Gregory Price <gourry@gourry.net>
Suggested-by: Waiman Long <longman@redhat.com>
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: Farhad Alemi <farhad.alemi@berkeley.edu>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Ridong Chen <ridong.chen@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Michal Koutný" <mkoutny@suse.com>
Cc: <stable@vger.kernel.org>
[ david: add a comment, slightly rephrase description ]
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/cgroup/cpuset.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=b7adeba2a21c98c7b20f18e27e3ead86bdb5e08d

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

The original Linux kernel CVE announcement for CVE-2026-72010 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72010

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: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: 0
  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).