[CVE-2026-97961][MODERATE REGULAR] perf/core: Allow list_del during perf_event_overflow() [ Upstream

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

CVE: CVE-2026-97961
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: perf/core: Allow list_del during perf_event_overflow() [ Upstream
Commit: 723e85fb2c3bcd237ac02cbd69502ed62ce0068c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=723e85fb2c3bcd237ac02cbd69502ed62ce0068c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97961
Analysis date: Fri, 25 Sep 2026 15:10:08 -0400
ActionableScore: 1
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-2026-97961 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97961

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 REGULAR
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-2026-97961	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97961 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-664;*CWE-672;**CWE-400;BEST CVSS score: '4.7';DESCR 'A perf scheduler callback list iteration can become invalid when a PMU callback reaches perf_event_overflow and removes its current sched_cb_list entry through perf_sched_cb_dec. The non safe iterator can subsequently access list links of the removed entry and cause a kernel Oops or panic. For the CVSS the PR:L value is used because a local user process must create and control a suitable perf event file descriptor. Triggering also depends on a PMU using the sched_task callback and on a specific event overflow state. The issue is not network reachable. Impact is local denial of service. The patch context does not demonstrate a use after free, out of bounds access, information leak, or controlled write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	YES	DANGER HARDWARE LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	YES	NO	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap was applied. The paranoid score does not increase because the patch establishes iterator invalidation and a crash-capable poisoned-list dereference, but does not establish a post-free object use, controlled list-pointer corruption, arbitrary write, or meaningful stale-object reuse.

2. Signal breakdown

* +1 Reliable kernel crash or strong DoS. `perf_pmu_sched_task()` iterates `sched_cb_list` with `list_for_each_entry()`, while the callback path can invoke `perf_sched_cb_dec()` and remove the currently iterated entry. A subsequent iterator step can consume the removed entry list links, which are normally poisoned by `list_del()`, causing a kernel Oops or panic.
* +0 Weak corruption concern. The bug involves invalid iterator state after removal, but no attacker-controlled pointer value, list-link write, target selection, or active object replacement is shown.
* +0 Local unprivileged trigger. The supplied context establishes a local perf-event file descriptor and `PERF_EVENT_IOC_REFRESH` path, but does not establish that the complete PMU-specific callback and overflow sequence is available to an ordinary unprivileged user under the deployed `perf_event_paranoid` policy.
* +0 Remote reachability. No network path is present.
* +0 Real UAF. `list_del()` removes the list membership of the `perf_cpu_pmu_context` entry, but the supplied patch does not show that the containing object is freed or dereferenced after its lifetime ends.
* +0 Controlled reclaim or object replacement. Not demonstrated.
* +0 Arbitrary or directed write. Not demonstrated.
* +0 Structured stale-object leverage. Not awarded because the observed unsafe operation is iterator progression through removed list links, not attacker-influenced consumption of reclaimed structured fields.
* +0 Weak LPE concern. Not awarded because the list corruption does not establish a useful post-crash primitive.
* +0 Additional Availability impact. Not awarded because the possible Oops or panic is already counted by the single DoS point.
* +0 Confidentiality and Integrity impact. Not awarded because no disclosure, unauthorized modification, controlled corruption sink, or security-boundary bypass is established.

3. Reachability analysis

The triggering operation is local. The attacker needs a suitable perf event file descriptor, must invoke `PERF_EVENT_IOC_REFRESH`, and must cause the event limit to reach zero while a PMU `sched_task` callback is running.

The supplied patch does not identify the affected PMU implementation, its event configuration requirements, or the exact `perf_event_open()` permission policy. Linux perf access can be limited by `perf_event_paranoid`, capability checks, PMU availability, and distribution policy. Therefore, neither ordinary below-host-admin reachability nor host-admin-equivalent privilege is positively established.

No network namespace, user namespace, or capability-scope information is supplied. The complete trigger cannot be classified as namespace-scoped. No special hardware requirement is proven, although the relevant PMU callback support is a real functional prerequisite rather than a generic perf requirement.

This is not a conventional concurrent race between independently scheduled attackers. It is a reentrant ordered callback sequence. The specific PMU callback, overflow condition, and event-limit transition are required, but the supplied evidence does not establish a narrow externally uncontrollable timing window sufficient for a negative race penalty.

4. Primitive and severity interpretation

The exact primitive is list iterator invalidation. `perf_pmu_sched_task()` uses the current `sched_cb_list` member during iteration. A callback may synchronously remove that current member through `perf_sched_cb_dec()`. The ordinary iterator later obtains the next entry through links belonging to the removed element, which may contain `LIST_POISON` values after `list_del()`.

This is not a demonstrated use-after-free. The patch changes `list_for_each_entry()` to `list_for_each_entry_safe()`, which preserves the next entry before executing a callback that may remove the current entry. The patch does not show freeing of `cpc`, controlled reuse of its storage, a second refcount operation, a stale destructor call, or any write through a dangling reference.

The appropriate classification is CLASS_C. The demonstrated consequence is local kernel crash or DoS. A stronger consequence such as privilege escalation, information disclosure, controlled list corruption, or arbitrary kernel write is speculative and unsupported.

ImportantCandidate is NO because the defect is constrained to an unsafe list traversal after a valid list removal, and no independently useful corruption primitive remains after excluding the crash. AutoDowngradeAllowed is YES because there is no demonstrated UAF, repeated lifetime mutation, authorization bypass, controlled corruption, or unresolved active-object reuse mechanism.

Likely operational severity is ordinary Moderate or lower priority depending on whether the affected PMU callback path is enabled and available to non-administrative perf users.

5. One-sentence report phrase

A local perf event overflow can remove the currently iterated scheduler callback list entry, causing an unsafe iterator to follow invalid list links and potentially crash the kernel.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm the affected PMU implementations, whether `pmu->sched_task` is enabled in the deployed kernel, and whether local non-administrative users can create the required perf event and reach the `PERF_EVENT_IOC_REFRESH` overflow sequence.

7. Call-site confidence

Call-site confidence: medium

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

Patch: perf/core: Allow list_del during perf_event_overflow() [ Upstream
Commit: 723e85fb2c3bcd237ac02cbd69502ed62ce0068c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=723e85fb2c3bcd237ac02cbd69502ed62ce0068c

Changed files:
  kernel/events/core.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=723e85fb2c3bcd237ac02cbd69502ed62ce0068c

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

The original Linux kernel CVE announcement for CVE-2026-97961 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97961

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: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: 1

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 REGULAR

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).