[CVE-2026-89500][MODERATE 7.0] ring-buffer: Make cpu_buffer::free_page a buffer_data_read_page [ Upstream

[CVE-2026-89500][MODERATE 7.0] ring-buffer: Make cpu_buffer::free_page a buffer_data_read_page [ Upstream

[AL-KERNEL]

CVE: CVE-2026-89500
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ring-buffer: Make cpu_buffer::free_page a buffer_data_read_page [ Upstream
Commit: a1dabe68fb53730bc0be60c5dbfd3f4c560084e7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a1dabe68fb53730bc0be60c5dbfd3f4c560084e7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89500
Analysis date: Fri, 11 Sep 2026 19:07:01 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89500 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89500

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 7.0
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-89500	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89500 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:H/I:H/A:H';CWE-362;CWE-763;*CWE-401;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in the tracing ring buffer can free a cached reader page with an allocation order that no longer matches the order used when the page was allocated. This can happen after a concurrent ring buffer subbuffer resize and may cause either a memory leak or a kernel crash due to an invalid free_pages order. For the CVSS the PR:L is used in the paranoid score because delegated tracefs access or reduced capability admin access may allow a local non root service to trigger tracing operations in some deployments. The issue is not network reachable and requires local interaction with tracing control paths. Impact is at least local denial of service via kernel crash. In the worst still defensible case, freeing pages with the wrong order may corrupt allocator state and may allow confidentiality or integrity impact, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)  SKIP CVE-2026-89500 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	OOB INIT TRACE SIMPLEFIX LEAK KERNEL_PANIC_PLUS_UAF HARDWARE LINUS  KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4	-	-	checked

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

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4. No floor or cap applied.
* Raw paranoid score: 5
* Paranoid score: 5. No floor or cap applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Conservative signals:

* +2: Concrete allocator/page lifetime corruption candidate. The patch establishes that a cached reader page can be freed with a free_pages() order different from the order used for allocation after concurrent ring buffer subbuffer resize.
* +1: Reliable kernel crash / strong DoS. The commit explicitly states that the mismatched order may crash the kernel or leak memory.
* +1: Memory layout invariant restoration. The fix stores the page address together with the actual allocation order, restoring consistency between allocation size and free size.

Conservative raw total: 4.

Paranoid additional signal:

* +1: Attacker-influenced repeatable configuration/lifetime manipulation is plausible for an actor that can access tracing control paths, because the same actor may be able to allocate or discard cached reader pages while changing subbuffer order.

Paranoid raw total: 5.

Non-awarded material signals:

* RealUAF not awarded. This is a wrong free_pages() order / allocator lifetime invariant bug, not a direct stale object dereference after free.
* Concrete repeated release/refcount not awarded. There is no visible first put/release followed by a second lifetime mutation on the same dangling reference.
* Strong CLASS_A corruption not awarded. The patch does not establish controlled reclaim, attacker-selected victim object, arbitrary write, callback control, or refcount takeover.
* Confidentiality and integrity points not awarded as direct signals. They are possible worst-case review concerns, but the patch itself establishes crash/leak behavior and wrong freeing, not a concrete read/write primitive.
* Extra availability not awarded. Kernel crash and memory leak are already represented by the single DoS signal.
* Race penalty not applied. The bug involves concurrency, but the supplied context does not prove a narrow one-shot or externally uncontrollable race.
* Host-admin penalty not applied. Tracing controls are often privileged, but the supplied evidence does not positively establish that host-admin-equivalent privilege is required for every practical deployment.
* Remote reachability not awarded. The vulnerable path is local tracing control/read-page handling, not packet or network input.

3. Reachability analysis

The vulnerable operation is reachable through kernel tracing ring buffer control paths involving cached reader pages and subbuffer resize. A practical trigger requires local ability to interact with tracing interfaces and to cause reader-page allocation/free together with ring buffer resize.

Ordinary unprivileged reachability is not established from the supplied patch. Host-admin-equivalent reachability is also not conclusively established from the supplied context, because tracefs permissions may be delegated to tracing services or reduced-privilege operational accounts. Therefore HostAdminRequired is UNKNOWN rather than YES or NO.

Namespace-scoped privilege is not established. This is not a netns or userns-scoped networking operation. NamespaceScopedPrivilege is NO.

Prior setup may exist if an administrator has mounted tracefs or delegated tracing access, but the patch itself does not prove a separate mandatory privileged setup beyond normal tracing availability. No special hardware is required. The race appears repeatable by an actor that can repeatedly exercise tracing read-page and resize operations, so no hard-race penalty is applied.

4. Primitive and severity interpretation

The exact primitive is a mismatched allocation/free invariant in the tracing ring buffer. cpu_buffer->free_page previously stored only the page address. After subbuffer order changes, code could later call free_pages() using a newer or stale global subbuf_order rather than the order that was actually used to allocate the cached reader page.

This is not an ordinary stale cleanup dereference and not a direct UAF. It is a CLASS_B memory-management/lifetime consistency issue because freeing with the wrong order can corrupt page allocator state or leak memory. If the free order is too small, memory can be leaked. If the free order is too large, the allocator may be told to free pages outside the original allocation, which is a meaningful unresolved kernel memory-management corruption concern.

No concrete repeated release/refcount operation exists. The first lifetime operation / exact surviving dangling reference / second lifetime mutation pattern is not present.

Demonstrated consequence is local denial of service through kernel crash or memory leak. Speculative consequence is broader allocator-state corruption with possible C/I relevance, but controlled exploitation is not demonstrated. Because the allocator corruption mechanism is concrete but exploitation leverage is unresolved, ImportantCandidate is YES and ManualReview is REQUIRED. AutoDowngradeAllowed is NO because automatically closing this as ordinary Moderate would discard a meaningful unresolved kernel memory-management corruption primitive.

Likely operational severity is Actionable Moderate, with Strong Important review justified if manual analysis finds attacker influence over allocation order, page placement, or allocator reuse sufficient for exploitation beyond crash.

5. One-sentence report phrase

A tracing ring buffer resize race can cause a cached reader page to be freed with the wrong allocation order, leading to kernel crash or memory leak and requiring manual review because allocator state corruption beyond DoS remains technically plausible.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch establishes a concrete wrong free_pages() order on kernel pages, which is stronger than a pure warning or logic bug and may corrupt allocator state even though controlled reclaim or privilege escalation is not demonstrated.

7. Call-site confidence

Call-site confidence: high

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

Patch: ring-buffer: Make cpu_buffer::free_page a buffer_data_read_page [ Upstream
Commit: a1dabe68fb53730bc0be60c5dbfd3f4c560084e7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a1dabe68fb53730bc0be60c5dbfd3f4c560084e7

Changed files:
  kernel/trace/ring_buffer.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=a1dabe68fb53730bc0be60c5dbfd3f4c560084e7

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

The original Linux kernel CVE announcement for CVE-2026-89500 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89500

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:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 4
  Paranoid ActionableScore: 5

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).