[CVE-2026-74602][MODERATE REGULAR] ring-buffer: Initialise reader page order in rb_allocate_cpu_buffer()

[CVE-2026-74602][MODERATE REGULAR] ring-buffer: Initialise reader page order in rb_allocate_cpu_buffer()

[AL-KERNEL]

CVE: CVE-2026-74602
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ring-buffer: Initialise reader page order in rb_allocate_cpu_buffer()
Commit: 2e37f2bf111429fbfa4d985b12df3ba496ca70aa
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2e37f2bf111429fbfa4d985b12df3ba496ca70aa
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74602
Analysis date: Sat, 22 Aug 2026 14:48:41 -0400
ActionableScore: 4
ActionableScore lower bound: 2
Actionable bucket: Borderline manual review recommended / not an Important candidate
Manual review required: YES

Summary:
A missing initialization of `bpage->order` in the tracing ring-buffer allocation path can cause large subbuffer pages to be freed with the wrong order, leading to memory leaks, allocator inconsistency, or kernel crash under privileged local tracing configurations.

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

The original Linux kernel CVE announcement for CVE-2026-74602 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74602

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: YES

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

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

CVE-2026-74602	MODERATE	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:L/I:L/A:H';CWE-665;CWE-404;CWE-763;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'ring-buffer CPU buffer allocation for tracing subbuffers larger than PAGE_SIZE can store an incorrect page order because bpage order remains 0 while the actual allocation uses buffer subbuf_order. When such a buffer page is later released, free_buffer_page relies on the stored order and may free the allocation with the wrong order, which can leak pages or destabilize the kernel memory allocator. For the CVSS the PR:L is used for the paranoid score because some systems may delegate tracing control to a service account, container root, or reduced capability administrator rather than full host root. The issue is local and is not network reachable. Impact is at least denial of service through memory leak, allocator inconsistency, or kernel crash. A limited confidentiality or integrity impact is kept only for paranoid triage because wrong order page freeing is a memory management bug, but there is no clear arbitrary write primitive in the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / not an Important candidate (with actual score 3)  SKIP CVE-2026-74602 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	TRACE SIMPLEFIX HARDWARE LINUS MEMORY  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=4
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended / not an Important candidate**::

## 2. Signal breakdown

Paranoid score signals:

* Memory corruption, Weak/indirect corruption candidate: +1
  `bpage->order` is used later by `free_buffer_page()`. A wrong order on free can cause wrong-size page freeing, leaked pages, or allocator state inconsistency.

* Memory layout invariant restoration: +1
  The patch restores consistency between the actual allocation size `buffer->subbuf_order` and the stored free-time metadata `bpage->order`.

* Real lifetime/free-path corruption: +1
  The bug affects metadata consumed by the free path, so it is more than cosmetic initialization.

* Reliable kernel crash / strong DoS concern: +1
  A wrong free order in kernel page allocation can realistically destabilize the kernel or cause later crashes, especially for subbuffers larger than `PAGE_SIZE`.

* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -1 in paranoid, -2 conservative
  Conservative scoring assumes tracing ring-buffer resizing/configuration is admin controlled. Paranoid scoring uses a reduced penalty because tracing control may be delegated to service accounts, container root, or reduced capability administrators in some environments.

* Rare / non-default runtime condition: -1
  The issue requires ring-buffer subbuffers larger than `PAGE_SIZE`, which is not the most common default tracing configuration.

No strong LPE bonus is awarded because the patch does not show attacker-controlled reclaim, controlled overwrite, callback control, type confusion, or arbitrary write.

## 3. Reachability analysis

The bug is local and not network reachable. Triggering requires a tracing ring-buffer configuration with subbuffers larger than `PAGE_SIZE`, followed by freeing of the affected buffer page. In normal deployments this is controlled by privileged tracing interfaces, usually requiring root or `CAP_SYS_ADMIN`. Namespaces or delegated tracing setups may reduce the practical privilege requirement, but this is environment dependent. The path is not a default remote attack surface.

Call-site confidence: medium. The patch shows the allocation site and commit states that `free_buffer_page()` relies on the omitted field, but the full free path is not included in the supplied diff.

## 4. Severity interpretation

This behaves like a memory-management correctness bug with DoS potential, not like a demonstrated Important-class privilege escalation. The theoretical risk is higher than a simple leak because wrong-order freeing can corrupt allocator assumptions. Realistic exploitation evidence is limited because there is no demonstrated reclaim primitive, overwrite target, or user-controlled payload. This should not be auto-treated as a trivial cleanup, but it also should not be escalated to Important without further allocator-path analysis.

## 5. One-sentence report phrase

A missing initialization of `bpage->order` in the tracing ring-buffer allocation path can cause large subbuffer pages to be freed with the wrong order, leading to memory leaks, allocator inconsistency, or kernel crash under privileged local tracing configurations.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: wrong-order page freeing is a kernel memory-management issue and may have allocator corruption consequences, but the available patch does not demonstrate a practical privilege-escalation primitive.

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

Patch: ring-buffer: Initialise reader page order in rb_allocate_cpu_buffer()
Commit: 2e37f2bf111429fbfa4d985b12df3ba496ca70aa
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2e37f2bf111429fbfa4d985b12df3ba496ca70aa

Commit description:

In rb_allocate_cpu_buffer(), bpage->order was omitted, leaving it as 0.
This is an issue for a ring-buffer with subbufs bigger than PAGE_SIZE if
when freed: free_buffer_page() relies on this value. Align the value
with the actual allocation size (buffer::subbuf_order).

Cc: stable@vger.kernel.org
Fixes: f9b94da ("ring-buffer: Set new size of the ring buffer sub page")
Link: https://patch.msgid.link/20260806211306.3704194-4-vdonnefort@google.com
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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=2e37f2bf111429fbfa4d985b12df3ba496ca70aa

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

The original Linux kernel CVE announcement for CVE-2026-74602 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74602

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:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 2
  Paranoid ActionableScore: 4

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).