[CVE-2026-74601][LOW] ring-buffer: Use current_context for safe per-CPU buffer swap

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

CVE: CVE-2026-74601
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ring-buffer: Use current_context for safe per-CPU buffer swap
Commit: 5b926fb04cb9ef3156dcf88c69a59d3d1a1c4f9f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5b926fb04cb9ef3156dcf88c69a59d3d1a1c4f9f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74601
Analysis date: Sat, 22 Aug 2026 15:10:29 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A race in ring_buffer_swap_cpu can allow a per-CPU ring buffer swap while a write is still in progress, causing inconsistent tracing state and RB_WARN_ON, but exploitation is local, timing-dependent, and appears limited to DoS or tracing disruption.

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

The original Linux kernel CVE announcement for CVE-2026-74601 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74601

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.

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

CVE-2026-74601	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-362;CWE-667;CWE-703;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'ring_buffer_swap_cpu can race with an active per CPU ring buffer write because the old committing counter may temporarily drop to 0 before the write operation is fully finished. An interrupt or concurrent swap in that window can exchange the CPU buffers while the writer still relies on the previous buffer state, leading to inconsistent tracing state and RB_WARN_ON in rb_commit. For the CVSS the PR:L is used in the paranoid score because some environments may delegate tracing or reduced admin capabilities to service accounts or container root, although typical host tracing control is PR:H. The issue is not network reachable and is triggered through local tracing control paths rather than packet or remote input. Impact is denial of service or tracing disruption only, with high attack complexity due to the race timing window.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	WARNONLY TRACE RACE HARDWARE LINUS 	NO	NO	checked

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

ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Conservative:

* WARN/state-corruption concern: +1. The race can lead to inconsistent ring-buffer state and RB_WARN_ON in rb_commit.
* Broad/core tracing infrastructure: +1. The affected code is in the kernel tracing ring buffer, but exposure is mainly through tracing control paths.
* Hard or unreliable race / special timing required: -1. The issue requires hitting a narrow window where committing temporarily drops to 0 during rb_move_tail.
* Requires admin/root/CAP-like tracing privileges in typical deployments: -2. ring_buffer_swap_cpu and tracing buffer swap operations are normally controlled by privileged tracing interfaces.

Paranoid:

* Same as above, but privilege penalty is reduced to -1 because some environments may delegate tracing or debugfs/tracefs access to reduced-privilege service accounts or container-like admin roles.
* No generic memory corruption signal is awarded. The patch shows inconsistent buffer state and WARN_ON, but not UAF, OOB write, double-free, stale callback, refcount takeover, or attacker-controlled object reuse.
* No LPE signal is awarded. There is no demonstrated reclaim, overwrite, callback dispatch, type confusion, or controlled corruption primitive.
* No remote/network signal is awarded. The path is local tracing control, not packet or remote input.

## 3. Reachability analysis

The realistic trigger is a local privileged tracing user or process that can invoke per-CPU ring-buffer swap operations while tracing writes are active. In normal deployments this is administrator-controlled, usually via tracing/debug interfaces, so conservative scoring treats it as requiring high privileges. Namespace or container setups could lower practical privileges if tracefs/debugfs or tracing control is delegated, but that is not the default safe assumption. The race is timing-dependent and requires an interrupt or concurrent swap during a narrow in-progress write window.

Call-site confidence: high, because the affected function and described failing call sequence are included in the input.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like kernel correctness/DoS issue, not an Important-class vulnerability. The theoretical concern is inconsistent ring-buffer state, but the patch and commit context show RB_WARN_ON/tracing disruption rather than a concrete memory corruption primitive. Realistic exploitation evidence supports local DoS or tracing disruption only, with high attack complexity and no confidentiality or integrity impact.

## 5. One-sentence report phrase

A race in ring_buffer_swap_cpu can allow a per-CPU ring buffer swap while a write is still in progress, causing inconsistent tracing state and RB_WARN_ON, but exploitation is local, timing-dependent, and appears limited to DoS or tracing disruption.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: local privileged or delegated tracing access is required, the race is narrow, and the provided patch does not show UAF, OOB access, double-free, type confusion, privilege escalation, or a network-reachable path.

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

Patch: ring-buffer: Use current_context for safe per-CPU buffer swap
Commit: 5b926fb04cb9ef3156dcf88c69a59d3d1a1c4f9f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5b926fb04cb9ef3156dcf88c69a59d3d1a1c4f9f

Commit description:

The ring_buffer_swap_cpu() function currently checks the per-CPU
committing counter to determine if a buffer is actively being written to
before performing the swap. However, there exists a race window where
this check can be bypassed:

    ring_buffer_lock_reserve
        cpu_buffer = buffer->buffers[cpu];       // cpu_buffer_a
        rb_reserve_next_event
            rb_start_commit // inc committing
            if (unlikely(READ_ONCE(cpu_buffer->buffer) != buffer)) {...}
            __rb_reserve_next
                rb_move_tail
                    rb_end_commit(cpu_buffer);   // dec committing => 0
                    /* interrupt hits here, successfully swaps! */
                    local_inc(&cpu_buffer->committing);

    ring_buffer_unlock_commit
        cpu_buffer = buffer->buffers[cpu];      // cpu_buffer_b
        rb_commit
            rb_end_commit
            RB_WARN_ON(cpu_buffer, !local_read(&cpu_buffer->committing))
                                                // triggers warning

The committing counter can temporarily drop to 0 during a single write
operation (within rb_move_tail), creating a window where swap can
succeed even though the write is still in progress. This leads to
inconsistent buffer state and triggers the RB_WARN_ON in rb_commit().

Replace the committing counter check with current_context checks, which
are set at the entry of ring_buffer_lock_reserve() and remain valid
throughout the entire write operation, providing a reliable indicator of
buffer busy state during swap.

Cc: stable@vger.kernel.org
Fixes: 4239c38 ("ring-buffer: Process commits whenever moving to a new page.")
Link: https://patch.msgid.link/20260803005640.2445666-2-wutengda@huaweicloud.com
Signed-off-by: Tengda Wu <wutengda@huaweicloud.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=5b926fb04cb9ef3156dcf88c69a59d3d1a1c4f9f

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

The original Linux kernel CVE announcement for CVE-2026-74601 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74601

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:L
  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: 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: 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).