[CVE-2026-72012][MODERATE 7.0] tracing/osnoise: Call synchronize_rcu() when unregistering

[CVE-2026-72012][MODERATE 7.0] tracing/osnoise: Call synchronize_rcu() when unregistering

[AL-KERNEL]

CVE: CVE-2026-72012
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: tracing/osnoise: Call synchronize_rcu() when unregistering
Commit: 3c693635bb7b3a9b6645831a84fed2af46cdf249
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3c693635bb7b3a9b6645831a84fed2af46cdf249
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72012
Analysis date: Sat, 15 Aug 2026 04:34:22 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
An RCU lifetime race in tracing/osnoise instance unregister can leave readers using tracer state after unregister, making a local kernel crash likely and limited UAF-style confidentiality or integrity impact possible in the paranoid case.

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

The original Linux kernel CVE announcement for CVE-2026-72012 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72012

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.

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

CVE-2026-72012	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-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'tracing osnoise instance unregister can race with RCU readers that traverse the instance list and still use the trace_array reference stored through the instance. The old cleanup path deferred freeing the instance object but did not guarantee that all readers had finished before the referenced tracer state could become invalid. This is an RCU race and a possible use after free or stale pointer dereference scenario. For the CVSS the PR:L is used for the paranoid score because reliable triggering normally needs local tracing control, but some deployments may delegate tracefs or tracing control to less privileged service accounts or container roots. The issue is not network reachable and is triggered through local tracing control plane operations. Impact is at least local denial of service via kernel crash. In worst case it may allow limited confidentiality or integrity impact due to UAF style memory corruption and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	TRACE SIMPLEFIX LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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

ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Memory corruption, weak/indirect corruption candidate: +1
  The patch fixes an RCU lifetime window where readers may still traverse an osnoise instance and use the referenced tracer or trace_array state after unregister.

* Real lifetime corruption: +1
  This is an RCU lifetime issue. kvfree_rcu_mightsleep protected the instance object itself, but did not guarantee that all readers finished before the referenced tracer state could become invalid.

* Reliable kernel crash / strong DoS: +1
  A stale trace_array or tracer reference in kernel tracing code can plausibly lead to an Oops or kernel crash.

* Confidentiality impact plausible, paranoid only: +1
  Limited C impact is possible in the paranoid interpretation because stale pointer or UAF style bugs may expose unintended kernel state, but no concrete info leak primitive is shown.

* Integrity impact plausible, paranoid only: +1
  Limited I impact is possible in the paranoid interpretation due to UAF style memory lifetime corruption, but no write primitive, callback control, or object replacement is demonstrated.

* Availability impact realistic, paranoid only: +1
  Kernel crash from a tracing lifetime bug is host-wide if triggered.

Negative signals:

* Hard or unreliable race / special timing required: -1
  The bug depends on unregister racing with RCU readers traversing the instance list.

* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2 for conservative score
  Managing tracing or osnoise instances normally requires privileged tracefs access.

Not awarded:

* No remote/network-triggerable bonus.
* No strong LPE bonus.
* No strong memory corruption primitive bonus.
* No arbitrary write, callback dispatch, refcount takeover, or attacker-controlled reclaim is shown.

Call-site confidence: medium. The changed function and lifetime relationship are visible, but detailed reader call sites are not included in the supplied patch.

## 3. Reachability analysis

The bug is local and triggered through tracing/osnoise control-plane operations, especially unregistering an osnoise instance while RCU readers may still traverse the instance list. In typical deployments this requires root or CAP_SYS_ADMIN because tracefs and tracer instance management are privileged.

Namespaces and containers can change the practical interpretation. If tracefs control is delegated to a container root, service account, or reduced-capability administrator, the effective attacker model can be closer to PR:L rather than full host-root. The path is not remotely reachable through packets or network traffic. osnoise tracing is also not a default high-exposure user API, but tracing is commonly built into production kernels.

## 4. Severity interpretation

This is not an ordinary resource leak or cleanup-only issue. It is an RCU lifetime bug with possible stale pointer or UAF behavior, so auto-closing as low-risk would be unsafe.

Realistically, the most likely demonstrated impact is local denial of service through a kernel crash. Theoretical confidentiality or integrity impact is possible only in the paranoid interpretation because the bug class is UAF-like, but the patch does not show controlled reclaim, object replacement, write-after-free, callback control, or a concrete privilege escalation primitive. Therefore it fits Actionable Moderate rather than a Strong Important candidate.

## 5. One-sentence report phrase

An RCU lifetime race in tracing/osnoise instance unregister can leave readers using tracer state after unregister, making a local kernel crash likely and limited UAF-style confidentiality or integrity impact possible in the paranoid case.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This should be reviewed manually because it is an RCU lifetime issue and possible UAF candidate, even though the available patch context supports DoS more strongly than practical privilege escalation.

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

Patch: tracing/osnoise: Call synchronize_rcu() when unregistering
Commit: 3c693635bb7b3a9b6645831a84fed2af46cdf249
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3c693635bb7b3a9b6645831a84fed2af46cdf249

Commit description:

This ensures that any RCU readers traversing the instance list
have finished, before releasing the reference on the tracer that
the instance points to.

Cc: stable@vger.kernel.org
Fixes: a6ed2ae ("tracing: Switch to kvfree_rcu() API")
Link: https://patch.msgid.link/20260609045430.1589786-1-crwood@redhat.com
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Crystal Wood <crwood@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/trace/trace_osnoise.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=3c693635bb7b3a9b6645831a84fed2af46cdf249

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

The original Linux kernel CVE announcement for CVE-2026-72012 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72012

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: 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: NO
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).