[CVE-2026-99237][IMPORTANT] tracing: Hold trace_types_lock when resetting last boot data from readers

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

CVE: CVE-2026-99237
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: tracing: Hold trace_types_lock when resetting last boot data from readers
Commit: 92b69f6db640dadc0851762ee2e12db99f083cad
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=92b69f6db640dadc0851762ee2e12db99f083cad
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99237
Analysis date: Mon, 02 Nov 2026 22:09:11 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
Concurrent tracefs readers can race the LAST_BOOT reset and free the same `module_delta` allocation twice, with a notifier also able to access it during destruction.

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

The original Linux kernel CVE announcement for CVE-2026-99237 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99237

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: IMPORTANT
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-2026-99237	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-99237 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=IMPORTANT RESULT=DIFF INDEPENDENT_LEGACY=IMPORTANT INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_WINS_DISAGREEMENT PRE_MERGE_LEGACY=IMPORTANT (final Legacy and Aegis differ; FINAL: IMPORTANT, Aegis: MODERATE_KPANIC)	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-415;*CWE-416;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in committed tracing allows two readers to pass the LAST_BOOT state check and free module_delta twice. A module notifier can also update module_delta concurrently while the object is being freed, providing concrete double free and use after free candidates rather than a warning only condition. For the CVSS the PR:L value is selected because reliable triggering requires local access to the affected tracefs files, although those permissions can be delegated to an unprivileged diagnostic user or service. AC:H reflects the need to align two readers or a reader and module notifier within a race window. The likely impact is a kernel crash, while controlled kernel heap corruption and local privilege escalation remain plausible worst case consequences that require validation. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. final reconciliation stage IMPORTANT to IMPORTANT because KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and TEMP_KPANIC_MERGE_IMPORTANT_WINS and KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 2 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	READ TRACE SIMPLEFIX LEAK LINUS TEST INCREASED_TO_HIGH_BASED_ON_GUESSCVSS TEMP_KPANIC_MERGE_IMPORTANT_WINS KPANIC_UNSUPPORTED_REMOVED	-	-	checked

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

ActionableScore=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 3.
* Conservative score: 5. REAL UAF FLOOR 5 applied because the first free can end `module_delta` lifetime and another reader can free the same stale object again.
* Raw paranoid score: 4.
* Paranoid score: 5. The same floor applies; no unsupported exploit effects were added.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 real lifetime violation: the commit explicitly states that two readers can free `module_delta` twice.
* +1 concrete repeated release: both readers retain the same pointer after independently passing the LAST_BOOT check; the first free can end lifetime and the second free is another lifetime-mutating operation.
* +1 plausible kernel crash/strong DoS from double-free or concurrent notifier access.
* -1 hard timing: the supplied evidence requires two readers, or a reader and notifier, to overlap within a race window.
* Paranoid +1: the second free acts through already-freed storage and may mutate allocator state. This supports unknown post-lifetime corruption, not arbitrary write or LPE.
* Controlled reclaim, attacker-selected payload/target, disclosure, and C/I impact are not shown. No separate availability point is awarded.
* FLOOR 5 applied; structured-stale leverage and Weak LPE were not separately counted for the same double-free fact.

3. Reachability analysis

The vulnerable entries include tracefs read paths and `tracing_open(O_TRUNC)`. Access requires permission to the affected tracefs files, but the patch does not establish whether an ordinary user, delegated diagnostic service, or host administrator has that access. Thus host-admin and namespace scope remain unknown. The two-reader trigger does not require the module-notifier branch, although LAST_BOOT tracing state is a prerequisite. The race is timing-sensitive but can plausibly be retried by an actor with file access.

4. Primitive and severity reading

This is a CLASS_B heap lifetime violation: normal stale cleanup would merely dereference freed data, whereas here a second reader performs an actual second free after the first may have destroyed the object. A module notifier may additionally update it during destruction, but the exact write and consumed fields are not visible. Crash is plausible; controlled heap corruption or privilege escalation is unproven. The specific double-free leaves material exploit leverage unresolved, requiring Important-vs-Moderate review and prohibiting automatic downgrade.

5. One-sentence report phrase

Concurrent tracefs readers can race the LAST_BOOT reset and free the same `module_delta` allocation twice, with a notifier also able to access it during destruction.

6. Manual review advice

MANUAL CHECK REQUIRED

The confirmed repeated lifetime mutation may corrupt allocator state, while trigger permissions and exploit leverage remain unresolved.

7. Call-site confidence

Call-site confidence: medium

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

Patch: tracing: Hold trace_types_lock when resetting last boot data from readers
Commit: 92b69f6db640dadc0851762ee2e12db99f083cad
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=92b69f6db640dadc0851762ee2e12db99f083cad

Commit description:

update_last_data_if_empty() is called from tracing_open() with O_TRUNC,
tracing_read_pipe() and tracing_buffers_read() without trace_types_lock.
Two readers can both pass the LAST_BOOT test and free module_delta
twice, and a module notifier can update module_delta while it is being
freed.

Take trace_types_lock in those paths and keep the callers that already
hold it on an unlocked variant.

Cc: stable@vger.kernel.org
Fixes: 32dc004 ("tracing: Reset last-boot buffers when reading out all cpu buffers")
Link: https://patch.msgid.link/20261016061638.214847-2-devnexen@gmail.com
Signed-off-by: David Carlier <devnexen@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/trace/trace.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=92b69f6db640dadc0851762ee2e12db99f083cad

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

The original Linux kernel CVE announcement for CVE-2026-99237 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99237

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:L/UI:N/S:U/C:L/I:L/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: unknown
  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: IMPORTANT
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): IMPORTANT

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).