[CVE-2026-80622][MODERATE 7.0] char: tlclk: fix use-after-free in tlclk_cleanup() [ Upstream

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

CVE: CVE-2026-80622
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: char: tlclk: fix use-after-free in tlclk_cleanup() [ Upstream
Commit: 09d8d2a46a9ec9ff728f3159a174a2ab25dd0f0a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=09d8d2a46a9ec9ff728f3159a174a2ab25dd0f0a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80622
Analysis date: Fri, 28 Aug 2026 05:01:39 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A use-after-free can occur in the tlclk character driver because open file operations and blocked readers may survive module cleanup, allowing local interaction with the device to race with teardown and potentially crash the kernel or require further review for lifetime based privilege impact.

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

The original Linux kernel CVE announcement for CVE-2026-80622 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80622

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-2026-80622	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use after free can occur in the tlclk character driver because tlclk_fops did not pin the module with owner THIS_MODULE while user space could still hold an open device file or block in the read path. During module cleanup, blocked readers and timer based activity could race with resource release and alarm_events deallocation, creating a stale access window after the device is being removed. For the CVSS the PR:L is used for the paranoid score because a local user may be able to interact with the device node and keep file operations active while module cleanup is triggered by the system or an administrator. The issue is not network reachable and requires local interaction with the tlclk device and module lifetime. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel use after free, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	OOB RACE UAF HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

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

## 2. Signal breakdown

Paranoid score signals:

* Local unprivileged trigger: +1. A local user may be able to open the tlclk character device and keep file operations active, depending on device node permissions.
* Memory corruption, weak or indirect corruption candidate: +1. The patch explicitly addresses a use-after-free class issue, but no attacker-controlled reclaim, overwrite target, or arbitrary write primitive is shown.
* Real lifetime corruption: +1. Missing `.owner = THIS_MODULE` and cleanup ordering can leave user-space file operations, waitqueue readers, or timer activity racing with module teardown and freed driver state.
* Reliable kernel crash / strong DoS: +1. A stale access after module cleanup can plausibly crash the kernel.
* Weak LPE concern: +1. The missing module owner is a known module lifetime hazard where stale callbacks or code/data lifetime issues may exist, but exploitation beyond DoS is not demonstrated.
* Hard or unreliable race / special timing required: -1. Reliable triggering likely requires coordinating open/read or waitqueue state with module unload or cleanup.
* Rare hardware/configuration: 0 in paranoid scoring. tlclk is niche hardware, but if present it exposes an ordinary local character-device interface.

Conservative score signals:

* Real lifetime corruption: +1.
* Reliable kernel crash / DoS: +1.
* Local user participation possible: +1.
* Requires privileged module unload or driver cleanup in typical deployments: -1.
* Race/timing dependency: -1.

## 3. Reachability analysis

The bug is local, not network reachable. A local process may keep the tlclk device open or block in the read path while module cleanup proceeds. In typical deployments, unloading the module requires root or CAP_SYS_MODULE, so a fully reliable trigger is not purely unprivileged. However, the local user can participate in the vulnerable lifetime window by holding device state while cleanup is initiated by an administrator, service, or system management action.

Namespaces and containers usually do not make this reachable unless the device node and module-management path are delegated into the container. The affected driver is hardware-specific and likely uncommon, so broad default exposure is low.

Call-site confidence: medium. The patch shows the vulnerable file operations table and cleanup path, but not all read waitqueue and timer callback details.

## 4. Severity interpretation

This is stronger than an ordinary cleanup bug because it explicitly involves use-after-free and module lifetime semantics. Realistic impact is most likely local DoS via kernel crash. Privilege escalation is not proven, but stale module/file-operation lifetime bugs deserve manual review because they can sometimes become more serious if freed module memory or driver objects are reused in attacker-influenced ways.

Overall this is best treated as Actionable Moderate rather than auto-closed Low or ordinary Moderate.

## 5. One-sentence report phrase

A use-after-free can occur in the tlclk character driver because open file operations and blocked readers may survive module cleanup, allowing local interaction with the device to race with teardown and potentially crash the kernel or require further review for lifetime based privilege impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK.

Reason: the patch explicitly fixes a UAF/race in a kernel character driver cleanup path and adds `.owner = THIS_MODULE`, which is a module lifetime safety fix. The likely impact is DoS, but the lifetime class is serious enough to avoid automatic closure.

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

Patch: char: tlclk: fix use-after-free in tlclk_cleanup() [ Upstream
Commit: 09d8d2a46a9ec9ff728f3159a174a2ab25dd0f0a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=09d8d2a46a9ec9ff728f3159a174a2ab25dd0f0a

Changed files:
  drivers/char/tlclk.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=09d8d2a46a9ec9ff728f3159a174a2ab25dd0f0a

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

The original Linux kernel CVE announcement for CVE-2026-80622 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80622

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: 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).