[CVE-2026-80572][MODERATE 7.0] Input: byd - synchronize timer deletion before freeing private data

[CVE-2026-80572][MODERATE 7.0] Input: byd - synchronize timer deletion before freeing private data

[AL-KERNEL]

CVE: CVE-2026-80572
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Input: byd - synchronize timer deletion before freeing private data
Commit: 8dbfd8e32a13e116790780ed0be82b5a05eb9916
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8dbfd8e32a13e116790780ed0be82b5a05eb9916
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80572
Analysis date: Wed, 26 Aug 2026 12:14:38 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in the Input byd driver disconnect path allows a timer callback to access freed private data after `timer_delete()`, creating a local UAF condition that is most realistically a kernel crash risk but should receive manual review for possible privilege escalation impact.

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

The original Linux kernel CVE announcement for CVE-2026-80572 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80572

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
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CVE-2026-80572	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 race in the Input byd mouse driver can occur during disconnect because timer_delete does not wait for an already running byd_clear_touch callback. The callback can dereference the driver private data and the related psmouse pointer after byd_disconnect has freed that private data, which creates a kernel use-after-free condition. The realistic impact is at least a local denial of service via kernel crash because the race happens on the disconnect path and requires a narrow timing window. For the CVSS the PR:L is used in the paranoid score because a local user with delegated device management, reduced root, or access to driver unbind paths could potentially trigger disconnect while input activity keeps the timer active. The issue is not network reachable and normally applies only to systems using the byd psmouse driver. Impact may include privilege escalation in the worst case because the bug class is UAF after kfree, so this should not be treated as DoS only without manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	INIT SIMPLEFIX TIMER LINUS  INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Memory corruption, weak primitive: +1
  The patch fixes a timer callback race where `byd_clear_touch()` can dereference freed `byd_data`. This is a real UAF, but the patch does not show attacker controlled reclaim, overwrite, type confusion, or object replacement.

* Real lifetime corruption: +1
  `timer_delete()` does not wait for an already running callback, and the freed private data can remain reachable by the timer callback.

* Reliable kernel crash / strong DoS: +1
  A stale timer callback dereferencing freed driver private data can plausibly crash the kernel.

* Privileged kernel/device-management lifetime path: +1 in paranoid scoring
  The bug is in input driver disconnect cleanup and object lifetime handling.

* Hard or unreliable race / special timing required: -1
  The issue requires overlap between disconnect, timer callback execution, and possibly timer rearm.

* Requires admin/root/device-management control in typical deployments: -2 for conservative scoring
  Triggering `byd_disconnect()` normally requires device removal, driver unbind, module unload, suspend teardown, or similar privileged or physical/device-management conditions.

Paranoid adjustment:

* The full conservative privilege penalty is relaxed for paranoid scoring because delegated device management, reduced root, containerized service control, or physical hotplug style environments may lower practical trigger requirements.
* The score is capped at 5 under the Race-UAF downgrade rule because there is no demonstrated reclaim, write-after-free, type confusion, callback target control, or refcount takeover.

## 3. Reachability analysis

The bug is local and not network reachable. A realistic trigger normally requires the affected BYD psmouse driver to be in use and a disconnect or teardown path to run while the timer callback or byte processing path is active. In ordinary deployments, causing this disconnect path is usually privileged or tied to physical/device-management events. Namespaces do not normally make PS/2 mouse driver teardown available to an unprivileged user, but delegated device control or reduced-privilege service accounts could make the paranoid PR:L interpretation defensible.

Call-site confidence: high. The provided patch directly shows the vulnerable lifetime sequence in `byd_disconnect()`, replacing `timer_delete()` with `timer_shutdown_sync()` immediately before `kfree()`.

## 4. Severity interpretation

This behaves like an actionable Moderate kernel lifetime bug, not an ordinary low-risk cleanup. The theoretical risk is higher than pure DoS because the bug class is UAF after `kfree()`. The realistic evidence supports local kernel crash more strongly than privilege escalation, because no controlled reclaim, overwrite, type confusion, or attacker-controlled callback target is shown. Therefore, it should not be auto-closed, but it is weaker than a strong Important candidate.

## 5. One-sentence report phrase

A race in the Input byd driver disconnect path allows a timer callback to access freed private data after `timer_delete()`, creating a local UAF condition that is most realistically a kernel crash risk but should receive manual review for possible privilege escalation impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a real kernel UAF/lifetime race fixed by switching to `timer_shutdown_sync()`. Even though practical exploitation appears constrained and likely DoS-only, UAF after `kfree()` in a driver teardown path should not be auto-closed without manual review.

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

Patch: Input: byd - synchronize timer deletion before freeing private data
Commit: 8dbfd8e32a13e116790780ed0be82b5a05eb9916
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8dbfd8e32a13e116790780ed0be82b5a05eb9916

Commit description:

byd_disconnect() uses timer_delete() before freeing the driver's private
data.  This does not wait for a running byd_clear_touch() callback, which
dereferences the private data and its psmouse pointer.  A callback racing
with disconnect can therefore access the private data after it has been
freed.  The timer can also still be re-armed by byd_process_byte() while
the disconnect is in progress.

Use timer_shutdown_sync() before freeing the private data: it waits for
a running callback and turns any later re-arm attempt into a no-op.

Fixes: 2d5f561 ("Input: byd - enable absolute mode")
Cc: stable@vger.kernel.org
Signed-off-by: Linmao Li <lilinmao@kylinos.cn>
Link: https://patch.msgid.link/20260720061259.1601281-1-lilinmao@kylinos.cn
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/input/mouse/byd.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=8dbfd8e32a13e116790780ed0be82b5a05eb9916

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

The original Linux kernel CVE announcement for CVE-2026-80572 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80572

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: 3
  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).