[CVE-2026-46180][MODERATE 7.0] wifi: brcmfmac: Fix potential use-after-free issue when stopping watchdog task

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

CVE: CVE-2026-46180
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: wifi: brcmfmac: Fix potential use-after-free issue when stopping watchdog task
Commit: ed4168d1a50fef5be8eca947fbbf05a28507d265
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ed4168d1a50fef5be8eca947fbbf05a28507d265
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46180
Analysis date: Thu, 28 May 2026 06:15:11 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in brcmfmac SDIO watchdog shutdown can free `watchdog_tsk` between `send_sig()` and `kthread_stop()`, causing a local timing-dependent `task_struct` use-after-free and possible kernel crash.

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

The original Linux kernel CVE announcement for CVE-2026-46180 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46180

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-2026-46180	MODERATE	CHECK	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-672;*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 brcmfmac SDIO watchdog shutdown can leave bus watchdog_tsk pointing to a freed task_struct if the watchdog thread exits between send_sig() and kthread_stop(). A local actor able to trigger WiFi device stop, driver remove, or a similar brcmfmac lifecycle path may hit a use-after-free and crash the kernel. For the CVSS the PR:L is used for the paranoid score because some systems delegate WiFi or device management to local service contexts rather than full administrator only. The issue is not directly network reachable by packet traffic and requires a timing window. Impact is at least local denial of service, and worst case may include confidentiality or integrity impact because this is a real kernel lifetime corruption bug.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 4)	YES	REMOTE UAF NETWORK HARDWARE  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: **3**
* Paranoid score: **5**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* **Generic memory corruption, strong corruption primitive: +2**
  The commit explicitly describes a use-after-free where `watchdog_tsk` may be freed after `send_sig()` and before `kthread_stop()`.

* **Real lifetime corruption: +1**
  This is a task lifetime/reference bug fixed by taking a `task_struct` reference with `get_task_struct()` and releasing it through `kthread_stop_put()`.

* **Reliable kernel crash / strong DoS: +1**
  A stale `task_struct` pointer passed to `kthread_stop()` can plausibly crash the kernel during device teardown.

* **Weak LPE concern, paranoid only: +1**
  A `task_struct` UAF is a real kernel lifetime corruption issue, but the patch does not show a reclaim or controlled overwrite primitive. This supports manual review, not an assumed exploit.

* **Hard or unreliable race / special timing required: -1**
  The bug requires the watchdog task to exit in a narrow window between `send_sig()` and `kthread_stop()`.

* **Requires admin or device-management privilege in typical deployments: -2 conservative / -1 paranoid**
  Conservative scoring assumes triggering requires driver remove, bus stop, device detach, or similar privileged lifecycle control. Paranoid scoring reduces the penalty because WiFi/device control may be delegated to local services or desktop users on some systems.

* **Rare or hardware-specific condition: -1 conservative only**
  The affected path is specific to brcmfmac SDIO hardware. This limits broad exposure, though it does not remove risk on affected devices.

## 3. Reachability analysis

The bug is local and tied to brcmfmac SDIO device lifecycle paths such as bus stop, remove, detach, or driver shutdown. It is not directly reachable through ordinary WiFi packet traffic based on the patch. Typical exploitation requires local control over WiFi device management or privileged driver lifecycle operations. Containers usually do not gain access unless device management is explicitly delegated. Realistic exploitation is timing-dependent, but the underlying primitive is a real UAF.

## 4. Severity interpretation

This is not a simple warning or resource leak. It is a real lifetime corruption bug in a kernel driver and should be treated at least as an actionable Moderate candidate. Conservative practical impact is local DoS during device teardown. Paranoid impact justifies manual review because `task_struct` UAF bugs can sometimes be more serious than the visible crash path, although this patch does not demonstrate a concrete privilege escalation primitive.

## 5. One-sentence report phrase

A race in brcmfmac SDIO watchdog shutdown can free `watchdog_tsk` between `send_sig()` and `kthread_stop()`, causing a local timing-dependent `task_struct` use-after-free and possible kernel crash.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

The issue is timing-dependent and hardware-specific, but it is still a genuine kernel UAF involving `task_struct` lifetime management, so it should not be auto-closed as DoS-only without review.

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

Patch: wifi: brcmfmac: Fix potential use-after-free issue when stopping watchdog task
Commit: ed4168d1a50fef5be8eca947fbbf05a28507d265
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ed4168d1a50fef5be8eca947fbbf05a28507d265

Commit description:

Watchdog task might end between send_sig() and kthread_stop() calls, what
results in the use-after-free issue. Fix this by increasing watchdog task
reference count before calling send_sig() and dropping it by switching to
kthread_stop_put().

Cc: stable@vger.kernel.org
Fixes: 373c83a ("brcmfmac: stop watchdog before detach and free everything")
Fixes: a9ffda8 ("brcm80211: fmac: abstract bus_stop interface function pointer")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Link: https://patch.msgid.link/20260416093339.2066829-1-m.szyprowski@samsung.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.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=ed4168d1a50fef5be8eca947fbbf05a28507d265

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

The original Linux kernel CVE announcement for CVE-2026-46180 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46180

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).