[CVE-2026-64586][MODERATE 7.0] wifi: brcmfmac: drain bus_reset work on device removal

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

CVE: CVE-2026-64586
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: wifi: brcmfmac: drain bus_reset work on device removal
Commit: 177a25be1195f8bdc6160ba5f1a5699f7041c985
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=177a25be1195f8bdc6160ba5f1a5699f7041c985
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64586
Analysis date: Thu, 06 Aug 2026 03:55:13 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A brcmfmac bus_reset work item may outlive the freed drvr object during PCIe, SDIO, or USB device removal, causing a race-dependent use-after-free that is most likely a local DoS but has enough kernel lifetime-corruption risk to require manual review.

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

The original Linux kernel CVE announcement for CVE-2026-64586 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64586

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-2026-64586	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-667;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 brcmfmac because the shared bus_reset work item may remain pending or running while device removal frees the drvr object through brcmf_free and wiphy_free. The bus_reset callback recovers drvr with container_of and dereferences it, so a reset armed by brcmf_fw_crashed or debugfs reset can outlive the object lifetime during PCIe, SDIO, or USB removal. For the CVSS the PR:L is used in the paranoid score because some deployments may expose reset, hotplug, suspend, or firmware crash triggering to a local service account, container root, or otherwise reduced local privilege rather than only full administrator control. The issue is not directly network reachable as AV:N from the patch context. A wireless adjacent contribution through a firmware crash producer is possible only as a device specific hypothesis and should not be treated as the primary vector without more evidence. Impact is at least local denial of service via kernel crash. In the worst defensible case, the UAF may allow confidentiality and integrity impact or privilege escalation due to kernel memory corruption, so manual review is needed.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	REMOTE OOB LOCK DEADLOCK DANGER INIT NETWORK DMAorINTERRUPT KERNEL_PANIC_PLUS_UAF HARDWARE DEBUGFS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	guess

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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: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Real lifetime corruption: +1. `drvr->bus_reset` can remain pending or running while `drvr` is freed through `brcmf_free -> wiphy_free`.
* Memory corruption, weak primitive: +1. This is a real UAF, but the patch does not show attacker-controlled reclaim, overwrite, type confusion, or arbitrary write.
* Reliable kernel crash / strong DoS: +1. The stale work callback uses `container_of()` and dereferences freed `drvr`, which can plausibly crash the kernel.
* Privileged kernel/device-management lifetime path: +1. The bug is in driver reset and device removal lifetime management.
* Requires admin/root/device-management control in typical deployments: -2. Reliable triggering usually needs debugfs reset, device removal, suspend/remove, hotplug, driver unbind, or firmware reset control.
* Hard or unreliable race / special timing required: -1. Triggering requires reset work to overlap with teardown/removal.

Conservative total: 3.

Paranoid additional signals:

* Firmware-mediated external influence: +1. `brcmf_fw_crashed()` can be reached from firmware halt reporting paths, so external wireless or firmware behavior may contribute, but this is not enough for direct remote reachability.
* Weak LPE concern: +1. Because this is a stale async work callback using a freed kernel object, limited privilege escalation concern is defensible for manual triage, even though no reclaim or overwrite primitive is shown.
* Reduced privilege interpretation instead of full admin only: +1. Some systems may expose reset, suspend, hotplug, or firmware-crash triggering to a local service, container root, or other reduced-privilege actor.

Race-UAF cap applied: paranoid score capped at 5 because no concrete reclaim, write-after-free, type confusion, refcount takeover, or arbitrary write primitive is demonstrated.

## 3. Reachability analysis

Typical triggering is local and tied to device-management operations. The debugfs reset path, PCIe or SDIO removal, suspend power-off, USB disconnect, and firmware-crash recovery paths can interact with the shared `bus_reset` work item.

In normal deployments, reliable triggering likely requires administrator-level control over the wireless device, debugfs, driver unbind, suspend, or physical/device hotplug behavior. A lower-privilege interpretation is still worth considering where a service account, container root, desktop power-management path, or delegated device-management component can influence reset or removal timing.

This is not directly network reachable from the patch context. A wireless-adjacent or firmware-mediated trigger is plausible only if external inputs can reliably crash the Broadcom firmware, which is device-specific and not established by the patch.

Path default exposure depends on Broadcom `brcmfmac` hardware being present and the driver loaded. This is common enough on laptops and embedded systems to avoid treating it as an obscure-only path, but it is not a core networking path.

Call-site confidence: high. The patch shows the producers, the shared work item, the removal paths, and the cancellation/drain logic.

## 4. Severity interpretation

This is more than an ordinary Moderate cleanup because it fixes a real kernel object lifetime UAF in an asynchronous workqueue path. Realistic impact is most likely local privileged DoS through kernel crash during reset/removal races.

Theoretical escalation risk exists because a freed kernel object is later accessed by a work callback, but the patch does not demonstrate attacker-controlled reclaim, controlled object replacement, write-after-free, function-pointer control, or refcount takeover. Therefore this should not be scored as a strong Important case by default, but it should also not be auto-closed as a low-risk DoS-only bug.

Overall handling: actionable Moderate, manual review recommended.

## 5. One-sentence report phrase

A brcmfmac bus_reset work item may outlive the freed drvr object during PCIe, SDIO, or USB device removal, causing a race-dependent use-after-free that is most likely a local DoS but has enough kernel lifetime-corruption risk to require manual review.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: real UAF in driver workqueue teardown, possible firmware-mediated trigger, and possible reduced-privilege device-management exposure. No direct evidence currently supports remote reachability or reliable privilege escalation, so this is not automatically Important, but it should not be auto-closed.

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

Patch: wifi: brcmfmac: drain bus_reset work on device removal
Commit: 177a25be1195f8bdc6160ba5f1a5699f7041c985
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=177a25be1195f8bdc6160ba5f1a5699f7041c985

Commit description:

brcmf_fw_crashed() and the debugfs "reset" entry both schedule
drvr->bus_reset, whose callback recovers drvr through container_of()
and dereferences it.  The removal path frees drvr (brcmf_free ->
wiphy_free) without draining the work, so a bus_reset callback pending
or running during removal can outlive drvr.

Cancellation cannot live in brcmf_detach() or brcmf_free(): the work
callback reaches teardown through the bus .reset op (PCIe
brcmf_pcie_reset -> brcmf_detach; SDIO brcmf_sdio_bus_reset ->
brcmf_sdiod_remove -> brcmf_free), so cancelling there would wait for
the running work and deadlock.

Add a per-bus mutex (bus_reset_lock) and route all arming through
brcmf_bus_schedule_reset(), which under the lock skips when the bus is
marked removing.  Each bus remove entry calls
brcmf_bus_cancel_reset_work(), which under the same lock sets removing
and cancels the work.  Holding the mutex across cancel_work_sync() makes
the set-removing + drain step atomic.  Every producer reaches the arming
path from process context -- the PCIe firmware-halt notification runs in
the threaded IRQ handler (brcmf_pcie_isr_thread) and the SDIO hostmail
path runs from the data workqueue -- so the mutex is taken only in
sleepable contexts.  Where applicable the remove entry first stops the
firmware-crash producer: on PCIe mask the mailbox and synchronize_irq;
on SDIO unregister the bus interrupt and cancel the data worker, which
also reports firmware halts through brcmf_fw_crashed().  The mutex is
initialized at bus allocation.  The SDIO suspend power-off path frees
drvr through the same brcmf_sdiod_remove() and takes the same lock;
resume re-allows the work only on a successful re-probe.

Also guard brcmf_fw_crashed() against a NULL bus_if/drvr: it can fire
before brcmf_attach() wires up drvr, and it dereferences drvr
(bphy_err/brcmf_dev_coredump) before reaching the arming gate.

The bus_reset work is shared across buses, so the drain is applied to
every remove path: PCIe (the .reset op introduced by the Fixes commit),
SDIO (arms the same work through brcmf_fw_crashed()), and USB (via the
debugfs "reset" entry).  cancel_work_sync() drains a running or pending
bus_reset work item before removal frees drvr, and patch 1/2 makes the
scratch-buffer release safe when reset teardown has already released
those DMA buffers.

This patch fixes the lifetime of the bus_reset work item itself.  It does
not attempt to address the separate, pre-existing lifetime of the
asynchronous firmware completion started by the PCIe reset path.  That
callback needs its own lifetime/ownership protocol and is being tracked
separately.

This issue was found by an in-house static analysis tool.

Fixes: 4684997 ("brcmfmac: reset PCIe bus on a firmware crash")
Cc: stable@vger.kernel.org
Signed-off-by: Fan Wu <fanwu01@zju.edu.cn>
Assisted-by: Codex:gpt-5.6
Acked-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Link: https://patch.msgid.link/20260718024353.3147201-3-fanwu01@zju.edu.cn
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/bcmsdh.c
  drivers/net/wireless/broadcom/brcm80211/brcmfmac/bus.h
  drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c
  drivers/net/wireless/broadcom/brcm80211/brcmfmac/pcie.c
  drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.c
  drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.h
  drivers/net/wireless/broadcom/brcm80211/brcmfmac/usb.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=177a25be1195f8bdc6160ba5f1a5699f7041c985

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

The original Linux kernel CVE announcement for CVE-2026-64586 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64586

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).