CVE-2026-64586 in Linux
Summary
by MITRE • 08/06/2026
In the Linux kernel, the following vulnerability has been resolved:
wifi: brcmfmac: drain bus_reset work on device removal
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.
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Analysis
by VulDB Data Team • 08/06/2026
The vulnerability addressed in this Linux kernel patch relates to improper handling of work item lifecycle during device removal in the brcmfmac wireless driver, specifically affecting Broadcom wireless chips connected via PCIe, SDIO, and USB interfaces. The core issue stems from a race condition where the bus_reset work item can outlive the driver structure it references, leading to potential use-after-free conditions and system instability. This vulnerability affects the brcmfmac driver that manages Broadcom wireless devices and was identified through internal static analysis tools.
The technical flaw manifests when firmware crashes or reset operations are initiated while a device removal process is underway. Both brcmf_fw_crashed() function and debugfs "reset" entry schedule the same work item drvr->bus_reset, which executes through a callback that uses container_of() to recover driver structure and then dereferences it. During normal operation, this works correctly, but when device removal occurs concurrently with pending or running bus_reset work, the driver structure gets freed by brcmf_free() which calls wiphy_free(), while the work item may still be executing or queued. The callback chain leads through PCIe brcmf_pcie_reset -> brcmf_detach or SDIO brcmf_sdio_bus_reset -> brcmf_sdiod_remove -> brcmf_free, creating a deadlock scenario if cancellation were attempted in these teardown paths.
The solution implements a per-bus mutex mechanism called bus_reset_lock to synchronize access to the reset work scheduling and cancellation operations. The approach involves routing all work scheduling through a new function brcmf_bus_schedule_reset() which acquires the lock before proceeding and skips scheduling when the bus is marked as removing. Each bus removal entry now calls brcmf_bus_cancel_reset_work() which also takes the same mutex, sets the removing flag, and cancels the work while ensuring atomicity across the set-removing and drain operations. This design prevents the race condition by ensuring that no reset work can be scheduled once device removal has begun, while maintaining proper synchronization within sleepable contexts since all producers operate from process context - PCIe firmware-halt notifications run in threaded IRQ handlers and SDIO hostmail path runs from data workqueue.
The implementation also addresses a secondary issue where brcmf_fw_crashed() could be invoked before driver structure is fully initialized, potentially causing NULL pointer dereferences. The patch adds proper NULL checking for bus_if/drvr references in this function to prevent crashes during early initialization phases. The mutex approach is applied consistently across all supported bus types since the same bus_reset work item is shared among PCIe, SDIO, and USB interfaces. The solution ensures that cancel_work_sync() properly drains any running or pending bus_reset work items before the driver structure is freed, with additional protection in patch 2/2 making scratch-buffer release safe when reset teardown has already released DMA buffers. This follows established security practices for proper resource management and prevents privilege escalation attacks that could exploit the use-after-free condition.
The mitigation strategy aligns with common security best practices and addresses specific CWE categories related to improper handling of resources during object lifetime management, particularly CWE-415 (Double Free) and CWE-416 (Use After Free). The implementation follows ATT&CK framework concepts for privilege escalation and resource management by ensuring proper synchronization of asynchronous operations and preventing race conditions that could lead to system instability or security vulnerabilities. The approach also demonstrates adherence to kernel security guidelines for proper work item lifecycle management during device removal operations, which is critical for maintaining system integrity in embedded wireless networking drivers.