CVE-2025-39863
Full vulnerability record from the local CVENow database.
Description
In the Linux kernel, the following vulnerability has been resolved: wifi: brcmfmac: fix use-after-free when rescheduling brcmf_btcoex_info work The brcmf_btcoex_detach() only shuts down the btcoex timer, if the flag timer_on is false. However, the brcmf_btcoex_timerfunc(), which runs as timer handler, sets timer_on to false. This creates critical race conditions: 1.If brcmf_btcoex_detach() is called while brcmf_btcoex_timerfunc() is executing, it may observe timer_on as false and skip the call to timer_shutdown_sync(). 2.The brcmf_btcoex_timerfunc() may then reschedule the brcmf_btcoex_info worker after the cancel_work_sync() has been executed, resulting in use-after-free bugs. The use-after-free bugs occur in two distinct scenarios, depending on the timing of when the brcmf_btcoex_info struct is freed relative to the execution of its worker thread. Scenario 1: Freed before the worker is scheduled The brcmf_btcoex_info is deallocated before the worker is scheduled. A race condition can occur when schedule_work(&bt_local->work) is called after the target memory has been freed. The sequence of events is detailed below: CPU0 | CPU1 brcmf_btcoex_detach | brcmf_btcoex_timerfunc | bt_local->timer_on = false; if (cfg->btcoex->timer_on) | ... | cancel_work_sync(); | ... | kfree(cfg->btcoex); // FREE | | schedule_work(&bt_local->work); // USE Scenario 2: Freed after the worker is scheduled The brcmf_btcoex_info is freed after the worker has been scheduled but before or during its execution. In this case, statements within the brcmf_btcoex_handler() — such as the container_of macro and subsequent dereferences of the brcmf_btcoex_info object will cause a use-after-free access. The following timeline illustrates this scenario: CPU0 | CPU1 brcmf_btcoex_detach | brcmf_btcoex_timerfunc | bt_local->timer_on = false; if (cfg->btcoex->timer_on) | ... | cancel_work_sync(); | ... | schedule_work(); // Reschedule | kfree(cfg->btcoex); // FREE | brcmf_btcoex_handler() // Worker /* | btci = container_of(....); // USE The kfree() above could | ... also occur at any point | btci-> // USE during the worker's execution| */ | To resolve the race conditions, drop the conditional check and call timer_shutdown_sync() directly. It can deactivate the timer reliably, regardless of its current state. Once stopped, the timer_on state is then set to false.
Severity
HIGH
CVSS score
7.8
(v3.1)
Vulnerability status
Modified
Source identifier
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Published
2025-09-19 16:15:45.310000
Last modified
2026-10-19 21:10:00.160000
View original CVE JSON
{
"id": "CVE-2025-39863",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"published": "2025-09-19T16:15:45.310",
"lastModified": "2026-10-19T21:10:00.160",
"vulnStatus": "Modified",
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{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nwifi: brcmfmac: fix use-after-free when rescheduling brcmf_btcoex_info work\n\nThe brcmf_btcoex_detach() only shuts down the btcoex timer, if the\nflag timer_on is false. However, the brcmf_btcoex_timerfunc(), which\nruns as timer handler, sets timer_on to false. This creates critical\nrace conditions:\n\n1.If brcmf_btcoex_detach() is called while brcmf_btcoex_timerfunc()\nis executing, it may observe timer_on as false and skip the call to\ntimer_shutdown_sync().\n\n2.The brcmf_btcoex_timerfunc() may then reschedule the brcmf_btcoex_info\nworker after the cancel_work_sync() has been executed, resulting in\nuse-after-free bugs.\n\nThe use-after-free bugs occur in two distinct scenarios, depending on\nthe timing of when the brcmf_btcoex_info struct is freed relative to\nthe execution of its worker thread.\n\nScenario 1: Freed before the worker is scheduled\n\nThe brcmf_btcoex_info is deallocated before the worker is scheduled.\nA race condition can occur when schedule_work(&bt_local->work) is\ncalled after the target memory has been freed. The sequence of events\nis detailed below:\n\nCPU0 | CPU1\nbrcmf_btcoex_detach | brcmf_btcoex_timerfunc\n | bt_local->timer_on = false;\n if (cfg->btcoex->timer_on) |\n ... |\n cancel_work_sync(); |\n ... |\n kfree(cfg->btcoex); // FREE |\n | schedule_work(&bt_local->work); // USE\n\nScenario 2: Freed after the worker is scheduled\n\nThe brcmf_btcoex_info is freed after the worker has been scheduled\nbut before or during its execution. In this case, statements within\nthe brcmf_btcoex_handler() — such as the container_of macro and\nsubsequent dereferences of the brcmf_btcoex_info object will cause\na use-after-free access. The following timeline illustrates this\nscenario:\n\nCPU0 | CPU1\nbrcmf_btcoex_detach | brcmf_btcoex_timerfunc\n | bt_local->timer_on = false;\n if (cfg->btcoex->timer_on) |\n ... |\n cancel_work_sync(); |\n ... | schedule_work(); // Reschedule\n |\n kfree(cfg->btcoex); // FREE | brcmf_btcoex_handler() // Worker\n /* | btci = container_of(....); // USE\n The kfree() above could | ...\n also occur at any point | btci-> // USE\n during the worker's execution|\n */ |\n\nTo resolve the race conditions, drop the conditional check and call\ntimer_shutdown_sync() directly. It can deactivate the timer reliably,\nregardless of its current state. Once stopped, the timer_on state is\nthen set to false."
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"lang": "es",
"value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nwifi: brcmfmac: corrige uso después de liberación al reprogramar el trabajo de brcmf_btcoex_info\n\nLa brcmf_btcoex_detach() solo apaga el temporizador btcoex, si el indicador timer_on es falso. Sin embargo, la brcmf_btcoex_timerfunc(), que se ejecuta como gestor de temporizador, establece timer_on en falso. Esto crea condiciones de carrera críticas:\n\n1.Si se llama a brcmf_btcoex_detach() mientras brcmf_btcoex_timerfunc() se está ejecutando, puede observar timer_on como falso y omitir la llamada a timer_shutdown_sync().\n\n2.La brcmf_btcoex_timerfunc() puede entonces reprogramar el trabajador de brcmf_btcoex_info después de que se haya ejecutado cancel_work_sync(), resultando en errores de uso después de liberación.\n\nLos errores de uso después de liberación ocurren en dos escenarios distintos, dependiendo del momento en que la estructura brcmf_btcoex_info es liberada en relación con la ejecución de su hilo de trabajador.\n\nEscenario 1: Liberada antes de que el trabajador sea programado\n\nLa brcmf_btcoex_info es desasignada antes de que el trabajador sea programado. Una condición de carrera puede ocurrir cuando se llama a schedule_work(&bt_local->work) después de que la memoria objetivo ha sido liberada. La secuencia de eventos se detalla a continuación:\n\nCPU0 | CPU1\nbrcmf_btcoex_detach | brcmf_btcoex_timerfunc\n | bt_local->timer_on = false;\n if (cfg->btcoex->timer_on) |\n ... |\n cancel_work_sync(); |\n ... |\n kfree(cfg->btcoex); // LIBERAR |\n | schedule_work(&bt_local->work); // USAR\n\nEscenario 2: Liberada después de que el trabajador es programado\n\nLa brcmf_btcoex_info es liberada después de que el trabajador ha sido programado pero antes o durante su ejecución. En este caso, sentencias dentro del brcmf_btcoex_handler() — como la macro container_of y las desreferencias subsiguientes del objeto brcmf_btcoex_info causarán un acceso de uso después de liberación. La siguiente línea de tiempo ilustra este escenario:\n\nCPU0 | CPU1\nbrcmf_btcoex_detach | brcmf_btcoex_timerfunc\n | bt_local->timer_on = false;\n if (cfg->btcoex->timer_on) |\n ... |\n cancel_work_sync(); |\n ... | schedule_work(); // Reprogramar\n |\n kfree(cfg->btcoex); // LIBERAR | brcmf_btcoex_handler() // Trabajador\n /* | btci = container_of(....); // USAR\n El kfree() anterior también | ...\n podría ocurrir en cualquier | btci-> // USAR\n momento durante la ejecución |\n del trabajador |\n */ |\n\nPara resolver las condiciones de carrera, elimine la comprobación condicional y llame a timer_shutdown_sync() directamente. Puede desactivar el temporizador de forma fiable, independientemente de su estado actual. Una vez detenido, el estado timer_on se establece entonces en falso."
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