GHSA-C7CR-CH33-3XR3
Vulnerability from github – Published: 2025-09-22 21:30 – Updated: 2026-06-19 15:33In 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.
{
"affected": [],
"aliases": [
"CVE-2025-39863"
],
"database_specific": {
"cwe_ids": [
"CWE-416"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-09-19T16:15:45Z",
"severity": "HIGH"
},
"details": "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(\u0026bt_local-\u003ework) 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-\u003etimer_on = false;\n if (cfg-\u003ebtcoex-\u003etimer_on) |\n ... |\n cancel_work_sync(); |\n ... |\n kfree(cfg-\u003ebtcoex); // FREE |\n | schedule_work(\u0026bt_local-\u003ework); // 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() \u2014 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-\u003etimer_on = false;\n if (cfg-\u003ebtcoex-\u003etimer_on) |\n ... |\n cancel_work_sync(); |\n ... | schedule_work(); // Reschedule\n |\n kfree(cfg-\u003ebtcoex); // FREE | brcmf_btcoex_handler() // Worker\n /* | btci = container_of(....); // USE\n The kfree() above could | ...\n also occur at any point | btci-\u003e // USE\n during the worker\u0027s 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.",
"id": "GHSA-c7cr-ch33-3xr3",
"modified": "2026-06-19T15:33:07Z",
"published": "2025-09-22T21:30:18Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-39863"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/2f6fbc8e04ca1d1d5c560be694199f847229c625"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/3e789f8475f6c857c88de5c5bf4b24b11a477dd7"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9cb83d4be0b9b697eae93d321e0da999f9cdfcfc"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ae58f70bde0433f27ef4b388ab50634736607bf6"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/c75600e69e66a751cc046cd9c407b942f298d852"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f1150153c4e5940fe49ab51136343c5b4fe49d63"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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