Entreprise française de cybersécurité depuis 2004
☎ 03 60 47 09 81 - info@securiteinfo.com
☎ 03 60 47 09 81 - info@securiteinfo.com
In the Linux kernel, the following vulnerability has been resolved:wifi: brcmfmac: fix use-after-free when rescheduling brcmf_btcoex_info workThe brcmf_btcoex_detach() only shuts down the btcoex timer, if theflag timer_on is false. However, the brcmf_btcoex_timerfunc(), whichruns as timer handler, sets timer_on to false. This creates criticalrace 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 totimer_shutdown_sync().2.The brcmf_btcoex_timerfunc() may then reschedule the brcmf_btcoex_infoworker after the cancel_work_sync() has been executed, resulting inuse-after-free bugs.The use-after-free bugs occur in two distinct scenarios, depending onthe timing of when the brcmf_btcoex_info struct is freed relative tothe execution of its worker thread.Scenario 1: Freed before the worker is scheduledThe brcmf_btcoex_info is deallocated before the worker is scheduled.A race condition can occur when schedule_work(&bt_local->work) iscalled after the target memory has been freed. The sequence of eventsis detailed below:CPU0 | CPU1brcmf_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); // USEScenario 2: Freed after the worker is scheduledThe brcmf_btcoex_info is freed after the worker has been scheduledbut before or during its execution. In this case, statements withinthe brcmf_btcoex_handler() — such as the container_of macro andsubsequent dereferences of the brcmf_btcoex_info object will causea use-after-free access. The following timeline illustrates thisscenario:CPU0 | CPU1brcmf_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 calltimer_shutdown_sync() directly. It can deactivate the timer reliably,regardless of its current state. Once stopped, the timer_on state isthen set to false.
No PoCs from references.
- https://github.com/w4zu/Debian_security