posix-cpu-timers: fix race between handle_posix_cpu_timers() and posix_cpu_timer_del()

Cybersecurity and Infrastructure Security Agency Known Exploited Vulnerabilities CVE-2025-38352

Linux kernel contains a time-of-check time-of-use (TOCTOU) race condition vulnerability that has a high impact on confidentiality, integrity, and availability.

Open Source Vulnerabilities ASB-A-425282960

In run_posix_cpu_timers of posix-cpu-timers.c, there is a possible way to trigger a use-after-free on a sigqueue object due to memory corruption. This could lead to local escalation of privilege with no additional execution privileges needed. User interaction is not needed for exploitation.

Open Source Vulnerabilities CVE-2025-38352

In the Linux kernel, the following vulnerability has been resolved: posix-cpu-timers: fix race between handle_posix_cpu_timers() and posix_cpu_timer_del() If an exiting non-autoreaping task has already passed exit_notify() and calls handle_posix_cpu_timers() from IRQ, it can be reaped by its parent or debugger right after unlock_task_sighand(). If a concurrent posix_cpu_timer_del() runs at that moment, it won't be able to detect timer->it.cpu.firing != 0: cpu_timer_task_rcu() and/or lock_task_sighand() will fail. Add the tsk->exit_state check into run_posix_cpu_timers() to fix this. This fix is not needed if CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y, because exit_task_work() is called before exit_notify(). But the check still makes sense, task_work_add(&tsk->posix_cputimers_work.work) will fail anyway in this case.