CVE-2025-38352
Description
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.
Summary dbcve.org
Race condition in Linux kernel's POSIX CPU timers where an exiting non-autoreaping task that has passed exit_notify() can be reaped by parent/debugger while handle_posix_cpu_timers() runs from IRQ context, causing concurrent posix_cpu_timer_del() to fail detecting timer->it.cpu.firing != 0 due to cpu_timer_task_rcu() or lock_task_sighand() failures. Fix adds tsk->exit_state check to run_posix_cpu_timers().
Mitigation
Apply kernel patch adding exit_state check; alternatively, ensure CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y (though the check still provides defense-in-depth).