perf: Fix event leak upon exit

Summary

In the Linux kernel, the following vulnerability has been resolved: perf: Fix event leak upon exit When a task is scheduled out, pending sigtrap deliveries are deferred to the target task upon resume to userspace via task_work. However failures while adding an event's callback to the task_work engine are ignored. And since the last call for events exit happen after task work is eventually closed, there is a small window during which pending sigtrap can be queued though ignored, leaking the event refcount addition such as in the following scenario: TASK A ----- do_exit() exit_task_work(tsk); <IRQ> perf_event_overflow() event->pending_sigtrap = pending_id; irq_work_queue(&event->pending_irq); </IRQ> =========> PREEMPTION: TASK A -> TASK B event_sched_out() event->pending_sigtrap = 0; atomic_long_inc_not_zero(&event->refcount) // FAILS: task work has exited task_work_add(&event->pending_task) [...] <IRQ WORK> perf_pending_irq() // early return: event->oncpu = -1 </IRQ WORK> [...] =========> TASK B -> TASK A perf_event_exit_task(tsk) perf_event_exit_event() free_event() WARN(atomic_long_cmpxchg(&event->refcount, 1, 0) != 1) // leak event due to unexpected refcount == 2 As a result the event is never released while the task exits. Fix this with appropriate task_work_add()'s error handling.

Timeline

1. Aug 21, 2024, 12:06 AM UTCCVE published20 days
2. Sep 10, 2024, 4:06 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

   620 days (about 2 years)
3. May 23, 2026, 3:53 PM UTCRecord last updated

Affected versions

• Linux Linux

  From 5.15.84 · fixed in 5.15.165; From 6.0.14 · fixed in 6.1

• Linux Linux

  6.1

References 5