CVE-2022-49607 Information

Mar 01, 2025 cve

Description

In the Linux kernel the following vulnerability has been resolved:

perf/core: Fix data race between perf_event_set_output() and perf_mmap_close()

Yang Jihing reported a race between perf_event_set_output() and perf_mmap_close():

CPU1					CPU2

perf_mmap_close(e2)
  if (atomic_dec_and_test(&e2->rb->mmap_count)) // 1 - > 0
    detach_rest = true

					ioctl(e1 IOC_SET_OUTPUT e2)
					  perf_event_set_output(e1 e2)

  ...
  list_for_each_entry_rcu(e &e2->rb->event_list rb_entry)
    ring_buffer_attach(e NULL);
    // e1 isn't yet added and
    // therefore not detached

					    ring_buffer_attach(e1 e2->rb)
					      list_add_rcu(&e1->rb_entry
							   &e2->rb->event_list)

After this; e1 is attached to an unmapped rb and a subsequent perf_mmap() will loop forever more:

again:
	mutex_lock(&e->mmap_mutex);
	if (event->rb) 
		...
		if (!atomic_inc_not_zero(&e->rb->mmap_count)) 
			...
			mutex_unlock(&e->mmap_mutex);
			goto again;

The loop in perf_mmap_close() holds e2->mmap_mutex while the attach in perf_event_set_output() holds e1->mmap_mutex. As such there is no serialization to avoid this race.

Change perf_event_set_output() to take both e1->mmap_mutex and e2->mmap_mutex to alleviate that problem. Additionally have the loop in perf_mmap() detach the rb directly this avoids having to wait for the concurrent perf_mmap_close() to get around to doing it to make progress.

Reference

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