CVE-2022-48950

In the Linux kernel, the following vulnerability has been resolved:

perf: Fix perf_pending_task() UaF

Per syzbot it is possible for perf_pending_task() to run after the

event is free()'d. There are two related but distinct cases:

- the task_work was already queued before destroying the event;

- destroying the event itself queues the task_work.

The first cannot be solved using task_work_cancel() since

perf_release() itself might be called from a task_work (____fput),

which means the current->task_works list is already empty and

task_work_cancel() won't be able to find the perf_pending_task()

entry.

The simplest alternative is extending the perf_event lifetime to cover

the task_work.

The second is just silly, queueing a task_work while you know the

event is going away makes no sense and is easily avoided by

re-arranging how the event is marked STATE_DEAD and ensuring it goes

through STATE_OFF on the way down.