Merge tag 'perf_urgent_for_v6.1_rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull perf fix from Borislav Petkov:

- Fix a use-after-free case where the perf pending task callback would
see an already freed event

* tag 'perf_urgent_for_v6.1_rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
perf: Fix perf_pending_task() UaF

kernel/events/core.c

···
 		    !event->pending_work) {
 			event->pending_work = 1;
 			dec = false;
+			WARN_ON_ONCE(!atomic_long_inc_not_zero(&event->refcount));
 			task_work_add(current, &event->pending_task, TWA_RESUME);
 		}
 		if (dec)
···
 
 #define DETACH_GROUP	0x01UL
 #define DETACH_CHILD	0x02UL
+#define DETACH_DEAD	0x04UL
 
 /*
  * Cross CPU call to remove a performance event
···
 		update_cgrp_time_from_cpuctx(cpuctx, false);
 	}
 
+	/*
+	 * Ensure event_sched_out() switches to OFF, at the very least
+	 * this avoids raising perf_pending_task() at this time.
+	 */
+	if (flags & DETACH_DEAD)
+		event->pending_disable = 1;
 	event_sched_out(event, cpuctx, ctx);
 	if (flags & DETACH_GROUP)
 		perf_group_detach(event);
 	if (flags & DETACH_CHILD)
 		perf_child_detach(event);
 	list_del_event(event, ctx);
+	if (flags & DETACH_DEAD)
+		event->state = PERF_EVENT_STATE_DEAD;
 
 	if (!ctx->nr_events && ctx->is_active) {
 		if (ctx == &cpuctx->ctx)
···
 
 	ctx = perf_event_ctx_lock(event);
 	WARN_ON_ONCE(ctx->parent_ctx);
-	perf_remove_from_context(event, DETACH_GROUP);
 
-	raw_spin_lock_irq(&ctx->lock);
 	/*
 	 * Mark this event as STATE_DEAD, there is no external reference to it
 	 * anymore.
···
 	 * Thus this guarantees that we will in fact observe and kill _ALL_
 	 * child events.
 	 */
-	event->state = PERF_EVENT_STATE_DEAD;
-	raw_spin_unlock_irq(&ctx->lock);
+	perf_remove_from_context(event, DETACH_GROUP|DETACH_DEAD);
 
 	perf_event_ctx_unlock(event, ctx);
 
···
 	if (rctx >= 0)
 		perf_swevent_put_recursion_context(rctx);
 	preempt_enable_notrace();
+
+	put_event(event);
 }
 
 #ifdef CONFIG_GUEST_PERF_EVENTS