From 3d7a63352a93bdb8a1cdf29606bf617d3ac1c22a Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Fri, 21 Jun 2024 11:16:00 +0200 Subject: [PATCH] perf: Fix event leak upon exit commit 2fd5ad3f310de22836cdacae919dd99d758a1f1b upstream. 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); perf_event_overflow() event->pending_sigtrap = pending_id; irq_work_queue(&event->pending_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) [...] perf_pending_irq() // early return: event->oncpu = -1 [...] =========> 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. Fixes: 517e6a301f34 ("perf: Fix perf_pending_task() UaF") Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20240621091601.18227-4-frederic@kernel.org Signed-off-by: Greg Kroah-Hartman --- kernel/events/core.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 053e546d5bf0..554d8ba93b8a 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -2284,18 +2284,15 @@ event_sched_out(struct perf_event *event, struct perf_event_context *ctx) } if (event->pending_sigtrap) { - bool dec = true; - event->pending_sigtrap = 0; if (state != PERF_EVENT_STATE_OFF && - !event->pending_work) { - event->pending_work = 1; - dec = false; + !event->pending_work && + !task_work_add(current, &event->pending_task, TWA_RESUME)) { WARN_ON_ONCE(!atomic_long_inc_not_zero(&event->refcount)); - task_work_add(current, &event->pending_task, TWA_RESUME); - } - if (dec) + event->pending_work = 1; + } else { local_dec(&event->ctx->nr_pending); + } } perf_event_set_state(event, state);