[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20240516140936.13694-4-frederic@kernel.org>
Date: Thu, 16 May 2024 16:09:35 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>,
Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH 3/4] 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 en 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.
Fixes: 517e6a301f34 ("perf: Fix perf_pending_task() UaF")
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
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 724e6d7e128f..f2a366e736a4 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);
--
2.34.1
Powered by blists - more mailing lists