[RFC PATCH v3 01/37] perf/events/core: fix race in bpf program unregister

Wang Nan
2015-05-17T11:04:50Z

there is a race between perf_event_free_bpf_prog() and free_trace_kprobe():

__free_event()
event->destroy(event)
tp_perf_event_destroy()
perf_trace_destroy()
perf_trace_event_unreg()

which is dropping event->tp_event->perf_refcount and allows to proceed in:

unregister_trace_kprobe()
unregister_kprobe_event()
trace_remove_event_call()
probe_remove_event_call()
free_trace_kprobe()

while __free_event does:
call_rcu(&event->rcu_head, free_event_rcu);
free_event_rcu()
perf_event_free_bpf_prog()

To fix the race simply move perf_event_free_bpf_prog() before
event->destroy(), since event->tp_event is still valid at that point.

Note, perf_trace_destroy() is not racing with trace_remove_event_call()
since they both grab event_mutex.

Fixes: 2541517c32be ("tracing, perf: Implement BPF programs attached to kprobes")
Reported-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
---
kernel/events/core.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 81aa3a4..2288b48 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3422,7 +3422,6 @@ static void free_event_rcu(struct rcu_head *head)
if (event->ns)
put_pid_ns(event->ns);
perf_event_free_filter(event);
- perf_event_free_bpf_prog(event);
kfree(event);
}

@@ -3553,6 +3552,8 @@ static void __free_event(struct perf_event *event)
put_callchain_buffers();
}

+ perf_event_free_bpf_prog(event);
+
if (event->destroy)
event->destroy(event);

--
1.8.3.4