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

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Message-ID: <1431860222-61636-2-git-send-email-wangnan0@huawei.com>
Date:	Sun, 17 May 2015 10:56:26 +0000
From:	Wang Nan <wangnan0@...wei.com>
To:	<paulus@...ba.org>, <a.p.zijlstra@...llo.nl>, <mingo@...hat.com>,
	<acme@...nel.org>, <namhyung@...nel.org>, <jolsa@...nel.org>,
	<dsahern@...il.com>, <ast@...mgrid.com>, <daniel@...earbox.net>,
	<brendan.d.gregg@...il.com>, <masami.hiramatsu.pt@...achi.com>
CC:	<lizefan@...wei.com>, <linux-kernel@...r.kernel.org>,
	<pi3orama@....com>
Subject: [RFC PATCH v3 01/37] perf/events/core: fix race in bpf program unregister

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@...wei.com>
Signed-off-by: Alexei Starovoitov <ast@...mgrid.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

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