perf: Fix race in BPF program unregister
authorAlexei Starovoitov <ast@plumgrid.com>
Fri, 15 May 2015 19:15:21 +0000 (12:15 -0700)
committerIngo Molnar <mingo@kernel.org>
Wed, 27 May 2015 06:46:15 +0000 (08:46 +0200)
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.

Reported-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: lizefan@huawei.com
Cc: pi3orama@163.com
Fixes: 2541517c32be ("tracing, perf: Implement BPF programs attached to kprobes")
Link: http://lkml.kernel.org/r/1431717321-28772-1-git-send-email-ast@plumgrid.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
kernel/events/core.c

index 1a3bf48743ce1c62c26077d642084cbdc8b40d6b..eddf1ed4155eaa5b4bc9c5321d99596a1c70d751 100644 (file)
@@ -3442,7 +3442,6 @@ 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);
 }
 
@@ -3573,6 +3572,8 @@ static void __free_event(struct perf_event *event)
                        put_callchain_buffers();
        }
 
+       perf_event_free_bpf_prog(event);
+
        if (event->destroy)
                event->destroy(event);