perf: 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. 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>
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@ -3442,7 +3442,6 @@ static void free_event_rcu(struct rcu_head *head)
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if (event->ns)
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put_pid_ns(event->ns);
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perf_event_free_filter(event);
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perf_event_free_bpf_prog(event);
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kfree(event);
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}
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@ -3573,6 +3572,8 @@ static void __free_event(struct perf_event *event)
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put_callchain_buffers();
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}
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perf_event_free_bpf_prog(event);
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if (event->destroy)
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event->destroy(event);
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