tracing: dynevent: Add a missing lockdown check on dynevent

Since dynamic_events interface on tracefs is compatible with
kprobe_events and uprobe_events, it should also check the lockdown
status and reject if it is set.

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/175824455687.45175.3734166065458520748.stgit@devnote2
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: mhiramat

kernel/trace/trace_dynevent.c

@@ -230,6 +230,10 @@ static int dyn_event_open(struct inode *inode, struct file *file)
 {
 	int ret;
 
+	ret = security_locked_down(LOCKDOWN_TRACEFS);
+	if (ret)
+		return ret;
+
 	ret = tracing_check_open_get_tr(NULL);
 	if (ret)
 		return ret;