tracing/filters: fix bug in copy_pred()

Impact: fix potential crash on subsystem filter expression freeing

When making a copy of the predicate, pred->field_name needs to be
duplicated in the copy as well, otherwise bad things can happen due to
later multiple frees of the same string.

This affects only per-subsystem event filtering.
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: =?ISO-8859-1?Q?Fr=E9d=E9ric?= Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1237796802.7527.39.camel@charm-linux>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/trace_events_filter.c

@@ -276,11 +276,19 @@ static struct filter_pred *copy_pred(struct filter_pred *pred)
 		return NULL;
 
 	memcpy(new_pred, pred, sizeof(*pred));
+
+	if (pred->field_name) {
+		new_pred->field_name = kstrdup(pred->field_name, GFP_KERNEL);
+		if (!new_pred->field_name) {
+			kfree(new_pred);
+			return NULL;
+		}
+	}
+
 	if (pred->str_val) {
 		new_pred->str_val = kstrdup(pred->str_val, GFP_KERNEL);
-		new_pred->field_name = kstrdup(pred->field_name, GFP_KERNEL);
 		if (!new_pred->str_val) {
-			kfree(new_pred);
+			filter_free_pred(new_pred);
 			return NULL;
 		}
 	}