tracing: Fix memory leak in set_trigger_filter()

BugLink: https://bugs.launchpad.net/bugs/1811252

commit 3cec638b upstream.

When create_event_filter() fails in set_trigger_filter(), the filter may
still be allocated and needs to be freed. The caller expects the
data->filter to be updated with the new filter, even if the new filter
failed (we could add an error message by setting set_str parameter of
create_event_filter(), but that's another update).

But because the error would just exit, filter was left hanging and
nothing could free it.

Found by kmemleak detector.

Cc: stable@vger.kernel.org
Fixes: bac5fb97 ("tracing: Add and use generic set_trigger_filter() implementation")
Reviewed-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

kernel/trace/trace_events_trigger.c

@@ -727,8 +727,10 @@ static int set_trigger_filter(char *filter_str,
 
 	/* The filter is for the 'trigger' event, not the triggered event */
 	ret = create_event_filter(file->event_call, filter_str, false, &filter);
-	if (ret)
-		goto out;
+	/*
+	 * If create_event_filter() fails, filter still needs to be freed.
+	 * Which the calling code will do with data->filter.
+	 */
  assign:
 	tmp = rcu_access_pointer(data->filter);