From coverity:
gnome-control-center-3.14.5/panels/network/connection-editor/firewall-helpers.c:75:9: warning: passing argument 1 of 'g_free' discards 'const' qualifier from pointer target type [enabled by default]
https://bugzilla.gnome.org/show_bug.cgi?id=749897
The call to nm_setting_connection_get_zone() returns a pointer to
memory that will be freed before the D-Bus reply handler is called.
Make sure to take a copy of the string, and free it when finished.
https://bugzilla.gnome.org/show_bug.cgi?id=739971