ofproto: Fix potential NULL dereference in ofproto_ct_*_zone_timeout_…

…policy().

Spotted during code inspection.

Fixes: 993cae6 ("ofproto-dpif: Consume CT_Zone, and CT_Timeout_Policy tables")
Signed-off-by: Dumitru Ceara <dceara@redhat.com>
Acked-by: Paolo Valerio <pvalerio@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

ofproto/ofproto.c

@@ -981,7 +981,7 @@ ofproto_ct_set_zone_timeout_policy(const char *datapath_type, uint16_t zone_id,
     datapath_type = ofproto_normalize_type(datapath_type);
     const struct ofproto_class *class = ofproto_class_find__(datapath_type);
 
-    if (class->ct_set_zone_timeout_policy) {
+    if (class && class->ct_set_zone_timeout_policy) {
         class->ct_set_zone_timeout_policy(datapath_type, zone_id,
                                           timeout_policy);
     }
@@ -993,7 +993,7 @@ ofproto_ct_del_zone_timeout_policy(const char *datapath_type, uint16_t zone_id)
     datapath_type = ofproto_normalize_type(datapath_type);
     const struct ofproto_class *class = ofproto_class_find__(datapath_type);
 
-    if (class->ct_del_zone_timeout_policy) {
+    if (class && class->ct_del_zone_timeout_policy) {
         class->ct_del_zone_timeout_policy(datapath_type, zone_id);
     }