Defensive programming: check for the argument being NULL.

core/net/rpl/rpl-dag.c

@@ -1022,6 +1022,10 @@ rpl_local_repair(rpl_instance_t *instance)
 {
   int i;
 
+  if(instance == NULL) {
+    PRINTF("RPL: local repair requested for instance NULL\n");
+    return;
+  }
   PRINTF("RPL: Starting a local instance repair\n");
   for(i = 0; i < RPL_MAX_DAG_PER_INSTANCE; i++) {
     if(instance->dag_table[i].used) {

core/net/rpl/rpl-icmp6.c

@@ -750,9 +750,27 @@ dao_output_target(rpl_parent_t *parent, uip_ipaddr_t *prefix, uint8_t lifetime)
 
   /* Destination Advertisement Object */
 
+  if(parent == NULL) {
+    PRINTF("RPL dao_output_target error parent NULL\n");
+    return;
+  }
+
   dag = parent->dag;
+  if(dag == NULL) {
+    PRINTF("RPL dao_output_target error dag NULL\n");
+    return;
+  }
+
   instance = dag->instance;
 
+  if(instance == NULL) {
+    PRINTF("RPL dao_output_target error instance NULL\n");
+    return;
+  }
+  if(prefix == NULL) {
+    PRINTF("RPL dao_output_target error prefix NULL\n");
+    return;
+  }
 #ifdef RPL_DEBUG_DAO_OUTPUT
   RPL_DEBUG_DAO_OUTPUT(parent);
 #endif

core/net/uip-ds6-nbr.c

@@ -143,12 +143,14 @@ uip_ds6_nbr_t *
 uip_ds6_nbr_lookup(uip_ipaddr_t *ipaddr)
 {
   uip_ds6_nbr_t *nbr = nbr_table_head(ds6_neighbors);
+  if(ipaddr != NULL) {
     while(nbr != NULL) {
       if(uip_ipaddr_cmp(&nbr->ipaddr, ipaddr)) {
         return nbr;
       }
       nbr = nbr_table_next(ds6_neighbors, nbr);
     }
+  }
   return NULL;
 }
 /*---------------------------------------------------------------------------*/