dhcp: remove acd handle when stopping dhcp

see bug #57706

src/core/ipv4/acd.c

@@ -141,6 +141,34 @@ acd_add(struct netif *netif, struct acd *acd,
   return ERR_OK;
 }
 
+/**
+ * @ingroup acd
+ * Remvoe ACD client from the client list
+ *
+ * @param netif network interface from which to remove the acd client
+ * @param acd   acd module to be removed from the list
+ */
+void
+acd_remove(struct netif *netif, struct acd *acd)
+{
+  struct acd *acd2, *prev = NULL;
+
+  LWIP_ASSERT_CORE_LOCKED();
+
+  for (acd2 = netif->acd_list; acd2 != NULL; acd2 = acd2->next) {
+    if (acd2 == acd) {
+      if (prev) {
+        prev->next = acd->next;
+      } else {
+        netif->acd_list = acd->next;
+      }
+      return;
+    }
+  }
+  LWIP_ASSERT(0, ("acd_remove(): acd not on list\n"));
+}
+
+
 /**
  * @ingroup acd
  * Start ACD client

src/core/ipv4/dhcp.c

@@ -308,6 +308,9 @@ dhcp_conflict_callback(struct netif *netif, acd_callback_enum_t state)
   struct dhcp *dhcp = netif_dhcp_data(netif);
   u16_t msecs;
 
+  LWIP_ASSERT("DHCP should be enabled at this point, but it is not!",
+              (dhcp != NULL) && (dhcp->state != DHCP_STATE_OFF));
+
   switch (state) {
     case ACD_IP_OK:
       dhcp_bind(netif);
@@ -1361,6 +1364,11 @@ dhcp_release_and_stop(struct netif *netif)
      dhcp_set_state(dhcp, DHCP_STATE_OFF);
   }
 
+#if LWIP_DHCP_DOES_ACD_CHECK
+  /* stop acd because we may be in checking state and the callback would trigger a bind */
+  acd_remove(netif, &dhcp->acd);
+#endif
+
   if (dhcp->pcb_allocated != 0) {
     dhcp_dec_pcb_refcount(); /* free DHCP PCB if not needed any more */
     dhcp->pcb_allocated = 0;