net: dhcp: Remove only added DNS servers when stopping

Make sure that we remove only the added DNS servers when
the DHCP is stopped.

Signed-off-by: Jukka Rissanen <[email protected]>

Author: jukkar

include/zephyr/net/dns_resolve.h

@@ -594,6 +594,19 @@ int dns_resolve_reconfigure_with_interfaces(struct dns_resolve_context *ctx,
  */
 int dns_resolve_remove(struct dns_resolve_context *ctx, int if_index);
 
+/**
+ * @brief Remove servers from the DNS resolving context that were added by
+ *        a specific source.
+ *
+ * @param ctx DNS context
+ * @param if_index Network interface from which the DNS servers are removed.
+ * @param source Source of the DNS servers, e.g., manual, DHCPv4/6, etc.
+ *
+ * @return 0 if ok, <0 if error.
+ */
+int dns_resolve_remove_source(struct dns_resolve_context *ctx, int if_index,
+			      enum dns_server_source source);
+
 /**
  * @brief Cancel a pending DNS query.
  *

subsys/net/lib/dhcpv4/dhcpv4.c

@@ -1691,8 +1691,9 @@ static void dhcpv4_iface_event_handler(struct net_mgmt_event_callback *cb,
 			 * comes back up.
 			 */
 			if (IS_ENABLED(CONFIG_NET_DHCPV4_DNS_SERVER_VIA_INTERFACE)) {
-				dns_resolve_remove(dns_resolve_get_default(),
-						   net_if_get_by_iface(iface));
+				dns_resolve_remove_source(dns_resolve_get_default(),
+							  net_if_get_by_iface(iface),
+							  DNS_SOURCE_DHCPV4);
 			}
 		}
 	} else if (mgmt_event == NET_EVENT_IF_UP) {
@@ -1966,6 +1967,12 @@ void net_dhcpv4_stop(struct net_if *iface)
 		NET_DBG("state=%s",
 			net_dhcpv4_state_name(iface->config.dhcpv4.state));
 
+		if (IS_ENABLED(CONFIG_NET_DHCPV4_DNS_SERVER_VIA_INTERFACE)) {
+			dns_resolve_remove_source(dns_resolve_get_default(),
+						  net_if_get_by_iface(iface),
+						  DNS_SOURCE_DHCPV4);
+		}
+
 		sys_slist_find_and_remove(&dhcpv4_ifaces,
 					  &iface->config.dhcpv4.node);
 

subsys/net/lib/dhcpv6/dhcpv6.c

@@ -2226,8 +2226,9 @@ static void dhcpv6_iface_event_handler(struct net_mgmt_event_callback *cb,
 		 * comes back up.
 		 */
 		if (IS_ENABLED(CONFIG_NET_DHCPV6_DNS_SERVER_VIA_INTERFACE)) {
-			dns_resolve_remove(dns_resolve_get_default(),
-					   net_if_get_by_iface(iface));
+			dns_resolve_remove_source(dns_resolve_get_default(),
+						  net_if_get_by_iface(iface),
+						  DNS_SOURCE_DHCPV6);
 		}
 	} else if (mgmt_event == NET_EVENT_IF_UP) {
 		NET_DBG("Interface %p coming up", iface);
@@ -2323,6 +2324,12 @@ void net_dhcpv6_stop(struct net_if *iface)
 
 		(void)dhcpv6_enter_state(iface, NET_DHCPV6_DISABLED);
 
+		if (IS_ENABLED(CONFIG_NET_DHCPV6_DNS_SERVER_VIA_INTERFACE)) {
+			dns_resolve_remove_source(dns_resolve_get_default(),
+						  net_if_get_by_iface(iface),
+						  DNS_SOURCE_DHCPV6);
+		}
+
 		sys_slist_find_and_remove(&dhcpv6_ifaces,
 					  &iface->config.dhcpv6.node);
 

subsys/net/lib/dns/resolve.c

@@ -2209,7 +2209,9 @@ int dns_resolve_reconfigure(struct dns_resolve_context *ctx,
 					  source);
 }
 
-int dns_resolve_remove(struct dns_resolve_context *ctx, int if_index)
+static int dns_resolve_remove_and_check_source(struct dns_resolve_context *ctx, int if_index,
+					       bool check_source,
+					       enum dns_server_source source)
 {
 	int i;
 	int ret = -ENOENT;
@@ -2234,6 +2236,10 @@ int dns_resolve_remove(struct dns_resolve_context *ctx, int if_index)
 			continue;
 		}
 
+		if (check_source && ctx->servers[i].source != source) {
+			continue;
+		}
+
 		ctx->servers[i].if_index = 0;
 
 		/* See comment in dns_resolve_close_locked() about
@@ -2255,6 +2261,18 @@ int dns_resolve_remove(struct dns_resolve_context *ctx, int if_index)
 	return st;
 }
 
+int dns_resolve_remove(struct dns_resolve_context *ctx, int if_index)
+{
+	return dns_resolve_remove_and_check_source(ctx, if_index, false,
+						   DNS_SOURCE_UNKNOWN);
+}
+
+int dns_resolve_remove_source(struct dns_resolve_context *ctx, int if_index,
+			      enum dns_server_source source)
+{
+	return dns_resolve_remove_and_check_source(ctx, if_index, true, source);
+}
+
 struct dns_resolve_context *dns_resolve_get_default(void)
 {
 	return &dns_default_ctx;