dhcpv6_client: add DNS recursive name server option handling

Signed-off-by: Martine Lenders <m.lenders@fu-berlin.de>

makefiles/pseudomodules.inc.mk

@@ -24,6 +24,7 @@ PSEUDOMODULES += cpu_check_address
 PSEUDOMODULES += dbgpin
 PSEUDOMODULES += devfs_%
 PSEUDOMODULES += dhcpv6_%
+PSEUDOMODULES += dhcpv6_client_dns
 PSEUDOMODULES += ecc_%
 PSEUDOMODULES += event_%
 PSEUDOMODULES += event_timeout_ztimer

sys/Makefile.dep

@@ -102,6 +102,9 @@ ifneq (,$(filter dhcpv6_client,$(USEMODULE)))
   USEMODULE += event
   USEMODULE += random
   USEMODULE += xtimer
+  ifneq (,$(filter sock_dns,$(USEMODULE)))
+    USEMODULE += dhcpv6_client_dns
+  endif
 endif
 
 ifneq (,$(filter fuzzing,$(USEMODULE)))

sys/include/net/dhcpv6.h

@@ -65,6 +65,7 @@ extern "C" {
 #define DHCPV6_OPT_PREF             (7U)    /**< preference option */
 #define DHCPV6_OPT_ELAPSED_TIME     (8U)    /**< elapsed time option */
 #define DHCPV6_OPT_STATUS           (13U)   /**< status code option */
+#define DHCPV6_OPT_DNS_RNS          (23U)   /**< DNS recursive name server option */
 #define DHCPV6_OPT_IA_PD            (25U)   /**< identity association for prefix
                                              *   delegation (IA_PD) option */
 #define DHCPV6_OPT_IAPFX            (26U)   /**< IA prefix option */

sys/net/application_layer/dhcpv6/_dhcpv6.h

@@ -172,6 +172,19 @@ typedef struct __attribute__((packed)) {
     char msg[];                     /**< UTF-8 encoded text string (not 0-terminated!) */
 } dhcpv6_opt_status_t;
 
+/**
+ * @brief   DHCPv6 DNS recursive name server option
+ * @see [RFC 3646, section 3]
+ *      (https://datatracker.ietf.org/doc/html/rfc3646#section-3)
+ * @note    Only parsed with `dhcpv6_client_dns` module compiled in.
+ */
+typedef struct __attribute__((packed)) {
+    network_uint16_t type;          /**< @ref DHCPV6_OPT_DNS_RNS */
+    network_uint16_t len;           /**< length of dhcpv6_opt_status_t::dns_rns in byte */
+    ipv6_addr_t dns_rns[];          /**< addresses of DNS recursive name servers
+                                     *   in order of preference */
+} dhcpv6_opt_dns_rns_t;
+
 /**
  * @brief   DHCPv6 identity association for prefix delegation option (IA_PD)
  *          format
@@ -224,6 +237,17 @@ typedef struct __attribute__((packed)) {
     char mud_string[];       /**< MUD URL using the "https" scheme */
 } dhcpv6_opt_mud_url_t;
 
+/**
+ * @brief   Configures a DNS recursive name server provided by the server.
+ *
+ * @note    Only available with module `dhcpv6_client_dns`.
+ *
+ * @param[in] opt       A legal DNS recursive name option.
+ * @param[in] netif     Network interface the message carrying @p opt came in.
+ */
+void dhcpv6_client_dns_rns_conf(const dhcpv6_opt_dns_rns_t *opt,
+                                uint16_t netif);
+
 #ifdef __cplusplus
 }
 #endif

sys/net/application_layer/dhcpv6/client.c

@@ -636,6 +636,12 @@ static bool _parse_reply(uint8_t *rep, size_t len)
     for (dhcpv6_opt_t *opt = (dhcpv6_opt_t *)(&rep[sizeof(dhcpv6_msg_t)]);
          len > 0; len -= _opt_len(opt), opt = _opt_next(opt)) {
         switch (byteorder_ntohs(opt->type)) {
+#if IS_USED(MODULE_DHCPV6_CLIENT_DNS)
+            case DHCPV6_OPT_DNS_RNS:
+                dhcpv6_client_dns_rns_conf((dhcpv6_opt_dns_rns_t *)opt,
+                                           remote.netif);
+                break;
+#endif  /* IS_USED(MODULE_DHCPV6_CLIENT_DNS) */
             case DHCPV6_OPT_IA_PD:
                 for (unsigned i = 0; i < CONFIG_DHCPV6_CLIENT_PFX_LEASE_MAX; i++) {
                     dhcpv6_opt_iapfx_t *iapfx = NULL;

sys/net/application_layer/dhcpv6/client_dns.c

@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2021 Freie Universität Berlin
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @{
+ *
+ * @file
+ * @author  Martine Lenders <m.lenders@fu-berlin.de>
+ */
+
+#include "net/dhcpv6/client.h"
+#if IS_USED(MODULE_SOCK_DNS)
+#include "net/sock/dns.h"
+#endif
+
+#include "_dhcpv6.h"
+
+#define ENABLE_DEBUG 0
+#include "debug.h"
+
+static char addr_str[IPV6_ADDR_MAX_STR_LEN];
+
+void dhcpv6_client_dns_rns_conf(const dhcpv6_opt_dns_rns_t *opt, uint16_t netif)
+{
+    if (byteorder_ntohs(opt->len) < sizeof(ipv6_addr_t)) {
+        DEBUG("dhcpv6_client_dns: no DNS recursive name server provided.\n");
+        return;
+    }
+#if IS_USED(MODULE_SOCK_DNS) && IS_ACTIVE(SOCK_HAS_IPV6)
+    DEBUG("Overriding sock_dns_server with %s\n",
+          ipv6_addr_to_str(addr_str, opt->dns_rns, sizeof(addr_str)));
+    sock_dns_server.port = SOCK_DNS_PORT;
+    sock_dns_server.family = AF_INET6;
+    sock_dns_server.netif = netif;
+    memcpy(sock_dns_server.addr.ipv6, opt->dns_rns,
+           sizeof(sock_dns_server.addr.ipv6));
+    return;
+#endif
+}
+
+/** @} */