dhcp/systemd: accept default gateway in classless static routes option

RFC 3442 allows a default gateway to be specified in option 121
(Classless Static Routes) and override the Router option.  Implement
this in the internal DHCP client.

https://bugzilla.gnome.org/show_bug.cgi?id=761268

diff --git a/src/dhcp-manager/nm-dhcp-systemd.c b/src/dhcp-manager/nm-dhcp-systemd.c
index 3a40225..3a6de91 100644 (file)
--- a/src/dhcp-manager/nm-dhcp-systemd.c
+++ b/src/dhcp-manager/nm-dhcp-systemd.c
@@ -218,6 +218,7 @@ lease_to_ip4_config (const char *iface,
        const void *data;
        gsize data_len;
        gboolean metered = FALSE;
+       gboolean static_default_gateway = FALSE;
 
        g_return_val_if_fail (lease != NULL, NULL);
 
@@ -255,15 +256,6 @@ lease_to_ip4_config (const char *iface,
        address.source = NM_IP_CONFIG_SOURCE_DHCP;
        nm_ip4_config_add_address (ip4_config, &address);
 
-       /* Gateway */
-       r = sd_dhcp_lease_get_router (lease, &tmp_addr);
-       if (r == 0) {
-               nm_ip4_config_set_gateway (ip4_config, tmp_addr.s_addr);
-               str = nm_utils_inet4_ntop (tmp_addr.s_addr, NULL);
-               LOG_LEASE (LOGD_DHCP4, "  gateway %s", str);
-               add_option (options, dhcp4_requests, SD_DHCP_OPTION_ROUTER, str);
-       }
-
        /* DNS Servers */
        num = sd_dhcp_lease_get_dns (lease, &addr_list);
        if (num > 0) {
@@ -325,20 +317,48 @@ lease_to_ip4_config (const char *iface,
                                continue;
                        route.gateway = a.s_addr;
 
-                       route.source = NM_IP_CONFIG_SOURCE_DHCP;
-                       route.metric = default_priority;
-                       nm_ip4_config_add_route (ip4_config, &route);
-
-                       str = nm_utils_inet4_ntop (route.network, buf);
-                       gw_str = nm_utils_inet4_ntop (route.gateway, NULL);
-                       LOG_LEASE (LOGD_DHCP4, "  static route %s/%d gw %s", str, route.plen, gw_str);
-
-                       g_string_append_printf (l, "%s%s/%d %s", l->len ? " " : "", str, route.plen, gw_str);
+                       if (route.plen) {
+                               route.source = NM_IP_CONFIG_SOURCE_DHCP;
+                               route.metric = default_priority;
+                               nm_ip4_config_add_route (ip4_config, &route);
+
+                               str = nm_utils_inet4_ntop (route.network, buf);
+                               gw_str = nm_utils_inet4_ntop (route.gateway, NULL);
+                               LOG_LEASE (LOGD_DHCP4, "  static route %s/%d gw %s", str, route.plen, gw_str);
+
+                               g_string_append_printf (l, "%s%s/%d %s", l->len ? " " : "", str, route.plen, gw_str);
+                       } else {
+                               if (!static_default_gateway) {
+                                       static_default_gateway = TRUE;
+                                       nm_ip4_config_set_gateway (ip4_config, route.gateway);
+
+                                       str = nm_utils_inet4_ntop (route.gateway, NULL);
+                                       LOG_LEASE (LOGD_DHCP4, "  gateway %s", str);
+                                       add_option (options, dhcp4_requests, SD_DHCP_OPTION_ROUTER, str);
+                               }
+                       }
                }
-               add_option (options, dhcp4_requests, SD_DHCP_OPTION_CLASSLESS_STATIC_ROUTE, l->str);
+               if (l->len)
+                       add_option (options, dhcp4_requests, SD_DHCP_OPTION_CLASSLESS_STATIC_ROUTE, l->str);
                g_string_free (l, TRUE);
        }
 
+       /* If the DHCP server returns both a Classless Static Routes option and a
+        * Router option, the DHCP client MUST ignore the Router option [RFC 3442].
+        * Be more lenient and ignore the Router option only if Classless Static
+        * Routes contain a default gateway (as other DHCP backends do).
+        */
+       /* Gateway */
+       if (!static_default_gateway) {
+               r = sd_dhcp_lease_get_router (lease, &tmp_addr);
+               if (r == 0) {
+                       nm_ip4_config_set_gateway (ip4_config, tmp_addr.s_addr);
+                       str = nm_utils_inet4_ntop (tmp_addr.s_addr, NULL);
+                       LOG_LEASE (LOGD_DHCP4, "  gateway %s", str);
+                       add_option (options, dhcp4_requests, SD_DHCP_OPTION_ROUTER, str);
+               }
+       }
+
        /* MTU */
        r = sd_dhcp_lease_get_mtu (lease, &mtu);
        if (r == 0 && mtu) {