dns: sd-resolved: reset interface configuration on deactivation

If an update doesn't contain an interface but the previous update did,
the systemd-resolved DNS plugin must send a request to clear the
previous configuration. Otherwise the previous DNS configuration would
persist even after interface deactivation.

https://bugzilla.redhat.com/show_bug.cgi?id=1888229
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/662

src/dns/nm-dns-systemd-resolved.c

@@ -51,6 +51,7 @@ typedef struct {
 
 typedef struct {
     GDBusConnection *dbus_connection;
+    GHashTable *     dirty_interfaces;
     GCancellable *   cancellable;
     CList            request_queue_lst_head;
     guint            name_owner_changed_id;
@@ -134,7 +135,7 @@ call_done(GObject *source, GAsyncResult *r, gpointer user_data)
         priv->send_updates_warn_ratelimited = FALSE;
 }
 
-static void
+static gboolean
 update_add_ip_config(NMDnsSystemdResolved *self,
                      GVariantBuilder *     dns,
                      GVariantBuilder *     domains,
@@ -146,12 +147,13 @@ update_add_ip_config(NMDnsSystemdResolved *self,
     gboolean     is_routing;
     const char **iter;
     const char * domain;
+    gboolean     has_config = FALSE;
 
     addr_family = nm_ip_config_get_addr_family(data->ip_config);
     addr_size   = nm_utils_addr_family_to_size(addr_family);
 
     if (!data->domains.search || !data->domains.search[0])
-        return;
+        return FALSE;
 
     n = nm_ip_config_get_num_nameservers(data->ip_config);
     for (i = 0; i < n; i++) {
@@ -164,12 +166,16 @@ update_add_ip_config(NMDnsSystemdResolved *self,
                                       addr_size,
                                       1));
         g_variant_builder_close(dns);
+        has_config = TRUE;
     }
 
     for (iter = data->domains.search; *iter; iter++) {
         domain = nm_utils_parse_dns_domain(*iter, &is_routing);
         g_variant_builder_add(domains, "(sb)", domain[0] ? domain : ".", is_routing);
+        has_config = TRUE;
     }
+
+    return has_config;
 }
 
 static void
@@ -183,7 +189,7 @@ free_pending_updates(NMDnsSystemdResolved *self)
         _request_item_free(request_item);
 }
 
-static void
+static gboolean
 prepare_one_interface(NMDnsSystemdResolved *self, InterfaceConfig *ic)
 {
     NMDnsSystemdResolvedPrivate *priv = NM_DNS_SYSTEMD_RESOLVED_GET_PRIVATE(self);
@@ -192,6 +198,7 @@ prepare_one_interface(NMDnsSystemdResolved *self, InterfaceConfig *ic)
     NMSettingConnectionMdns      mdns     = NM_SETTING_CONNECTION_MDNS_DEFAULT;
     NMSettingConnectionLlmnr     llmnr    = NM_SETTING_CONNECTION_LLMNR_DEFAULT;
     const char *                 mdns_arg = NULL, *llmnr_arg = NULL;
+    gboolean                     has_config = FALSE;
 
     g_variant_builder_init(&dns, G_VARIANT_TYPE("(ia(iay))"));
     g_variant_builder_add(&dns, "i", ic->ifindex);
@@ -205,7 +212,7 @@ prepare_one_interface(NMDnsSystemdResolved *self, InterfaceConfig *ic)
         NMDnsIPConfigData *data      = elem->data;
         NMIPConfig *       ip_config = data->ip_config;
 
-        update_add_ip_config(self, &dns, &domains, data);
+        has_config |= update_add_ip_config(self, &dns, &domains, data);
 
         if (NM_IS_IP4_CONFIG(ip_config)) {
             mdns  = NM_MAX(mdns, nm_ip4_config_mdns_get(NM_IP4_CONFIG(ip_config)));
@@ -248,6 +255,9 @@ prepare_one_interface(NMDnsSystemdResolved *self, InterfaceConfig *ic)
     }
     nm_assert(llmnr_arg);
 
+    if (!nm_str_is_empty(mdns_arg) || !nm_str_is_empty(llmnr_arg))
+        has_config = TRUE;
+
     _request_item_append(&priv->request_queue_lst_head, "SetLinkDNS", g_variant_builder_end(&dns));
     _request_item_append(&priv->request_queue_lst_head,
                          "SetLinkDomains",
@@ -258,6 +268,8 @@ prepare_one_interface(NMDnsSystemdResolved *self, InterfaceConfig *ic)
     _request_item_append(&priv->request_queue_lst_head,
                          "SetLinkLLMNR",
                          g_variant_new("(is)", ic->ifindex, llmnr_arg ?: ""));
+
+    return has_config;
 }
 
 static void
@@ -336,19 +348,21 @@ update(NMDnsPlugin *            plugin,
        const char *             hostname,
        GError **                error)
 {
-    NMDnsSystemdResolved *self                = NM_DNS_SYSTEMD_RESOLVED(plugin);
+    NMDnsSystemdResolved *       self         = NM_DNS_SYSTEMD_RESOLVED(plugin);
+    NMDnsSystemdResolvedPrivate *priv         = NM_DNS_SYSTEMD_RESOLVED_GET_PRIVATE(self);
     gs_unref_hashtable GHashTable *interfaces = NULL;
     gs_free gpointer * interfaces_keys        = NULL;
     guint              interfaces_len;
-    guint              i;
+    int                ifindex;
     NMDnsIPConfigData *ip_data;
+    GHashTableIter     iter;
+    guint              i;
 
     interfaces =
         g_hash_table_new_full(nm_direct_hash, NULL, NULL, (GDestroyNotify) _interface_config_free);
 
     c_list_for_each_entry (ip_data, ip_config_lst_head, ip_config_lst) {
         InterfaceConfig *ic = NULL;
-        int              ifindex;
 
         ifindex = ip_data->data->ifindex;
         nm_assert(ifindex == nm_ip_config_get_ifindex(ip_data->ip_config));
@@ -371,7 +385,28 @@ update(NMDnsPlugin *            plugin,
     for (i = 0; i < interfaces_len; i++) {
         InterfaceConfig *ic = g_hash_table_lookup(interfaces, GINT_TO_POINTER(interfaces_keys[i]));
 
-        prepare_one_interface(self, ic);
+        if (prepare_one_interface(self, ic))
+            g_hash_table_add(priv->dirty_interfaces, GINT_TO_POINTER(ic->ifindex));
+        else
+            g_hash_table_remove(priv->dirty_interfaces, GINT_TO_POINTER(ic->ifindex));
+    }
+
+    /* If we previously configured an ifindex with non-empty values in
+     * resolved, and the current update doesn't contain that interface,
+     * reset the resolved configuration for that ifindex. */
+    g_hash_table_iter_init(&iter, priv->dirty_interfaces);
+    while (g_hash_table_iter_next(&iter, (gpointer *) &ifindex, NULL)) {
+        if (!g_hash_table_contains(interfaces, GINT_TO_POINTER(ifindex))) {
+            InterfaceConfig ic;
+
+            _LOGT("clear previously configured ifindex %d", ifindex);
+            ic = (InterfaceConfig){
+                .ifindex          = ifindex,
+                .configs_lst_head = C_LIST_INIT(ic.configs_lst_head),
+            };
+            prepare_one_interface(self, &ic);
+            g_hash_table_iter_remove(&iter);
+        }
     }
 
     send_updates(self);
@@ -489,6 +524,8 @@ nm_dns_systemd_resolved_init(NMDnsSystemdResolved *self)
                                            priv->cancellable,
                                            get_name_owner_cb,
                                            self);
+
+    priv->dirty_interfaces = g_hash_table_new(nm_direct_hash, NULL);
 }
 
 NMDnsPlugin *
@@ -510,6 +547,7 @@ dispose(GObject *object)
     nm_clear_g_cancellable(&priv->cancellable);
 
     g_clear_object(&priv->dbus_connection);
+    nm_clear_pointer(&priv->dirty_interfaces, g_hash_table_unref);
 
     G_OBJECT_CLASS(nm_dns_systemd_resolved_parent_class)->dispose(object);
 }