dhcp/dhclient: implement accept/decline (ACD) for dhclient plugin

dhclient itself doesn't do ACD. However, it expects the dhclient-script
to exit with non-zero status, which causes dhclient to send a DECLINE.

`man dhclient-script`:

  BOUND:
     Before actually configuring the address, dhclient-script should
     somehow ARP for it and exit with a nonzero status if it receives a
     reply. In this case, the client will send a DHCPDECLINE  message  to
     the server and acquire a different address.   This may also be done in
     the RENEW, REBIND, or REBOOT states, but is not required, and indeed may
     not be desirable.

See also Fedora's dhclient-script ([1]).

https://gitlab.isc.org/isc-projects/dhcp/-/issues/67#note_97226
33226f2d76/client/dhclient.c (L1652)

[1] a8f6fd046f/f/dhclient-script (_878)

https://bugzilla.redhat.com/show_bug.cgi?id=1713380

src/core/dhcp/nm-dhcp-client.c

@@ -50,7 +50,9 @@ typedef struct _NMDhcpClientPrivate {
 
     union {
         struct {
-            int _unused;
+            struct {
+                GDBusMethodInvocation *invocation;
+            } bound;
         } v4;
         struct {
             GSource *lladdr_timeout_source;
@@ -74,7 +76,6 @@ G_DEFINE_ABSTRACT_TYPE(NMDhcpClient, nm_dhcp_client, G_TYPE_OBJECT)
 /*****************************************************************************/
 
 static gboolean _dhcp_client_accept(NMDhcpClient *self, const NML3ConfigData *l3cd, GError **error);
-static gboolean _dhcp_client_can_accept(NMDhcpClient *self);
 
 _nm_unused static gboolean _dhcp_client_decline(NMDhcpClient         *self,
                                                 const NML3ConfigData *l3cd,
@@ -419,8 +420,7 @@ _nm_dhcp_client_notify(NMDhcpClient         *self,
      * as a static address (bypassing ACD), then NML3Cfg is aware of that and signals
      * immediate success. */
 
-    if (_dhcp_client_can_accept(self) && client_event_type == NM_DHCP_CLIENT_EVENT_TYPE_BOUND
+    if (client_event_type == NM_DHCP_CLIENT_EVENT_TYPE_BOUND && priv->l3cd
-        && priv->l3cd
         && nm_l3_config_data_get_num_addresses(priv->l3cd, priv->config.addr_family) > 0) {
         priv->l3cfg_notify.wait_dhcp_commit = TRUE;
     } else {
@@ -483,6 +483,25 @@ nm_dhcp_client_stop_watch_child(NMDhcpClient *self, pid_t pid)
     watch_cleanup(self);
 }
 
+static gboolean
+_accept(NMDhcpClient *self, const NML3ConfigData *l3cd, GError **error)
+{
+    NMDhcpClientPrivate *priv = NM_DHCP_CLIENT_GET_PRIVATE(self);
+
+    if (!NM_IS_IPv4(priv->config.addr_family))
+        return TRUE;
+
+    if (!priv->v4.bound.invocation) {
+        nm_utils_error_set(error,
+                           NM_UTILS_ERROR_UNKNOWN,
+                           "calling accept in unexpected script state");
+        return FALSE;
+    }
+
+    g_dbus_method_invocation_return_value(g_steal_pointer(&priv->v4.bound.invocation), NULL);
+    return TRUE;
+}
+
 static gboolean
 _dhcp_client_accept(NMDhcpClient *self, const NML3ConfigData *l3cd, GError **error)
 {
@@ -495,27 +514,29 @@ _dhcp_client_accept(NMDhcpClient *self, const NML3ConfigData *l3cd, GError **err
 
     g_return_val_if_fail(NM_DHCP_CLIENT_GET_PRIVATE(self)->l3cd, FALSE);
 
-    if (!klass->accept)
-        return TRUE;
-
     return klass->accept(self, l3cd, error);
 }
 
 static gboolean
-_dhcp_client_can_accept(NMDhcpClient *self)
+decline(NMDhcpClient *self, const NML3ConfigData *l3cd, const char *error_message, GError **error)
 {
-    gboolean can_accept;
+    NMDhcpClientPrivate *priv = NM_DHCP_CLIENT_GET_PRIVATE(self);
-    NMDhcpClientClass *klass;
 
-    nm_assert(NM_IS_DHCP_CLIENT(self));
+    if (!NM_IS_IPv4(priv->config.addr_family))
+        return TRUE;
 
-    klass = NM_DHCP_CLIENT_GET_CLASS(self);
+    if (!priv->v4.bound.invocation) {
+        nm_utils_error_set(error,
+                           NM_UTILS_ERROR_UNKNOWN,
+                           "calling decline in unexpected script state");
+        return FALSE;
+    }
 
-    can_accept = !!klass->accept;
+    g_dbus_method_invocation_return_error(g_steal_pointer(&priv->v4.bound.invocation),
-
+                                          NM_DEVICE_ERROR,
-    nm_assert(can_accept == (!!klass->decline));
+                                          NM_DEVICE_ERROR_FAILED,
-
+                                          "acd failed");
-    return can_accept;
+    return TRUE;
 }
 
 static gboolean
@@ -533,9 +554,6 @@ _dhcp_client_decline(NMDhcpClient         *self,
 
     g_return_val_if_fail(NM_DHCP_CLIENT_GET_PRIVATE(self)->l3cd, FALSE);
 
-    if (!klass->decline)
-        return TRUE;
-
     return klass->decline(self, l3cd, error_message, error);
 }
 
@@ -801,6 +819,13 @@ nm_dhcp_client_stop(NMDhcpClient *self, gboolean release)
 
     priv->is_stopped = TRUE;
 
+    if (NM_IS_IPv4(priv->config.addr_family) && priv->v4.bound.invocation) {
+        g_dbus_method_invocation_return_error(g_steal_pointer(&priv->v4.bound.invocation),
+                                              NM_DEVICE_ERROR,
+                                              NM_DEVICE_ERROR_FAILED,
+                                              "dhcp stopping");
+    }
+
     priv->l3cfg_notify.wait_dhcp_commit = FALSE;
     priv->l3cfg_notify.wait_ll_address  = FALSE;
     l3_cfg_notify_check_connected(self);
@@ -934,12 +959,13 @@ nm_dhcp_client_emit_ipv6_prefix_delegated(NMDhcpClient *self, const NMPlatformIP
 }
 
 gboolean
-nm_dhcp_client_handle_event(gpointer      unused,
+nm_dhcp_client_handle_event(gpointer               unused,
-                            const char   *iface,
+                            const char            *iface,
-                            int           pid,
+                            int                    pid,
-                            GVariant     *options,
+                            GVariant              *options,
-                            const char   *reason,
+                            const char            *reason,
-                            NMDhcpClient *self)
+                            GDBusMethodInvocation *invocation,
+                            NMDhcpClient          *self)
 {
     NMDhcpClientPrivate                    *priv;
     nm_auto_unref_l3cd_init NML3ConfigData *l3cd = NULL;
@@ -953,6 +979,7 @@ nm_dhcp_client_handle_event(gpointer      unused,
     g_return_val_if_fail(pid > 0, FALSE);
     g_return_val_if_fail(g_variant_is_of_type(options, G_VARIANT_TYPE_VARDICT), FALSE);
     g_return_val_if_fail(reason != NULL, FALSE);
+    g_return_val_if_fail(G_IS_DBUS_METHOD_INVOCATION(invocation), FALSE);
 
     priv = NM_DHCP_CLIENT_GET_PRIVATE(self);
 
@@ -964,7 +991,7 @@ nm_dhcp_client_handle_event(gpointer      unused,
     _LOGD("DHCP event (reason: '%s')", reason);
 
     if (NM_IN_STRSET_ASCII_CASE(reason, "preinit"))
-        return TRUE;
+        goto out_handled;
 
     if (NM_IN_STRSET_ASCII_CASE(reason, "bound", "bound6", "static"))
         client_event_type = NM_DHCP_CLIENT_EVENT_TYPE_BOUND;
@@ -1028,7 +1055,7 @@ nm_dhcp_client_handle_event(gpointer      unused,
          * of the DHCP client instance. Instead, we just signal the prefix
          * to the device. */
         nm_dhcp_client_emit_ipv6_prefix_delegated(self, &prefix);
-        return TRUE;
+        goto out_handled;
     }
 
     if (NM_IN_SET(client_event_type,
@@ -1040,7 +1067,20 @@ nm_dhcp_client_handle_event(gpointer      unused,
         client_event_type = NM_DHCP_CLIENT_EVENT_TYPE_FAIL;
     }
 
+    if (priv->v4.bound.invocation)
+        g_dbus_method_invocation_return_value(g_steal_pointer(&priv->v4.bound.invocation), NULL);
+
+    if (NM_IS_IPv4(priv->config.addr_family)
+        && NM_IN_SET(client_event_type,
+                     NM_DHCP_CLIENT_EVENT_TYPE_BOUND,
+                     NM_DHCP_CLIENT_EVENT_TYPE_EXTENDED))
+        priv->v4.bound.invocation = g_steal_pointer(&invocation);
+
     _nm_dhcp_client_notify(self, client_event_type, l3cd);
+
+out_handled:
+    if (invocation)
+        g_dbus_method_invocation_return_value(invocation, NULL);
     return TRUE;
 }
 
@@ -1185,7 +1225,10 @@ set_property(GObject *object, guint prop_id, const GValue *value, GParamSpec *ps
          * explicitly initialize the respective union member. */
         if (NM_IS_IPv4(priv->config.addr_family)) {
             priv->v4 = (typeof(priv->v4)){
-                ._unused = 0,
+                .bound =
+                    {
+                        .invocation = NULL,
+                    },
             };
         } else {
             priv->v6 = (typeof(priv->v6)){
@@ -1255,6 +1298,8 @@ nm_dhcp_client_class_init(NMDhcpClientClass *client_class)
     object_class->dispose      = dispose;
     object_class->finalize     = finalize;
     object_class->set_property = set_property;
+    client_class->accept       = _accept;
+    client_class->decline      = decline;
 
     client_class->stop     = stop;
     client_class->get_duid = get_duid;

src/core/dhcp/nm-dhcp-client.h

@@ -261,12 +261,13 @@ void _nm_dhcp_client_notify(NMDhcpClient         *self,
                             NMDhcpClientEventType client_event_type,
                             const NML3ConfigData *l3cd);
 
-gboolean nm_dhcp_client_handle_event(gpointer      unused,
+gboolean nm_dhcp_client_handle_event(gpointer               unused,
-                                     const char   *iface,
+                                     const char            *iface,
-                                     int           pid,
+                                     int                    pid,
-                                     GVariant     *options,
+                                     GVariant              *options,
-                                     const char   *reason,
+                                     const char            *reason,
-                                     NMDhcpClient *self);
+                                     GDBusMethodInvocation *invocation,
+                                     NMDhcpClient          *self);
 
 void nm_dhcp_client_emit_ipv6_prefix_delegated(NMDhcpClient               *self,
                                                const NMPlatformIP6Address *prefix);

src/core/dhcp/nm-dhcp-helper.c

@@ -100,21 +100,6 @@ next:;
     return g_variant_ref_sink(g_variant_new("(a{sv})", &builder));
 }
 
-static void
-kill_pid(void)
-{
-    const char *pid_str;
-    pid_t       pid = 0;
-
-    pid_str = getenv("pid");
-    if (pid_str)
-        pid = strtol(pid_str, NULL, 10);
-    if (pid) {
-        _LOGI("a fatal error occurred, kill dhclient instance with pid %d", pid);
-        kill(pid, SIGTERM);
-    }
-}
-
 int
 main(int argc, char *argv[])
 {
@@ -180,7 +165,7 @@ do_notify:
                                          parameters,
                                          NULL,
                                          G_DBUS_CALL_FLAGS_NONE,
-                                         1000,
+                                         60000,
                                          NULL,
                                          &error);
 
@@ -236,7 +221,5 @@ do_notify:
     }
 
 out:
-    if (!success)
-        kill_pid();
     return success ? EXIT_SUCCESS : EXIT_FAILURE;
 }

src/core/dhcp/nm-dhcp-listener.c

@@ -128,7 +128,7 @@ get_option(GVariant *options, const char *key)
 }
 
 static void
-_method_call_handle(NMDhcpListener *self, GVariant *parameters)
+_method_call_handle(NMDhcpListener *self, GDBusMethodInvocation *invocation, GVariant *parameters)
 {
     gs_free char              *iface   = NULL;
     gs_free char              *pid_str = NULL;
@@ -142,23 +142,23 @@ _method_call_handle(NMDhcpListener *self, GVariant *parameters)
     iface = get_option(options, "interface");
     if (iface == NULL) {
         _LOGW("dhcp-event: didn't have associated interface.");
-        return;
+        goto out;
     }
 
     pid_str = get_option(options, "pid");
     pid     = _nm_utils_ascii_str_to_int64(pid_str, 10, 0, G_MAXINT32, -1);
     if (pid == -1) {
         _LOGW("dhcp-event: couldn't convert PID '%s' to an integer", pid_str ?: "(null)");
-        return;
+        goto out;
     }
 
     reason = get_option(options, "reason");
     if (reason == NULL) {
         _LOGW("dhcp-event: (pid %d) DHCP event didn't have a reason", pid);
-        return;
+        goto out;
     }
 
-    g_signal_emit(self, signals[EVENT], 0, iface, pid, options, reason, &handled);
+    g_signal_emit(self, signals[EVENT], 0, iface, pid, options, reason, invocation, &handled);
     if (!handled) {
         if (g_ascii_strcasecmp(reason, "RELEASE") == 0) {
             /* Ignore event when the dhcp client gets killed and we receive its last message */
@@ -166,6 +166,10 @@ _method_call_handle(NMDhcpListener *self, GVariant *parameters)
         } else
             _LOGW("dhcp-event: (pid %d) unhandled DHCP event for interface %s", pid, iface);
     }
+
+out:
+    if (!handled)
+        g_dbus_method_invocation_return_value(invocation, NULL);
 }
 
 static void
@@ -190,8 +194,7 @@ _method_call(GDBusConnection       *connection,
         return;
     }
 
-    _method_call_handle(self, parameters);
+    _method_call_handle(self, invocation, parameters);
-    g_dbus_method_invocation_return_value(invocation, NULL);
 }
 
 static GDBusInterfaceInfo *const interface_info = NM_DEFINE_GDBUS_INTERFACE_INFO(
@@ -311,9 +314,10 @@ nm_dhcp_listener_class_init(NMDhcpListenerClass *listener_class)
                                   NULL,
                                   NULL,
                                   G_TYPE_BOOLEAN, /* listeners return TRUE if handled */
-                                  4,
+                                  5,
                                   G_TYPE_STRING,  /* iface */
                                   G_TYPE_INT,     /* pid */
                                   G_TYPE_VARIANT, /* options */
-                                  G_TYPE_STRING); /* reason */
+                                  G_TYPE_STRING,  /* reason */
+                                  G_TYPE_DBUS_METHOD_INVOCATION /* invocation*/);
 }