network: only reload firewall after firewalld is finished restarting

The network driver used to reload the firewall rules whenever a dbus
NameOwnerChanged message for org.fedoraproject.FirewallD1 was
received. Presumably at some point in the past this was successful at
reloading our rules after a firewalld restart. Recently though I
noticed that once firewalld was restarted, libvirt's logs would get this
message:

  The name org.fedoraproject.FirewallD1 was not provided by any .service files

After this point, no networks could be started until libvirtd itself
was restarted.

The problem is that the NameOwnerChanged message is sent twice during
a firewalld restart - once when the old firewalld is stopped, and
again when the new firewalld is started. If we try to reload at the
point the old firewalld is stopped, none of the firewalld dbus calls
will succeed.

The solution is to check the new_owner field of the message - we
should reload our firewall rules only if new_owner is non-empty (it is
set to "" when firewalld is stopped, and some sort of epoch number
when it is again started).
Signed-off-by: NLaine Stump <laine@laine.org>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>

src/network/bridge_driver.c

@@ -543,12 +543,32 @@ firewalld_dbus_filter_bridge(DBusConnection *connection ATTRIBUTE_UNUSED,
                              void *user_data)
 {
     virNetworkDriverStatePtr driver = user_data;
+    bool reload = false;
 
-    if (dbus_message_is_signal(message, DBUS_INTERFACE_DBUS,
-                               "NameOwnerChanged") ||
-        dbus_message_is_signal(message, "org.fedoraproject.FirewallD1",
-                               "Reloaded"))
-    {
+    if (dbus_message_is_signal(message,
+                               "org.fedoraproject.FirewallD1", "Reloaded")) {
+        reload = true;
+
+    } else if (dbus_message_is_signal(message,
+                                      DBUS_INTERFACE_DBUS, "NameOwnerChanged")) {
+
+        VIR_AUTOFREE(char *) name = NULL;
+        VIR_AUTOFREE(char *) old_owner = NULL;
+        VIR_AUTOFREE(char *) new_owner = NULL;
+
+        if (virDBusMessageDecode(message, "sss", &name, &old_owner, &new_owner) < 0) {
+            VIR_WARN("Failed to decode DBus NameOwnerChanged message");
+            return DBUS_HANDLER_RESULT_NOT_YET_HANDLED;
+        }
+        /*
+         * if new_owner is empty, firewalld is shutting down. If it is
+         * non-empty, then it is starting
+         */
+        if (new_owner && *new_owner)
+            reload = true;
+    }
+
+    if (reload) {
         VIR_DEBUG("Reload in bridge_driver because of firewalld.");
         networkReloadFirewallRules(driver, false);
     }