ui/vnc: fix skipping SASL SSF on UNIX sockets

The 'is_unix' flag is set on the VNC server during startup, however,
a regression in:

  commit 8bd22f477f68bbd7a9c88e926e7a58bf65605e39
  Author: Daniel P. Berrangé <berrange@redhat.com>
  Date:   Fri Feb 3 12:06:46 2017 +0000

    ui: extract code to connect/listen from vnc_display_open

meant we stopped setting the 'is_unix' flag when QEMU listens for
VNC sockets, only setting when QEMU does a reverse VNC connection.

Rather than fixing setting of the 'is_unix' flag, remove it, and
directly check the live client socket address. This is more robust
to a possible situation where the VNC server was listening on a
mixture of INET and UNIX sockets.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

ui/vnc-auth-sasl.c

@@ -551,6 +551,13 @@ vnc_socket_ip_addr_string(QIOChannelSocket *ioc,
     return 0;
 }
 
+static bool
+vnc_socket_is_unix(QIOChannelSocket *ioc)
+{
+    SocketAddress *addr = qio_channel_socket_get_local_address(ioc, NULL);
+    return addr && addr->type == SOCKET_ADDRESS_TYPE_UNIX;
+}
+
 void start_auth_sasl(VncState *vs)
 {
     const char *mechlist = NULL;
@@ -627,10 +634,11 @@ void start_auth_sasl(VncState *vs)
     memset (&secprops, 0, sizeof secprops);
     /* Inform SASL that we've got an external SSF layer from TLS.
      *
-     * Disable SSF, if using TLS+x509+SASL only. TLS without x509
-     * is not sufficiently strong
+     * Disable SSF, if using TLS+x509+SASL only, or UNIX sockets.
+     * TLS without x509 is not sufficiently strong, nor is plain
+     * TCP
      */
-    if (vs->vd->is_unix ||
+    if (vnc_socket_is_unix(vs->sioc) ||
         (vs->auth == VNC_AUTH_VENCRYPT &&
          vs->subauth == VNC_AUTH_VENCRYPT_X509SASL)) {
         /* If we've got TLS or UNIX domain sock, we don't care about SSF */

ui/vnc.c

@@ -3430,7 +3430,6 @@ static void vnc_display_close(VncDisplay *vd)
     if (!vd) {
         return;
     }
-    vd->is_unix = false;
 
     if (vd->listener) {
         qio_net_listener_disconnect(vd->listener);
@@ -3932,8 +3931,6 @@ static int vnc_display_connect(VncDisplay *vd,
         error_setg(errp, "Expected a single address in reverse mode");
         return -1;
     }
-    /* TODO SOCKET_ADDRESS_TYPE_FD when fd has AF_UNIX */
-    vd->is_unix = saddr_list->value->type == SOCKET_ADDRESS_TYPE_UNIX;
     sioc = qio_channel_socket_new();
     qio_channel_set_name(QIO_CHANNEL(sioc), "vnc-reverse");
     if (qio_channel_socket_connect_sync(sioc, saddr_list->value, errp) < 0) {

ui/vnc.h

@@ -168,7 +168,6 @@ struct VncDisplay
 
     const char *id;
     QTAILQ_ENTRY(VncDisplay) next;
-    bool is_unix;
     char *password;
     time_t expires;
     int auth;