vnc: fix segfault

Commit "c7628bf vnc: only alloc server surface with clients connected"
missed one rarely used codepath (cirrus with guest drivers using 2d
accel) where we have to check for the server surface being present,
to avoid qemu crashing with a NULL pointer dereference.  Add the check.

Reported-by: Anthony PERARD <anthony.perard@citrix.com>
Tested-by: Anthony PERARD <anthony.perard@citrix.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/ui/vnc.c b/ui/vnc.c
index c9f2fed..7538405 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -931,6 +931,11 @@ static void vnc_dpy_copy(DisplayChangeListener *dcl,
     int i, x, y, pitch, inc, w_lim, s;
     int cmp_bytes;
 
+    if (!vd->server) {
+        /* no client connected */
+        return;
+    }
+
     vnc_refresh_server_surface(vd);
     QTAILQ_FOREACH_SAFE(vs, &vd->clients, next, vn) {
         if (vnc_has_feature(vs, VNC_FEATURE_COPYRECT)) {