From: Marc-André Lureau <marcandre.lureau@redhat.com>

When spice_qxl_gl_scanout2() isn't available, the fallback code
incorrectly handles NULL arguments to disable the scanout, leading to:

Program terminated with signal SIGSEGV, Segmentation fault.
#0  spice_server_gl_scanout (qxl=0x55a25ce57ae8, fd=0x0, width=0, height=0, offset=0x0, stride=0x0, num_planes=0, format=0, modifier=72057594037927935, y_0_top=0)
    at ../ui/spice-display.c:983
983         if (num_planes <= 1) {

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2391334
Fixes: 98a050ca93afd8 ("ui/spice: support multi plane dmabuf scanout")
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Message-Id: <20250903193818.2460914-1-marcandre.lureau@redhat.com>
(cherry picked from commit 62fd247a24290dba2b2de4ee8575624a7993973c)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

diff --git a/ui/spice-display.c b/ui/spice-display.c
index 669832c561..db71e866f8 100644
--- a/ui/spice-display.c
+++ b/ui/spice-display.c
@@ -980,7 +980,9 @@ static void spice_server_gl_scanout(QXLInstance *qxl,
     spice_qxl_gl_scanout2(qxl, fd, width, height, offset, stride,
                           num_planes, format, modifier, y_0_top);
 #else
-    if (num_planes <= 1) {
+    if (fd == NULL) {
+        spice_qxl_gl_scanout(qxl, -1, 0, 0, 0, 0, false);
+    } else if (num_planes <= 1) {
         spice_qxl_gl_scanout(qxl, fd[0], width, height, stride[0], format, y_0_top);
     } else {
         error_report("SPICE server does not support multi plane GL scanout");
-- 
2.47.3