From 94451181c2d6f65d761cb79020a4de2909ece353 Mon Sep 17 00:00:00 2001
From: "Enrico Weigelt, metux IT consult" <info@metux.net>
Date: Thu, 18 Apr 2024 18:51:36 +0200
Subject: [PATCH] xnest: fix segfault in miCreateScreenResources()

With aa3f5023e3fae0df74039702b6c8218bc14dc679, pScreen->devPrivate now is
initialized only once, which uncovered a silent bug in xnestOpenScreen:
It's NULL'ing the pScreen->devPrivate pointer which already had been
initialized by previous miScreenDevPrivateInit() call.

Fixes: aa3f5023e3fae0df74039702b6c8218bc14dc679
Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1495>
---
 hw/xnest/Screen.c |  5 +++--
 mi/mi_priv.h      | 12 ++++++++++++
 mi/miscrinit.c    | 11 +++++++++++
 3 files changed, 26 insertions(+), 2 deletions(-)
 create mode 100644 mi/mi_priv.h

diff --git a/hw/xnest/Screen.c b/hw/xnest/Screen.c
index 14763e0e7..6eb767233 100644
--- a/hw/xnest/Screen.c
+++ b/hw/xnest/Screen.c
@@ -20,6 +20,8 @@ is" without express or implied warranty.
 #include <X11/Xdefs.h>
 #include <X11/Xproto.h>
 
+#include "mi/mi_priv.h"
+
 #include "scrnintstr.h"
 #include "dix.h"
 #include "mi.h"
@@ -257,7 +259,6 @@ xnestOpenScreen(ScreenPtr pScreen, int argc, char *argv[])
     pScreen->blackPixel = xnestBlackPixel;
     /* GCperDepth */
     /* defaultStipple */
-    pScreen->devPrivate = NULL;
     /* WindowPrivateLen */
     /* WindowPrivateSizes */
     /* totalWindowSize */
@@ -419,7 +420,7 @@ xnestCloseScreen(ScreenPtr pScreen)
         free(pScreen->allowedDepths[i].vids);
     free(pScreen->allowedDepths);
     free(pScreen->visuals);
-    free(pScreen->devPrivate);
+    miScreenClose(pScreen);
 
     /*
        If xnestDoFullGeneration all x resources will be destroyed upon closing
diff --git a/mi/mi_priv.h b/mi/mi_priv.h
new file mode 100644
index 000000000..26c9d158f
--- /dev/null
+++ b/mi/mi_priv.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: MIT OR X11
+ *
+ * Copyright © 2024 Enrico Weigelt, metux IT consult <info@metux.net>
+ */
+#ifndef _XSERVER_MI_PRIV_H
+#define _XSERVER_MI_PRIV_H
+
+#include "screenint.h"
+
+void miScreenClose(ScreenPtr pScreen);
+
+#endif /* _XSERVER_MI_PRIV_H */
diff --git a/mi/miscrinit.c b/mi/miscrinit.c
index 2030674a9..57571b9ab 100644
--- a/mi/miscrinit.c
+++ b/mi/miscrinit.c
@@ -31,6 +31,9 @@ from The Open Group.
 #endif
 
 #include <X11/X.h>
+
+#include "mi/mi_priv.h"
+
 #include "servermd.h"
 #include "misc.h"
 #include "mi.h"
@@ -309,3 +312,11 @@ miSetZeroLineBias(ScreenPtr pScreen, unsigned int bias)
     dixSetPrivate(&pScreen->devPrivates, miZeroLineScreenKey,
                   (unsigned long *) (unsigned long) bias);
 }
+
+void miScreenClose(ScreenPtr pScreen)
+{
+    if (pScreen->devPrivate) {
+        free(pScreen->devPrivate);
+        pScreen->devPrivate = NULL;
+    }
+}