Backport v2025 <- v2026dev1: Update from debian/bookworm-security

Backport of !84 (merged)

debian/patches/CVE-2025-26594/0001-Cursor-Refuse-to-free-the-root-cursor.patch

+From efca605c45ff51b57f136222b966ce1d610ebc33 Mon Sep 17 00:00:00 2001
+From: Olivier Fourdan <ofourdan@redhat.com>
+Date: Wed, 27 Nov 2024 11:27:05 +0100
+Subject: [PATCH xserver 1/2] Cursor: Refuse to free the root cursor
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+If a cursor reference count drops to 0, the cursor is freed.
+
+The root cursor however is referenced with a specific global variable,
+and when the root cursor is freed, the global variable may still point
+to freed memory.
+
+Make sure to prevent the rootCursor from being explicitly freed by a
+client.
+
+CVE-2025-26594, ZDI-CAN-25544
+
+This vulnerability was discovered by:
+Jan-Niklas Sohn working with Trend Micro Zero Day Initiative
+
+v2: Explicitly forbid XFreeCursor() on the root cursor (Peter Hutterer
+<peter.hutterer@who-t.net>)
+v3: Return BadCursor instead of BadValue (Michel Dänzer
+<michel@daenzer.net>)
+
+Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
+Suggested-by: Peter Hutterer <peter.hutterer@who-t.net>
+Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
+---
+ dix/dispatch.c | 4 ++++
+ 1 file changed, 4 insertions(+)
+
+--- a/dix/dispatch.c
++++ b/dix/dispatch.c
+@@ -3107,6 +3107,10 @@ ProcFreeCursor(ClientPtr client)
+     rc = dixLookupResourceByType((void **) &pCursor, stuff->id, RT_CURSOR,
+                                  client, DixDestroyAccess);
+     if (rc == Success) {
++        if (pCursor == rootCursor) {
++            client->errorValue = stuff->id;
++            return BadCursor;
++        }
+         FreeResource(stuff->id, RT_NONE);
+         return Success;
+     }