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From 01642f263f12becf803b19be4db95a4a83f94acc Mon Sep 17 00:00:00 2001
From: Olivier Fourdan <ofourdan@redhat.com>
Date: Wed, 27 Nov 2024 11:27:05 +0100
Subject: [PATCH] Cursor: Refuse to free the root cursor
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 Danzer
<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>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1828>
Upstream-Status: Backport [https://gitlab.freedesktop.org/xorg/xserver/-/commit/01642f26]
CVE: CVE-2025-26594
Signed-off-by: Vijay Anusuri <vanusuri@mvista.com>
---
dix/dispatch.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/dix/dispatch.c b/dix/dispatch.c
index 4602961..30b95c1 100644
--- 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;
}
--
2.25.1
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