From 364f06788f1de4edc0547c7f29d338e6deffc138 Mon Sep 17 00:00:00 2001
From: Olivier Fourdan <ofourdan@redhat.com>
Date: Wed, 10 Sep 2025 16:30:29 +0200
Subject: [PATCH 4/4] xkb: Prevent overflow in XkbSetCompatMap()
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The XkbCompatMap structure stores its "num_si" and "size_si" fields
using an unsigned short.

However, the function _XkbSetCompatMap() will store the sum of the
input data "firstSI" and "nSI" in both XkbCompatMap's "num_si" and
"size_si" without first checking if the sum overflows the maximum
unsigned short value, leading to a possible overflow.

To avoid the issue, check whether the sum does not exceed the maximum
unsigned short value, or return a "BadValue" error otherwise.

CVE-2025-62231, ZDI-CAN-27560

This vulnerability was discovered by:
Jan-Niklas Sohn working with Trend Micro Zero Day Initiative

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
(cherry picked from commit 475d9f49acd0e55bc0b089ed77f732ad18585470)

Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/2087>

CVE: CVE-2025-62231
Upstream-Status: Backport
Signed-off-by: Ross Burton <ross.burton@arm.com>
---
 xkb/xkb.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/xkb/xkb.c b/xkb/xkb.c
index 26d965d48..137d70da2 100644
--- a/xkb/xkb.c
+++ b/xkb/xkb.c
@@ -2992,6 +2992,8 @@ _XkbSetCompatMap(ClientPtr client, DeviceIntPtr dev,
         XkbSymInterpretPtr sym;
         unsigned int skipped = 0;
 
+        if ((unsigned) (req->firstSI + req->nSI) > USHRT_MAX)
+            return BadValue;
         if ((unsigned) (req->firstSI + req->nSI) > compat->size_si) {
             compat->num_si = compat->size_si = req->firstSI + req->nSI;
             compat->sym_interpret = reallocarray(compat->sym_interpret,
-- 
2.43.0

