From 144849ea27230962227e62a943b399e2ab304787 Mon Sep 17 00:00:00 2001
From: Matthieu Herrb <matthieu@herrb.eu>
Date: Tue, 18 Aug 2020 14:52:29 +0200
Subject: [PATCH] Fix XkbSelectEvents() integer underflow

CVE-2020-14361 ZDI-CAN 11573
reference：https://gitlab.freedesktop.org/xorg/xserver/-/commit/144849ea27230962227e62a943b399e2ab304787

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

Signed-off-by: Matthieu Herrb <matthieu@herrb.eu>

---
 xkb/xkbSwap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xkb/xkbSwap.c b/xkb/xkbSwap.c
index 1c1ed5f..50cabb9 100644
--- a/xkb/xkbSwap.c
+++ b/xkb/xkbSwap.c
@@ -76,7 +76,7 @@ SProcXkbSelectEvents(ClientPtr client)
         register unsigned bit, ndx, maskLeft, dataLeft, size;
 
         from.c8 = (CARD8 *) &stuff[1];
-        dataLeft = (stuff->length * 4) - SIZEOF(xkbSelectEventsReq);
+        dataLeft = (client->req_len * 4) - SIZEOF(xkbSelectEventsReq);
         maskLeft = (stuff->affectWhich & (~XkbMapNotifyMask));
         for (ndx = 0, bit = 1; (maskLeft != 0); ndx++, bit <<= 1) {
             if (((bit & maskLeft) == 0) || (ndx == XkbMapNotify))
-- 
2.27.0