https://bugs.gentoo.org/857483
https://gitlab.freedesktop.org/xorg/xserver/-/issues/1310
https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/953

From f61307631203ab0266c035db07c2f776cf7c6cf4 Mon Sep 17 00:00:00 2001
From: Olivier Fourdan <ofourdan@redhat.com>
Date: Tue, 12 Jul 2022 14:44:48 +0200
Subject: [PATCH] dix: Fix overzealous caching of ResourceClientBits()

Commit c7311654 cached the value of ResourceClientBits(), but that value
depends on the `MaxClients` value set either from the command line or
from the configuration file.

For the latter, a call to ResourceClientBits() is issued before the
configuration file is read, meaning that the cached value is from the
default, not from the maximum number of clients set in the configuration
file.

That obviously causes all sort of issues, including memory corruption
and crashes of the Xserver when reaching the default limit value.

To avoid that issue, also keep the LimitClient value, and recompute the
ilog2() value if that changes, as on startup when the value is set from
the the xorg.conf ServerFlags section.

v2: Drop the `cache == 0` test
    Rename cache vars

Fixes: c7311654 - dix: cache ResourceClientBits() value
Closes: https://gitlab.freedesktop.org/xorg/xserver/-/issues/1310
Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
(cherry picked from commit 2efa6d659508346358a1ef27b2393e18843f66a3)
--- a/dix/resource.c
+++ b/dix/resource.c
@@ -620,12 +620,15 @@ ilog2(int val)
 unsigned int
 ResourceClientBits(void)
 {
-    static unsigned int cached = 0;
+    static unsigned int cache_ilog2 = 0;
+    static unsigned int cache_limit = 0;
 
-    if (cached == 0)
-      cached = ilog2(LimitClients);
+    if (LimitClients != cache_limit) {
+        cache_limit = LimitClients;
+        cache_ilog2 = ilog2(LimitClients);
+    }
 
-    return cached;
+    return cache_ilog2;
 }
 
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