From 79c572fbd349cb6373f685a502e430552f856995 Mon Sep 17 00:00:00 2001
From: FeepingCreature <feepingcreature@gmail.com>
Date: Sat, 20 Aug 2022 20:12:31 +0200
Subject: [PATCH] xkb: Avoid length-check failure on empty strings.

_XkbCheckRequestBounds assumes that from..to is at least one byte.
However, request strings can be empty, causing spurious failures in
XkbGetKbdByName calls. To avoid this, before checking bounds make
sure that the length is nonzero.
---
 xkb/xkb.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/xkb/xkb.c b/xkb/xkb.c
index 1841cff26..f9e3acbdc 100644
--- a/xkb/xkb.c
+++ b/xkb/xkb.c
@@ -5817,11 +5817,11 @@ GetComponentSpec(ClientPtr client, xkbGetKbdByNameReq *stuff,
         return NULL;
     }
     len = (*(unsigned char *) wire++);
-    if (!_XkbCheckRequestBounds(client, stuff, wire, wire + len)) {
-        *errRtrn = BadLength;
-        return NULL;
-    }
     if (len > 0) {
+        if (!_XkbCheckRequestBounds(client, stuff, wire, wire + len)) {
+            *errRtrn = BadLength;
+            return NULL;
+        }
         str = calloc(1, len + 1);
         if (str) {
             tmp = str;