From 9a9b22aac1279c69b2d1c373093ca64251d71077 Mon Sep 17 00:00:00 2001
From: Katayama Hirofumi MZ <katayama.hirofumi.mz@gmail.com>
Date: Wed, 10 Jan 2024 08:01:37 +0900
Subject: [PATCH] [NTUSER] Check class name existence on
 IntGetAtomFromStringOrAtom (#6184)

Based on I_Kill_Bugs' class_error.patch.
JIRA issue: CORE-13422, CORE-7531, CORE-18639
---
 win32ss/user/ntuser/class.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/win32ss/user/ntuser/class.c b/win32ss/user/ntuser/class.c
index 548bef255e6..1ad90351265 100644
--- a/win32ss/user/ntuser/class.c
+++ b/win32ss/user/ntuser/class.c
@@ -1355,9 +1355,17 @@ IntGetAtomFromStringOrAtom(
     }
     else
     {
-        ASSERT(IS_ATOM(ClassName->Buffer));
-        *Atom = (RTL_ATOM)((ULONG_PTR)ClassName->Buffer);
-        Ret = TRUE;
+        if (ClassName->Buffer)
+        {
+            *Atom = (RTL_ATOM)((ULONG_PTR)ClassName->Buffer);
+            Ret = TRUE;
+        }
+        else
+        {
+            *Atom = 0;
+            EngSetLastError(ERROR_CLASS_DOES_NOT_EXIST);
+            Ret = FALSE;
+        }
     }
 
     return Ret;