win32u: Use the correct length for kernel object names in object attributes.

dlls/win32u/sysparams.c

@@ -450,7 +450,8 @@ static HANDLE get_display_device_init_mutex( void )
 
     snprintf( buffer, ARRAY_SIZE(buffer), "\\Sessions\\%u\\BaseNamedObjects\\display_device_init",
               (int)NtCurrentTeb()->Peb->SessionId );
-    name.Length = name.MaximumLength = asciiz_to_unicode( bufferW, buffer );
+    name.MaximumLength = asciiz_to_unicode( bufferW, buffer );
+    name.Length = name.MaximumLength - sizeof(WCHAR);
 
     InitializeObjectAttributes( &attr, &name, OBJ_OPENIF, NULL, NULL );
     if (NtCreateMutant( &mutex, MUTEX_ALL_ACCESS, &attr, FALSE ) < 0) return 0;

dlls/win32u/winstation.c

@@ -554,7 +554,8 @@ static HANDLE get_winstations_dir_handle(void)
 
     sprintf( bufferA, "\\Sessions\\%u\\Windows\\WindowStations", (int)NtCurrentTeb()->Peb->SessionId );
     str.Buffer = buffer;
-    str.Length = str.MaximumLength = asciiz_to_unicode( buffer, bufferA ) - sizeof(WCHAR);
+    str.MaximumLength = asciiz_to_unicode( buffer, bufferA );
+    str.Length = str.MaximumLength - sizeof(WCHAR);
     InitializeObjectAttributes( &attr, &str, 0, 0, NULL );
     status = NtOpenDirectoryObject( &dir, DIRECTORY_CREATE_OBJECT | DIRECTORY_TRAVERSE, &attr );
     return status ? 0 : dir;

dlls/winex11.drv/x11drv_main.c

@@ -1008,7 +1008,8 @@ static HANDLE get_display_device_init_mutex(void)
 
     snprintf( buffer, ARRAY_SIZE(buffer), "\\Sessions\\%u\\BaseNamedObjects\\display_device_init",
               (int)NtCurrentTeb()->Peb->SessionId );
-    name.Length = name.MaximumLength = asciiz_to_unicode( bufferW, buffer );
+    name.MaximumLength = asciiz_to_unicode( bufferW, buffer );
+    name.Length = name.MaximumLength - sizeof(WCHAR);
 
     InitializeObjectAttributes( &attr, &name, OBJ_OPENIF, NULL, NULL );
     if (NtCreateMutant( &mutex, MUTEX_ALL_ACCESS, &attr, FALSE ) < 0) return 0;