Check alternate desktop before applying integrity label

sandbox/win/src/sandbox_policy_base.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sandbox/win/src/sandbox_policy_base.h"
 
 #include <sddl.h>
 
 #include "base/basictypes.h"
 #include "base/callback.h"
@@ skipping 441 matching lines @@
   // with the process and therefore with any thread that is not impersonating.
   DWORD result = CreateRestrictedToken(lockdown, lockdown_level_,
                                        integrity_level_, PRIMARY);
   if (ERROR_SUCCESS != result)
     return SBOX_ERROR_GENERIC;
 
   // If we're launching on the alternate desktop we need to make sure the
   // integrity label on the object is no higher than the sandboxed process's
   // integrity level. So, we lower the label on the desktop process if it's
   // not already low enough for our process.
-  if (use_alternate_desktop_ &&
+  if (alternate_desktop_handle_ && use_alternate_desktop_ &&
       integrity_level_ != INTEGRITY_LEVEL_LAST &&
       alternate_desktop_integrity_level_label_ < integrity_level_ &&
       base::win::OSInfo::GetInstance()->version() >= base::win::VERSION_VISTA) {
     // Integrity label enum is reversed (higher level is a lower value).
     static_assert(INTEGRITY_LEVEL_SYSTEM < INTEGRITY_LEVEL_UNTRUSTED,
                   "Integrity level ordering reversed.");
     result = SetObjectIntegrityLabel(alternate_desktop_handle_,
                                      SE_WINDOW_OBJECT,
                                      L"",
                                      GetIntegrityLevelString(integrity_level_));
@@ skipping 267 matching lines @@
       break;
     }
 
     default: { return SBOX_ERROR_UNSUPPORTED; }
   }
 
   return SBOX_ALL_OK;
 }
 
 }  // namespace sandbox