Make PrependWindowsSessionPath thread safe

content/common/sandbox_policy.cc

 // Copyright (c) 2011 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 "content/common/sandbox_policy.h"
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/debug/debugger.h"
@@ skipping 180 matching lines @@
 // Eviction of injected DLLs is done by the sandbox so that the injected module
 // does not get a chance to execute any code.
 void AddDllEvictionPolicy(sandbox::TargetPolicy* policy) {
   for (int ix = 0; ix != arraysize(kTroublesomeDlls); ++ix)
     BlacklistAddOneDll(kTroublesomeDlls[ix], policy);
 }
 
 // Returns the object path prepended with the current logon session.
 string16 PrependWindowsSessionPath(const char16* object) {
   // Cache this because it can't change after process creation.
-  static string16* session_prefix = NULL;
-  if (!session_prefix) {
+  uintptr_t s_session_id = 0;
+  if (s_session_id == 0) {
     HANDLE token;
-    DWORD session_id;
     DWORD session_id_length;
+    DWORD session_id = 0;
 
     CHECK(::OpenProcessToken(::GetCurrentProcess(), TOKEN_QUERY, &token));
     CHECK(::GetTokenInformation(token, TokenSessionId, &session_id,
         sizeof(session_id), &session_id_length));
     CloseHandle(token);
-
-    session_prefix = new string16(base::StringPrintf(L"\\Sessions\\%d",
-        session_id));
+    s_session_id = session_id;
   }
 
-  return *session_prefix + object;
+  return base::StringPrintf(L"\\Sessions\\%d%ls", s_session_id, object);
 }
 
 // Closes handles that are opened at process creation and initialization.
 void AddBaseHandleClosePolicy(sandbox::TargetPolicy* policy) {
   // Being able to manipulate anything BaseNamedObjects is bad.
   policy->AddKernelObjectToClose(L"Directory", PrependWindowsSessionPath(
       L"\\BaseNamedObjects").data());
   policy->AddKernelObjectToClose(L"Section", PrependWindowsSessionPath(
       L"\\BaseNamedObjects\\windows_shell_global_counters").data());
 }
@@ skipping 276 matching lines @@
 
   // Help the process a little. It can't start the debugger by itself if
   // the process is in a sandbox.
   if (child_needs_help)
     base::debug::SpawnDebuggerOnProcess(target.dwProcessId);
 
   return process;
 }
 
 }  // namespace sandbox