rlz/win/lib/lib_mutex.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4 //
   5 // Mutex to guarantee serialization of RLZ key accesses.
   6
   7 #include "rlz/win/lib/lib_mutex.h"
   8
   9 #include <windows.h>
  10 #include <Sddl.h>    // For SDDL_REVISION_1, ConvertStringSecurityDescript..
  11 #include <Aclapi.h>  // For SetSecurityInfo
  12
  13 #include "base/logging.h"
  14 #include "base/win/windows_version.h"
  15
  16 namespace {
  17
  18 const wchar_t kMutexName[] = L"{A946A6A9-917E-4949-B9BC-6BADA8C7FD63}";
  19
  20 }  // namespace anonymous
  21
  22 namespace rlz_lib {
  23
  24 // Needed to allow synchronization across integrity levels.
  25 static bool SetObjectToLowIntegrity(HANDLE object,
  26     SE_OBJECT_TYPE type = SE_KERNEL_OBJECT) {
  27   if (base::win::GetVersion() < base::win::VERSION_VISTA)
  28     return true;  // Not needed on XP.
  29
  30   // The LABEL_SECURITY_INFORMATION SDDL SACL to be set for low integrity.
  31   static const wchar_t kLowIntegritySddlSacl[] = L"S:(ML;;NW;;;LW)";
  32
  33   bool result = false;
  34   DWORD error = ERROR_SUCCESS;
  35   PSECURITY_DESCRIPTOR security_descriptor = NULL;
  36   PACL sacl = NULL;
  37   BOOL sacl_present = FALSE;
  38   BOOL sacl_defaulted = FALSE;
  39
  40   if (ConvertStringSecurityDescriptorToSecurityDescriptorW(
  41           kLowIntegritySddlSacl, SDDL_REVISION_1, &security_descriptor, NULL)) {
  42     if (GetSecurityDescriptorSacl(security_descriptor, &sacl_present,
  43             &sacl, &sacl_defaulted)) {
  44       error = SetSecurityInfo(object, type, LABEL_SECURITY_INFORMATION,
  45                               NULL, NULL, NULL, sacl);
  46       result = (ERROR_SUCCESS == error);
  47     }
  48     LocalFree(security_descriptor);
  49   }
  50
  51   return result;
  52 }
  53
  54 LibMutex::LibMutex() : acquired_(false), mutex_(NULL) {
  55   mutex_ = CreateMutex(NULL, false, kMutexName);
  56   bool result = SetObjectToLowIntegrity(mutex_);
  57   if (result) {
  58     acquired_ = (WAIT_OBJECT_0 == WaitForSingleObject(mutex_, 5000L));
  59   }
  60 }
  61
  62 LibMutex::~LibMutex() {
  63   if (acquired_) ReleaseMutex(mutex_);
  64   CloseHandle(mutex_);
  65 }
  66
  67 }  // namespace rlz_lib