《windows核心编程》笔记（三）

命名内核对象有一种问题：任何程序都可以创建一个命名对象，这样如果某个程序要实现单例运行而创建了一个内核对象，这种情况下另一程序也创建了同名的内核对象时，该单例程序就无法正常运行了。这是DoS攻击的一种。

在Vista中有一种机制使得用户创建的命名内核对象永远不会和其它程序创建的对象冲突，要使用定制的前缀并把它作为人的私有命名空间，如Global和Local，服务进程会确保为内核对象定义一边界描述符来保护命名空间。

下面是检查实例的代码：

void CheckInstances() 

{//检查实例

   // Create the boundary descriptor

   g_hBoundary = CreateBoundaryDescriptor(g_szBoundary, 0);

   // Create a SID corresponding to the Local Administrator group

   BYTE localAdminSID[SECURITY_MAX_SID_SIZE];

   PSID pLocalAdminSID = &localAdminSID;

   DWORD cbSID = sizeof(localAdminSID);

   if (!CreateWellKnownSid(

      WinBuiltinAdministratorsSid, NULL, pLocalAdminSID, &cbSID)

      ) {

      AddText(TEXT("AddSIDToBoundaryDescriptor failed: %u\r\n"), 

         GetLastError());

      return;

   }

   // Associate the Local Admin SID to the boundary descriptor

   // --> only applications running under an administrator user

   //     will be able to access the kernel objects in the same namespace

   if (!AddSIDToBoundaryDescriptor(&g_hBoundary, pLocalAdminSID)) {

   // Create the namespace for Local Administrators only

   SECURITY_ATTRIBUTES sa;

   sa.nLength = sizeof(sa);

   sa.bInheritHandle = FALSE;

   if (!ConvertStringSecurityDescriptorToSecurityDescriptor(

      TEXT("D:(A;;GA;;;BA)"), 

      SDDL_REVISION_1, &sa.lpSecurityDescriptor, NULL)) {

      AddText(TEXT("Security Descriptor creation failed: %u\r\n"), GetLastError());

   g_hNamespace = 

      CreatePrivateNamespace(&sa, g_hBoundary, g_szNamespace);

   // Don't forget to release memory for the security descriptor

   LocalFree(sa.lpSecurityDescriptor);

   // Check the private namespace creation result

   DWORD dwLastError = GetLastError();

   if (g_hNamespace == NULL) 

   {

      // Nothing to do if access is denied

      // --> this code must run under a Local Administrator account

      if (dwLastError == ERROR_ACCESS_DENIED) 

      {

         AddText(TEXT("Access denied when creating the namespace.\r\n"));

         AddText(TEXT("   You must be running as Administrator.\r\n\r\n"));

         return;

      }

      else 

      { 

         if (dwLastError == ERROR_ALREADY_EXISTS) 

         {

         // If another instance has already created the namespace, 

         // we need to open it instead. 

            AddText(TEXT("CreatePrivateNamespace failed: %u\r\n"), dwLastError);

            g_hNamespace = OpenPrivateNamespace(g_hBoundary, g_szNamespace);

            if (g_hNamespace == NULL) 

            {

               AddText(TEXT("   and OpenPrivateNamespace failed: %u\r\n"), 

               dwLastError);

               return;

            } 

            else 

               g_bNamespaceOpened = TRUE;

               AddText(TEXT("   but OpenPrivateNamespace succeeded\r\n\r\n"));

            }

         } 

         else

            AddText(TEXT("Unexpected error occured: %u\r\n\r\n"),dwLastError);

            return;

         }

   // Try to create the mutex object with a name 

   // based on the private namespace 

   TCHAR szMutexName[64];

   StringCchPrintf(szMutexName, _countof(szMutexName), TEXT("%s\\%s"), g_szNamespace, TEXT("Singleton"));

   g_hSingleton = CreateMutex(NULL, FALSE, szMutexName);//创建互斥量

   if (GetLastError() == ERROR_ALREADY_EXISTS) 

      // There is already an instance of this Singleton object

      AddText(TEXT("Another instance of Singleton is running:\r\n"));

      AddText(TEXT("--> Impossible to access application features.\r\n"));

   else  

      // First time the Singleton object is created

      AddText(TEXT("First instance of Singleton:\r\n"));

      AddText(TEXT("--> Access application features now.\r\n"));

}

void AddText(PCTSTR pszFormat, ) {

   va_list argList;

   va_start(argList, pszFormat);

   TCHAR sz[20 * 1024];

   Edit_GetText(DETAILS_CTRL, sz, _countof(sz));

   _vstprintf_s(

      _tcschr(sz, TEXT('\0')), _countof(sz) - _tcslen(sz), 

      pszFormat, argList);

   Edit_SetText(DETAILS_CTRL, sz);

   va_end(argList);

本文转自Phinecos(洞庭散人)博客园博客，原文链接：http://www.cnblogs.com/phinecos/archive/2008/06/08/1216009.html，如需转载请自行联系原作者