穿透Session 0 隔离（二）

     上一篇我们已经对Session 0 隔离有了进一步认识，如果在开发过程中确实需要服务与桌面用户进行交互，可以通过远程桌面服务的API 绕过Session 0 的隔离完成交互操作。

     对于简单的交互，服务可以通过WTSSendMessage 函数，在用户Session 上显示消息窗口。对于一些复杂的UI 交互，必须调用CreateProcessAsUser 或其他方法（WCF、.NET远程处理等）进行跨Session 通信，在桌面用户上创建一个应用程序界面。

WTSSendMessage 函数

     如果服务只是简单的向桌面用户Session 发送消息窗口，则可以使用WTSSendMessage 函数实现。首先，在上一篇下载的代码中加入一个Interop.cs 类，并在类中加入如下代码：

public static IntPtr WTS_CURRENT_SERVER_HANDLE = IntPtr.Zero;

public static void ShowMessageBox(string message, string title)
{
    int resp = 0;
    WTSSendMessage(
        WTS_CURRENT_SERVER_HANDLE, 
        WTSGetActiveConsoleSessionId(),
        title, title.Length, 
        message, message.Length, 
        0, 0, out resp, false);
}

[DllImport("kernel32.dll", SetLastError = true)]
public static extern int WTSGetActiveConsoleSessionId();

[DllImport("wtsapi32.dll", SetLastError = true)]
public static extern bool WTSSendMessage(
    IntPtr hServer,
    int SessionId,
    String pTitle,
    int TitleLength,
    String pMessage,
    int MessageLength,
    int Style,
    int Timeout,
    out int pResponse,
    bool bWait);

     在ShowMessageBox 函数中调用了WTSSendMessage 来发送信息窗口，这样我们就可以在Service 的OnStart 函数中使用，打开Service1.cs 加入下面代码：

protected override void OnStart(string[] args)
{
    Interop.ShowMessageBox("This a message from AlertService.",
"AlertService Message");
}

     编译程序后在服务管理器中重新启动AlertService 服务，从下图中可以看到消息窗口是在当前用户桌面显示的，而不是Session 0 中。

CreateProcessAsUser 函数

     如果想通过服务向桌面用户Session 创建一个复杂UI 程序界面，则需要使用CreateProcessAsUser 函数为用户创建一个新进程用来运行相应的程序。打开Interop 类继续添加下面代码：

public static void CreateProcess(string app, string path)
{
    bool result;
    IntPtr hToken = WindowsIdentity.GetCurrent().Token;
    IntPtr hDupedToken = IntPtr.Zero;

    PROCESS_INFORMATION pi = new PROCESS_INFORMATION();
    SECURITY_ATTRIBUTES sa = new SECURITY_ATTRIBUTES();
    sa.Length = Marshal.SizeOf(sa);

    STARTUPINFO si = new STARTUPINFO();
    si.cb = Marshal.SizeOf(si);

    int dwSessionID = WTSGetActiveConsoleSessionId();
    result = WTSQueryUserToken(dwSessionID, out hToken);
    
    if (!result)
    {
        ShowMessageBox("WTSQueryUserToken failed", "AlertService Message");
    }

    result = DuplicateTokenEx(
          hToken,
          GENERIC_ALL_ACCESS,
          ref sa,
          (int)SECURITY_IMPERSONATION_LEVEL.SecurityIdentification,
          (int)TOKEN_TYPE.TokenPrimary,
          ref hDupedToken
       );

    if (!result)
    {
        ShowMessageBox("DuplicateTokenEx failed" ,"AlertService Message");
    }

    IntPtr lpEnvironment = IntPtr.Zero;
    result = CreateEnvironmentBlock(out lpEnvironment, hDupedToken, false);

    if (!result)
    {
        ShowMessageBox("CreateEnvironmentBlock failed", "AlertService Message");
    }

    result = CreateProcessAsUser(
                         hDupedToken,
                         app,
                         String.Empty,
                         ref sa, ref sa,
                         false, 0, IntPtr.Zero,
                         path, ref si, ref pi);

    if (!result)
    {
        int error = Marshal.GetLastWin32Error();
        string message = String.Format("CreateProcessAsUser Error: {0}", error);
        ShowMessageBox(message, "AlertService Message");
    }

    if (pi.hProcess != IntPtr.Zero)
        CloseHandle(pi.hProcess);
    if (pi.hThread != IntPtr.Zero)
        CloseHandle(pi.hThread);
    if (hDupedToken != IntPtr.Zero)
        CloseHandle(hDupedToken);
}

[StructLayout(LayoutKind.Sequential)]
public struct STARTUPINFO
{
    public Int32 cb;
    public string lpReserved;
    public string lpDesktop;
    public string lpTitle;
    public Int32 dwX;
    public Int32 dwY;
    public Int32 dwXSize;
    public Int32 dwXCountChars;
    public Int32 dwYCountChars;
    public Int32 dwFillAttribute;
    public Int32 dwFlags;
    public Int16 wShowWindow;
    public Int16 cbReserved2;
    public IntPtr lpReserved2;
    public IntPtr hStdInput;
    public IntPtr hStdOutput;
    public IntPtr hStdError;
}

[StructLayout(LayoutKind.Sequential)]
public struct PROCESS_INFORMATION
{
    public IntPtr hProcess;
    public IntPtr hThread;
    public Int32 dwProcessID;
    public Int32 dwThreadID;
}

[StructLayout(LayoutKind.Sequential)]
public struct SECURITY_ATTRIBUTES
{
    public Int32 Length;
    public IntPtr lpSecurityDescriptor;
    public bool bInheritHandle;
}

public enum SECURITY_IMPERSONATION_LEVEL
{
    SecurityAnonymous,
    SecurityIdentification,
    SecurityImpersonation,
    SecurityDelegation
}

public enum TOKEN_TYPE
{
    TokenPrimary = 1,
    TokenImpersonation
}

public const int GENERIC_ALL_ACCESS = 0x10000000;

[DllImport("kernel32.dll", SetLastError = true,
    CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
public static extern bool CloseHandle(IntPtr handle);

[DllImport("advapi32.dll", SetLastError = true,
    CharSet = CharSet.Ansi, CallingConvention = CallingConvention.StdCall)]
public static extern bool CreateProcessAsUser(
    IntPtr hToken,
    string lpApplicationName,
    string lpCommandLine,
    ref SECURITY_ATTRIBUTES lpProcessAttributes,
    ref SECURITY_ATTRIBUTES lpThreadAttributes,
    bool bInheritHandle,
    Int32 dwCreationFlags,
    IntPtr lpEnvrionment,
    string lpCurrentDirectory,
    ref STARTUPINFO lpStartupInfo,
    ref PROCESS_INFORMATION lpProcessInformation);

[DllImport("advapi32.dll", SetLastError = true)]
public static extern bool DuplicateTokenEx(
    IntPtr hExistingToken,
    Int32 dwDesiredAccess,
    ref SECURITY_ATTRIBUTES lpThreadAttributes,
    Int32 ImpersonationLevel,
    Int32 dwTokenType,
    ref IntPtr phNewToken);

[DllImport("wtsapi32.dll", SetLastError=true)]
public static extern bool WTSQueryUserToken(
    Int32 sessionId, 
    out IntPtr Token);

[DllImport("userenv.dll", SetLastError = true)]
static extern bool CreateEnvironmentBlock(
    out IntPtr lpEnvironment, 
    IntPtr hToken, 
    bool bInherit);

     在CreateProcess 函数中同时也涉及到DuplicateTokenEx、WTSQueryUserToken、CreateEnvironmentBlock 函数的使用，有兴趣的朋友可通过MSDN 进行学习。完成CreateProcess 函数创建后，就可以真正的通过它来调用应用程序了，回到Service1.cs 修改一下OnStart 我们来打开一个CMD 窗口。如下代码：

protected override void OnStart(string[] args)
{
    Interop.CreateProcess("cmd.exe",@"C:\Windows\System32\");
}

     重新编译程序，启动AlertService 服务便可看到下图界面。至此，我们已经可以通过一些简单的方法对Session 0 隔离问题进行解决。大家也可以通过WCF 等技术完成一些更复杂的跨Session 通信方式，实现在Windows 7 及Vista 系统中服务与桌面用户的交互操作。

参考资料

1. WTSSendMessage Function
http://msdn.microsoft.com/en-us/library/aa383842(VS.85).aspx

2. CreateProcessAsUser Function
http://msdn.microsoft.com/en-us/library/ms682429(v=VS.85).aspx

3. WTSSendMessage (wtsapi32)
http://www.pinvoke.net/default.aspx/wtsapi32/WTSSendMessage.html

4. WTSQueryUserToken Function
http://msdn.microsoft.com/en-us/library/aa383840(VS.85).aspx

5. http://www.pinvoke.net/

代码下载