CreateProcessAsUser Creating Window in Active Session

Question

I am using CreateProcessAsUser from a windows service (please can we stay on-topic and assume I have a very good reason for doing this). Contrary to what everyone else is asking here I am getting a window in my active terminal session (session 1) instead of the same session as the service (session 0) - which is undesirable.

I appropriated Scott Allen's code; and came up with the following. Notable changes are the "revert to self", the "CREATE_NO_WINDOW" and command-line args support.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Security;
using System.Runtime.InteropServices;
using System.Diagnostics;
using System.Security.Principal;
using System.ComponentModel;
using System.IO;

namespace SourceCode.Runtime.ChildProcessService
{
    [SuppressUnmanagedCodeSecurity]
    class NativeMethods
    {
        [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;
        public const int CREATE_NO_WINDOW = 0x08000000;

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

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

        public static Process CreateProcessAsUser(string filename, string args)
        {
            var hToken = WindowsIdentity.GetCurrent().Token;
            var hDupedToken = IntPtr.Zero;

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

            try
            {
                if (!DuplicateTokenEx(
                        hToken,
                        GENERIC_ALL_ACCESS,
                        ref sa,
                        (int)SECURITY_IMPERSONATION_LEVEL.SecurityIdentification,
                        (int)TOKEN_TYPE.TokenPrimary,
                        ref hDupedToken
                    ))
                    throw new Win32Exception(Marshal.GetLastWin32Error());

                var si = new STARTUPINFO();
                si.cb = Marshal.SizeOf(si);
                si.lpDesktop = "";

                var path = Path.GetFullPath(filename);
                var dir = Path.GetDirectoryName(path);

                // Revert to self to create the entire process; not doing this might
                // require that the currently impersonated user has "Replace a process
                // level token" rights - we only want our service account to need
                // that right.
                using (var ctx = WindowsIdentity.Impersonate(IntPtr.Zero))
                {
                    if (!CreateProcessAsUser(
                                            hDupedToken,
                                            path,
                                            string.Format("\"{0}\" {1}", filename.Replace("\"", "\"\""), args),
                                            ref sa, ref sa,
                                            false, 0, IntPtr.Zero,
                                            dir, ref si, ref pi
                                    ))
                        throw new Win32Exception(Marshal.GetLastWin32Error());
                }

                return Process.GetProcessById(pi.dwProcessID);
            }
            finally
            {
                if (pi.hProcess != IntPtr.Zero)
                    CloseHandle(pi.hProcess);
                if (pi.hThread != IntPtr.Zero)
                    CloseHandle(pi.hThread);
                if (hDupedToken != IntPtr.Zero)
                    CloseHandle(hDupedToken);
            }
        }
    }
}

Now assume that the service is running under 'Domain\MyService' and I am currently logged in as 'Domain\Administrator' - and I am booting a console application as a worker process. When I use a client application to access the service (the service isn't started in console mode i.e. it is in session 0) and execute the method that invokes the CreateProcessAsUser the worker process appears on my desktop.

Now I could make it a windows application with no window to side-step the creation of the console window; however, at the end of the day it's still being created in session 1.

Any ideas why the console application isn't being created in the same session as the service?

Answer 1

As you are probably aware already, the isolation of Session 0 is for security reason and you can read more about it here http://msdn.microsoft.com/en-us/windows/hardware/gg463353.aspx

With regard to why your console app is created in active session (e.g. session 1), this actually linked back directly to your user token. When you ask for current user token, this token automatically carried with it the session id information - in this case it is the login terminal services session (session 1). This session id is reference by the token which then replicated in the DuplicateTokenEx and then used in the CreateProcessAsUser call. In order to force the creation of the your console application in session 0, you will need to make an explicit call to the SetTokenInformation API (advapi32.dll), passed in your hDupedToken before calling CreateProcessAsUser like below

..................
UInt32 dwSessionId = 0;  // set it to session 0
SetTokenInformation(hDupedToken, TokenInformationClass.TokenSessionId, ref dwSessionId, (UInt32) IntPtr.Size);
.................
CreateProcessAsUser(hDupedToken, ....)

Here is more info on SetTokenInformation http://msdn.microsoft.com/en-us/library/windows/desktop/aa379591(v=vs.85).aspx