How to call CreateProcess() with STARTUPINFOEX from C# and re-parent the child

Question

I need to create a new process but so that it is a \"child\" of another process not the current process eg re-parent the new process.

The following have got me almos

Answer 1

There are two issues with your code. First, the lpAttributeList parameter of the InitializeProcThreadAttributeList and UpdateProcThreadAttribute functions must be typed as IntPtr with no out modifier. Second, the lpValue parameter of the UpdateProcThreadAttribute function must be a pointer to the attribute value (in your case, parentHandle), not the value itself. Below is the fixed code.

using System;
using System.Diagnostics;
using System.IO;
using System.Runtime.InteropServices;

public class ProcessCreator
{
    [DllImport("kernel32.dll")]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool CreateProcess(
        string lpApplicationName, string lpCommandLine, ref SECURITY_ATTRIBUTES lpProcessAttributes,
        ref SECURITY_ATTRIBUTES lpThreadAttributes, bool bInheritHandles, uint dwCreationFlags,
        IntPtr lpEnvironment, string lpCurrentDirectory, [In] ref STARTUPINFOEX lpStartupInfo,
        out PROCESS_INFORMATION lpProcessInformation);

    [DllImport("kernel32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool UpdateProcThreadAttribute(
        IntPtr lpAttributeList, uint dwFlags, IntPtr Attribute, IntPtr lpValue,
        IntPtr cbSize, IntPtr lpPreviousValue, IntPtr lpReturnSize);

    [DllImport("kernel32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool InitializeProcThreadAttributeList(
        IntPtr lpAttributeList, int dwAttributeCount, int dwFlags, ref IntPtr lpSize);

    [DllImport("kernel32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool DeleteProcThreadAttributeList(IntPtr lpAttributeList);

    [DllImport("kernel32.dll", SetLastError = true)]
    static extern bool CloseHandle(IntPtr hObject);

    public static bool CreateProcess(int parentProcessId)
    {
        const uint EXTENDED_STARTUPINFO_PRESENT = 0x00080000;
        const int PROC_THREAD_ATTRIBUTE_PARENT_PROCESS = 0x00020000;

        var pInfo = new PROCESS_INFORMATION();
        var sInfoEx = new STARTUPINFOEX();
        sInfoEx.StartupInfo.cb = Marshal.SizeOf(sInfoEx);
        IntPtr lpValue = IntPtr.Zero;

        try
        {
            if (parentProcessId > 0)
            {
                var lpSize = IntPtr.Zero;
                var success = InitializeProcThreadAttributeList(IntPtr.Zero, 1, 0, ref lpSize);
                if (success || lpSize == IntPtr.Zero)
                {
                    return false;
                }

                sInfoEx.lpAttributeList = Marshal.AllocHGlobal(lpSize);
                success = InitializeProcThreadAttributeList(sInfoEx.lpAttributeList, 1, 0, ref lpSize);
                if (!success)
                {
                    return false;
                }

                var parentHandle = Process.GetProcessById(parentProcessId).Handle;
                // This value should persist until the attribute list is destroyed using the DeleteProcThreadAttributeList function
                lpValue = Marshal.AllocHGlobal(IntPtr.Size);
                Marshal.WriteIntPtr(lpValue, parentHandle);

                success = UpdateProcThreadAttribute(
                    sInfoEx.lpAttributeList,
                    0,
                    (IntPtr)PROC_THREAD_ATTRIBUTE_PARENT_PROCESS,
                    lpValue,
                    (IntPtr)IntPtr.Size,
                    IntPtr.Zero,
                    IntPtr.Zero);
                if (!success)
                {
                    return false;
                }
            }

            var pSec = new SECURITY_ATTRIBUTES();
            var tSec = new SECURITY_ATTRIBUTES();
            pSec.nLength = Marshal.SizeOf(pSec);
            tSec.nLength = Marshal.SizeOf(tSec);
            var lpApplicationName = Path.Combine(Environment.SystemDirectory, "notepad.exe");
            return CreateProcess(lpApplicationName, null, ref pSec, ref tSec, false, EXTENDED_STARTUPINFO_PRESENT, IntPtr.Zero, null, ref sInfoEx, out pInfo);
        }
        finally
        {
            // Free the attribute list
            if (sInfoEx.lpAttributeList != IntPtr.Zero)
            {
                DeleteProcThreadAttributeList(sInfoEx.lpAttributeList);
                Marshal.FreeHGlobal(sInfoEx.lpAttributeList);
            }
            Marshal.FreeHGlobal(lpValue);

            // Close process and thread handles
            if (pInfo.hProcess != IntPtr.Zero)
            {
                CloseHandle(pInfo.hProcess);
            }
            if (pInfo.hThread != IntPtr.Zero)
            {
                CloseHandle(pInfo.hThread);
            }
        }
    }

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
    struct STARTUPINFOEX
    {
        public STARTUPINFO StartupInfo;
        public IntPtr lpAttributeList;
    }

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
    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 dwYSize;
        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)]
    internal struct PROCESS_INFORMATION
    {
        public IntPtr hProcess;
        public IntPtr hThread;
        public int dwProcessId;
        public int dwThreadId;
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct SECURITY_ATTRIBUTES
    {
        public int nLength;
        public IntPtr lpSecurityDescriptor;
        public int bInheritHandle;
    }
}