Run as interactive user from service

The code below runs a program on interactive desktop with logged on user privileges, as it was started by user himself. Must be executed by Local System, for example, by Windows service.

stdafx.h:

#include <WtsApi32.h>
#pragma comment(lib, "WtsApi32.lib")

#include <Userenv.h>
#pragma comment(lib, "Userenv.lib")

RunAsInteractiveUser function:

BOOL bRet;
HRESULT hr;

HANDLE processToken = NULL;
TOKEN_PRIVILEGES oldTokenPrivileges = { 0 };

HANDLE impersonationToken = NULL;
HANDLE userToken = NULL;

LPVOID pEnvironment = NULL;
PROCESS_INFORMATION processInformation = { 0 };

__try {
    bRet = OpenProcessToken(GetCurrentProcess(), TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, &processToken);
    if (!bRet) {
        hr = GetLastError();
        return hr;
    }

    // This step might not be necessary because SeTcbPrivilege is enabled by default for Local System
    LUID luid;
    bRet = LookupPrivilegeValue(NULL, _T("SeTcbPrivilege"), &luid);
    if (!bRet) {
        hr = GetLastError();
        return hr;
    }

    TOKEN_PRIVILEGES adjTokenPrivileges = { 0 };
    adjTokenPrivileges.PrivilegeCount = 1;
    adjTokenPrivileges.Privileges[0].Luid = luid;
    adjTokenPrivileges.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED;

    DWORD dwOldTPLen;
    bRet = AdjustTokenPrivileges(processToken, FALSE, &adjTokenPrivileges, sizeof(TOKEN_PRIVILEGES), &oldTokenPrivileges, &dwOldTPLen);
    if (bRet) {
        hr = GetLastError();
        if (hr == ERROR_SUCCESS);
        else if (hr == ERROR_NOT_ALL_ASSIGNED) {
            // Enabled by default
        }
    }
    else {
        hr = GetLastError();
        return hr;
    }

    DWORD conSessId = WTSGetActiveConsoleSessionId();
    if (conSessId == 0xFFFFFFFF) {
        // There is no session attached to the console
        return ERROR_SUCCESS;
    }

    bRet = WTSQueryUserToken(conSessId, &impersonationToken);
    if (!bRet) {
        hr = GetLastError();
        return hr;
    }

    bRet = DuplicateTokenEx(impersonationToken, MAXIMUM_ALLOWED, NULL, SecurityIdentification, TokenPrimary, &userToken);
    if (!bRet) {
        hr = GetLastError();
        return hr;
    }

    STARTUPINFO si = { 0 };
    si.cb = sizeof(STARTUPINFO);
    si.lpDesktop = _T("winsta0\\default");

    bRet = CreateEnvironmentBlock(&pEnvironment, userToken, TRUE);
    if (!bRet) {
        hr = GetLastError();
        return hr;
    }

    bRet = CreateProcessAsUser(userToken, _T("C:\\Windows\\notepad.exe"), NULL, NULL, NULL, FALSE, CREATE_UNICODE_ENVIRONMENT, pEnvironment, NULL, &si, &processInformation);
    if (!bRet) {
        hr = GetLastError();
        return hr;
    }
}
__finally {
    if (processInformation.hThread) {
        CloseHandle(processInformation.hThread);
    }
    if (processInformation.hProcess) {
        CloseHandle(processInformation.hProcess);
    }
    if (pEnvironment) {
        bRet = DestroyEnvironmentBlock(pEnvironment);
    }
    if (userToken) {
        CloseHandle(userToken);
    }
    if (impersonationToken) {
        CloseHandle(impersonationToken);
    }
    if (processToken) {
        bRet = AdjustTokenPrivileges(processToken, FALSE, &oldTokenPrivileges, sizeof(TOKEN_PRIVILEGES), NULL, NULL);
        CloseHandle(processToken);
    }
}