CreateEnvironmentBlock crashes service - c++

Question

I'm trying to start GUI application from windows service. But when I call CreateEnvironmentBlock() function, It hangs there for a while then crashes displaying dialog box "SampleService.exe stopped working and was closed. A problem caused the application to stop working correctly. windows will notify you if a solution is available." Following is my code.
DWORD dwSessionId = 0; // Session ID
HANDLE hToken = NULL; // Active session token
HANDLE hDupToken = NULL; // Duplicate session token
WCHAR szErr[1024] = {0};
STARTUPINFO* startupInfo;
PROCESS_INFORMATION processInformation;
PWTS_SESSION_INFO pSessionInfo = 0;
DWORD dwCount = 0;
LPVOID lpEnvironment = NULL; // Environtment block
OutputDebugString(_T("My Sample Service: startApplication: Entry"));
// Get the list of all terminal sessions
WTSEnumerateSessions(WTS_CURRENT_SERVER_HANDLE, 0, 1, &pSessionInfo, &dwCount);
int dataSize = sizeof(WTS_SESSION_INFO);
// look over obtained list in search of the active session
for (DWORD i = 0; i < dwCount; ++i)
{
WTS_SESSION_INFO si = pSessionInfo[i];
if (WTSActive == si.State)
{
// If the current session is active – store its ID
dwSessionId = si.SessionId;
break;
}
}
OutputDebugString(_T("My Sample Service: startApplication: freewtsmemory"));
WTSFreeMemory(pSessionInfo);
OutputDebugString(_T("My Sample Service: startApplication: WTSQueryUserToken"));
// Get token of the logged in user by the active session ID
BOOL bRet = WTSQueryUserToken(dwSessionId, &hToken);
if (!bRet)
{
swprintf(szErr, _T("WTSQueryUserToken Error: %d"), GetLastError());
OutputDebugString(szErr);
return false;
}
OutputDebugString(_T("My Sample Service: startApplication: duplicatetokenex"));
// Get duplicate token from the active logged in user's token
bRet = DuplicateTokenEx(hToken, // Active session token
TOKEN_ASSIGN_PRIMARY | TOKEN_ALL_ACCESS, // Desired access
NULL, // Token attributes
SecurityImpersonation, // Impersonation level
TokenPrimary, // Token type
&hDupToken); // New/Duplicate token
if (!bRet)
{
swprintf(szErr, _T("DuplicateTokenEx Error: %d"), GetLastError());
OutputDebugString(szErr);
return false;
}
// Get all necessary environment variables of logged in user
// to pass them to the process
OutputDebugString(_T("My Sample Service: startApplication: createenvironmentblock"));
try{
bRet = CreateEnvironmentBlock(&lpEnvironment, hDupToken, FALSE);
}
catch( const exception &e)
{
swprintf(szErr, _T("CreateEnvironmentBlock Exception: %s"), e);
OutputDebugString(szErr);
return false;
}
if(!bRet)
{
swprintf(szErr, _T("CreateEnvironmentBlock Error: %d"), GetLastError());
OutputDebugString(szErr);
return false;
}
// Initialize Startup and Process info
startupInfo->cb = sizeof(STARTUPINFO);
OutputDebugString(_T("My Sample Service: startApplication: createprocess"));
// Start the process on behalf of the current user
BOOL returnCode = CreateProcessAsUser(hDupToken,
NULL,
L"C:\\KM\\TEST.exe",
NULL,
NULL,
FALSE,
NORMAL_PRIORITY_CLASS | CREATE_NEW_CONSOLE | CREATE_UNICODE_ENVIRONMENT,
lpEnvironment,
NULL,
startupInfo,
&processInformation);
if( !returnCode)
{
swprintf(szErr, _T("CreateProcessAsUser Error: %d"), GetLastError());
OutputDebugString(szErr);
return false;
}
CloseHandle(hDupToken);
return true;
It shows "My Sample Service: startApplication: createenvironmentblock" in debugview and stopped service. please help me out regarding this issue. please note i m using windows vista.
Regards,
KM.

Answer 1

You need to initialise pointers before you can use them in a defined fashion.
STARTUPINFO* startupInfo;
...
startupInfo->cb = sizeof(STARTUPINFO);
This mistake might have been more obvious to spot if your variables were declared closer to where they are used. If you follow some rule that variables can only be declared at the start of a function, you might want to consider making more functions.
And, for what it's worth, when troubleshooting these sorts of issues you can always attach Visual Studio's debugger to the service process instead of relying on OutputDebugString. Just make sure the service process is the last thing built by Visual Studio and process, symbol files and source code should all be aligned.