Execute program capturing screenshots from windows service - c

Question

I'm writing a windows service, which will manage some agent program capturing screenshots. Agent program works fine, no problems at all - it just takes screenshot and saves it into bmp file.
But when i try to execute this agent program from my service - it doesnt't work, all i get is black pictures (as if i tried to capture screenshot directly from my service)
My code inside service is:
ServiceStatus.dwCurrentState = SERVICE_RUNNING;
SetServiceStatus (hStatus, &ServiceStatus);
SHELLEXECUTEINFO seInfo;
seInfo.cbSize = sizeof(SHELLEXECUTEINFO);
seInfo.fMask = SEE_MASK_NOCLOSEPROCESS;
seInfo.hwnd = NULL;
seInfo.lpVerb = TEXT("open");
seInfo.lpFile = TEXT("D:\\dev\\work\\agent.exe");
seInfo.lpDirectory = TEXT("D:\\dev\\work\\");
seInfo.nShow = SW_SHOWNORMAL;
seInfo.hInstApp = NULL;
ShellExecuteEx(&seInfo);
I tried to change service properties - to allow it interacting with desktop, change service user from SYSTEM to my local account - nothing helpes.
What can i do to make it work properely?
UPD. Well, i suppose, this happenes because my service executes program in session0. I tried CreateProcess() and CreateProcessAsUser() as well - no result. So how can i create procees NOT in session0?

Answer 1

Aliostad did all the heavy lifting for this. Take a look at his code, it's an excellent start. Keep in mind, you'll need a separate app to take the screenshot since a new process has to be kicked off while impersonating the logged in user.
https://stackoverflow.com/a/4147868/125406
Here is my version of it (fully based on Aliostad's code). It adds command line params, a wait for the process to finish and return of the exit code.
public static class ProcessAsCurrentUser
{
/// <summary>
/// Connection state of a session.
/// </summary>
public enum ConnectionState
{
/// <summary>
/// A user is logged on to the session.
/// </summary>
Active,
/// <summary>
/// A client is connected to the session.
/// </summary>
Connected,
/// <summary>
/// The session is in the process of connecting to a client.
/// </summary>
ConnectQuery,
/// <summary>
/// This session is shadowing another session.
/// </summary>
Shadowing,
/// <summary>
/// The session is active, but the client has disconnected from it.
/// </summary>
Disconnected,
/// <summary>
/// The session is waiting for a client to connect.
/// </summary>
Idle,
/// <summary>
/// The session is listening for connections.
/// </summary>
Listening,
/// <summary>
/// The session is being reset.
/// </summary>
Reset,
/// <summary>
/// The session is down due to an error.
/// </summary>
Down,
/// <summary>
/// The session is initializing.
/// </summary>
Initializing
}
[StructLayout(LayoutKind.Sequential)]
class SECURITY_ATTRIBUTES
{
public int nLength;
public IntPtr lpSecurityDescriptor;
public int bInheritHandle;
}
[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;
}
enum LOGON_TYPE
{
LOGON32_LOGON_INTERACTIVE = 2,
LOGON32_LOGON_NETWORK,
LOGON32_LOGON_BATCH,
LOGON32_LOGON_SERVICE,
LOGON32_LOGON_UNLOCK = 7,
LOGON32_LOGON_NETWORK_CLEARTEXT,
LOGON32_LOGON_NEW_CREDENTIALS
}
enum LOGON_PROVIDER
{
LOGON32_PROVIDER_DEFAULT,
LOGON32_PROVIDER_WINNT35,
LOGON32_PROVIDER_WINNT40,
LOGON32_PROVIDER_WINNT50
}
[Flags]
enum CreateProcessFlags : uint
{
CREATE_BREAKAWAY_FROM_JOB = 0x01000000,
CREATE_DEFAULT_ERROR_MODE = 0x04000000,
CREATE_NEW_CONSOLE = 0x00000010,
CREATE_NEW_PROCESS_GROUP = 0x00000200,
CREATE_NO_WINDOW = 0x08000000,
CREATE_PROTECTED_PROCESS = 0x00040000,
CREATE_PRESERVE_CODE_AUTHZ_LEVEL = 0x02000000,
CREATE_SEPARATE_WOW_VDM = 0x00000800,
CREATE_SHARED_WOW_VDM = 0x00001000,
CREATE_SUSPENDED = 0x00000004,
CREATE_UNICODE_ENVIRONMENT = 0x00000400,
DEBUG_ONLY_THIS_PROCESS = 0x00000002,
DEBUG_PROCESS = 0x00000001,
DETACHED_PROCESS = 0x00000008,
EXTENDED_STARTUPINFO_PRESENT = 0x00080000,
INHERIT_PARENT_AFFINITY = 0x00010000
}
[StructLayout(LayoutKind.Sequential)]
public struct WTS_SESSION_INFO
{
public int SessionID;
[MarshalAs(UnmanagedType.LPTStr)] public string WinStationName;
public ConnectionState State;
}
[DllImport("wtsapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
public static extern Int32 WTSEnumerateSessions(IntPtr hServer, int reserved, int version,
ref IntPtr sessionInfo, ref int count);
[DllImport("advapi32.dll", EntryPoint = "CreateProcessAsUserW", SetLastError = true, CharSet = CharSet.Auto)]
static extern bool CreateProcessAsUser(
IntPtr hToken,
string lpApplicationName,
string lpCommandLine,
IntPtr lpProcessAttributes,
IntPtr lpThreadAttributes,
bool bInheritHandles,
UInt32 dwCreationFlags,
IntPtr lpEnvironment,
string lpCurrentDirectory,
ref STARTUPINFO lpStartupInfo,
out PROCESS_INFORMATION lpProcessInformation);
[DllImport("kernel32.dll", SetLastError = true)]
public static extern Int32 WaitForSingleObject(IntPtr handle, Int32 wait);
public const Int32 INFINITE = -1;
public const Int32 WAIT_ABANDONED = 0x80;
public const Int32 WAIT_OBJECT_0 = 0x00;
public const Int32 WAIT_TIMEOUT = 0x102;
public const Int32 WAIT_FAILED = -1;
[DllImport("kernel32.dll", SetLastError = true)]
public static extern bool GetExitCodeProcess(IntPtr hProcess, out uint exitCode);
[DllImport("wtsapi32.dll")]
public static extern void WTSFreeMemory(IntPtr memory);
[DllImport("kernel32.dll")]
private static extern UInt32 WTSGetActiveConsoleSessionId();
[DllImport("wtsapi32.dll", SetLastError = true)]
static extern int WTSQueryUserToken(UInt32 sessionId, out IntPtr Token);
[DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
public extern static bool DuplicateTokenEx(
IntPtr hExistingToken,
uint dwDesiredAccess,
IntPtr lpTokenAttributes,
int ImpersonationLevel,
int TokenType,
out IntPtr phNewToken);
private const int TokenImpersonation = 2;
private const int SecurityIdentification = 1;
private const int MAXIMUM_ALLOWED = 0x2000000;
private const int TOKEN_DUPLICATE = 0x2;
private const int TOKEN_QUERY = 0x00000008;
/// <summary>
/// Launches a process for the current logged on user if there are any.
/// If none, return false as well as in case of
///
/// ##### !!! BEWARE !!! #### ------------------------------------------
/// This code will only work when running in a windows service (where it is really needed)
/// so in case you need to test it, it needs to run in the service. Reason
/// is a security privileg which only services have (SE_??? something, cant remember)!
/// </summary>
/// <param name="processExe"></param>
/// <returns></returns>
public static uint CreateProcessAsCurrentUser(string processExe, string commandLine)
{
IntPtr duplicate = new IntPtr();
STARTUPINFO info = new STARTUPINFO();
PROCESS_INFORMATION procInfo = new PROCESS_INFORMATION();
Debug.WriteLine(string.Format("CreateProcessAsCurrentUser. processExe: " + processExe));
IntPtr p = GetCurrentUserToken();
bool result = DuplicateTokenEx(p, MAXIMUM_ALLOWED | TOKEN_QUERY | TOKEN_DUPLICATE, IntPtr.Zero,
SecurityIdentification, SecurityIdentification, out duplicate);
Debug.WriteLine(string.Format("DuplicateTokenEx result: {0}", result));
Debug.WriteLine(string.Format("duplicate: {0}", duplicate));
if (result)
{
//NOTE: CREATE_NO_WINDOW will hide the console
//If there are commandline options, pass them AND the exe in
//commandLine and leave processExe empty.
result = CreateProcessAsUser(duplicate, processExe, commandLine,
// IntPtr.Zero, IntPtr.Zero, false, (UInt32) CreateProcessFlags.CREATE_NEW_CONSOLE, IntPtr.Zero, null,
IntPtr.Zero, IntPtr.Zero, false, (UInt32)CreateProcessFlags.CREATE_NO_WINDOW, IntPtr.Zero, null,
ref info, out procInfo);
Debug.WriteLine(string.Format("CreateProcessAsUser result: {0}", result));
}
if (p.ToInt32() != 0)
{
Marshal.Release(p);
Debug.WriteLine(string.Format("Released handle p: {0}", p));
}
if (duplicate.ToInt32() != 0)
{
Marshal.Release(duplicate);
Debug.WriteLine(string.Format("Released handle duplicate: {0}", duplicate));
}
//Wait for the process to complete
WaitForSingleObject(procInfo.hProcess, (int)INFINITE);
//Get and return the exit code
uint exitcode;
GetExitCodeProcess(procInfo.hProcess, out exitcode);
return exitcode;
}
public static int GetCurrentSessionId()
{
uint sessionId = WTSGetActiveConsoleSessionId();
Debug.WriteLine(string.Format("sessionId: {0}", sessionId));
if (sessionId == 0xFFFFFFFF)
return -1;
else
return (int)sessionId;
}
public static bool IsUserLoggedOn()
{
List<WTS_SESSION_INFO> wtsSessionInfos = ListSessions();
Debug.WriteLine(string.Format("Number of sessions: {0}", wtsSessionInfos.Count));
int activeSessionCount = 0;
foreach (var session in wtsSessionInfos)
{
if (session.State == ConnectionState.Active)
activeSessionCount++;
}
//return wtsSessionInfos.Where(x => x.State == ConnectionState.Active).Count() > 0;
return activeSessionCount > 0;
}
private static IntPtr GetCurrentUserToken()
{
List<WTS_SESSION_INFO> wtsSessionInfos = ListSessions();
int sessionId = 0;
foreach (var session in wtsSessionInfos)
{
if (session.State == ConnectionState.Active)
{
sessionId = session.SessionID;
break;
}
}
//Old Linq method
//int sessionId = wtsSessionInfos.Where(x => x.State == ConnectionState.Active).FirstOrDefault().SessionID;
//int sessionId = GetCurrentSessionId();
Debug.WriteLine(string.Format("sessionId: {0}", sessionId));
if (sessionId == int.MaxValue)
{
return IntPtr.Zero;
}
else
{
IntPtr p = new IntPtr();
int result = WTSQueryUserToken((UInt32)sessionId, out p);
Debug.WriteLine(string.Format("WTSQueryUserToken result: {0}", result));
Debug.WriteLine(string.Format("WTSQueryUserToken p: {0}", p));
return p;
}
}
public static List<WTS_SESSION_INFO> ListSessions()
{
IntPtr server = IntPtr.Zero;
List<WTS_SESSION_INFO> ret = new List<WTS_SESSION_INFO>();
try
{
IntPtr ppSessionInfo = IntPtr.Zero;
Int32 count = 0;
Int32 retval = WTSEnumerateSessions(IntPtr.Zero, 0, 1, ref ppSessionInfo, ref count);
Int32 dataSize = Marshal.SizeOf(typeof(WTS_SESSION_INFO));
Int64 current = (int)ppSessionInfo;
if (retval != 0)
{
for (int i = 0; i < count; i++)
{
WTS_SESSION_INFO si =
(WTS_SESSION_INFO)Marshal.PtrToStructure((System.IntPtr)current,
typeof(WTS_SESSION_INFO));
current += dataSize;
ret.Add(si);
}
WTSFreeMemory(ppSessionInfo);
}
}
catch (Exception exception)
{
Debug.WriteLine(exception.ToString());
}
return ret;
}
}
We pass a filename as a parameter to the screenshot app and then wait for it to complete. The service then picks up the file and processes and deletes it.
We also found another way around this using named pipes. I'm less familiar with that solution.