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MODULE EE3

WINDOWS SERVICES

Part 6: FINAL PART

What we have in this Module?

1. Sending control requests to a service program example.

2. Modifying the DACL for a service program example.

My Training Period: xx hours. Before you begin, read someinstruction here.

  // If no command line argument supplied...

  if (argc < 2)

   {

      printf("usage: %s <ServiceName>\n", argv[0]);

         printf("Try again.\n");

     return 1;

   }

   lpszServiceName = argv[1];

      // Open a handle to the SC Manager database...

       schSCManager = OpenSCManager(

       NULL,                   // local machine

       NULL,                   // SERVICES_ACTIVE_DATABASE database is opened by default

       SC_MANAGER_ALL_ACCESS);  // full access rights

if (NULL == schSCManager)

   printf("OpenSCManager(), Open a handle to the SC Manager database failed, error: %d.\n", GetLastError());

else

   printf("OpenSCManager(), Open a handle to the SC Manager database looks OK.\n");

   // The required service object access depends on the control...

   switch (fdwControl)

    {

       case SERVICE_CONTROL_STOP:

            fdwAccess = SERVICE_STOP;

           break;

       case SERVICE_CONTROL_PAUSE:

       case SERVICE_CONTROL_CONTINUE:

            fdwAccess = SERVICE_PAUSE_CONTINUE;

           break;

       case SERVICE_CONTROL_INTERROGATE:

            fdwAccess = SERVICE_INTERROGATE;

           break;

       default:

            fdwAccess = SERVICE_INTERROGATE;

    }

   // Open a handle to the service.

    schService = OpenService(

        schSCManager,        // SCManager database

        lpszServiceName,     // name of service

        fdwAccess);              // specify the access right

      if (schService == NULL)

         printf("OpenService(), open a handle to a service with appropriate access failed, error: %d", GetLastError());

      else

         printf("OpenService(), open a handle to a service with appropriate access looks OK.\n");

   // Send a control value to the service...

   if (!ControlService(

            schService,   // handle to service

            fdwControl,   // control value to send, here is SERVICE_CONTROL_STOP

            &ssStatus))   // address of status info

       printf("ControlService(), sending control value to stop a service failed, error: %d\n", GetLastError());

   else

       printf("ControlService(), sending control value to a stop service looks OK.\n");

   // Print the service status.

    printf("\nStatus of %s: \n", lpszServiceName);

    printf("  Service Type: 0x%x\n", ssStatus.dwServiceType);

    printf("  Current State: 0x%x\n", ssStatus.dwCurrentState);

    printf("  Controls Accepted: 0x%x\n", ssStatus.dwControlsAccepted);

    printf("  Exit Code: %d\n", ssStatus.dwWin32ExitCode);

    printf("  Service Specific Exit Code: %d\n", ssStatus.dwServiceSpecificExitCode);

    printf("  Check Point: %d\n", ssStatus.dwCheckPoint);

    printf("  Wait Hint: %d\n", ssStatus.dwWaitHint);

   return 0;

}

Running the program at the command prompt, the following are sample outputs.

F:\myproject\myservices\Release>myservices dhcp

OpenSCManager(), Open a handle to the SC Manager database looks OK.

OpenService(), open a handle to a service with appropriate access looks OK.

ControlService(), sending control value to a stop service looks OK.

 

Status of dhcp:

  Service Type: 0x20

  Current State: 0x3

  Controls Accepted: 0x5

  Exit Code: 0

  Service Specific Exit Code: 0

  Check Point: 1

  Wait Hint: 25000

 

F:\myproject\myservices\Release>myservices iisadmin

OpenSCManager(), Open a handle to the SC Manager database looks OK.

OpenService(), open a handle to a service with appropriate access looks OK.

ControlService(), sending control value to stop a service failed, error: 1051

 

Status of iisadmin:

  Service Type: 0x20

  Current State: 0x4

  Controls Accepted: 0x7

  Exit Code: 0

  Service Specific Exit Code: 0

  Check Point: 0

  Wait Hint: 0

 

F:\myproject\myservices\Release>myservices w3svc

OpenSCManager(), Open a handle to the SC Manager database looks OK.

OpenService(), open a handle to a service with appropriate access looks OK.

ControlService(), sending control value to a stop service looks OK.

 

Status of w3svc:

  Service Type: 0x20

  Current State: 0x3

  Controls Accepted: 0x7

  Exit Code: 0

  Service Specific Exit Code: 0

  Check Point: 0

  Wait Hint: 0

 

F:\myproject\myservices\Release>

By assuming the dhcp,w3svc and IISADMIN services are running, from the output, services that do not have dependencies such asdhcp and w3svc have been stopped but the IISADMIN (depend on thew3svc service)  failed because its dependency on w3svc that should be stopped first. You can verify those services through the Servicescontrol panel. Error 1051 says that “A stop control has been sent to a service that other running services are dependent on”, (ERROR_DEPENDENT_SERVICES_RUNNING).

Modifying the DACL for a Service

An application can create or modify the DACL associated with a Service object in order to control access. To retrieve the DACL associated with a service object, use the QueryServiceObjectSecurity() function. To set the DACL, use the SetServiceObjectSecurity() function. Any changes made to the SECURITY_DESCRIPTOR associated with the service object are persistent until the service is removed from the system.

The following sample code creates and sets a new DACL for the service specified on the command line. The sample code merges one Access Control Entry (ACE) to the existing DACL for the service. The new ACE grants the Guest account start, stop, delete, and READ_CONTROL access to the specified service. Access to the service can be modified by theAccessPermissions parameter passed to the BuildExplicitAccessWithName() function. Note that for critical and security aware services, this program example not a good one to be executed :o)

// ForWinXp

#define _WIN32_WINNT 0x0501

#include <windows.h>

#include <aclapi.h>

#include <stdio.h>

#include <tchar.h>

// Simple user defined error messages...

void DisplayError(DWORD dwError, LPTSTR pszAPI)

{

   LPVOID lpvMessageBuffer;

   FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |

                 FORMAT_MESSAGE_FROM_SYSTEM,

                 NULL, dwError,

                 MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),

                (LPTSTR)&lpvMessageBuffer, 0, NULL);

  // Display the string.

   _tprintf(TEXT("ERROR: API        = %s.\n"), pszAPI);

   _tprintf(TEXT("       error code     = %u.\n"), dwError);

   _tprintf(TEXT("       message       = %s.\n"), (LPTSTR)lpvMessageBuffer);

  // Free the buffer allocated by the system.

   LocalFree(lpvMessageBuffer);

   ExitProcess(dwError);

}

// Using _tmain(), TCHAR - A WCHAR if UNICODE/wide character is defined, a CHAR otherwise.

int _tmain(int argc, TCHAR *argv[ ])

{

   BOOL                 bDaclPresent   = FALSE;

   BOOL                 bDaclDefaulted = FALSE;

   DWORD                dwError        = 0;

   DWORD                dwSize         = 0;

   EXPLICIT_ACCESS      ea;

   PACL                 pacl           = NULL;

   PACL                 pNewAcl        = NULL;

   PSECURITY_DESCRIPTOR psd;

   SC_HANDLE            schManager     = NULL;

   SC_HANDLE            schService     = NULL;

   SECURITY_DESCRIPTOR  sd;

  if (argc != 2)

   {

       _tprintf(TEXT("Usage: %s [service name].\n"), argv[0]);

       _tprintf(TEXT("Please try again.\n"));

      return 1;

   }

  // Obtain a handle to the Service Controller.

   schManager = OpenSCManager(NULL, NULL, SC_MANAGER_CONNECT);

  if (schManager == NULL)

      DisplayError(GetLastError(), TEXT("OpenSCManager()"));

  else

      _tprintf(TEXT("OpenSCManager(), handle to the service controller obtained successfully.\n"));

  // Obtain a handle to the service.

   schService = OpenService(schManager, argv[1], READ_CONTROL | WRITE_DAC);

  if (schService == NULL)

      DisplayError(GetLastError(), TEXT("OpenService()"));

  else

      _tprintf(TEXT("OpenSCManager(), handle to the service obtained successfully.\n"));

  // Get the current security descriptor.

  if (!QueryServiceObjectSecurity(schService, DACL_SECURITY_INFORMATION, &psd, 0, &dwSize))

   {

     if (GetLastError() == ERROR_INSUFFICIENT_BUFFER)

      {

         psd = (PSECURITY_DESCRIPTOR)HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, dwSize);

        if (psd == NULL)

         {

            DisplayError(0, TEXT("HeapAlloc()"));

           // note HeapAlloc() does not support GetLastError()

         }

         else

           _tprintf(TEXT("HeapAlloc() looks OK.\n"));

        if (!QueryServiceObjectSecurity(schService, DACL_SECURITY_INFORMATION, psd, dwSize, &dwSize))

            DisplayError(GetLastError(), TEXT("QueryServiceObjectSecurity()"));

         else

           _tprintf(TEXT("QueryServiceObjectSecurity() looks OK.\n"));

      }

     else

         DisplayError(GetLastError(), TEXT("QueryServiceObjectSecurity()"));

   }

  // Initialize a NEW Security Descriptor.

  if (!InitializeSecurityDescriptor(&sd, SECURITY_DESCRIPTOR_REVISION))

      DisplayError(GetLastError(), TEXT("InitializeSecurityDescriptor()"));

  else

       _tprintf(TEXT("SetEntriesInAcl() looks OK.\n"));

  // Set the new DACL in the Security Descriptor.

  if (!SetSecurityDescriptorDacl(&sd, TRUE, pNewAcl, FALSE))

      DisplayError(GetLastError(), TEXT("SetSecurityDescriptorDacl()"));

  else

       _tprintf(TEXT("SetSecurityDescriptorDacl() looks OK.\n"));

  // Set the new DACL for the service object.

  if (!SetServiceObjectSecurity(schService, DACL_SECURITY_INFORMATION, &sd))

      DisplayError(GetLastError(), TEXT("SetServiceObjectSecurity()"));

  else

       _tprintf(TEXT("SetServiceObjectSecurity() looks OK.\n"));

  // Close the handles.

  if (!CloseServiceHandle(schManager))

      DisplayError(GetLastError(), TEXT("CloseServiceHandle() schManager"));

  else

       _tprintf(TEXT("CloseServiceHandle() schManager looks OK.\n"));

  if (!CloseServiceHandle(schService))

      DisplayError(GetLastError(), TEXT("CloseServiceHandle() schService"));

  else

       _tprintf(TEXT("CloseServiceHandle() schService looks OK.\n"));

  // Free buffers.

   LocalFree((HLOCAL)pNewAcl);

   HeapFree(GetProcessHeap(), 0, (LPVOID)psd);

  return 0;

}

We test our program by changing the spooler service’s Discretionary Access List (DACL) by adding guest user with start, stop,delete, and READ_CONTROL access right. Tenouk failed to verify this…:o) Using the program property page didn’t show the sign! May need to enumerate…

--------------------------------------------------End examples---------------------------------------------

Service Reference

The following are functions and structures used with services.

Service Functions

The following functions are used or implemented by services.

The following functions are used by programs that control or configure services.

Applications can use the following functions for manipulating window station objects.

Applications can use the following functions for manipulating desktop objects.

Service Structures

The following structures are used with services:

1. ENUM_SERVICE_STATUS

2. ENUM_SERVICE_STATUS_PROCESS

3. QUERY_SERVICE_CONFIG

4. QUERY_SERVICE_LOCK_STATUS

5. SC_ACTION

6. SERVICE_DESCRIPTION

7. SERVICE_FAILURE_ACTIONS

8. SERVICE_STATUS

9. SERVICE_STATUS_PROCESS

10. SERVICE_TABLE_ENTRY

11. USEROBJECTFLAGS

-------------End Windows Services Examples-------------

Further reading and digging:

1. Structure, enum, union and typedef story can be foundC/C++ struct, enum, union & typedef.

2. For Multi bytes, Unicode characters and Localization please refer to Locale, wide characters & Unicode (Story) and Windows users & groups programming tutorials (Implementation).

3. Windows data types areWindows data types.

4. Microsoft Visual C++, online MSDN.

5. ReactOS - Windows binary compatible OS - C/C++ source code repository, Doxygen.

6. Check the best selling C / C++ and Windows books at Amazon.com.

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