¿Qué está haciendo que este descriptor de seguridad se estropee?

Question

estoy tratando de leer el acceso de los archivos y directorios en Windows utilizando este código (modelado después Tim Golden's proposed patch to os.access to make it read from ACLs on Windows):

from ctypes import(
    windll, 
    wintypes, 
    c_char_p, 
    c_void_p, 
    byref 
    ) 
from win32api import GetCurrentThread 
from win32security import (
    GetFileSecurity, 
    DACL_SECURITY_INFORMATION, 
    ImpersonateSelf, 
    SecurityImpersonation, 
    OpenThreadToken, 
    TOKEN_ALL_ACCESS, 
    MapGenericMask 
    ) 
from ntsecuritycon import (
    FILE_READ_DATA, 
    FILE_WRITE_DATA, 
    FILE_EXECUTE, 
    FILE_ALL_ACCESS 
    ) 
import pywintypes 
import winnt 

TRUE = 1 

def CheckAccess(path,AccessDesired): 
    result = wintypes.BOOL() 
    granted = wintypes.DWORD(0) 
    privsetlength = wintypes.DWORD(0) 

    fileSD = GetFileSecurity(path, DACL_SECURITY_INFORMATION) 
    if not fileSD.IsValid(): 
     raise Exception("Invalid security descriptor") 

    ImpersonateSelf(SecurityImpersonation) 
    token = OpenThreadToken(GetCurrentThread(), TOKEN_ALL_ACCESS, TRUE) 
    mapping = wintypes.DWORD(MapGenericMask(AccessDesired, 
     (FILE_READ_DATA, FILE_WRITE_DATA, FILE_EXECUTE, FILE_ALL_ACCESS))) 
    if not windll.advapi32.AccessCheck(
     c_char_p(str(buffer(fileSD))), 
     wintypes.HANDLE(int(token)), 
     AccessDesired, 
     byref(mapping), 
     c_void_p(0), #privilege set, optional 
     byref(privsetlength), #size of optional privilege set 
     byref(granted), 
     byref(result) 
     ): 
      code = GetLastError() 
      raise WindowsError(GetLastError(),FormatMessage(code)) 
    return bool(result) 

def HasReadAccess(path): 
    return CheckAccess(path,FILE_READ_DATA) 

def HasWriteAccess(path): 
    return CheckAccess(path,FILE_WRITE_DATA) 

if __name__ == "__main__": 
    print(HasReadAccess("C:/Python26")) 

Sin embargo, cada vez que ejecute esto, me sale esto:

WindowsError: [Error 1338] The security descriptor structure is invalid. 

¿Cómo se supone que paso el SecurityDescriptor a AccessCheck?

EDITAR: Cambiar DACL_SECURITY_INFORMATION a DACL_SECURITY_INFORMATION | GROUP_SECURITY_INFORMATION | OWNER_SECURITY_INFORMATION me da esto:

WindowsError: [Error 122] The data area passed to a system call is too small. 

Answer 1

parecer por "opcional" de Windows significa "necesaria". Lo arreglé asignando un buffer y pasando el tamaño de PRIVILEGE_SET (20).