Lib/test/symlink_support.py

"""
A module built to test if the current process has the privilege to
create symlinks on Windows.
"""

# allow script to run natively under python 2.6+
from __future__ import print_function

import ctypes
from ctypes import wintypes

GetCurrentProcess = ctypes.windll.kernel32.GetCurrentProcess
GetCurrentProcess.restype = wintypes.HANDLE
OpenProcessToken = ctypes.windll.advapi32.OpenProcessToken
OpenProcessToken.argtypes = (wintypes.HANDLE, wintypes.DWORD,
                             ctypes.POINTER(wintypes.HANDLE))
OpenProcessToken.restype = wintypes.BOOL

class LUID(ctypes.Structure):
    _fields_ = [
            ('low_part', wintypes.DWORD),
            ('high_part', wintypes.LONG),
            ]

    def __eq__(self, other):
        return (
                self.high_part == other.high_part and
                self.low_part == other.low_part
                )

    def __ne__(self, other):
        return not (self==other)

LookupPrivilegeValue = ctypes.windll.advapi32.LookupPrivilegeValueW
LookupPrivilegeValue.argtypes = (
        wintypes.LPWSTR, # system name
        wintypes.LPWSTR, # name
        ctypes.POINTER(LUID),
        )
LookupPrivilegeValue.restype = wintypes.BOOL

class TOKEN_INFORMATION_CLASS:
    TokenUser = 1
    TokenGroups = 2
    TokenPrivileges = 3
    # ... see http://msdn.microsoft.com/en-us/library/aa379626%28VS.85%29.aspx

SE_PRIVILEGE_ENABLED_BY_DEFAULT = (0x00000001)
SE_PRIVILEGE_ENABLED            = (0x00000002)
SE_PRIVILEGE_REMOVED            = (0x00000004)
SE_PRIVILEGE_USED_FOR_ACCESS    = (0x80000000)

class LUID_AND_ATTRIBUTES(ctypes.Structure):
    _fields_ = [
            ('LUID', LUID),
            ('attributes', wintypes.DWORD),
            ]

    def is_enabled(self):
        return bool(self.attributes & SE_PRIVILEGE_ENABLED)

    def enable(self):
        self.attributes |= SE_PRIVILEGE_ENABLED

    def get_name(self):
        size = wintypes.DWORD(10240)
        buf = ctypes.create_unicode_buffer(size.value)
        res = LookupPrivilegeName(None, self.LUID, buf, size)
        if res == 0:
            raise RuntimeError
        return buf[:size.value]

    def __str__(self):
        name = self.name
        fmt = ['{name}', '{name} (enabled)'][self.is_enabled()]
        return fmt.format(**vars())

LookupPrivilegeName = ctypes.windll.advapi32.LookupPrivilegeNameW
LookupPrivilegeName.argtypes = (
        wintypes.LPWSTR, # lpSystemName
        ctypes.POINTER(LUID), # lpLuid
        wintypes.LPWSTR, # lpName
        ctypes.POINTER(wintypes.DWORD), #cchName
        )
LookupPrivilegeName.restype = wintypes.BOOL

class TOKEN_PRIVILEGES(ctypes.Structure):
    _fields_ = [
            ('count', wintypes.DWORD),
            ('privileges', LUID_AND_ATTRIBUTES*0),
            ]

    def get_array(self):
        array_type = LUID_AND_ATTRIBUTES*self.count
        privileges = ctypes.cast(self.privileges,
                                 ctypes.POINTER(array_type)).contents
        return privileges

    def __iter__(self):
        return iter(self.get_array())

PTOKEN_PRIVILEGES = ctypes.POINTER(TOKEN_PRIVILEGES)

GetTokenInformation = ctypes.windll.advapi32.GetTokenInformation
GetTokenInformation.argtypes = [
        wintypes.HANDLE, # TokenHandle
        ctypes.c_uint, # TOKEN_INFORMATION_CLASS value
        ctypes.c_void_p, # TokenInformation
        wintypes.DWORD, # TokenInformationLength
        ctypes.POINTER(wintypes.DWORD), # ReturnLength
        ]
GetTokenInformation.restype = wintypes.BOOL

# http://msdn.microsoft.com/en-us/library/aa375202%28VS.85%29.aspx
AdjustTokenPrivileges = ctypes.windll.advapi32.AdjustTokenPrivileges
AdjustTokenPrivileges.restype = wintypes.BOOL
AdjustTokenPrivileges.argtypes = [
        wintypes.HANDLE,                # TokenHandle
        wintypes.BOOL,                  # DisableAllPrivileges
        PTOKEN_PRIVILEGES,              # NewState (optional)
        wintypes.DWORD,                 # BufferLength of PreviousState
        PTOKEN_PRIVILEGES,              # PreviousState (out, optional)
        ctypes.POINTER(wintypes.DWORD), # ReturnLength
        ]

def get_process_token():
    "Get the current process token"
    token = wintypes.HANDLE()
    TOKEN_ALL_ACCESS = 0xf01ff
    res = OpenProcessToken(GetCurrentProcess(), TOKEN_ALL_ACCESS, token)
    if not res > 0:
        raise RuntimeError("Couldn't get process token")
    return token

def get_symlink_luid():
    "Get the LUID for the SeCreateSymbolicLinkPrivilege"
    symlink_luid = LUID()
    res = LookupPrivilegeValue(None, "SeCreateSymbolicLinkPrivilege",
                               symlink_luid)
    if not res > 0:
        raise RuntimeError("Couldn't lookup privilege value")
    return symlink_luid

def get_privilege_information():
    "Get all privileges associated with the current process."
    # first call with zero length to determine what size buffer we need

    return_length = wintypes.DWORD()
    params = [
            get_process_token(),
            TOKEN_INFORMATION_CLASS.TokenPrivileges,
            None,
            0,
            return_length,
            ]

    res = GetTokenInformation(*params)

    # assume we now have the necessary length in return_length

    buffer = ctypes.create_string_buffer(return_length.value)
    params[2] = buffer
    params[3] = return_length.value

    res = GetTokenInformation(*params)
    assert res > 0, "Error in second GetTokenInformation (%d)" % res

    privileges = ctypes.cast(buffer, ctypes.POINTER(TOKEN_PRIVILEGES)).contents
    return privileges

def report_privilege_information():
    "Report all privilege information assigned to the current process."
    privileges = get_privilege_information()
    print("found {0} privileges".format(privileges.count))
    tuple(map(print, privileges))

def enable_symlink_privilege():
    """
    Try to assign the symlink privilege to the current process token.
    Return True if the assignment is successful.
    """
    # create a space in memory for a TOKEN_PRIVILEGES structure
    #  with one element
    size = ctypes.sizeof(TOKEN_PRIVILEGES)
    size += ctypes.sizeof(LUID_AND_ATTRIBUTES)
    buffer = ctypes.create_string_buffer(size)
    tp = ctypes.cast(buffer, ctypes.POINTER(TOKEN_PRIVILEGES)).contents
    tp.count = 1
    tp.get_array()[0].enable()
    tp.get_array()[0].LUID = get_symlink_luid()
    token = get_process_token()
    res = AdjustTokenPrivileges(token, False, tp, 0, None, None)
    if res == 0:
        raise RuntimeError("Error in AdjustTokenPrivileges")

    ERROR_NOT_ALL_ASSIGNED = 1300
    return ctypes.windll.kernel32.GetLastError() != ERROR_NOT_ALL_ASSIGNED

def main():
    assigned = enable_symlink_privilege()
    msg = ['failure', 'success'][assigned]

    print("Symlink privilege assignment completed with {0}".format(msg))

if __name__ == '__main__':
    main()