确定 Windows 进程是否有权创建符号链接

Question

我想以编程方式确定当前用户（或进程）是否有权创建符号链接。在 Windows（Vista 及更高版本）中，如果没有 SeCreateSymbolicLinkPrivilege，则无法创建符号链接，并且默认情况下，该权限仅分配给管理员。如果尝试在没有此权限的情况下创建符号链接，则会出现 Windows 错误 1314（客户端不持有所需的权限）。

为了演示此限制，我创建了 Windows 的全新安装，以初始管理员帐户登录（通过 UAC 限制），并且无法在主目录中创建符号链接。

运行命令提示符后作为管理员或禁用 UAC，该命令执行不会出错。

根据这篇文章，“每个进程代表用户执行的操作拥有[访问]令牌的副本”。

所以我创建了 一个 Python 脚本来查询权限。为了方便和后代，我在下面摘录了一段内容。

该脚本背后的想法是枚举所有权限并确定进程是否具有所需的权限。不幸的是，我发现当前进程实际上没有所需的权限，即使它可以创建符号链接。

我怀疑问题在于，即使当前用户的权限没有明确包含该权限，但他的组成员身份确实提供了该权限。

简而言之，我如何确定给定进程是否有权创建符号链接（而不尝试创建符号链接）？首选 C 或 C++ 或 Python 中的示例，但任何使用 Windows API 的示例都适用。

def get_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_privilege_information():
    # 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

privileges = get_privilege_information()
print("found {0} privileges".format(privileges.count))
map(print, privileges)

Answer 1

我找到了解决方案。以下 Python 代码是 Python 2.6 或 3.1 下的全功能脚本，演示了如何确定创建符号链接的权限。在管理员帐户下运行此命令会成功响应，在来宾帐户下运行此命令会失败。

请注意，脚本的前 3/4 大部分是 API 定义。这项新颖的工作从 get_process_token() 开始。

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):
        res = self.get_name()
        if self.is_enabled(): res += ' (enabled)'
        return res

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()