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Editing: pam.py
# (c) 2007 Chris AtLee <chris@atlee.ca> # Licensed under the MIT license: # http://www.opensource.org/licenses/mit-license.php # # Original author: Chris AtLee # # Modified by David Ford, 2011-12-6 # added py3 support and encoding # added pam_end # added pam_setcred to reset credentials after seeing Leon Walker's remarks # added byref as well # use readline to prestuff the getuser input ''' PAM module for python Provides an authenticate function that will allow the caller to authenticate a user against the Pluggable Authentication Modules (PAM) on the system. Implemented using ctypes, so no compilation is necessary. ''' __all__ = ['pam'] __version__ = '1.8.4' __author__ = 'David Ford <david@blue-labs.org>' __released__ = '2018 June 15' import sys from ctypes import CDLL, POINTER, Structure, CFUNCTYPE, cast, byref, sizeof from ctypes import c_void_p, c_size_t, c_char_p, c_char, c_int from ctypes import memmove from ctypes.util import find_library class PamHandle(Structure): """wrapper class for pam_handle_t pointer""" _fields_ = [ ("handle", c_void_p) ] def __init__(self): Structure.__init__(self) self.handle = 0 class PamMessage(Structure): """wrapper class for pam_message structure""" _fields_ = [ ("msg_style", c_int), ("msg", c_char_p) ] def __repr__(self): return "<PamMessage %i '%s'>" % (self.msg_style, self.msg) class PamResponse(Structure): """wrapper class for pam_response structure""" _fields_ = [ ("resp", c_char_p), ("resp_retcode", c_int) ] def __repr__(self): return "<PamResponse %i '%s'>" % (self.resp_retcode, self.resp) conv_func = CFUNCTYPE(c_int, c_int, POINTER(POINTER(PamMessage)), POINTER(POINTER(PamResponse)), c_void_p) class PamConv(Structure): """wrapper class for pam_conv structure""" _fields_ = [ ("conv", conv_func), ("appdata_ptr", c_void_p) ] # Various constants PAM_PROMPT_ECHO_OFF = 1 PAM_PROMPT_ECHO_ON = 2 PAM_ERROR_MSG = 3 PAM_TEXT_INFO = 4 PAM_REINITIALIZE_CRED = 8 libc = CDLL(find_library("c")) libpam = CDLL(find_library("pam")) calloc = libc.calloc calloc.restype = c_void_p calloc.argtypes = [c_size_t, c_size_t] # bug #6 (@NIPE-SYSTEMS), some libpam versions don't include this function if hasattr(libpam, 'pam_end'): pam_end = libpam.pam_end pam_end.restype = c_int pam_end.argtypes = [PamHandle, c_int] pam_start = libpam.pam_start pam_start.restype = c_int pam_start.argtypes = [c_char_p, c_char_p, POINTER(PamConv), POINTER(PamHandle)] pam_setcred = libpam.pam_setcred pam_setcred.restype = c_int pam_setcred.argtypes = [PamHandle, c_int] pam_strerror = libpam.pam_strerror pam_strerror.restype = c_char_p pam_strerror.argtypes = [PamHandle, c_int] pam_authenticate = libpam.pam_authenticate pam_authenticate.restype = c_int pam_authenticate.argtypes = [PamHandle, c_int] class pam(): code = 0 reason = None def __init__(self): pass def authenticate(self, username, password, service='login', encoding='utf-8', resetcreds=True): """username and password authentication for the given service. Returns True for success, or False for failure. self.code (integer) and self.reason (string) are always stored and may be referenced for the reason why authentication failed. 0/'Success' will be stored for success. Python3 expects bytes() for ctypes inputs. This function will make necessary conversions using the supplied encoding. Inputs: username: username to authenticate password: password in plain text service: PAM service to authenticate against, defaults to 'login' Returns: success: True failure: False """ @conv_func def my_conv(n_messages, messages, p_response, app_data): """Simple conversation function that responds to any prompt where the echo is off with the supplied password""" # Create an array of n_messages response objects addr = calloc(n_messages, sizeof(PamResponse)) response = cast(addr, POINTER(PamResponse)) p_response[0] = response for i in range(n_messages): if messages[i].contents.msg_style == PAM_PROMPT_ECHO_OFF: dst = calloc(len(password)+1, sizeof(c_char)) memmove(dst, cpassword, len(password)) response[i].resp = dst response[i].resp_retcode = 0 return 0 # python3 ctypes prefers bytes if sys.version_info >= (3,): if isinstance(username, str): username = username.encode(encoding) if isinstance(password, str): password = password.encode(encoding) if isinstance(service, str): service = service.encode(encoding) else: if isinstance(username, unicode): username = username.encode(encoding) if isinstance(password, unicode): password = password.encode(encoding) if isinstance(service, unicode): service = service.encode(encoding) if b'\x00' in username or b'\x00' in password or b'\x00' in service: self.code = 4 # PAM_SYSTEM_ERR in Linux-PAM self.reason = 'strings may not contain NUL' return False # do this up front so we can safely throw an exception if there's # anything wrong with it cpassword = c_char_p(password) handle = PamHandle() conv = PamConv(my_conv, 0) retval = pam_start(service, username, byref(conv), byref(handle)) if retval != 0: # This is not an authentication error, something has gone wrong starting up PAM self.code = retval self.reason = "pam_start() failed" return False retval = pam_authenticate(handle, 0) auth_success = retval == 0 if auth_success and resetcreds: retval = pam_setcred(handle, PAM_REINITIALIZE_CRED); # store information to inform the caller why we failed self.code = retval self.reason = pam_strerror(handle, retval) if sys.version_info >= (3,): self.reason = self.reason.decode(encoding) if hasattr(libpam, 'pam_end'): pam_end(handle, retval) return auth_success def authenticate(*vargs, **dargs): """ Compatibility function for older versions of python-pam. """ return pam().authenticate(*vargs, **dargs) if __name__ == "__main__": import readline, getpass def input_with_prefill(prompt, text): def hook(): readline.insert_text(text) readline.redisplay() readline.set_pre_input_hook(hook) if sys.version_info >= (3,): result = input(prompt) else: result = raw_input(prompt) readline.set_pre_input_hook() return result pam = pam() username = input_with_prefill('Username: ', getpass.getuser()) # enter a valid username and an invalid/valid password, to verify both failure and success pam.authenticate(username, getpass.getpass()) print('{} {}'.format(pam.code, pam.reason))
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