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Help with ctypes and PAM


I've been trying to write a PAM module using ctypes. In the
function (my_conv in the script below), you're passed in a
pointer. You're supposed to allocate an array of pam_response's and
the pointer's value to the new array. Then you fill in the array with
appropriate data.

I can't seem to get it working in python...The authenticate function
returns PAM_AUTHTOK_REC OVER_ERR (21), which I think means the response
make any sense.

I've tried saving the response array outside of my_conv to make sure
doesn't get garbage collected, but that doesn't seem to help.

Any pointers would be appreciated!


from ctypes import *

libpam = CDLL("libpam.so ")

class pam_handle(Stru cture):
_fields_ = [
("handle", c_void_p)

def __init__(self):
self.handle = 0

class pam_message(Str ucture):
_fields_ = [
("msg_style" , c_int),
("msg", c_char_p),

def __repr__(self):
return "<pam_messa ge %i '%s'>" % (self.msg_style , self.msg)

class pam_response(St ructure):
_fields_ = [
("resp", c_char_p),
("resp_retcode" , c_int),

def __repr__(self):
return "<pam_respo nse %i '%s'>" % (self.resp_retc ode,

conv_func = CFUNCTYPE(c_int ,
c_int, POINTER(POINTER (pam_message)),
POINTER(POINTER (pam_response)) , c_void_p)

class pam_conv(Struct ure):
_fields_ = [
("conv", conv_func),
("appdata_pt r", c_void_p)

pam_start = libpam.pam_star t
pam_start.resty pe = c_int
pam_start.argty pes = [c_char_p, c_char_p, POINTER(pam_con v),
POINTER(pam_han dle)]

pam_authenticat e = libpam.pam_auth enticate
pam_authenticat e.restype = c_int
pam_authenticat e.argtypes = [pam_handle, c_int]

if __name__ == "__main__":
import getpass, os, sys
def my_conv(nMessag es, messages, pResponse, appData):
# Create an array of nMessages response objects
# Does r get GC'ed after we're all done?
r = (pam_response * nMessages)()
pResponse.conte nts = cast(r, POINTER(pam_res ponse))
for i in range(nMessages ):
if messages[i].contents.msg == "Password: ":
p = getpass.getpass ()
pResponse.conte nts[0].resp_retcode = 0
pResponse.conte nts[0].resp = p
return 0

handle = pam_handle()
c = pam_conv(my_con v, 0)
retval = pam_start("logi n", os.getlogin(), pointer(c),
pointer(handle) )

if retval != 0:
print "Couldn't start pam session"

retval = pam_authenticat e(handle, 0)
if retval == 21:
print "Authentica tion information cannot be recovered"

print retval

May 30 '07 #1
0 1164

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