Segmentation Fault while running PAM functions - c

Question

I'm relatively new to C and cannot figure out why this program seg faults.
It could be a stupid error on my behalf but cannot seem to figure it out.
I also know its unusual using the embedding method I am, but this was down for sheer familiarity with Python3 and the ease of use.
#define PY_SSIZE_T_CLEAN
#define PAM_SM_AUTH
#define PAM_SM_ACCOUNT
//#define PAM_SM_SESSION
#include <dlfcn.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <security/pam_appl.h>
#include <security/pam_modules.h>
#include </usr/include/python3.6m/Python.h>
/* expected hook */
/*
PAM_EXTERN int pam_sm_setcred( pam_handle_t *pamh, int flags, int argc, const char **argv ) {
return PAM_SUCCESS;
}
PAM_EXTERN int pam_sm_acct_mgmt(pam_handle_t *pamh, int flags, int argc, const char **argv) {
printf("Acct mgmt\n");
return PAM_SUCCESS;
}
*/
/* expected hook, this is where custom stuff happens */
PAM_EXTERN int pam_sm_authenticate( pam_handle_t *pamh, int flags,int argc, const char **argv )
{
chdir("../code/facial"); // this changes it to the correct directory to execute
dlopen("/usr/lib/x86_64-linux-gnu/libpython3.6m.so",RTLD_LAZY | RTLD_GLOBAL);
Py_Initialize(); // Starts python interpreter
PyRun_SimpleString("import os\nimport sys\nsys.path.append(os.getcwd())"); // lets python know where we are
PyObject *mymod, *func1, *ret1;
mymod = PyImport_ImportModule("pam_detect"); // This is the .py
if (mymod != 0){ // check if the file file was loaded
func1 = PyObject_GetAttrString(mymod, "detect"); // hel is the function name in the file you declared earlier
ret1 = PyObject_CallObject(func1, NULL); // Null because the function doesnt take an argument.
if (ret1 == 1){
Py_Finalize();
return PAM_SUCCESS;
}
else{
Py_Finalize();
return PAM_AUTH_ERR;
}
}
else{
//printf("Error: can't find file!\n");
return 1;
}
Py_Finalize();
return 0;
}

Answer 1

You have defined the pointers but haven't assigned them to a memory address.
PyObject *mymod, *func1, *ret1;
This line in your code makes a pointer named mymod which can point to a memory containing PyObject, but you haven't given the memory address to it yet.
I don't know if calling the functions will return pointers correctly or not, So when you try to put anything there, it gives segmentation fault if you are trying to assign a variable to a pointer without a memory address.
I can only say this much without knowing where the fault occurred. try putting printf statement before assigning of all 3 pointers and see.