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/**
* cerberus – Minimal login program
*
* Copyright © 2013 Mattias Andrée (maandree@member.fsf.org)
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <string.h>
#include <security/pam_appl.h>
#include <security/pam_misc.h>
#include "config.h"
#include "pam.h"
#define __failed(RC) ((RC) != PAM_SUCCESS)
void quit_pam(int sig);
int conv_pam(int num_msg, const struct pam_message** msg, struct pam_response** resp, void* appdata_ptr);
/**
* Old signal action for SIGHUP
*/
struct sigaction signal_action_hup;
/**
* Old signal action for SIGTERM
*/
struct sigaction signal_action_term;
/**
* The process ID of the child process, 0 if none
*/
extern pid_t child_pid;
/**
* The PAM handle
*/
static pam_handle_t* handle = NULL;
/**
* The PAM convention
*/
static struct pam_conv conv = { conv_pam, NULL };
/**
* Whether the user was auto-authenticated
*/
static char auto_authenticated = 1;
/**
* Function that can be used to read a passphrase from the terminal
*/
static char* (*passphrase_reader)(void) = NULL;
/**
* Exit if a PAM instruction failed
*
* @param rc What the PAM instruction return
*/
static void do_pam(int rc)
{
if (__failed(rc))
{
const char* msg = pam_strerror(handle, rc);
if (msg)
fprintf(stderr, "%s\n", msg);
pam_end(handle, rc);
sleep(ERROR_SLEEP);
_exit(1);
}
}
/**
* Initialise PAM
*
* @param remote The remote computer, {@code NULL} for local login
* @param username The username of the user to log in to
* @param reader Function that can be used to read a passphrase from the terminal
*/
void initialise_pam(char* remote, char* username, char* (*reader)(void))
{
passphrase_reader = reader;
if (pam_start(remote ? "remote" : "local", username, &conv, &handle) != PAM_SUCCESS)
{
fprintf(stderr, "Cannot initialise PAM\n");
sleep(ERROR_SLEEP);
_exit(1);
}
do_pam(pam_set_item(handle, PAM_RHOST, remote ?: "localhost"));
do_pam(pam_set_item(handle, PAM_TTY, ttyname(STDIN_FILENO) ?: "(none)"));
}
/**
* Verify that the account may be used
*/
void verify_account_pam(void)
{
int rc = pam_acct_mgmt(handle, 0);
if (rc == PAM_NEW_AUTHTOK_REQD)
rc = pam_chauthtok(handle, PAM_CHANGE_EXPIRED_AUTHTOK);
do_pam(rc);
}
/**
* Open PAM session
*/
void open_session_pam(void)
{
int rc;
struct sigaction signal_action;
do_pam(pam_setcred(handle, PAM_ESTABLISH_CRED));
if (__failed(rc = pam_open_session(handle, 0)))
{
pam_setcred(handle, PAM_DELETE_CRED);
do_pam(rc);
}
if (__failed(rc = pam_setcred(handle, PAM_REINITIALIZE_CRED)))
{
pam_close_session(handle, 0);
do_pam(rc);
}
memset(&signal_action, 0, sizeof(signal_action));
signal_action.sa_handler = SIG_IGN;
sigaction(SIGINT, &signal_action, NULL);
sigaction(SIGHUP, &signal_action, &signal_action_hup);
signal_action.sa_handler = quit_pam;
sigaction(SIGHUP, &signal_action, NULL);
sigaction(SIGTERM, &signal_action, &signal_action_term);
}
/**
* Close PAM session
*/
void close_session_pam(void)
{
sigaction(SIGHUP, &signal_action_hup, NULL);
sigaction(SIGTERM, &signal_action_term, NULL);
pam_setcred(handle, PAM_DELETE_CRED);
pam_end(handle, pam_close_session(handle, 0));
}
/**
* Signal handler for cleanly exit PAM session
*
* @param sig The received signal
*/
void quit_pam(int sig)
{
if (child_pid)
kill(-child_pid, sig);
if (sig == SIGTERM)
kill(-child_pid, SIGHUP);
pam_setcred(handle, PAM_DELETE_CRED);
pam_end(handle, pam_close_session(handle, 0));
_exit(sig);
}
/**
* Perform token authentication
*
* @return Whether the user got automatically authenticated
*/
char authenticate_pam(void)
{
int rc;
if (__failed(rc = pam_authenticate(handle, 0)))
{
printf("Incorrect passphrase\n");
pam_end(handle, rc);
sleep(FAILURE_SLEEP);
_exit(1);
}
return auto_authenticated;
}
/**
* Callback function for converation between PAM this application
*
* @param num_msg Number of pointers in the array `msg`
* @param msg Message from PAM
* @param resp Responses to PAM for by index corresponding messages
* @param appdata_ptr (Not used)
* @return `PAM_SUCCESS`, `PAM_CONV_ERR` or `PAM_BUF_ERR`
*/
int conv_pam(int num_msg, const struct pam_message** msg, struct pam_response** resp, void* appdata_ptr)
{
int i;
(void) appdata_ptr;
for (i = 0; i < num_msg; i++)
{
((*resp) + i)->resp = NULL;
((*resp) + i)->resp_retcode = 0;
if ((**(msg + i)).msg_style == PAM_PROMPT_ECHO_OFF)
{
(*resp + i)->resp = passphrase_reader();
auto_authenticated = 0;
}
}
return PAM_SUCCESS;
}
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