pam/unix2_chkpwd.c

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/*
* Set*id helper program for PAM authentication.
*
* It is supposed to be called from pam_unix2's
* pam_sm_authenticate function if the function notices
* that it's unable to get the password from the shadow file
* because it doesn't have sufficient permissions.
*
* Copyright (C) 2002 SuSE Linux AG
*
* Written by okir@suse.de, loosely based on unix_chkpwd
* by Andrew Morgan.
*/
#include <security/pam_appl.h>
#include <security/_pam_macros.h>
#include <sys/types.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>
#include <pwd.h>
#include <signal.h>
#include <fcntl.h>
#include <ctype.h>
#include <errno.h>
#define BUFLEN 1024
#ifndef LOGINDEFS
#define LOGINDEFS "/etc/login.defs"
#endif
#define LOGINDEFS_FAIL_DELAY_KEY "FAIL_DELAY"
#define DEFAULT_FAIL_DELAY_S 10
#define PASSWD_CRACKER_DELAY_MS 100
enum {
UNIX_PASSED = 0,
UNIX_FAILED = 1
};
static char * program_name;
static char pass[64];
static int npass = -1;
/*
* Log error messages
*/
static void
_log_err(int err, const char *format,...)
{
va_list args;
va_start(args, format);
openlog(program_name, LOG_CONS | LOG_PID, LOG_AUTH);
vsyslog(err, format, args);
va_end(args);
closelog();
}
static void
su_sighandler(int sig)
{
if (sig > 0) {
_log_err(LOG_NOTICE, "caught signal %d.", sig);
exit(sig);
}
}
/*
* Setup signal handlers
*/
static void
setup_signals(void)
{
struct sigaction action;
memset((void *) &action, 0, sizeof(action));
action.sa_handler = su_sighandler;
action.sa_flags = SA_RESETHAND;
sigaction(SIGILL, &action, NULL);
sigaction(SIGTRAP, &action, NULL);
sigaction(SIGBUS, &action, NULL);
sigaction(SIGSEGV, &action, NULL);
action.sa_handler = SIG_IGN;
action.sa_flags = 0;
sigaction(SIGTERM, &action, NULL);
sigaction(SIGHUP, &action, NULL);
sigaction(SIGINT, &action, NULL);
sigaction(SIGQUIT, &action, NULL);
sigaction(SIGALRM, &action, NULL);
}
static int
_converse(int num_msg, const struct pam_message **msg,
struct pam_response **resp, void *appdata_ptr)
{
struct pam_response *reply;
int num;
if (!(reply = malloc(sizeof(*reply) * num_msg)))
return PAM_CONV_ERR;
for (num = 0; num < num_msg; num++) {
reply[num].resp_retcode = PAM_SUCCESS;
reply[num].resp = NULL;
switch (msg[num]->msg_style) {
case PAM_PROMPT_ECHO_ON:
return PAM_CONV_ERR;
case PAM_PROMPT_ECHO_OFF:
/* read the password from stdin */
if (npass < 0) {
npass = read(STDIN_FILENO, pass, sizeof(pass)-1);
if (npass < 0) {
_log_err(LOG_DEBUG, "error reading password");
return UNIX_FAILED;
}
pass[npass] = '\0';
}
reply[num].resp = strdup(pass);
break;
case PAM_TEXT_INFO:
case PAM_ERROR_MSG:
/* ignored */
break;
default:
/* Must be an error of some sort... */
return PAM_CONV_ERR;
}
}
*resp = reply;
return PAM_SUCCESS;
}
static int
_authenticate(const char *service, const char *user)
{
struct pam_conv conv = { _converse, NULL };
pam_handle_t *pamh;
int err;
err = pam_start(service, user, &conv, &pamh);
if (err != PAM_SUCCESS) {
_log_err(LOG_ERR, "pam_start(%s, %s) failed (errno %d)",
service, user, err);
return UNIX_FAILED;
}
err = pam_authenticate(pamh, 0);
if (err != PAM_SUCCESS)
_log_err(LOG_ERR, "pam_authenticate(%s, %s): %s",
service, user,
pam_strerror(pamh, err));
if (err == PAM_SUCCESS)
{
err = pam_acct_mgmt(pamh, 0);
if (err == PAM_SUCCESS)
{
int err2 = pam_setcred(pamh, PAM_REFRESH_CRED);
if (err2 != PAM_SUCCESS)
_log_err(LOG_ERR, "pam_setcred(%s, %s): %s",
service, user,
pam_strerror(pamh, err2));
/*
* ignore errors on refresh credentials.
* If this did not work we use the old once.
*/
} else {
_log_err(LOG_ERR, "pam_acct_mgmt(%s, %s): %s",
service, user,
pam_strerror(pamh, err));
}
}
pam_end(pamh, err);
if (err != PAM_SUCCESS)
return UNIX_FAILED;
return UNIX_PASSED;
}
static char *
getuidname(uid_t uid)
{
struct passwd *pw;
static char username[32];
pw = getpwuid(uid);
if (pw == NULL)
return NULL;
strncpy(username, pw->pw_name, sizeof(username));
username[sizeof(username) - 1] = '\0';
endpwent();
return username;
}
static int
sane_pam_service(const char *name)
{
const char *sp;
char path[128];
if (strlen(name) > 32)
return 0;
for (sp = name; *sp; sp++) {
if (!isalnum(*sp) && *sp != '_' && *sp != '-')
return 0;
}
snprintf(path, sizeof(path), "/etc/pam.d/%s", name);
return access(path, R_OK) == 0;
}
static int
get_system_fail_delay (void)
{
FILE *fs;
char buf[BUFLEN];
long int delay = -1;
char *s;
int l;
fs = fopen(LOGINDEFS, "r");
if (NULL == fs) {
goto bail_out;
}
while ((NULL != fgets(buf, BUFLEN, fs)) && (-1 == delay)) {
if (!strstr(buf, LOGINDEFS_FAIL_DELAY_KEY)) {
continue;
}
s = buf + strspn(buf, " \t");
l = strcspn(s, " \t");
if (strncmp(LOGINDEFS_FAIL_DELAY_KEY, s, l)) {
continue;
}
s += l;
s += strspn(s, " \t");
errno = 0;
delay = strtol(s, NULL, 10);
if (errno) {
delay = -1;
}
break;
}
fclose (fs);
bail_out:
delay = (delay < 0) ? DEFAULT_FAIL_DELAY_S : delay;
return (int)delay;
}
int
main(int argc, char *argv[])
{
const char *program_name;
char *service, *user;
int fd;
int result = UNIX_FAILED;
uid_t uid;
uid = getuid();
/*
* Make sure standard file descriptors are connected.
*/
while ((fd = open("/dev/null", O_RDWR)) <= 2)
;
close(fd);
/*
* Get the program name
*/
if (argc == 0)
program_name = "unix2_chkpwd";
else if ((program_name = strrchr(argv[0], '/')) != NULL)
program_name++;
else
program_name = argv[0];
/*
* Catch or ignore as many signal as possible.
*/
setup_signals();
/*
* Check argument list
*/
if (argc < 2 || argc > 3) {
_log_err(LOG_NOTICE, "Bad number of arguments (%d)", argc);
return UNIX_FAILED;
}
/*
* Get the service name and do some sanity checks on it
*/
service = argv[1];
if (!sane_pam_service(service)) {
_log_err(LOG_ERR, "Illegal service name '%s'", service);
return UNIX_FAILED;
}
/*
* Discourage users messing around (fat chance)
*/
if (isatty(STDIN_FILENO) && uid != 0) {
_log_err(LOG_NOTICE,
"Inappropriate use of Unix helper binary [UID=%d]",
uid);
fprintf(stderr,
"This binary is not designed for running in this way\n"
"-- the system administrator has been informed\n");
sleep(10); /* this should discourage/annoy the user */
return UNIX_FAILED;
}
/*
* determine the caller's user name
*/
user = getuidname(uid);
if (argc == 3 && strcmp(user, argv[2])) {
user = argv[2];
}
result = _authenticate(service, user);
/* Discourage use of this program as a
* password cracker */
usleep(PASSWD_CRACKER_DELAY_MS * 1000);
if (result != UNIX_PASSED && uid != 0)
sleep(get_system_fail_delay());
return result;
}