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sysvinit/src/sulogin.c

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/*
* sulogin This program gives Linux machines a reasonable
* secure way to boot single user. It forces the
* user to supply the root password before a
* shell is started.
*
* If there is a shadow password file and the
* encrypted root password is "x" the shadow
* password will be used.
*
* Version: @(#)sulogin 2.85-3 23-Apr-2003 miquels@cistron.nl
*
* Copyright (C) 1998-2003 Miquel van Smoorenburg.
*
* 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 2 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, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*
*/
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <signal.h>
#include <pwd.h>
#include <shadow.h>
#include <termios.h>
#include <errno.h>
#include <sys/ioctl.h>
#if defined(__GLIBC__)
# include <crypt.h>
#endif
#ifdef WITH_SELINUX
# include <selinux/selinux.h>
# include <selinux/get_context_list.h>
#endif
#define CHECK_DES 1
#define CHECK_MD5 1
#define F_PASSWD "/etc/passwd"
#define F_SHADOW "/etc/shadow"
#define BINSH "/bin/sh"
#define STATICSH "/bin/sash"
char *Version = "@(#)sulogin 2.85-3 23-Apr-2003 miquels@cistron.nl";
int timeout = 0;
int profile = 0;
#ifndef IUCLC
# define IUCLC 0
#endif
#if 0
/*
* Fix the tty modes and set reasonable defaults.
* (I'm not sure if this is needed under Linux, but..)
*/
void fixtty(void)
{
struct termios tty;
tcgetattr(0, &tty);
/*
* Set or adjust tty modes.
*/
tty.c_iflag &= ~(INLCR|IGNCR|IUCLC);
tty.c_iflag |= ICRNL;
tty.c_oflag &= ~(OCRNL|OLCUC|ONOCR|ONLRET|OFILL);
tty.c_oflag |= OPOST|ONLCR;
tty.c_cflag |= CLOCAL;
tty.c_lflag = ISIG|ICANON|ECHO|ECHOE|ECHOK|ECHOCTL|ECHOKE;
/*
* Set the most important characters */
*/
tty.c_cc[VINTR] = 3;
tty.c_cc[VQUIT] = 28;
tty.c_cc[VERASE] = 127;
tty.c_cc[VKILL] = 24;
tty.c_cc[VEOF] = 4;
tty.c_cc[VTIME] = 0;
tty.c_cc[VMIN] = 1;
tty.c_cc[VSTART] = 17;
tty.c_cc[VSTOP] = 19;
tty.c_cc[VSUSP] = 26;
tcsetattr(0, TCSANOW, &tty);
}
#endif
/*
* Called at timeout.
*/
void alrm_handler()
{
}
/*
* See if an encrypted password is valid. The encrypted
* password is checked for traditional-style DES and
* FreeBSD-style MD5 encryption.
*/
int valid(char *pass)
{
char *s;
int len;
if (pass[0] == 0) return 1;
#if CHECK_MD5
/*
* 3 bytes for the signature $1$
* up to 8 bytes for the salt
* $
* the MD5 hash (128 bits or 16 bytes) encoded in base64 = 22 bytes
*/
if (strncmp(pass, "$1$", 3) == 0) {
for(s = pass + 3; *s && *s != '$'; s++)
;
if (*s++ != '$') return 0;
len = strlen(s);
if (len < 22 || len > 24) return 0;
return 1;
}
#endif
#if CHECK_DES
if (strlen(pass) != 13) return 0;
for (s = pass; *s; s++) {
if ((*s < '0' || *s > '9') &&
(*s < 'a' || *s > 'z') &&
(*s < 'A' || *s > 'Z') &&
*s != '.' && *s != '/') return 0;
}
#endif
return 1;
}
/*
* Set a variable if the value is not NULL.
*/
void set(char **var, char *val)
{
if (val) *var = val;
}
/*
* Get the root password entry.
*/
struct passwd *getrootpwent(int try_manually)
{
static struct passwd pwd;
struct passwd *pw;
struct spwd *spw;
FILE *fp;
static char line[256];
static char sline[256];
char *p;
/*
* First, we try to get the password the standard
* way using normal library calls.
*/
if ((pw = getpwnam("root")) &&
!strcmp(pw->pw_passwd, "x") &&
(spw = getspnam("root")))
pw->pw_passwd = spw->sp_pwdp;
if (pw || !try_manually) return pw;
/*
* If we come here, we could not retrieve the root
* password through library calls and we try to
* read the password and shadow files manually.
*/
pwd.pw_name = "root";
pwd.pw_passwd = "";
pwd.pw_gecos = "Super User";
pwd.pw_dir = "/";
pwd.pw_shell = "";
pwd.pw_uid = 0;
pwd.pw_gid = 0;
if ((fp = fopen(F_PASSWD, "r")) == NULL) {
perror(F_PASSWD);
return &pwd;
}
/*
* Find root in the password file.
*/
while((p = fgets(line, 256, fp)) != NULL) {
if (strncmp(line, "root:", 5) != 0)
continue;
p += 5;
set(&pwd.pw_passwd, strsep(&p, ":"));
(void)strsep(&p, ":");
(void)strsep(&p, ":");
set(&pwd.pw_gecos, strsep(&p, ":"));
set(&pwd.pw_dir, strsep(&p, ":"));
set(&pwd.pw_shell, strsep(&p, "\n"));
p = line;
break;
}
fclose(fp);
/*
* If the encrypted password is valid
* or not found, return.
*/
if (p == NULL) {
fprintf(stderr, "%s: no entry for root\n", F_PASSWD);
return &pwd;
}
if (valid(pwd.pw_passwd)) return &pwd;
/*
* The password is invalid. If there is a
* shadow password, try it.
*/
strcpy(pwd.pw_passwd, "");
if ((fp = fopen(F_SHADOW, "r")) == NULL) {
fprintf(stderr, "%s: root password garbled\n", F_PASSWD);
return &pwd;
}
while((p = fgets(sline, 256, fp)) != NULL) {
if (strncmp(sline, "root:", 5) != 0)
continue;
p += 5;
set(&pwd.pw_passwd, strsep(&p, ":"));
break;
}
fclose(fp);
/*
* If the password is still invalid,
* NULL it, and return.
*/
if (p == NULL) {
fprintf(stderr, "%s: no entry for root\n", F_SHADOW);
strcpy(pwd.pw_passwd, "");
}
if (!valid(pwd.pw_passwd)) {
fprintf(stderr, "%s: root password garbled\n", F_SHADOW);
strcpy(pwd.pw_passwd, ""); }
return &pwd;
}
/*
* Ask for the password. Note that there is no
* default timeout as we normally skip this during boot.
*/
char *getpasswd(char *crypted)
{
struct sigaction sa;
struct termios old, tty;
static char pass[128];
char *ret = pass;
int i;
if (crypted[0])
printf("Give root password for maintenance\n");
else
printf("Press enter for maintenance\n");
printf("(or type Control-D to continue): ");
fflush(stdout);
tcgetattr(0, &old);
tcgetattr(0, &tty);
tty.c_iflag &= ~(IUCLC|IXON|IXOFF|IXANY);
tty.c_lflag &= ~(ECHO|ECHOE|ECHOK|ECHONL|TOSTOP);
tcsetattr(0, TCSANOW, &tty);
pass[sizeof(pass) - 1] = 0;
sa.sa_handler = alrm_handler;
sa.sa_flags = 0;
sigaction(SIGALRM, &sa, NULL);
if (timeout) alarm(timeout);
if (read(0, pass, sizeof(pass) - 1) <= 0)
ret = NULL;
else {
for(i = 0; i < sizeof(pass) && pass[i]; i++)
if (pass[i] == '\r' || pass[i] == '\n') {
pass[i] = 0;
break;
}
}
alarm(0);
tcsetattr(0, TCSANOW, &old);
printf("\n");
return ret;
}
/*
* Password was OK, execute a shell.
*/
void sushell(struct passwd *pwd)
{
char shell[128];
char home[128];
char *p;
char *sushell;
/*
* Set directory and shell.
*/
(void)chdir(pwd->pw_dir);
if ((p = getenv("SUSHELL")) != NULL)
sushell = p;
else if ((p = getenv("sushell")) != NULL)
sushell = p;
else {
if (pwd->pw_shell[0])
sushell = pwd->pw_shell;
else
sushell = BINSH;
}
if ((p = strrchr(sushell, '/')) == NULL)
p = sushell;
else
p++;
snprintf(shell, sizeof(shell), profile ? "-%s" : "%s", p);
/*
* Set some important environment variables.
*/
getcwd(home, sizeof(home));
setenv("HOME", home, 1);
setenv("LOGNAME", "root", 1);
setenv("USER", "root", 1);
if (!profile)
setenv("SHLVL","0",1);
/*
* Try to execute a shell.
*/
setenv("SHELL", sushell, 1);
signal(SIGINT, SIG_DFL);
signal(SIGTSTP, SIG_DFL);
signal(SIGQUIT, SIG_DFL);
#ifdef WITH_SELINUX
if (is_selinux_enabled > 0) {
security_context_t scon=NULL;
char *seuser=NULL;
char *level=NULL;
if (getseuserbyname("root", &seuser, &level) == 0)
if (get_default_context_with_level(seuser, level, 0, &scon) > 0) {
if (setexeccon(scon) != 0)
fprintf(stderr, "setexeccon faile\n");
freecon(scon);
}
free(seuser);
free(level);
}
#endif
execl(sushell, shell, NULL);
perror(sushell);
setenv("SHELL", BINSH, 1);
execl(BINSH, profile ? "-sh" : "sh", NULL);
perror(BINSH);
/* Fall back to staticly linked shell if both the users shell
and /bin/sh failed to execute. */
setenv("SHELL", STATICSH, 1);
execl(STATICSH, STATICSH, NULL);
perror(STATICSH);
}
void usage(void)
{
fprintf(stderr, "Usage: sulogin [-e] [-p] [-t timeout] [tty device]\n");
}
int main(int argc, char **argv)
{
char *tty = NULL;
char *p;
struct passwd *pwd;
int c, fd = -1;
int opt_e = 0;
pid_t pid, pgrp, ppgrp, ttypgrp;
/*
* See if we have a timeout flag.
*/
opterr = 0;
while((c = getopt(argc, argv, "ept:")) != EOF) switch(c) {
case 't':
timeout = atoi(optarg);
break;
case 'p':
profile = 1;
break;
case 'e':
opt_e = 1;
break;
default:
usage();
/* Do not exit! */
break;
}
if (geteuid() != 0) {
fprintf(stderr, "sulogin: only root can run sulogin.\n");
exit(1);
}
/*
* See if we need to open an other tty device.
*/
signal(SIGINT, SIG_IGN);
signal(SIGQUIT, SIG_IGN);
signal(SIGTSTP, SIG_IGN);
if (optind < argc) tty = argv[optind];
if (tty) {
if ((fd = open(tty, O_RDWR)) < 0) {
perror(tty);
} else if (!isatty(fd)) {
fprintf(stderr, "%s: not a tty\n", tty);
close(fd);
} else {
/*
* Only go through this trouble if the new
* tty doesn't fall in this process group.
*/
pid = getpid();
pgrp = getpgid(0);
ppgrp = getpgid(getppid());
ioctl(fd, TIOCGPGRP, &ttypgrp);
if (pgrp != ttypgrp && ppgrp != ttypgrp) {
if (pid != getsid(0)) {
if (pid == getpgid(0))
setpgid(0, getpgid(getppid()));
setsid();
}
signal(SIGHUP, SIG_IGN);
ioctl(0, TIOCNOTTY, (char *)1);
signal(SIGHUP, SIG_DFL);
close(0);
close(1);
close(2);
close(fd);
fd = open(tty, O_RDWR);
ioctl(0, TIOCSCTTY, (char *)1);
dup(fd);
dup(fd);
} else
close(fd);
}
} else if (getpid() == 1) {
/* We are init. We hence need to set a session anyway */
setsid();
if (ioctl(0, TIOCSCTTY, (char *)1))
perror("ioctl(TIOCSCTTY)");
}
/*
* Get the root password.
*/
if ((pwd = getrootpwent(opt_e)) == NULL) {
fprintf(stderr, "sulogin: cannot open password database!\n");
sleep(2);
}
/*
* Ask for the password.
*/
while(pwd) {
if ((p = getpasswd(pwd->pw_passwd)) == NULL) break;
if (pwd->pw_passwd[0] == 0 ||
strcmp(crypt(p, pwd->pw_passwd), pwd->pw_passwd) == 0)
sushell(pwd);
printf("Login incorrect.\n");
}
/*
* User pressed Control-D.
*/
return 0;
}
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