shadow/src/chsh.c

542 lines
14 KiB
C

/*
* SPDX-FileCopyrightText: 1989 - 1994, Julianne Frances Haugh
* SPDX-FileCopyrightText: 1996 - 2000, Marek Michałkiewicz
* SPDX-FileCopyrightText: 2001 - 2006, Tomasz Kłoczko
* SPDX-FileCopyrightText: 2007 - 2011, Nicolas François
*
* SPDX-License-Identifier: BSD-3-Clause
*/
#include <config.h>
#ident "$Id$"
#include <fcntl.h>
#include <getopt.h>
#include <pwd.h>
#include <stdio.h>
#include <sys/types.h>
#include "defines.h"
#include "getdef.h"
#include "nscd.h"
#include "sssd.h"
#include "prototypes.h"
#include "pwauth.h"
#include "pwio.h"
#ifdef USE_PAM
#include "pam_defs.h"
#endif
/*@-exitarg@*/
#include "exitcodes.h"
#include "shadowlog.h"
#ifndef SHELLS_FILE
#define SHELLS_FILE "/etc/shells"
#endif
/*
* Global variables
*/
const char *Prog; /* Program name */
static bool amroot; /* Real UID is root */
static char loginsh[BUFSIZ]; /* Name of new login shell */
/* command line options */
static bool sflg = false; /* -s - set shell from command line */
static bool pw_locked = false;
/* external identifiers */
/* local function prototypes */
static /*@noreturn@*/void fail_exit (int code);
static /*@noreturn@*/void usage (int status);
static void new_fields (void);
static bool shell_is_listed (const char *);
static bool is_restricted_shell (const char *);
static void process_flags (int argc, char **argv);
static void check_perms (const struct passwd *pw);
static void update_shell (const char *user, char *loginsh);
/*
* fail_exit - do some cleanup and exit with the given error code
*/
static /*@noreturn@*/void fail_exit (int code)
{
if (pw_locked) {
if (pw_unlock () == 0) {
fprintf (stderr, _("%s: failed to unlock %s\n"), Prog, pw_dbname ());
SYSLOG ((LOG_ERR, "failed to unlock %s", pw_dbname ()));
/* continue */
}
}
closelog ();
exit (code);
}
/*
* usage - print command line syntax and exit
*/
static /*@noreturn@*/void usage (int status)
{
FILE *usageout = (E_SUCCESS != status) ? stderr : stdout;
(void) fprintf (usageout,
_("Usage: %s [options] [LOGIN]\n"
"\n"
"Options:\n"),
Prog);
(void) fputs (_(" -h, --help display this help message and exit\n"), usageout);
(void) fputs (_(" -R, --root CHROOT_DIR directory to chroot into\n"), usageout);
(void) fputs (_(" -s, --shell SHELL new login shell for the user account\n"), usageout);
(void) fputs ("\n", usageout);
exit (status);
}
/*
* new_fields - change the user's login shell information interactively
*
* prompt the user for the login shell and change it according to the
* response, or leave it alone if nothing was entered.
*/
static void new_fields (void)
{
puts (_("Enter the new value, or press ENTER for the default"));
change_field (loginsh, sizeof loginsh, _("Login Shell"));
}
/*
* is_restricted_shell - return true if the shell is restricted
*
*/
static bool is_restricted_shell (const char *sh)
{
/*
* Shells not listed in /etc/shells are considered to be restricted.
* Changed this to avoid confusion with "rc" (the plan9 shell - not
* restricted despite the name starting with 'r'). --marekm
*/
return !shell_is_listed (sh);
}
/*
* shell_is_listed - see if the user's login shell is listed in /etc/shells
*
* The /etc/shells file is read for valid names of login shells. If the
* /etc/shells file does not exist the user cannot set any shell unless
* they are root.
*
* If getusershell() is available (Linux, *BSD, possibly others), use it
* instead of re-implementing it.
*/
static bool shell_is_listed (const char *sh)
{
char *cp;
bool found = false;
#ifndef HAVE_GETUSERSHELL
char buf[BUFSIZ];
FILE *fp;
#endif
#ifdef HAVE_GETUSERSHELL
setusershell ();
while ((cp = getusershell ())) {
if (strcmp (cp, sh) == 0) {
found = true;
break;
}
}
endusershell ();
#else
fp = fopen (SHELLS_FILE, "r");
if (NULL == fp) {
return false;
}
while (fgets (buf, sizeof (buf), fp) == buf) {
cp = strrchr (buf, '\n');
if (NULL != cp) {
*cp = '\0';
}
if (buf[0] == '#') {
continue;
}
if (strcmp (buf, sh) == 0) {
found = true;
break;
}
}
fclose (fp);
#endif
return found;
}
/*
* process_flags - parse the command line options
*
* It will not return if an error is encountered.
*/
static void process_flags (int argc, char **argv)
{
int c;
static struct option long_options[] = {
{"help", no_argument, NULL, 'h'},
{"root", required_argument, NULL, 'R'},
{"shell", required_argument, NULL, 's'},
{NULL, 0, NULL, '\0'}
};
while ((c = getopt_long (argc, argv, "hR:s:",
long_options, NULL)) != -1) {
switch (c) {
case 'h':
usage (E_SUCCESS);
/*@notreached@*/break;
case 'R': /* no-op, handled in process_root_flag () */
break;
case 's':
sflg = true;
STRFCPY (loginsh, optarg);
break;
default:
usage (E_USAGE);
}
}
/*
* There should be only one remaining argument at most and it should
* be the user's name.
*/
if (argc > (optind + 1)) {
usage (E_USAGE);
}
}
/*
* check_perms - check if the caller is allowed to add a group
*
* Non-root users are only allowed to change their shell, if their current
* shell is not a restricted shell.
*
* Non-root users must be authenticated.
*
* It will not return if the user is not allowed.
*/
static void check_perms (const struct passwd *pw)
{
#ifdef USE_PAM
pam_handle_t *pamh = NULL;
int retval;
struct passwd *pampw;
#endif
/*
* Non-privileged users are only allowed to change the shell if the
* UID of the user matches the current real UID.
*/
if (!amroot && pw->pw_uid != getuid ()) {
SYSLOG ((LOG_WARN, "can't change shell for '%s'", pw->pw_name));
fprintf (stderr,
_("You may not change the shell for '%s'.\n"),
pw->pw_name);
fail_exit (1);
}
/*
* Non-privileged users are only allowed to change the shell if it
* is not a restricted one.
*/
if (!amroot && is_restricted_shell (pw->pw_shell)) {
SYSLOG ((LOG_WARN, "can't change shell for '%s'", pw->pw_name));
fprintf (stderr,
_("You may not change the shell for '%s'.\n"),
pw->pw_name);
fail_exit (1);
}
#ifdef WITH_SELINUX
/*
* If the UID of the user does not match the current real UID,
* check if the change is allowed by SELinux policy.
*/
if ((pw->pw_uid != getuid ())
&& (check_selinux_permit("chsh") != 0)) {
SYSLOG ((LOG_WARN, "can't change shell for '%s'", pw->pw_name));
fprintf (stderr,
_("You may not change the shell for '%s'.\n"),
pw->pw_name);
fail_exit (1);
}
#endif
#ifndef USE_PAM
/*
* Non-privileged users are optionally authenticated (must enter
* the password of the user whose information is being changed)
* before any changes can be made. Idea from util-linux
* chfn/chsh. --marekm
*/
if (!amroot && getdef_bool ("CHSH_AUTH")) {
passwd_check (pw->pw_name, pw->pw_passwd, "chsh");
}
#else /* !USE_PAM */
pampw = getpwuid (getuid ()); /* local, no need for xgetpwuid */
if (NULL == pampw) {
fprintf (stderr,
_("%s: Cannot determine your user name.\n"),
Prog);
exit (E_NOPERM);
}
retval = pam_start ("chsh", pampw->pw_name, &conv, &pamh);
if (PAM_SUCCESS == retval) {
retval = pam_authenticate (pamh, 0);
}
if (PAM_SUCCESS == retval) {
retval = pam_acct_mgmt (pamh, 0);
}
if (PAM_SUCCESS != retval) {
fprintf (stderr, _("%s: PAM: %s\n"),
Prog, pam_strerror (pamh, retval));
SYSLOG((LOG_ERR, "%s", pam_strerror (pamh, retval)));
if (NULL != pamh) {
(void) pam_end (pamh, retval);
}
exit (E_NOPERM);
}
(void) pam_end (pamh, retval);
#endif /* USE_PAM */
}
/*
* update_shell - update the user's shell in the passwd database
*
* Commit the user's entry after changing her shell field.
*
* It will not return in case of error.
*/
static void update_shell (const char *user, char *newshell)
{
const struct passwd *pw; /* Password entry from /etc/passwd */
struct passwd pwent; /* New password entry */
/*
* Before going any further, raise the ulimit to prevent
* colliding into a lowered ulimit, and set the real UID
* to root to protect against unexpected signals. Any
* keyboard signals are set to be ignored.
*/
if (setuid (0) != 0) {
SYSLOG ((LOG_ERR, "can't setuid(0)"));
fputs (_("Cannot change ID to root.\n"), stderr);
fail_exit (1);
}
pwd_init ();
/*
* The passwd entry is now ready to be committed back to
* the password file. Get a lock on the file and open it.
*/
if (pw_lock () == 0) {
fprintf (stderr, _("%s: cannot lock %s; try again later.\n"),
Prog, pw_dbname ());
fail_exit (1);
}
pw_locked = true;
if (pw_open (O_CREAT | O_RDWR) == 0) {
fprintf (stderr, _("%s: cannot open %s\n"), Prog, pw_dbname ());
SYSLOG ((LOG_WARN, "cannot open %s", pw_dbname ()));
fail_exit (1);
}
/*
* Get the entry to update using pw_locate() - we want the real
* one from /etc/passwd, not the one from getpwnam() which could
* contain the shadow password if (despite the warnings) someone
* enables AUTOSHADOW (or SHADOW_COMPAT in libc). --marekm
*/
pw = pw_locate (user);
if (NULL == pw) {
fprintf (stderr,
_("%s: user '%s' does not exist in %s\n"),
Prog, user, pw_dbname ());
fail_exit (1);
}
/*
* Make a copy of the entry, then change the shell field. The other
* fields remain unchanged.
*/
pwent = *pw;
pwent.pw_shell = newshell;
/*
* Update the passwd file entry. If there is a DBM file, update
* that entry as well.
*/
if (pw_update (&pwent) == 0) {
fprintf (stderr,
_("%s: failed to prepare the new %s entry '%s'\n"),
Prog, pw_dbname (), pwent.pw_name);
fail_exit (1);
}
/*
* Changes have all been made, so commit them and unlock the file.
*/
if (pw_close () == 0) {
fprintf (stderr, _("%s: failure while writing changes to %s\n"), Prog, pw_dbname ());
SYSLOG ((LOG_ERR, "failure while writing changes to %s", pw_dbname ()));
fail_exit (1);
}
if (pw_unlock () == 0) {
fprintf (stderr, _("%s: failed to unlock %s\n"), Prog, pw_dbname ());
SYSLOG ((LOG_ERR, "failed to unlock %s", pw_dbname ()));
/* continue */
}
pw_locked= false;
}
/*
* chsh - this command controls changes to the user's shell
*
* The only supported option is -s which permits the the login shell to
* be set from the command line.
*/
int main (int argc, char **argv)
{
char *user; /* User name */
const struct passwd *pw; /* Password entry from /etc/passwd */
sanitize_env ();
/*
* Get the program name. The program name is used as a prefix to
* most error messages.
*/
Prog = Basename (argv[0]);
log_set_progname(Prog);
log_set_logfd(stderr);
(void) setlocale (LC_ALL, "");
(void) bindtextdomain (PACKAGE, LOCALEDIR);
(void) textdomain (PACKAGE);
process_root_flag ("-R", argc, argv);
/*
* This command behaves different for root and non-root users.
*/
amroot = (getuid () == 0);
OPENLOG ("chsh");
/* parse the command line options */
process_flags (argc, argv);
/*
* Get the name of the user to check. It is either the command line
* name, or the name getlogin() returns.
*/
if (optind < argc) {
user = argv[optind];
pw = xgetpwnam (user);
if (NULL == pw) {
fprintf (stderr,
_("%s: user '%s' does not exist\n"), Prog, user);
fail_exit (1);
}
} else {
pw = get_my_pwent ();
if (NULL == pw) {
fprintf (stderr,
_("%s: Cannot determine your user name.\n"),
Prog);
SYSLOG ((LOG_WARN, "Cannot determine the user name of the caller (UID %lu)",
(unsigned long) getuid ()));
fail_exit (1);
}
user = xstrdup (pw->pw_name);
}
#ifdef USE_NIS
/*
* Now we make sure this is a LOCAL password entry for this user ...
*/
if (__ispwNIS ()) {
char *nis_domain;
char *nis_master;
fprintf (stderr,
_("%s: cannot change user '%s' on NIS client.\n"),
Prog, user);
if (!yp_get_default_domain (&nis_domain) &&
!yp_master (nis_domain, "passwd.byname", &nis_master)) {
fprintf (stderr,
_("%s: '%s' is the NIS master for this client.\n"),
Prog, nis_master);
}
fail_exit (1);
}
#endif
check_perms (pw);
/*
* Now get the login shell. Either get it from the password
* file, or use the value from the command line.
*/
if (!sflg) {
STRFCPY (loginsh, pw->pw_shell);
}
/*
* If the login shell was not set on the command line, let the user
* interactively change it.
*/
if (!sflg) {
printf (_("Changing the login shell for %s\n"), user);
new_fields ();
}
/*
* Check all of the fields for valid information. The shell
* field may not contain any illegal characters. Non-privileged
* users are restricted to using the shells in /etc/shells.
* The shell must be executable by the user.
*/
if (valid_field (loginsh, ":,=\n") != 0) {
fprintf (stderr, _("%s: Invalid entry: %s\n"), Prog, loginsh);
fail_exit (1);
}
if ( !amroot
&& ( is_restricted_shell (loginsh)
|| (access (loginsh, X_OK) != 0))) {
fprintf (stderr, _("%s: %s is an invalid shell\n"), Prog, loginsh);
fail_exit (1);
}
/* Even for root, warn if an invalid shell is specified. */
if (access (loginsh, F_OK) != 0) {
fprintf (stderr, _("%s: Warning: %s does not exist\n"), Prog, loginsh);
} else if (access (loginsh, X_OK) != 0) {
fprintf (stderr, _("%s: Warning: %s is not executable\n"), Prog, loginsh);
}
update_shell (user, loginsh);
SYSLOG ((LOG_INFO, "changed user '%s' shell to '%s'", user, loginsh));
nscd_flush_cache ("passwd");
sssd_flush_cache (SSSD_DB_PASSWD);
closelog ();
exit (E_SUCCESS);
}