/* su for GNU. Run a shell with substitute user and group IDs.
Copyright (C) 1992-2004 Free Software Foundation, Inc.
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, 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 02111-1307, USA. */
/* Run a shell with the real and effective UID and GID and groups
of USER, default `root'.
The shell run is taken from USER's password entry, /bin/sh if
none is specified there. If the account has a password, su
prompts for a password unless run by a user with real UID 0.
Does not change the current directory.
Sets `HOME' and `SHELL' from the password entry for USER, and if
USER is not root, sets `USER' and `LOGNAME' to USER.
The subshell is not a login shell.
If one or more ARGs are given, they are passed as additional
arguments to the subshell.
Does not handle /bin/sh or other shells specially
(setting argv[0] to "-su", passing -c only to certain shells, etc.).
I don't see the point in doing that, and it's ugly.
This program intentionally does not support a "wheel group" that
restricts who can su to UID 0 accounts. RMS considers that to
be fascist.
Options:
-, -l, --login Make the subshell a login shell.
Unset all environment variables except
TERM, HOME and SHELL (set as above), and USER
and LOGNAME (set unconditionally as above), and
set PATH to a default value.
Change to USER's home directory.
Prepend "-" to the shell's name.
-c, --commmand=COMMAND
Pass COMMAND to the subshell with a -c option
instead of starting an interactive shell.
-f, --fast Pass the -f option to the subshell.
-m, -p, --preserve-environment
Do not change HOME, USER, LOGNAME, SHELL.
Run $SHELL instead of USER's shell from /etc/passwd
unless not the superuser and USER's shell is
restricted.
Overridden by --login and --shell.
-s, --shell=shell Run SHELL instead of USER's shell from /etc/passwd
unless not the superuser and USER's shell is
restricted.
Compile-time options:
-DSYSLOG_SUCCESS Log successful su's (by default, to root) with syslog.
-DSYSLOG_FAILURE Log failed su's (by default, to root) with syslog.
-DSYSLOG_NON_ROOT Log all su's, not just those to root (UID 0).
Never logs attempted su's to nonexistent accounts.
Written by David MacKenzie <djm@gnu.ai.mit.edu>. */
#include <config.h>
#include <stdio.h>
#include <getopt.h>
#include <sys/types.h>
#include <pwd.h>
#include <grp.h>
/* Hide any system prototype for getusershell.
This is necessary because some Cray systems have a conflicting
prototype (returning `int') in <unistd.h>. */
#define getusershell _getusershell_sys_proto_
#include "system.h"
#include "dirname.h"
#undef getusershell
#if HAVE_SYSLOG_H && HAVE_SYSLOG
# include <syslog.h>
#else
# undef SYSLOG_SUCCESS
# undef SYSLOG_FAILURE
# undef SYSLOG_NON_ROOT
#endif
#if HAVE_SYS_PARAM_H
# include <sys/param.h>
#endif
#ifndef HAVE_ENDGRENT
# define endgrent() ((void) 0)
#endif
#ifndef HAVE_ENDPWENT
# define endpwent() ((void) 0)
#endif
#if HAVE_SHADOW_H
# include <shadow.h>
#endif
#include "error.h"
/* The official name of this program (e.g., no `g' prefix). */
#define PROGRAM_NAME "su"
#define AUTHORS "David MacKenzie"
#if HAVE_PATHS_H
# include <paths.h>
#endif
/* The default PATH for simulated logins to non-superuser accounts. */
#ifdef _PATH_DEFPATH
# define DEFAULT_LOGIN_PATH _PATH_DEFPATH
#else
# define DEFAULT_LOGIN_PATH ":/usr/ucb:/bin:/usr/bin"
#endif
/* The default PATH for simulated logins to superuser accounts. */
#ifdef _PATH_DEFPATH_ROOT
# define DEFAULT_ROOT_LOGIN_PATH _PATH_DEFPATH_ROOT
#else
# define DEFAULT_ROOT_LOGIN_PATH "/usr/ucb:/bin:/usr/bin:/etc"
#endif
/* The shell to run if none is given in the user's passwd entry. */
#define DEFAULT_SHELL "/bin/sh"
/* The user to become if none is specified. */
#define DEFAULT_USER "root"
char *crypt ();
char *getpass ();
char *getusershell ();
void endusershell ();
void setusershell ();
extern char **environ;
static void run_shell (char const *, char const *, char **, size_t)
ATTRIBUTE_NORETURN;
/* The name this program was run with. */
char *program_name;
/* If true, pass the `-f' option to the subshell. */
static bool fast_startup;
/* If true, simulate a login instead of just starting a shell. */
static bool simulate_login;
/* If true, change some environment vars to indicate the user su'd to. */
static bool change_environment;
static struct option const longopts[] =
{
{"command", required_argument, NULL, 'c'},
{"fast", no_argument, NULL, 'f'},
{"login", no_argument, NULL, 'l'},
{"preserve-environment", no_argument, NULL, 'p'},
{"shell", required_argument, NULL, 's'},
{GETOPT_HELP_OPTION_DECL},
{GETOPT_VERSION_OPTION_DECL},
{NULL, 0, NULL, 0}
};
/* Add NAME=VAL to the environment, checking for out of memory errors. */
static void
xsetenv (char const *name, char const *val)
{
size_t namelen = strlen (name);
size_t vallen = strlen (val);
char *string = xmalloc (namelen + 1 + vallen + 1);
strcpy (string, name);
string[namelen] = '=';
strcpy (string + namelen + 1, val);
if (putenv (string) != 0)
xalloc_die ();
}
#if defined (SYSLOG_SUCCESS) || defined (SYSLOG_FAILURE)
/* Log the fact that someone has run su to the user given by PW;
if SUCCESSFUL is true, they gave the correct password, etc. */
static void
log_su (struct passwd const *pw, bool successful)
{
const char *new_user, *old_user, *tty;
# ifndef SYSLOG_NON_ROOT
if (pw->pw_uid)
return;
# endif
new_user = pw->pw_name;
/* The utmp entry (via getlogin) is probably the best way to identify
the user, especially if someone su's from a su-shell. */
old_user = getlogin ();
if (!old_user)
{
/* getlogin can fail -- usually due to lack of utmp entry.
Resort to getpwuid. */
struct passwd *pwd = getpwuid (getuid ());
old_user = (pwd ? pwd->pw_name : "");
}
tty = ttyname (STDERR_FILENO);
if (!tty)
tty = "none";
/* 4.2BSD openlog doesn't have the third parameter. */
openlog (base_name (program_name), 0
# ifdef LOG_AUTH
, LOG_AUTH
# endif
);
syslog (LOG_NOTICE,
# ifdef SYSLOG_NON_ROOT
"%s(to %s) %s on %s",
# else
"%s%s on %s",
# endif
successful ? "" : "FAILED SU ",
# ifdef SYSLOG_NON_ROOT
new_user,
# endif
old_user, tty);
closelog ();
}
#endif
/* Ask the user for a password.
Return true if the user gives the correct password for entry PW,
false if not. Return true without asking for a password if run by UID 0
or if PW has an empty password. */
static bool
correct_password (const struct passwd *pw)
{
char *unencrypted, *encrypted, *correct;
#if HAVE_GETSPNAM && HAVE_STRUCT_SPWD_SP_PWDP
/* Shadow passwd stuff for SVR3 and maybe other systems. */
struct spwd *sp = getspnam (pw->pw_name);
endspent ();
if (sp)
correct = sp->sp_pwdp;
else
#endif
correct = pw->pw_passwd;
if (getuid () == 0 || !correct || correct[0] == '\0')
return true;
unencrypted = getpass (_("Password:"));
if (!unencrypted)
{
error (0, 0, _("getpass: cannot open /dev/tty"));
return false;
}
encrypted = crypt (unencrypted, correct);
memset (unencrypted, 0, strlen (unencrypted));
return STREQ (encrypted, correct);
}
/* Update `environ' for the new shell based on PW, with SHELL being
the value for the SHELL environment variable. */
static void
modify_environment (const struct passwd *pw, const char *shell)
{
if (simulate_login)
{
/* Leave TERM unchanged. Set HOME, SHELL, USER, LOGNAME, PATH.
Unset all other environment variables. */
char const *term = getenv ("TERM");
if (term)
term = xstrdup (term);
environ = xmalloc ((6 + !!term) * sizeof (char *));
environ[0] = NULL;
if (term)
xsetenv ("TERM", term);
xsetenv ("HOME", pw->pw_dir);
xsetenv ("SHELL", shell);
xsetenv ("USER", pw->pw_name);
xsetenv ("LOGNAME", pw->pw_name);
xsetenv ("PATH", (pw->pw_uid
? DEFAULT_LOGIN_PATH
: DEFAULT_ROOT_LOGIN_PATH));
}
else
{
/* Set HOME, SHELL, and if not becoming a super-user,
USER and LOGNAME. */
if (change_environment)
{
xsetenv ("HOME", pw->pw_dir);
xsetenv ("SHELL", shell);
if (pw->pw_uid)
{
xsetenv ("USER", pw->pw_name);
xsetenv ("LOGNAME", pw->pw_name);
}
}
}
}
/* Become the user and group(s) specified by PW. */
static void
change_identity (const struct passwd *pw)
{
#ifdef HAVE_INITGROUPS
errno = 0;
if (initgroups (pw->pw_name, pw->pw_gid) == -1)
error (EXIT_FAIL, errno, _("cannot set groups"));
endgrent ();
#endif
if (setgid (pw->pw_gid))
error (EXIT_FAIL, errno, _("cannot set group id"));
if (setuid (pw->pw_uid))
error (EXIT_FAIL, errno, _("cannot set user id"));
}
/* Run SHELL, or DEFAULT_SHELL if SHELL is empty.
If COMMAND is nonzero, pass it to the shell with the -c option.
Pass ADDITIONAL_ARGS to the shell as more arguments; there
are N_ADDITIONAL_ARGS extra arguments. */
static void
run_shell (char const *shell, char const *command, char **additional_args,
size_t n_additional_args)
{
size_t n_args = 1 + fast_startup + 2 * !!command + n_additional_args + 1;
char const **args = xnmalloc (n_args, sizeof *args);
size_t argno = 1;
if (simulate_login)
{
char *arg0;
char *shell_basename;
shell_basename = base_name (shell);
arg0 = xmalloc (strlen (shell_basename) + 2);
arg0[0] = '-';
strcpy (arg0 + 1, shell_basename);
args[0] = arg0;
}
else
args[0] = base_name (shell);
if (fast_startup)
args[argno++] = "-f";
if (command)
{
args[argno++] = "-c";
args[argno++] = command;
}
memcpy (args + argno, additional_args, n_additional_args * sizeof *args);
args[argno + n_additional_args] = NULL;
execv (shell, (char **) args);
{
int exit_status = (errno == ENOENT ? EXIT_ENOENT : EXIT_CANNOT_INVOKE);
error (0, errno, "%s", shell);
exit (exit_status);
}
}
/* Return true if SHELL is a restricted shell (one not returned by
getusershell), else false, meaning it is a standard shell. */
static bool
restricted_shell (const char *shell)
{
char *line;
setusershell ();
while ((line = getusershell ()) != NULL)
{
if (*line != '#' && STREQ (line, shell))
{
endusershell ();
return false;
}
}
endusershell ();
return true;
}
void
usage (int status)
{
if (status != EXIT_SUCCESS)
fprintf (stderr, _("Try `%s --help' for more information.\n"),
program_name);
else
{
printf (_("Usage: %s [OPTION]... [-] [USER [ARG]...]\n"), program_name);
fputs (_("\
Change the effective user id and group id to that of USER.\n\
\n\
-, -l, --login make the shell a login shell\n\
-c, --commmand=COMMAND pass a single COMMAND to the shell with -c\n\
-f, --fast pass -f to the shell (for csh or tcsh)\n\
-m, --preserve-environment do not reset environment variables\n\
-p same as -m\n\
-s, --shell=SHELL run SHELL if /etc/shells allows it\n\
"), stdout);
fputs (HELP_OPTION_DESCRIPTION, stdout);
fputs (VERSION_OPTION_DESCRIPTION, stdout);
fputs (_("\
\n\
A mere - implies -l. If USER not given, assume root.\n\
"), stdout);
printf (_("\nReport bugs to <%s>.\n"), PACKAGE_BUGREPORT);
}
exit (status);
}
int
main (int argc, char **argv)
{
int optc;
const char *new_user = DEFAULT_USER;
char *command = NULL;
char *shell = NULL;
struct passwd *pw;
struct passwd pw_copy;
initialize_main (&argc, &argv);
program_name = argv[0];
setlocale (LC_ALL, "");
bindtextdomain (PACKAGE, LOCALEDIR);
textdomain (PACKAGE);
initialize_exit_failure (EXIT_FAIL);
atexit (close_stdout);
fast_startup = false;
simulate_login = false;
change_environment = true;
while ((optc = getopt_long (argc, argv, "c:flmps:", longopts, NULL)) != -1)
{
switch (optc)
{
case 'c':
command = optarg;
break;
case 'f':
fast_startup = true;
break;
case 'l':
simulate_login = true;
break;
case 'm':
case 'p':
change_environment = false;
break;
case 's':
shell = optarg;
break;
case_GETOPT_HELP_CHAR;
case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
default:
usage (EXIT_FAIL);
}
}
if (optind < argc && STREQ (argv[optind], "-"))
{
simulate_login = true;
++optind;
}
if (optind < argc)
new_user = argv[optind++];
pw = getpwnam (new_user);
if (! (pw && pw->pw_name && pw->pw_name[0] && pw->pw_dir && pw->pw_dir[0]
&& pw->pw_passwd))
error (EXIT_FAIL, 0, _("user %s does not exist"), new_user);
/* Make a copy of the password information and point pw at the local
copy instead. Otherwise, some systems (e.g. Linux) would clobber
the static data through the getlogin call from log_su.
Also, make sure pw->pw_shell is a nonempty string.
It may be NULL when NEW_USER is a username that is retrieved via NIS (YP),
but that doesn't have a default shell listed. */
pw_copy = *pw;
pw = &pw_copy;
pw->pw_name = xstrdup (pw->pw_name);
pw->pw_passwd = xstrdup (pw->pw_passwd);
pw->pw_dir = xstrdup (pw->pw_dir);
pw->pw_shell = xstrdup (pw->pw_shell && pw->pw_shell[0]
? pw->pw_shell
: DEFAULT_SHELL);
endpwent ();
if (!correct_password (pw))
{
#ifdef SYSLOG_FAILURE
log_su (pw, false);
#endif
error (EXIT_FAIL, 0, _("incorrect password"));
}
#ifdef SYSLOG_SUCCESS
else
{
log_su (pw, true);
}
#endif
if (!shell && !change_environment)
shell = getenv ("SHELL");
if (shell && getuid () != 0 && restricted_shell (pw->pw_shell))
{
/* The user being su'd to has a nonstandard shell, and so is
probably a uucp account or has restricted access. Don't
compromise the account by allowing access with a standard
shell. */
error (0, 0, _("using restricted shell %s"), pw->pw_shell);
shell = NULL;
}
shell = xstrdup (shell ? shell : pw->pw_shell);
modify_environment (pw, shell);
change_identity (pw);
if (simulate_login && chdir (pw->pw_dir) != 0)
error (0, errno, _("warning: cannot change directory to %s"), pw->pw_dir);
run_shell (shell, command, argv + optind, MAX (0, argc - optind));
}
