/* su for Linux. Run a shell with substitute user and group IDs.
Copyright (C) 1992-2006 Free Software Foundation, Inc.
Copyright (C) 2012 SUSE Linux Products GmbH, Nuernberg
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 02110-1301, 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.
Based on an implemenation by David MacKenzie <djm@gnu.ai.mit.edu>. */
enum
{
EXIT_CANNOT_INVOKE = 126,
EXIT_ENOENT = 127
};
#include <config.h>
#include <stdio.h>
#include <getopt.h>
#include <sys/types.h>
#include <pwd.h>
#include <grp.h>
#include <security/pam_appl.h>
#include <security/pam_misc.h>
#include <signal.h>
#include <sys/wait.h>
#include <syslog.h>
#include "err.h"
#include <stdbool.h>
#include "c.h"
#include "xalloc.h"
#include "nls.h"
#include "pathnames.h"
#include "env.h"
/* name of the pam configuration files. separate configs for su and su - */
#define PAM_SERVICE_NAME "su"
#define PAM_SERVICE_NAME_L "su-l"
#define is_pam_failure(_rc) ((_rc) != PAM_SUCCESS)
#include "logindefs.h"
#include "su-common.h"
/* 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"
#ifndef HAVE_ENVIRON_DECL
extern char **environ;
#endif
static void run_shell (char const *, char const *, char **, size_t)
__attribute__ ((__noreturn__));
/* 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;
/* If true, then don't call setsid() with a command. */
static int same_session = 0;
/* SU_MODE_{RUNUSER,SU} */
static int su_mode;
static bool _pam_session_opened;
static bool _pam_cred_established;
static sig_atomic_t volatile caught_signal = false;
static pam_handle_t *pamh = NULL;
static struct option const longopts[] =
{
{"command", required_argument, NULL, 'c'},
{"session-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'},
{"group", required_argument, NULL, 'g'},
{"supp-group", required_argument, NULL, 'G'},
{"help", no_argument, 0, 'h'},
{"version", no_argument, 0, 'V'},
{NULL, 0, NULL, 0}
};
/* 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;
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";
openlog (program_invocation_short_name, 0 , LOG_AUTH);
syslog (LOG_NOTICE, "%s(to %s) %s on %s",
successful ? "" : "FAILED SU ",
new_user, old_user, tty);
closelog ();
}
static struct pam_conv conv =
{
misc_conv,
NULL
};
static void
cleanup_pam (int retcode)
{
int saved_errno = errno;
if (_pam_session_opened)
pam_close_session (pamh, 0);
if (_pam_cred_established)
pam_setcred (pamh, PAM_DELETE_CRED | PAM_SILENT);
pam_end(pamh, retcode);
errno = saved_errno;
}
/* Signal handler for parent process. */
static void
su_catch_sig (int sig __attribute__((__unused__)))
{
caught_signal = true;
}
/* Export env variables declared by PAM modules. */
static void
export_pamenv (void)
{
char **env;
/* This is a copy but don't care to free as we exec later anyways. */
env = pam_getenvlist (pamh);
while (env && *env)
{
if (putenv (*env) != 0)
err (EXIT_FAILURE, NULL);
env++;
}
}
static void
create_watching_parent (void)
{
pid_t child;
sigset_t ourset;
int status = 0;
int retval;
retval = pam_open_session (pamh, 0);
if (is_pam_failure(retval))
{
cleanup_pam (retval);
errx (EXIT_FAILURE, _("cannot not open session: %s"),
pam_strerror (pamh, retval));
}
else
_pam_session_opened = 1;
child = fork ();
if (child == (pid_t) -1)
{
cleanup_pam (PAM_ABORT);
err (EXIT_FAILURE, _("cannot create child process"));
}
/* the child proceeds to run the shell */
if (child == 0)
return;
/* In the parent watch the child. */
/* su without pam support does not have a helper that keeps
sitting on any directory so let's go to /. */
if (chdir ("/") != 0)
warn (_("cannot change directory to %s"), "/");
sigfillset (&ourset);
if (sigprocmask (SIG_BLOCK, &ourset, NULL))
{
warn (_("cannot block signals"));
caught_signal = true;
}
if (!caught_signal)
{
struct sigaction action;
action.sa_handler = su_catch_sig;
sigemptyset (&action.sa_mask);
action.sa_flags = 0;
sigemptyset (&ourset);
if (!same_session)
{
if (sigaddset(&ourset, SIGINT) || sigaddset(&ourset, SIGQUIT))
{
warn (_("cannot set signal handler"));
caught_signal = true;
}
}
if (!caught_signal && (sigaddset(&ourset, SIGTERM)
|| sigaddset(&ourset, SIGALRM)
|| sigaction(SIGTERM, &action, NULL)
|| sigprocmask(SIG_UNBLOCK, &ourset, NULL))) {
warn (_("cannot set signal handler"));
caught_signal = true;
}
if (!caught_signal && !same_session && (sigaction(SIGINT, &action, NULL)
|| sigaction(SIGQUIT, &action, NULL)))
{
warn (_("cannot set signal handler"));
caught_signal = true;
}
}
if (!caught_signal)
{
pid_t pid;
for (;;)
{
pid = waitpid (child, &status, WUNTRACED);
if (pid != (pid_t)-1 && WIFSTOPPED (status))
{
kill (getpid (), SIGSTOP);
/* once we get here, we must have resumed */
kill (pid, SIGCONT);
}
else
break;
}
if (pid != (pid_t)-1)
if (WIFSIGNALED (status))
status = WTERMSIG (status) + 128;
else
status = WEXITSTATUS (status);
else
status = 1;
}
else
status = 1;
if (caught_signal)
{
fprintf (stderr, _("\nSession terminated, killing shell..."));
kill (child, SIGTERM);
}
cleanup_pam (PAM_SUCCESS);
if (caught_signal)
{
sleep (2);
kill (child, SIGKILL);
fprintf (stderr, _(" ...killed.\n"));
}
exit (status);
}
static void
authenticate (const struct passwd *pw)
{
const struct passwd *lpw;
const char *cp;
int retval;
retval = pam_start (simulate_login ? PAM_SERVICE_NAME_L : PAM_SERVICE_NAME,
pw->pw_name, &conv, &pamh);
if (is_pam_failure(retval))
goto done;
if (isatty (0) && (cp = ttyname (0)) != NULL)
{
const char *tty;
if (strncmp (cp, "/dev/", 5) == 0)
tty = cp + 5;
else
tty = cp;
retval = pam_set_item (pamh, PAM_TTY, tty);
if (is_pam_failure(retval))
goto done;
}
lpw = getpwuid (getuid ());
if (lpw && lpw->pw_name)
{
retval = pam_set_item (pamh, PAM_RUSER, (const void *) lpw->pw_name);
if (is_pam_failure(retval))
goto done;
}
retval = pam_authenticate (pamh, 0);
if (is_pam_failure(retval))
goto done;
retval = pam_acct_mgmt (pamh, 0);
if (retval == PAM_NEW_AUTHTOK_REQD)
{
/* Password has expired. Offer option to change it. */
retval = pam_chauthtok (pamh, PAM_CHANGE_EXPIRED_AUTHTOK);
}
done:
log_su (pw, !is_pam_failure(retval));
if (is_pam_failure(retval))
{
const char *msg = pam_strerror(pamh, retval);
pam_end(pamh, retval);
sleep (getlogindefs_num ("FAIL_DELAY", 1));
errx (EXIT_FAILURE, "%s", msg?msg:_("incorrect password"));
}
}
/* Add or clear /sbin and /usr/sbin for the su command
used without `-'. */
/* Set if /sbin is found in path. */
#define SBIN_MASK 0x01
/* Set if /usr/sbin is found in path. */
#define USBIN_MASK 0x02
static char *
addsbin (const char *const path)
{
unsigned char smask = 0;
char *ptr, *tmp, *cur, *ret = NULL;
size_t len;
if (!path || *path == 0)
return NULL;
tmp = xstrdup (path);
cur = tmp;
for (ptr = strsep (&cur, ":"); ptr != NULL; ptr = strsep (&cur, ":"))
{
if (!strcmp (ptr, "/sbin"))
smask |= SBIN_MASK;
if (!strcmp (ptr, "/usr/sbin"))
smask |= USBIN_MASK;
}
if ((smask & (USBIN_MASK|SBIN_MASK)) == (USBIN_MASK|SBIN_MASK))
{
free (tmp);
return NULL;
}
len = strlen (path);
if (!(smask & USBIN_MASK))
len += strlen ("/usr/sbin:");
if (!(smask & SBIN_MASK))
len += strlen (":/sbin");
ret = xmalloc (len + 1);
strcpy (tmp, path);
*ret = 0;
cur = tmp;
for (ptr = strsep (&cur, ":"); ptr; ptr = strsep (&cur, ":"))
{
if (!strcmp (ptr, "."))
continue;
if (*ret)
strcat (ret, ":");
if (!(smask & USBIN_MASK) && !strcmp (ptr, "/bin"))
{
strcat (ret, "/usr/sbin:");
strcat (ret, ptr);
smask |= USBIN_MASK;
continue;
}
if (!(smask & SBIN_MASK) && !strcmp (ptr, "/usr/bin"))
{
strcat (ret, ptr);
strcat (ret, ":/sbin");
smask |= SBIN_MASK;
continue;
}
strcat (ret, ptr);
}
free (tmp);
if (!(smask & USBIN_MASK))
strcat (ret, ":/usr/sbin");
if (!(smask & SBIN_MASK))
strcat (ret, ":/sbin");
return ret;
}
static char *
clearsbin (const char *const path)
{
char *ptr, *tmp, *cur, *ret = NULL;
if (!path || *path == 0)
return NULL;
tmp = xstrdup (path);
ret = xmalloc (strlen (path) + 1);
*ret = 0;
cur = tmp;
for (ptr = strsep (&cur, ":"); ptr; ptr = strsep (&cur, ":"))
{
if (!strcmp (ptr, "/sbin"))
continue;
if (!strcmp (ptr, "/usr/sbin"))
continue;
if (!strcmp (ptr, "/usr/local/sbin"))
continue;
if (*ret)
strcat (ret, ":");
strcat (ret, ptr);
}
free (tmp);
return ret;
}
static void
set_path(const struct passwd* pw)
{
int r;
if (pw->pw_uid)
r = logindefs_setenv("PATH", "ENV_PATH", _PATH_DEFPATH);
else if ((r = logindefs_setenv("PATH", "ENV_ROOTPATH", NULL)) != 0)
r = logindefs_setenv("PATH", "ENV_SUPATH", _PATH_DEFPATH_ROOT);
if (r != 0)
err (EXIT_FAILURE, _("failed to set PATH"));
}
/* 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, 1);
xsetenv ("HOME", pw->pw_dir, 1);
xsetenv ("SHELL", shell, 1);
xsetenv ("USER", pw->pw_name, 1);
xsetenv ("LOGNAME", pw->pw_name, 1);
set_path(pw);
}
else
{
/* Set HOME, SHELL, and if not becoming a super-user,
USER and LOGNAME. */
if (change_environment)
{
xsetenv ("HOME", pw->pw_dir, 1);
xsetenv ("SHELL", shell, 1);
if (getlogindefs_bool ("ALWAYS_SET_PATH", 0))
set_path(pw);
else
{
char const *path = getenv ("PATH");
char *new = NULL;
if (pw->pw_uid)
new = clearsbin (path);
else
new = addsbin (path);
if (new)
{
xsetenv ("PATH", new, 1);
free (new);
}
}
if (pw->pw_uid)
{
xsetenv ("USER", pw->pw_name, 1);
xsetenv ("LOGNAME", pw->pw_name, 1);
}
}
}
export_pamenv ();
}
/* Become the user and group(s) specified by PW. */
static void
init_groups (const struct passwd *pw, gid_t *groups, int num_groups)
{
int retval;
errno = 0;
if (num_groups)
retval = setgroups (num_groups, groups);
else
retval = initgroups (pw->pw_name, pw->pw_gid);
if (retval == -1)
{
cleanup_pam (PAM_ABORT);
err (EXIT_FAILURE, _("cannot set groups"));
}
endgrent ();
retval = pam_setcred (pamh, PAM_ESTABLISH_CRED);
if (is_pam_failure(retval))
errx (EXIT_FAILURE, "%s", pam_strerror (pamh, retval));
else
_pam_cred_established = 1;
}
static void
change_identity (const struct passwd *pw)
{
if (setgid (pw->pw_gid))
err (EXIT_FAILURE, _("cannot set group id"));
if (setuid (pw->pw_uid))
err (EXIT_FAILURE, _("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 = xcalloc (n_args, sizeof *args);
size_t argno = 1;
if (simulate_login)
{
char *arg0;
char *shell_basename;
shell_basename = basename (shell);
arg0 = xmalloc (strlen (shell_basename) + 2);
arg0[0] = '-';
strcpy (arg0 + 1, shell_basename);
args[0] = arg0;
}
else
args[0] = basename (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);
warn ("%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 != '#' && !strcmp (line, shell))
{
endusershell ();
return false;
}
}
endusershell ();
return true;
}
static void __attribute__((__noreturn__))
usage (int status)
{
if (status != EXIT_SUCCESS)
fprintf (stderr, _("Try `%s --help' for more information.\n"),
program_invocation_short_name);
else
{
fputs(USAGE_HEADER, stdout);
printf (_(" %s [options] [-] [USER [arg]...]\n"), program_invocation_short_name);
fputs (_("\n\
Change the effective user id and group id to that of USER.\n\
A mere - implies -l. If USER not given, assume root.\n"), stdout);
fputs(USAGE_OPTIONS, stdout);
fputs (_("\
-, -l, --login make the shell a login shell\n\
-c, --command <command> pass a single command to the shell with -c\n\
--session-command <command> pass a single command to the shell with -c\n\
and do not create a new session\n\
-g --group=group specify the primary group\n\
-G --supp-group=group specify a supplemental group\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(USAGE_SEPARATOR, stdout);
fputs(USAGE_HELP, stdout);
fputs(USAGE_VERSION, stdout);
printf(USAGE_MAN_TAIL("su(1)"));
}
exit (status);
}
static
void load_config(void)
{
logindefs_load_file("/etc/default/su");
logindefs_load_file(_PATH_LOGINDEFS);
}
/*
* Returns 1 if the current user is not root
*/
static int
evaluate_uid(void)
{
uid_t ruid = getuid();
uid_t euid = geteuid();
/* if we're really root and aren't running setuid */
return (uid_t) 0 == ruid && ruid == euid ? 0 : 1;
}
int
su_main (int argc, char **argv, int mode)
{
int optc;
const char *new_user = DEFAULT_USER;
char *command = NULL;
int request_same_session = 0;
char *shell = NULL;
struct passwd *pw;
struct passwd pw_copy;
struct group *gr;
gid_t groups[NGROUPS_MAX];
int num_supp_groups = 0;
int use_gid = 0;
int restricted;
setlocale (LC_ALL, "");
bindtextdomain (PACKAGE, LOCALEDIR);
textdomain (PACKAGE);
su_mode = mode;
fast_startup = false;
simulate_login = false;
change_environment = true;
while ((optc = getopt_long (argc, argv, "c:fg:G:lmps:hV", longopts, NULL)) != -1)
{
switch (optc)
{
case 'c':
command = optarg;
break;
case 'C':
command = optarg;
request_same_session = 1;
break;
case 'f':
fast_startup = true;
break;
case 'g':
gr = getgrnam(optarg);
if (!gr)
errx(EXIT_FAILURE, _("group %s does not exist"), optarg);
use_gid = 1;
groups[0] = gr->gr_gid;
break;
case 'G':
num_supp_groups++;
if (num_supp_groups >= NGROUPS_MAX)
errx(EXIT_FAILURE,
_("can't specify more than %d supplemental groups"),
NGROUPS_MAX - 1);
gr = getgrnam(optarg);
if (!gr)
errx(EXIT_FAILURE, _("group %s does not exist"), optarg);
groups[num_supp_groups] = gr->gr_gid;
break;
case 'l':
simulate_login = true;
break;
case 'm':
case 'p':
change_environment = false;
break;
case 's':
shell = optarg;
break;
case 'h':
usage(0);
case 'V':
printf(UTIL_LINUX_VERSION);
exit(EXIT_SUCCESS);
default:
usage (EXIT_FAILURE);
}
}
restricted = evaluate_uid ();
if (optind < argc && !strcmp (argv[optind], "-"))
{
simulate_login = true;
++optind;
}
if (optind < argc)
new_user = argv[optind++];
if ((num_supp_groups || use_gid) && restricted)
errx(EXIT_FAILURE, _("only root can specify alternative groups"));
logindefs_load_defaults = load_config;
pw = getpwnam (new_user);
if (! (pw && pw->pw_name && pw->pw_name[0] && pw->pw_dir && pw->pw_dir[0]
&& pw->pw_passwd))
errx (EXIT_FAILURE, _("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 (num_supp_groups && !use_gid)
{
pw->pw_gid = groups[1];
memmove (groups, groups + 1, sizeof(gid_t) * num_supp_groups);
}
else if (use_gid)
{
pw->pw_gid = groups[0];
num_supp_groups++;
}
authenticate (pw);
if (request_same_session || !command || !pw->pw_uid)
same_session = 1;
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. */
warnx (_("using restricted shell %s"), pw->pw_shell);
shell = NULL;
}
shell = xstrdup (shell ? shell : pw->pw_shell);
init_groups (pw, groups, num_supp_groups);
create_watching_parent ();
/* Now we're in the child. */
change_identity (pw);
if (!same_session)
setsid ();
/* Set environment after pam_open_session, which may put KRB5CCNAME
into the pam_env, etc. */
modify_environment (pw, shell);
if (simulate_login && chdir (pw->pw_dir) != 0)
warn (_("warning: cannot change directory to %s"), pw->pw_dir);
run_shell (shell, command, argv + optind, max (0, argc - optind));
}
// vim: sw=2 cinoptions=>4,n-2,{2,^-2,\:2,=2,g0,h2,p5,t0,+2,(0,u0,w1,m1
