build-sys: release++ (v2.38.1)

[thirdparty/util-linux.git] / login-utils / su-common.c

/*
 * su(1) 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
 * Copyright (C) 2016-2017 Karel Zak <kzak@redhat.com>
 *
 * 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.
 *
 *
 * Based on an implementation by David MacKenzie <djm@gnu.ai.mit.edu>.
 */
#include <stdio.h>
#include <getopt.h>
#include <sys/types.h>
#include <pwd.h>
#include <grp.h>
#include <security/pam_appl.h>
#ifdef HAVE_SECURITY_PAM_MISC_H
# include <security/pam_misc.h>
#elif defined(HAVE_SECURITY_OPENPAM_H)
# include <security/openpam.h>
#endif
#include <signal.h>
#include <sys/wait.h>
#include <syslog.h>
#include <utmpx.h>
#include <sys/time.h>

#ifdef HAVE_SYS_RESOURCE_H
# include <sys/resource.h>
#endif

#ifdef HAVE_PTY
# include <pty.h>
# include <poll.h>
# include <sys/signalfd.h>
# include "pty-session.h"
# define USE_PTY
#endif

#include "err.h"

#include <stdbool.h>

#include "c.h"
#include "xalloc.h"
#include "nls.h"
#include "pathnames.h"
#include "env.h"
#include "closestream.h"
#include "strv.h"
#include "strutils.h"
#include "ttyutils.h"
#include "pwdutils.h"
#include "optutils.h"

#include "logindefs.h"
#include "su-common.h"

#include "debug.h"

UL_DEBUG_DEFINE_MASK(su);
UL_DEBUG_DEFINE_MASKNAMES(su) = UL_DEBUG_EMPTY_MASKNAMES;

#define SU_DEBUG_INIT           (1 << 1)
#define SU_DEBUG_PAM            (1 << 2)
#define SU_DEBUG_PARENT         (1 << 3)
#define SU_DEBUG_TTY            (1 << 4)
#define SU_DEBUG_LOG            (1 << 5)
#define SU_DEBUG_MISC           (1 << 6)
#define SU_DEBUG_SIG            (1 << 7)
#define SU_DEBUG_PTY            (1 << 8)
#define SU_DEBUG_ALL            0xFFFF

#define DBG(m, x)       __UL_DBG(su, SU_DEBUG_, m, x)
#define ON_DBG(m, x)    __UL_DBG_CALL(su, SU_DEBUG_, m, x)

/* name of the pam configuration files. separate configs for su and su -  */
#define PAM_SRVNAME_SU "su"
#define PAM_SRVNAME_SU_L "su-l"

#define PAM_SRVNAME_RUNUSER "runuser"
#define PAM_SRVNAME_RUNUSER_L "runuser-l"

#ifdef HAVE_LIBECONF
#define _PATH_LOGINDEFS_SU      "default/su"
#define _PATH_LOGINDEFS_RUNUSER "default/runuser"
#else
#define _PATH_LOGINDEFS_SU      "/etc/default/su"
#define _PATH_LOGINDEFS_RUNUSER "/etc/default/runuser"
#endif

#define is_pam_failure(_rc)     ((_rc) != PAM_SUCCESS)

/* 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

enum {
        SIGTERM_IDX = 0,
        SIGINT_IDX,
        SIGQUIT_IDX,

        SIGNALS_IDX_COUNT
};

/*
 * su/runuser control struct
 */
struct su_context {
        pam_handle_t    *pamh;                  /* PAM handler */
        struct pam_conv conv;                   /* PAM conversation */

        struct passwd   *pwd;                   /* new user info */
        char            *pwdbuf;                /* pwd strings */

        const char      *tty_path;              /* tty device path */
        const char      *tty_name;              /* tty_path without /dev prefix */
        const char      *tty_number;            /* end of the tty_path */

        char            *new_user;              /* wanted user */
        char            *old_user;              /* original user */

        pid_t           child;                  /* fork() baby */
        int             childstatus;            /* wait() status */

        char            **env_whitelist_names;  /* environment whitelist */
        char            **env_whitelist_vals;

        struct sigaction oldact[SIGNALS_IDX_COUNT];     /* original sigactions indexed by SIG*_IDX */
#ifdef USE_PTY
        struct ul_pty   *pty;                   /* pseudo terminal handler (for --pty) */
#endif
        unsigned int runuser :1,                /* flase=su, true=runuser */
                     runuser_uopt :1,           /* runuser -u specified */
                     isterm :1,                 /* is stdin terminal? */
                     fast_startup :1,           /* pass the `-f' option to the subshell. */
                     simulate_login :1,         /* simulate a login instead of just starting a shell. */
                     change_environment :1,     /* change some environment vars to indicate the user su'd to.*/
                     same_session :1,           /* don't call setsid() with a command. */
                     suppress_pam_info:1,       /* don't print PAM info messages (Last login, etc.). */
                     pam_has_session :1,        /* PAM session opened */
                     pam_has_cred :1,           /* PAM cred established */
                     force_pty :1,              /* create pseudo-terminal */
                     restricted :1;             /* false for root user */
};


static sig_atomic_t volatile caught_signal = false;

/* Signal handler for parent process.  */
static void
su_catch_sig(int sig)
{
        caught_signal = sig;
}

static void su_init_debug(void)
{
        __UL_INIT_DEBUG_FROM_ENV(su, SU_DEBUG_, 0, SU_DEBUG);
}

static void init_tty(struct su_context *su)
{
        su->isterm = isatty(STDIN_FILENO) ? 1 : 0;
        DBG(TTY, ul_debug("initialize [is-term=%s]", su->isterm ? "true" : "false"));
        if (su->isterm)
                get_terminal_name(&su->tty_path, &su->tty_name, &su->tty_number);
}

/*
 * Note, this function has to be possible call more than once. If the child is
 * already dead than it returns saved result from the previous call.
 */
static int wait_for_child(struct su_context *su)
{
        pid_t pid = (pid_t) -1;
        int status = 0;

        if (su->child == (pid_t) -1)
                return su->childstatus;

        if (su->child != (pid_t) -1) {
                /*
                 * The "su" parent process spends all time here in waitpid(),
                 * but "su --pty" uses pty_proxy_master() and waitpid() is only
                 * called to pick up child status or to react to SIGSTOP.
                 */
                DBG(SIG, ul_debug("waiting for child [%d]...", su->child));
                for (;;) {
                        pid = waitpid(su->child, &status, WUNTRACED);

                        if (pid != (pid_t) - 1 && WIFSTOPPED(status)) {
                                DBG(SIG, ul_debug(" child got SIGSTOP -- stop all session"));
                                kill(getpid(), SIGSTOP);
                                /* once we get here, we must have resumed */
                                kill(pid, SIGCONT);
                                DBG(SIG, ul_debug(" session resumed -- continue"));
#ifdef USE_PTY
                                /* Let's go back to pty_proxy_master() */
                                if (su->force_pty && ul_pty_is_running(su->pty)) {
                                        DBG(SIG, ul_debug(" leaving on child SIGSTOP"));
                                        return 0;
                                }
#endif
                        } else
                                break;
                }
        }
        if (pid != (pid_t) -1) {
                if (WIFSIGNALED(status)) {
                        fprintf(stderr, "%s%s\n",
                                strsignal(WTERMSIG(status)),
                                WCOREDUMP(status) ? _(" (core dumped)")
                                : "");
                        status = WTERMSIG(status) + 128;
                } else
                        status = WEXITSTATUS(status);

                DBG(SIG, ul_debug("child %d is dead", su->child));
                su->child = (pid_t) -1; /* Don't use the PID anymore! */
                su->childstatus = status;
#ifdef USE_PTY
                /* inform pty suff that we have no child anymore */
                if (su->force_pty)
                        ul_pty_set_child(su->pty, (pid_t) -1);
#endif
        } else if (caught_signal)
                status = caught_signal + 128;
        else
                status = 1;

        DBG(SIG, ul_debug("child status=%d", status));
        return status;
}

#ifdef USE_PTY
static void wait_for_child_cb(
                        void *data,
                        pid_t child __attribute__((__unused__)))
{
        wait_for_child((struct su_context *) data);
}

static void chownmod_pty(struct su_context *su)
{
        gid_t gid = su->pwd->pw_gid;
        mode_t mode = (mode_t) getlogindefs_num("TTYPERM", TTY_MODE);
        const char *grname = getlogindefs_str("TTYGROUP", TTYGRPNAME);

        if (grname && *grname) {
                struct group *gr = getgrnam(grname);
                if (gr) /* group by name */
                        gid = gr->gr_gid;
                else    /* group by ID */
                        gid = (gid_t) getlogindefs_num("TTYGROUP", gid);
        }

        if (ul_pty_chownmod_slave(su->pty,
                                  su->pwd->pw_uid,
                                  gid, mode))
                warn(_("change owner or mode for pseudo-terminal failed"));
}
#endif

/* 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_syslog(struct su_context *su, bool successful)
{
        DBG(LOG, ul_debug("syslog logging"));

        openlog(program_invocation_short_name, LOG_PID, LOG_AUTH);
        syslog(LOG_NOTICE, "%s(to %s) %s on %s",
               successful ? "" :
               su->runuser ? "FAILED RUNUSER " : "FAILED SU ",
               su->new_user, su->old_user ? : "",
               su->tty_name ? : "none");
        closelog();
}

/*
 * Log failed login attempts in _PATH_BTMP if that exists.
 */
static void log_btmp(struct su_context *su)
{
        struct utmpx ut;
        struct timeval tv;

        DBG(LOG, ul_debug("btmp logging"));

        memset(&ut, 0, sizeof(ut));
        str2memcpy(ut.ut_user,
                su->pwd && su->pwd->pw_name ? su->pwd->pw_name : "(unknown)",
                sizeof(ut.ut_user));

        if (su->tty_number)
                str2memcpy(ut.ut_id, su->tty_number, sizeof(ut.ut_id));
        if (su->tty_name)
                str2memcpy(ut.ut_line, su->tty_name, sizeof(ut.ut_line));

        gettimeofday(&tv, NULL);
        ut.ut_tv.tv_sec = tv.tv_sec;
        ut.ut_tv.tv_usec = tv.tv_usec;
        ut.ut_type = LOGIN_PROCESS;     /* XXX doesn't matter */
        ut.ut_pid = getpid();

        updwtmpx(_PATH_BTMP, &ut);
}

static int supam_conv(  int num_msg,
                        const struct pam_message **msg,
                        struct pam_response **resp,
                        void *data)
{
        struct su_context *su = (struct su_context *) data;

        if (su->suppress_pam_info
            && num_msg == 1
            && msg && msg[0]->msg_style == PAM_TEXT_INFO)
                return PAM_SUCCESS;

#ifdef HAVE_SECURITY_PAM_MISC_H
        return misc_conv(num_msg, msg, resp, data);
#elif defined(HAVE_SECURITY_OPENPAM_H)
        return openpam_ttyconv(num_msg, msg, resp, data);
#endif
}

static void supam_cleanup(struct su_context *su, int retcode)
{
        const int errsv = errno;

        DBG(PAM, ul_debug("cleanup"));

        if (su->pam_has_session)
                pam_close_session(su->pamh, 0);
        if (su->pam_has_cred)
                pam_setcred(su->pamh, PAM_DELETE_CRED | PAM_SILENT);
        pam_end(su->pamh, retcode);
        errno = errsv;
}


static void supam_export_environment(struct su_context *su)
{
        char **env;

        DBG(PAM, ul_debug("init environ[]"));

        /* This is a copy but don't care to free as we exec later anyways.  */
        env = pam_getenvlist(su->pamh);

        while (env && *env) {
                if (putenv(*env) != 0)
                        err(EXIT_FAILURE, _("failed to modify environment"));
                env++;
        }
}

static void supam_authenticate(struct su_context *su)
{
        const char *srvname = NULL;
        int rc;

        srvname = su->runuser ?
                   (su->simulate_login ? PAM_SRVNAME_RUNUSER_L : PAM_SRVNAME_RUNUSER) :
                   (su->simulate_login ? PAM_SRVNAME_SU_L : PAM_SRVNAME_SU);

        DBG(PAM, ul_debug("start [name: %s]", srvname));

        rc = pam_start(srvname, su->pwd->pw_name, &su->conv, &su->pamh);
        if (is_pam_failure(rc))
                goto done;

        if (su->tty_path) {
                rc = pam_set_item(su->pamh, PAM_TTY, su->tty_path);
                if (is_pam_failure(rc))
                        goto done;
        }
        if (su->old_user) {
                rc = pam_set_item(su->pamh, PAM_RUSER, (const void *) su->old_user);
                if (is_pam_failure(rc))
                        goto done;
        }
        if (su->runuser) {
                /*
                 * This is the only difference between runuser(1) and su(1). The command
                 * runuser(1) does not required authentication, because user is root.
                 */
                if (su->restricted)
                        errx(EXIT_FAILURE, _("may not be used by non-root users"));
                return;
        }

        rc = pam_authenticate(su->pamh, 0);
        if (is_pam_failure(rc))
                goto done;

        /* Check password expiration and offer option to change it.  */
        rc = pam_acct_mgmt(su->pamh, 0);
        if (rc == PAM_NEW_AUTHTOK_REQD)
                rc = pam_chauthtok(su->pamh, PAM_CHANGE_EXPIRED_AUTHTOK);
 done:
        log_syslog(su, !is_pam_failure(rc));

        if (is_pam_failure(rc)) {
                const char *msg;

                DBG(PAM, ul_debug("authentication failed"));
                log_btmp(su);

                msg = pam_strerror(su->pamh, rc);
                pam_end(su->pamh, rc);
                sleep(getlogindefs_num("FAIL_DELAY", 1));
                errx(EXIT_FAILURE, "%s", msg ? msg : _("authentication failed"));
        }
}

static void supam_open_session(struct su_context *su)
{
        int rc;

        DBG(PAM, ul_debug("opening session"));

        rc = pam_open_session(su->pamh, 0);
        if (is_pam_failure(rc)) {
                supam_cleanup(su, rc);
                errx(EXIT_FAILURE, _("cannot open session: %s"),
                     pam_strerror(su->pamh, rc));
        } else
                su->pam_has_session = 1;
}

static void parent_setup_signals(struct su_context *su)
{
        sigset_t ourset;

        /*
         * Signals setup
         *
         * 1) block all signals
         */
        DBG(SIG, ul_debug("initialize signals"));

        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);

                /* 2a) add wanted signals to the mask (for session) */
                if (!su->same_session
                    && (sigaddset(&ourset, SIGINT)
                       || sigaddset(&ourset, SIGQUIT))) {

                        warn(_("cannot initialize signal mask for session"));
                        caught_signal = true;
                }
                /* 2b) add wanted generic signals to the mask */
                if (!caught_signal
                    && (sigaddset(&ourset, SIGTERM)
                       || sigaddset(&ourset, SIGALRM))) {

                        warn(_("cannot initialize signal mask"));
                        caught_signal = true;
                }

                /* 3a) set signal handlers (for session) */
                if (!caught_signal
                    && !su->same_session
                    && (sigaction(SIGINT, &action, &su->oldact[SIGINT_IDX])
                       || sigaction(SIGQUIT, &action, &su->oldact[SIGQUIT_IDX]))) {

                        warn(_("cannot set signal handler for session"));
                        caught_signal = true;
                }

                /* 3b) set signal handlers */
                if (!caught_signal
                     && sigaction(SIGTERM, &action, &su->oldact[SIGTERM_IDX])) {

                        warn(_("cannot set signal handler"));
                        caught_signal = true;
                }

                /* 4) unblock wanted signals */
                if (!caught_signal
                    && sigprocmask(SIG_UNBLOCK, &ourset, NULL)) {

                        warn(_("cannot set signal mask"));
                        caught_signal = true;
                }
        }
}

static void create_watching_parent(struct su_context *su)
{
        struct sigaction action;
        int status;

        DBG(MISC, ul_debug("forking..."));
#ifdef USE_PTY
        if (su->force_pty) {
                struct ul_pty_callbacks *cb;

                /* set callbacks */
                ul_pty_set_callback_data(su->pty, (void *) su);

                cb = ul_pty_get_callbacks(su->pty);
                cb->child_wait    = wait_for_child_cb;
                cb->child_sigstop = wait_for_child_cb;

                ul_pty_slave_echo(su->pty, 1);

                /* create pty */
                if (ul_pty_setup(su->pty))
                        err(EXIT_FAILURE, _("failed to create pseudo-terminal"));
        }
#endif
        fflush(stdout);                 /* ??? */

        /* set default handler for SIGCHLD */
        sigemptyset(&action.sa_mask);
        action.sa_flags = 0;
        action.sa_handler = SIG_DFL;
        if (sigaction(SIGCHLD, &action, NULL)) {
                supam_cleanup(su, PAM_ABORT);
#ifdef USE_PTY
                if (su->force_pty)
                        ul_pty_cleanup(su->pty);
#endif
                err(EXIT_FAILURE, _("cannot set child signal handler"));
        }

        switch ((int) (su->child = fork())) {
        case -1: /* error */
                supam_cleanup(su, PAM_ABORT);
#ifdef USE_PTY
                if (su->force_pty)
                        ul_pty_cleanup(su->pty);
#endif
                err(EXIT_FAILURE, _("cannot create child process"));
                break;

        case 0: /* child */
                return;

        default: /* parent */
                DBG(MISC, ul_debug("child [pid=%d]", (int) su->child));
                break;
        }

        /* free unnecessary stuff */
        free_getlogindefs_data();

        /* 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"), "/");
#ifdef USE_PTY
        if (su->force_pty) {
                ul_pty_set_child(su->pty, su->child);

                ul_pty_proxy_master(su->pty);

                /* ul_pty_proxy_master() keeps classic signal handler are out of game */
                caught_signal = ul_pty_get_delivered_signal(su->pty);

                ul_pty_cleanup(su->pty);
        } else
#endif
                parent_setup_signals(su);

        /*
         * Wait for child
         */
        if (!caught_signal)
                status = wait_for_child(su);
        else
                status = 1;

        DBG(SIG, ul_debug("final child status=%d", status));

        if (caught_signal && su->child != (pid_t)-1) {
                fprintf(stderr, _("\nSession terminated, killing shell..."));
                kill(su->child, SIGTERM);
        }

        supam_cleanup(su, PAM_SUCCESS);

        if (caught_signal) {
                if (su->child != (pid_t)-1) {
                        DBG(SIG, ul_debug("killing child"));
                        sleep(2);
                        kill(su->child, SIGKILL);
                        fprintf(stderr, _(" ...killed.\n"));
                }

                /* Let's terminate itself with the received signal.
                 *
                 * It seems that shells use WIFSIGNALED() rather than our exit status
                 * value to detect situations when is necessary to cleanup (reset)
                 * terminal settings (kzak -- Jun 2013).
                 */
                DBG(SIG, ul_debug("restore signals setting"));
                switch (caught_signal) {
                case SIGTERM:
                        sigaction(SIGTERM, &su->oldact[SIGTERM_IDX], NULL);
                        break;
                case SIGINT:
                        sigaction(SIGINT, &su->oldact[SIGINT_IDX], NULL);
                        break;
                case SIGQUIT:
                        sigaction(SIGQUIT, &su->oldact[SIGQUIT_IDX], NULL);
                        break;
                default:
                        /* just in case that signal stuff initialization failed and
                         * caught_signal = true */
                        caught_signal = SIGKILL;
                        break;
                }
                DBG(SIG, ul_debug("self-send %d signal", caught_signal));
                kill(getpid(), caught_signal);
        }

        DBG(MISC, ul_debug("exiting [rc=%d]", status));
        exit(status);
}

/* Adds @name from the current environment to the whitelist. If @name is not
 * set then nothing is added to the whitelist and returns 1.
 */
static int env_whitelist_add(struct su_context *su, const char *name)
{
        const char *env = getenv(name);

        if (!env)
                return 1;
        if (strv_extend(&su->env_whitelist_names, name))
                err_oom();
        if (strv_extend(&su->env_whitelist_vals, env))
                err_oom();
        return 0;
}

static int env_whitelist_setenv(struct su_context *su, int overwrite)
{
        char **one;
        size_t i = 0;
        int rc;

        STRV_FOREACH(one, su->env_whitelist_names) {
                rc = setenv(*one, su->env_whitelist_vals[i], overwrite);
                if (rc)
                        return rc;
                i++;
        }

        return 0;
}

/* Creates (add to) whitelist from comma delimited string */
static int env_whitelist_from_string(struct su_context *su, const char *str)
{
        char **all = strv_split(str, ",");
        char **one;

        if (!all) {
                if (errno == ENOMEM)
                        err_oom();
                return -EINVAL;
        }

        STRV_FOREACH(one, all)
                env_whitelist_add(su, *one);
        strv_free(all);
        return 0;
}

static void setenv_path(const struct passwd *pw)
{
        int rc;

        DBG(MISC, ul_debug("setting PATH"));

        if (pw->pw_uid)
                rc = logindefs_setenv("PATH", "ENV_PATH", _PATH_DEFPATH);

        else if ((rc = logindefs_setenv("PATH", "ENV_SUPATH", NULL)) != 0)
                rc = logindefs_setenv("PATH", "ENV_ROOTPATH", _PATH_DEFPATH_ROOT);

        if (rc)
                err(EXIT_FAILURE, _("failed to set the PATH environment variable"));
}

static void modify_environment(struct su_context *su, const char *shell)
{
        const struct passwd *pw = su->pwd;


        DBG(MISC, ul_debug("modify environ[]"));

        /* Leave TERM unchanged.  Set HOME, SHELL, USER, LOGNAME, PATH.
         *
         * Unset all other environment variables, but follow
         * --whitelist-environment if specified.
         */
        if (su->simulate_login) {
                /* leave TERM unchanged */
                env_whitelist_add(su, "TERM");

                /* Note that original su(1) has allocated environ[] by malloc
                 * to the number of expected variables. This seems unnecessary
                 * optimization as libc later re-alloc(current_size+2) and for
                 * empty environ[] the curren_size is zero. It seems better to
                 * keep all logic around environment in glibc's hands.
                 *                                           --kzak [Aug 2018]
                 */
#ifdef HAVE_CLEARENV
                clearenv();
#else
                environ = NULL;
#endif
                /* always reset */
                if (shell)
                        xsetenv("SHELL", shell, 1);

                setenv_path(pw);

                xsetenv("HOME", pw->pw_dir, 1);
                xsetenv("USER", pw->pw_name, 1);
                xsetenv("LOGNAME", pw->pw_name, 1);

                /* apply all from whitelist, but no overwrite */
                env_whitelist_setenv(su, 0);

        /* Set HOME, SHELL, and (if not becoming a superuser) USER and LOGNAME.
         */
        } else if (su->change_environment) {
                xsetenv("HOME", pw->pw_dir, 1);
                if (shell)
                        xsetenv("SHELL", shell, 1);

                if (getlogindefs_bool("ALWAYS_SET_PATH", 0))
                        setenv_path(pw);

                if (pw->pw_uid) {
                        xsetenv("USER", pw->pw_name, 1);
                        xsetenv("LOGNAME", pw->pw_name, 1);
                }
        }

        supam_export_environment(su);
}

static void init_groups(struct su_context *su, gid_t *groups, size_t ngroups)
{
        int rc;

        DBG(MISC, ul_debug("initialize groups"));

        errno = 0;
        if (ngroups)
                rc = setgroups(ngroups, groups);
        else
                rc = initgroups(su->pwd->pw_name, su->pwd->pw_gid);

        if (rc == -1) {
                supam_cleanup(su, PAM_ABORT);
                err(EXIT_FAILURE, _("cannot set groups"));
        }
        endgrent();

        rc = pam_setcred(su->pamh, PAM_ESTABLISH_CRED);
        if (is_pam_failure(rc))
                errx(EXIT_FAILURE, _("failed to establish user credentials: %s"),
                                        pam_strerror(su->pamh, rc));
        su->pam_has_cred = 1;
}

static void change_identity(const struct passwd *pw)
{
        DBG(MISC, ul_debug("changing identity [GID=%d, UID=%d]", pw->pw_gid, pw->pw_uid));

        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, 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(
                struct su_context *su,
                char const *shell, char const *command, char **additional_args,
                size_t n_additional_args)
{
        size_t n_args = 1 + su->fast_startup + 2 * ! !command + n_additional_args + 1;
        const char **args = xcalloc(n_args, sizeof *args);
        size_t argno = 1;

        DBG(MISC, ul_debug("starting shell [shell=%s, command=\"%s\"%s%s]",
                                shell, command,
                                su->simulate_login ? " login" : "",
                                su->fast_startup ? " fast-start" : ""));

        if (su->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 (su->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);
        errexec(shell);
}

/* Return true if SHELL is a restricted shell (one not returned by
 * getusershell), else false, meaning it is a standard shell.
 */
static bool is_restricted_shell(const char *shell)
{
        char *line;

        setusershell();
        while ((line = getusershell()) != NULL) {
                if (*line != '#' && !strcmp(line, shell)) {
                        endusershell();
                        return false;
                }
        }
        endusershell();

        DBG(MISC, ul_debug("%s is restricted shell (not in /etc/shells)", shell));
        return true;
}

static void usage_common(void)
{
        fputs(_(" -m, -p, --preserve-environment      do not reset environment variables\n"), stdout);
        fputs(_(" -w, --whitelist-environment <list>  don't reset specified variables\n"), stdout);
        fputs(USAGE_SEPARATOR, stdout);

        fputs(_(" -g, --group <group>             specify the primary group\n"), stdout);
        fputs(_(" -G, --supp-group <group>        specify a supplemental group\n"), stdout);
        fputs(USAGE_SEPARATOR, stdout);

        fputs(_(" -, -l, --login                  make the shell a login shell\n"), stdout);
        fputs(_(" -c, --command <command>         pass a single command to the shell with -c\n"), stdout);
        fputs(_(" --session-command <command>     pass a single command to the shell with -c\n"
                "                                   and do not create a new session\n"), stdout);
        fputs(_(" -f, --fast                      pass -f to the shell (for csh or tcsh)\n"), stdout);
        fputs(_(" -s, --shell <shell>             run <shell> if /etc/shells allows it\n"), stdout);
        fputs(_(" -P, --pty                       create a new pseudo-terminal\n"), stdout);

        fputs(USAGE_SEPARATOR, stdout);
        printf(USAGE_HELP_OPTIONS(33));
}

static void usage_runuser(void)
{
        fputs(USAGE_HEADER, stdout);
        fprintf(stdout,
                _(" %1$s [options] -u <user> [[--] <command>]\n"
                  " %1$s [options] [-] [<user> [<argument>...]]\n"),
                program_invocation_short_name);

        fputs(USAGE_SEPARATOR, stdout);
        fputs(_("Run <command> with the effective user ID and group ID of <user>.  If -u is\n"
               "not given, fall back to su(1)-compatible semantics and execute standard shell.\n"
               "The options -c, -f, -l, and -s are mutually exclusive with -u.\n"), stdout);

        fputs(USAGE_OPTIONS, stdout);
        fputs(_(" -u, --user <user>               username\n"), stdout);
        usage_common();
        fputs(USAGE_SEPARATOR, stdout);

        fprintf(stdout, USAGE_MAN_TAIL("runuser(1)"));
}

static void usage_su(void)
{
        fputs(USAGE_HEADER, stdout);
        fprintf(stdout,
                _(" %s [options] [-] [<user> [<argument>...]]\n"),
                program_invocation_short_name);

        fputs(USAGE_SEPARATOR, stdout);
        fputs(_("Change the effective user ID and group ID to that of <user>.\n"
                "A mere - implies -l.  If <user> is not given, root is assumed.\n"), stdout);

        fputs(USAGE_OPTIONS, stdout);
        usage_common();

        fprintf(stdout, USAGE_MAN_TAIL("su(1)"));
}

static void __attribute__((__noreturn__)) usage(int mode)
{
        if (mode == SU_MODE)
                usage_su();
        else
                usage_runuser();

        exit(EXIT_SUCCESS);
}

static void load_config(void *data)
{
        struct su_context *su = (struct su_context *) data;

        DBG(MISC, ul_debug("loading logindefs"));
#ifndef HAVE_LIBECONF
        logindefs_load_file(_PATH_LOGINDEFS);
#endif
        logindefs_load_file(su->runuser ? _PATH_LOGINDEFS_RUNUSER : _PATH_LOGINDEFS_SU);
}

/*
 * Returns 1 if the current user is not root
 */
static int is_not_root(void)
{
        const uid_t ruid = getuid();
        const uid_t euid = geteuid();

        /* if we're really root and aren't running setuid */
        return (uid_t) 0 == ruid && ruid == euid ? 0 : 1;
}

/* Don't rely on PAM and reset the most important limits. */
static void sanitize_prlimits(void)
{
#ifdef HAVE_SYS_RESOURCE_H
        struct rlimit lm = { .rlim_cur = 0, .rlim_max = 0 };

        /* reset to zero */
#ifdef RLIMIT_NICE
        setrlimit(RLIMIT_NICE, &lm);
#endif
#ifdef RLIMIT_RTPRIO
        setrlimit(RLIMIT_RTPRIO, &lm);
#endif

        /* reset to unlimited */
        lm.rlim_cur = RLIM_INFINITY;
        lm.rlim_max = RLIM_INFINITY;
        setrlimit(RLIMIT_FSIZE, &lm);
        setrlimit(RLIMIT_AS, &lm);

        /* reset soft limit only */
        getrlimit(RLIMIT_NOFILE, &lm);
        if (lm.rlim_cur != FD_SETSIZE) {
                lm.rlim_cur = FD_SETSIZE;
                setrlimit(RLIMIT_NOFILE, &lm);
        }
#endif
}

static gid_t add_supp_group(const char *name, gid_t **groups, size_t *ngroups)
{
        struct group *gr;

        if (*ngroups >= NGROUPS_MAX)
                errx(EXIT_FAILURE,
                     P_("specifying more than %d supplemental group is not possible",
                        "specifying more than %d supplemental groups is not possible",
                        NGROUPS_MAX - 1), NGROUPS_MAX - 1);

        gr = getgrnam(name);
        if (!gr)
                errx(EXIT_FAILURE, _("group %s does not exist"), name);

        DBG(MISC, ul_debug("add %s group [name=%s, GID=%d]", name, gr->gr_name, (int) gr->gr_gid));

        *groups = xrealloc(*groups, sizeof(gid_t) * (*ngroups + 1));
        (*groups)[*ngroups] = gr->gr_gid;
        (*ngroups)++;

        return gr->gr_gid;
}

int su_main(int argc, char **argv, int mode)
{
        struct su_context _su = {
                .conv                   = { supam_conv, NULL },
                .runuser                = (mode == RUNUSER_MODE ? 1 : 0),
                .change_environment     = 1,
                .new_user               = DEFAULT_USER
        }, *su = &_su;

        int optc;
        char *command = NULL;
        int request_same_session = 0;
        char *shell = NULL;

        gid_t *groups = NULL;
        size_t ngroups = 0;
        bool use_supp = false;
        bool use_gid = false;
        gid_t gid = 0;

        static const struct option 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'},
                {"pty", no_argument, NULL, 'P'},
                {"shell", required_argument, NULL, 's'},
                {"group", required_argument, NULL, 'g'},
                {"supp-group", required_argument, NULL, 'G'},
                {"user", required_argument, NULL, 'u'}, /* runuser only */
                {"whitelist-environment", required_argument, NULL, 'w'},
                {"help", no_argument, 0, 'h'},
                {"version", no_argument, 0, 'V'},
                {NULL, 0, NULL, 0}
        };
        static const ul_excl_t excl[] = {       /* rows and cols in ASCII order */
                { 'm', 'w' },                   /* preserve-environment, whitelist-environment */
                { 'p', 'w' },                   /* preserve-environment, whitelist-environment */
                { 0 }
        };
        int excl_st[ARRAY_SIZE(excl)] = UL_EXCL_STATUS_INIT;

        setlocale(LC_ALL, "");
        bindtextdomain(PACKAGE, LOCALEDIR);
        textdomain(PACKAGE);
        close_stdout_atexit();

        su_init_debug();
        su->conv.appdata_ptr = (void *) su;

        while ((optc =
                getopt_long(argc, argv, "c:fg:G:lmpPs:u:hVw:", longopts,
                            NULL)) != -1) {

                err_exclusive_options(optc, longopts, excl, excl_st);

                switch (optc) {
                case 'c':
                        command = optarg;
                        break;

                case 'C':
                        command = optarg;
                        request_same_session = 1;
                        break;

                case 'f':
                        su->fast_startup = true;
                        break;

                case 'g':
                        use_gid = true;
                        gid = add_supp_group(optarg, &groups, &ngroups);
                        break;

                case 'G':
                        use_supp = true;
                        add_supp_group(optarg, &groups, &ngroups);
                        break;

                case 'l':
                        su->simulate_login = true;
                        break;

                case 'm':
                case 'p':
                        su->change_environment = false;
                        break;

                case 'w':
                        env_whitelist_from_string(su, optarg);
                        break;

                case 'P':
#ifdef USE_PTY
                        su->force_pty = 1;
#else
                        errx(EXIT_FAILURE, _("--pty is not supported for your system"));
#endif
                        break;

                case 's':
                        shell = optarg;
                        break;

                case 'u':
                        if (!su->runuser)
                                errtryhelp(EXIT_FAILURE);
                        su->runuser_uopt = 1;
                        su->new_user = optarg;
                        break;

                case 'h':
                        usage(mode);

                case 'V':
                        print_version(EXIT_SUCCESS);
                default:
                        errtryhelp(EXIT_FAILURE);
                }
        }

        su->restricted = is_not_root();

        if (optind < argc && !strcmp(argv[optind], "-")) {
                su->simulate_login = true;
                ++optind;
        }

        if (su->simulate_login && !su->change_environment) {
                warnx(_
                      ("ignoring --preserve-environment, it's mutually exclusive with --login"));
                su->change_environment = true;
        }

        switch (mode) {
        case RUNUSER_MODE:
                /* runuser -u <user> <command>
                 *
                 * If -u <user> is not specified, then follow traditional su(1) behavior and
                 * fallthrough
                 */
                if (su->runuser_uopt) {
                        if (shell || su->fast_startup || command || su->simulate_login)
                                errx(EXIT_FAILURE,
                                     _("options --{shell,fast,command,session-command,login} and "
                                      "--user are mutually exclusive"));
                        if (optind == argc)
                                errx(EXIT_FAILURE, _("no command was specified"));
                        break;
                }
                /* fallthrough */
        case SU_MODE:
                if (optind < argc)
                        su->new_user = argv[optind++];
                break;
        }

        if ((use_supp || use_gid) && su->restricted)
                errx(EXIT_FAILURE,
                     _("only root can specify alternative groups"));

        logindefs_set_loader(load_config, (void *) su);
        init_tty(su);

        su->pwd = xgetpwnam(su->new_user, &su->pwdbuf);
        if (!su->pwd
            || !su->pwd->pw_passwd
            || !su->pwd->pw_name || !*su->pwd->pw_name
            || !su->pwd->pw_dir  || !*su->pwd->pw_dir)
                errx(EXIT_FAILURE,
                     _("user %s does not exist or the user entry does not "
                       "contain all the required fields"), su->new_user);

        su->new_user = su->pwd->pw_name;
        su->old_user = xgetlogin();

        if (!su->pwd->pw_shell || !*su->pwd->pw_shell)
                su->pwd->pw_shell = DEFAULT_SHELL;

        if (use_supp && !use_gid)
                su->pwd->pw_gid = groups[0];
        else if (use_gid)
                su->pwd->pw_gid = gid;

        supam_authenticate(su);

        if (request_same_session || !command || !su->pwd->pw_uid)
                su->same_session = 1;

        /* initialize shell variable only if "-u <user>" not specified */
        if (su->runuser_uopt) {
                shell = NULL;
        } else {
                if (!shell && !su->change_environment)
                        shell = getenv("SHELL");

                if (shell
                    && strcmp(shell, su->pwd->pw_shell) != 0
                    && getuid() != 0
                    && is_restricted_shell(su->pwd->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"), su->pwd->pw_shell);
                        shell = NULL;
                }
                shell = xstrdup(shell ? shell : su->pwd->pw_shell);
        }

        init_groups(su, groups, ngroups);

        if (!su->simulate_login || command)
                su->suppress_pam_info = 1;      /* don't print PAM info messages */

        sanitize_prlimits();

        supam_open_session(su);

#ifdef USE_PTY
        if (su->force_pty) {
                ON_DBG(PTY, ul_pty_init_debug(0xffff));

                su->pty = ul_new_pty(su->isterm);
                if (!su->pty)
                        err(EXIT_FAILURE, _("failed to allocate pty handler"));
        }
#endif
        create_watching_parent(su);
        /* Now we're in the child.  */

#ifdef USE_PTY
        if (su->force_pty)
                chownmod_pty(su);
#endif
        change_identity(su->pwd);
        if (!su->same_session) {
                /* note that on --pty we call setsid() in ul_pty_init_slave() */
                DBG(MISC, ul_debug("call setsid()"));
                setsid();
        }
#ifdef USE_PTY
        if (su->force_pty)
                ul_pty_init_slave(su->pty);
#endif
        /* Set environment after pam_open_session, which may put KRB5CCNAME
           into the pam_env, etc.  */

        modify_environment(su, shell);

        if (su->simulate_login && chdir(su->pwd->pw_dir) != 0)
                warn(_("warning: cannot change directory to %s"), su->pwd->pw_dir);

        /* http://www.linux-pam.org/Linux-PAM-html/adg-interface-by-app-expected.html#adg-pam_end */
        (void) pam_end(su->pamh, PAM_SUCCESS|PAM_DATA_SILENT);

        if (shell)
                run_shell(su, shell, command, argv + optind, max(0, argc - optind));

        execvp(argv[optind], &argv[optind]);
        err(EXIT_FAILURE, _("failed to execute %s"), argv[optind]);
}