include: rename writeall.h to all-io.h

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

/*
 * login(1)
 *
 * This program is derived from 4.3 BSD software and is subject to the
 * copyright notice below.
 *
 * Copyright (C) 2011 Karel Zak <kzak@redhat.com>
 * Rewritten to PAM-only version.
 *
 * Michael Glad (glad@daimi.dk)
 * Computer Science Department, Aarhus University, Denmark
 * 1990-07-04
 *
 * Copyright (c) 1980, 1987, 1988 The Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */
#include <sys/param.h>
#include <stdio.h>
#include <ctype.h>
#include <unistd.h>
#include <getopt.h>
#include <memory.h>
#include <time.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/file.h>
#include <termios.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/wait.h>
#include <signal.h>
#include <errno.h>
#include <grp.h>
#include <pwd.h>
#include <utmp.h>
#include <stdlib.h>
#include <sys/syslog.h>
#include <sys/sysmacros.h>
#include <linux/major.h>
#include <netdb.h>
#include <lastlog.h>
#include <security/pam_appl.h>
#include <security/pam_misc.h>
#include <sys/sendfile.h>

#ifdef HAVE_LIBAUDIT
# include <libaudit.h>
#endif

#include "c.h"
#include "setproctitle.h"
#include "pathnames.h"
#include "strutils.h"
#include "nls.h"
#include "xalloc.h"
#include "all-io.h"
#include "fileutils.h"

#include "logindefs.h"

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

#define LOGIN_MAX_TRIES        3
#define LOGIN_EXIT_TIMEOUT     5
#define LOGIN_TIMEOUT          60

#ifdef USE_TTY_GROUP
# define TTY_MODE 0620
#else
# define TTY_MODE 0600
#endif

#define TTYGRPNAME      "tty"   /* name of group to own ttys */
#define VCS_PATH_MAX    64

/*
 * Login control struct
 */
struct login_context {
        const char      *tty_path;      /* ttyname() return value */
        const char      *tty_name;      /* tty_path without /dev prefix */
        const char      *tty_number;    /* end of the tty_path */
        mode_t          tty_mode;       /* chmod() mode */

        char            *username;      /* from command line or PAM */

        struct passwd   *pwd;           /* user info */

        pam_handle_t    *pamh;          /* PAM handler */
        struct pam_conv conv;           /* PAM conversation */

#ifdef LOGIN_CHOWN_VCS
        char            vcsn[VCS_PATH_MAX];     /* virtual console name */
        char            vcsan[VCS_PATH_MAX];
#endif

        char            thishost[MAXHOSTNAMELEN + 1];   /* this machine */
        char            *thisdomain;                    /* this machine domain */
        char            *hostname;                      /* remote machine */
        char            hostaddress[16];                /* remote address */

        pid_t           pid;
        int             quiet;          /* 1 is hush file exists */

        unsigned int    remote:1,       /* login -h */
                        nohost:1,       /* login -H */
                        noauth:1,       /* login -f */
                        keep_env:1;     /* login -p */
};

/*
 * This bounds the time given to login.  Not a define so it can
 * be patched on machines where it's too small.
 */
static int timeout = LOGIN_TIMEOUT;
static int child_pid = 0;
static volatile int got_sig = 0;

#ifdef LOGIN_CHOWN_VCS
/* true if the filedescriptor fd is a console tty, very Linux specific */
static int is_consoletty(int fd)
{
        struct stat stb;

        if ((fstat(fd, &stb) >= 0)
            && (major(stb.st_rdev) == TTY_MAJOR)
            && (minor(stb.st_rdev) < 64)) {
                return 1;
        }
        return 0;
}
#endif


/*
 * Robert Ambrose writes:
 * A couple of my users have a problem with login processes hanging around
 * soaking up pts's.  What they seem to hung up on is trying to write out the
 * message 'Login timed out after %d seconds' when the connection has already
 * been dropped.
 * What I did was add a second timeout while trying to write the message so
 * the process just exits if the second timeout expires.
 */
static void __attribute__ ((__noreturn__))
timedout2(int sig __attribute__ ((__unused__)))
{
        struct termios ti;

        /* reset echo */
        tcgetattr(0, &ti);
        ti.c_lflag |= ECHO;
        tcsetattr(0, TCSANOW, &ti);
        exit(EXIT_SUCCESS);     /* %% */
}

static void timedout(int sig __attribute__ ((__unused__)))
{
        signal(SIGALRM, timedout2);
        alarm(10);
        /* TRANSLATORS: The standard value for %d is 60. */
        warnx(_("timed out after %d seconds"), timeout);
        signal(SIGALRM, SIG_IGN);
        alarm(0);
        timedout2(0);
}

/*
 * This handler allows to inform a shell about signals to login. If you have
 * (root) permissions you can kill all login childrent by one signal to login
 * process.
 *
 * Also, parent who is session leader is able (before setsid() in child) to
 * inform child when controlling tty goes away (e.g. modem hangup, SIGHUP).
 */
static void sig_handler(int signal)
{
        if (child_pid)
                kill(-child_pid, signal);
        else
                got_sig = 1;
        if (signal == SIGTERM)
                kill(-child_pid, SIGHUP);       /* because the shell often ignores SIGTERM */
}

/*
 * Let use delay for all exit() calls when user is not authenticated or
 * session fully initialized (loginpam_session()).
 */
static void __attribute__ ((__noreturn__)) sleepexit(int eval)
{
        sleep(getlogindefs_num("FAIL_DELAY", LOGIN_EXIT_TIMEOUT));
        exit(eval);
}

static const char *get_thishost(struct login_context *cxt, const char **domain)
{
        if (!*cxt->thishost) {
                if (gethostname(cxt->thishost, sizeof(cxt->thishost))) {
                        if (domain)
                                *domain = NULL;
                        return NULL;
                }
                cxt->thishost[sizeof(cxt->thishost) -1] = '\0';
                cxt->thisdomain = strchr(cxt->thishost, '.');
                if (cxt->thisdomain)
                        *cxt->thisdomain++ = '\0';
        }

        if (domain)
                *domain = cxt->thisdomain;
        return cxt->thishost;
}

/*
 * Output the /etc/motd file
 *
 * motd() determines the name of a login announcement file and outputs it to
 * the user's terminal at login time.  The MOTD_FILE configuration option is a
 * colon-delimited list of filenames. The empty MOTD_FILE option disables motd
 * printing at all.
 */
static void motd(void)
{
        char *motdlist, *motdfile;
        const char *mb;

        mb = getlogindefs_str("MOTD_FILE", _PATH_MOTDFILE);
        if (!mb || !*mb)
                return;

        motdlist = xstrdup(mb);

        for (motdfile = strtok(motdlist, ":"); motdfile;
             motdfile = strtok(NULL, ":")) {

                struct stat st;
                int fd;

                if (stat(motdfile, &st) || !st.st_size)
                        continue;
                fd = open(motdfile, O_RDONLY, 0);
                if (fd < 0)
                        continue;

                sendfile(fileno(stdout), fd, NULL, st.st_size);
                close(fd);
        }

        free(motdlist);
}

/*
 * Nice and simple code provided by Linus Torvalds 16-Feb-93
 * Nonblocking stuff by Maciej W. Rozycki, macro@ds2.pg.gda.pl, 1999.
 *
 * He writes: "Login performs open() on a tty in a blocking mode.
 * In some cases it may make login wait in open() for carrier infinitely,
 * for example if the line is a simplistic case of a three-wire serial
 * connection. I believe login should open the line in the non-blocking mode
 * leaving the decision to make a connection to getty (where it actually
 * belongs).
 */
static void open_tty(const char *tty)
{
        int i, fd, flags;

        fd = open(tty, O_RDWR | O_NONBLOCK);
        if (fd == -1) {
                syslog(LOG_ERR, _("FATAL: can't reopen tty: %m"));
                sleepexit(EXIT_FAILURE);
        }

        if (!isatty(fd)) {
                close(fd);
                syslog(LOG_ERR, _("FATAL: %s is not a terminal"), tty);
                sleepexit(EXIT_FAILURE);
        }

        flags = fcntl(fd, F_GETFL);
        flags &= ~O_NONBLOCK;
        fcntl(fd, F_SETFL, flags);

        for (i = 0; i < fd; i++)
                close(i);
        for (i = 0; i < 3; i++)
                if (fd != i)
                        dup2(fd, i);
        if (fd >= 3)
                close(fd);
}

#define chown_err(_what, _uid, _gid) \
                syslog(LOG_ERR, _("chown (%s, %lu, %lu) failed: %m"), \
                        (_what), (unsigned long) (_uid), (unsigned long) (_gid))

#define chmod_err(_what, _mode) \
                syslog(LOG_ERR, _("chmod (%s, %u) failed: %m"), (_what), (_mode))

static void chown_tty(struct login_context *cxt)
{
        const char *grname;
        uid_t uid = cxt->pwd->pw_uid;
        gid_t gid = cxt->pwd->pw_gid;

        grname = getlogindefs_str("TTYGROUP", TTYGRPNAME);
        if (grname && *grname) {
                if (*grname >= 0 && *grname <= 9)               /* group by ID */
                        gid = getlogindefs_num("TTYGROUP", gid);
                else {                                          /* group by name */
                        struct group *gr = getgrnam(grname);
                        if (gr)
                                gid = gr->gr_gid;
                }
        }

        if (fchown(0, uid, gid))                                /* tty */
                chown_err(cxt->tty_name, uid, gid);
        if (fchmod(0, cxt->tty_mode))
                chmod_err(cxt->tty_name, cxt->tty_mode);

#ifdef LOGIN_CHOWN_VCS
        if (is_consoletty(0)) {
                if (chown(cxt->vcsn, uid, gid))                 /* vcs */
                        chown_err(cxt->vcsn, uid, gid);
                if (chmod(cxt->vcsn, cxt->tty_mode))
                        chmod_err(cxt->vcsn, cxt->tty_mode);

                if (chown(cxt->vcsan, uid, gid))                        /* vcsa */
                        chown_err(cxt->vcsan, uid, gid);
                if (chmod(cxt->vcsan, cxt->tty_mode))
                        chmod_err(cxt->vcsan, cxt->tty_mode);
        }
#endif
}

/*
 * Reads the currect terminal path and initialize cxt->tty_* variables.
 */
static void init_tty(struct login_context *cxt)
{
        const char *p;
        struct stat st;
        struct termios tt, ttt;

        cxt->tty_mode = (mode_t) getlogindefs_num("TTYPERM", TTY_MODE);

        cxt->tty_path = ttyname(0);             /* libc calls istty() here */

        /*
         * In case login is suid it was possible to use a hardlink as stdin
         * and exploit races for a local root exploit. (Wojciech Purczynski).
         *
         * More precisely, the problem is  ttyn := ttyname(0); ...; chown(ttyn);
         * here ttyname() might return "/tmp/x", a hardlink to a pseudotty.
         * All of this is a problem only when login is suid, which it isnt.
         */
        if (!cxt->tty_path || !*cxt->tty_path ||
            lstat(cxt->tty_path, &st) != 0 || !S_ISCHR(st.st_mode) ||
            (st.st_nlink > 1 && strncmp(cxt->tty_path, "/dev/", 5)) ||
            access(cxt->tty_path, R_OK | W_OK) != 0) {

                syslog(LOG_ERR, _("FATAL: bad tty"));
                sleepexit(EXIT_FAILURE);
        }

        if (strncmp(cxt->tty_path, "/dev/", 5) == 0)
                cxt->tty_name = cxt->tty_path + 5;
        else
                cxt->tty_name = cxt->tty_path;

        for (p = cxt->tty_name; p && *p; p++) {
                if (isdigit(*p)) {
                        cxt->tty_number = p;
                        break;
                }
        }

#ifdef LOGIN_CHOWN_VCS
        /* find names of Virtual Console devices, for later mode change */
        snprintf(cxt->vcsn, sizeof(cxt->vcsn), "/dev/vcs%s", cxt->tty_number);
        snprintf(cxt->vcsan, sizeof(cxt->vcsan), "/dev/vcsa%s", cxt->tty_number);
#endif

        tcgetattr(0, &tt);
        ttt = tt;
        ttt.c_cflag &= ~HUPCL;

        if ((fchown(0, 0, 0) || fchmod(0, cxt->tty_mode)) && errno != EROFS) {

                syslog(LOG_ERR, _("FATAL: %s: change permissions failed: %m"),
                                cxt->tty_path);
                sleepexit(EXIT_FAILURE);
        }

        /* Kill processes left on this tty */
        tcsetattr(0, TCSAFLUSH, &ttt);

        signal(SIGHUP, SIG_IGN);        /* so vhangup() wont kill us */
        vhangup();
        signal(SIGHUP, SIG_DFL);

        /* open stdin,stdout,stderr to the tty */
        open_tty(cxt->tty_path);

        /* restore tty modes */
        tcsetattr(0, TCSAFLUSH, &tt);
}


/*
 * Log failed login attempts in _PATH_BTMP if that exists.
 * Must be called only with username the name of an actual user.
 * The most common login failure is to give password instead of username.
 */
static void log_btmp(struct login_context *cxt)
{
        struct utmp ut;
        struct timeval tv;

        memset(&ut, 0, sizeof(ut));

        strncpy(ut.ut_user,
                cxt->username ? cxt->username : "(unknown)",
                sizeof(ut.ut_user));

        if (cxt->tty_number)
                strncpy(ut.ut_id, cxt->tty_number, sizeof(ut.ut_id));
        if (cxt->tty_name)
                xstrncpy(ut.ut_line, cxt->tty_name, sizeof(ut.ut_line));

#if defined(_HAVE_UT_TV)        /* in <utmpbits.h> included by <utmp.h> */
        gettimeofday(&tv, NULL);
        ut.ut_tv.tv_sec = tv.tv_sec;
        ut.ut_tv.tv_usec = tv.tv_usec;
#else
        {
                time_t t;
                time(&t);
                ut.ut_time = t; /* ut_time is not always a time_t */
        }
#endif

        ut.ut_type = LOGIN_PROCESS;     /* XXX doesn't matter */
        ut.ut_pid = cxt->pid;

        if (cxt->hostname) {
                xstrncpy(ut.ut_host, cxt->hostname, sizeof(ut.ut_host));
                if (*cxt->hostaddress)
                        memcpy(&ut.ut_addr_v6, cxt->hostaddress,
                               sizeof(ut.ut_addr_v6));
        }

        updwtmp(_PATH_BTMP, &ut);
}


#ifdef HAVE_LIBAUDIT
static void log_audit(struct login_context *cxt, int status)
{
        int audit_fd;
        struct passwd *pwd = cxt->pwd;

        audit_fd = audit_open();
        if (audit_fd == -1)
                return;
        if (!pwd && cxt->username)
                pwd = getpwnam(cxt->username);

        audit_log_acct_message(audit_fd,
                               AUDIT_USER_LOGIN,
                               NULL,
                               "login",
                               cxt->username ? cxt->username : "(unknown)",
                               pwd ? pwd->pw_uid : (unsigned int) -1,
                               cxt->hostname,
                               NULL,
                               cxt->tty_name,
                               status);

        close(audit_fd);
}
#else                           /* !HAVE_LIBAUDIT */
# define log_audit(cxt, status)
#endif                          /* HAVE_LIBAUDIT */

static void log_lastlog(struct login_context *cxt)
{
        struct lastlog ll;
        time_t t;
        int fd;

        if (!cxt->pwd)
                return;

        fd = open(_PATH_LASTLOG, O_RDWR, 0);
        if (fd < 0)
                return;

        lseek(fd, (off_t) cxt->pwd->pw_uid * sizeof(ll), SEEK_SET);

        /*
         * Print last log message
         */
        if (!cxt->quiet) {
                if (read(fd, (char *)&ll, sizeof(ll)) == sizeof(ll) &&
                                                        ll.ll_time != 0) {
                        time_t ll_time = (time_t) ll.ll_time;

                        printf(_("Last login: %.*s "), 24 - 5, ctime(&ll_time));
                        if (*ll.ll_host != '\0')
                                printf(_("from %.*s\n"),
                                       (int)sizeof(ll.ll_host), ll.ll_host);
                        else
                                printf(_("on %.*s\n"),
                                       (int)sizeof(ll.ll_line), ll.ll_line);
                }
                lseek(fd, (off_t) cxt->pwd->pw_uid * sizeof(ll), SEEK_SET);
        }

        memset((char *)&ll, 0, sizeof(ll));

        time(&t);
        ll.ll_time = t;         /* ll_time is always 32bit */

        if (cxt->tty_name)
                xstrncpy(ll.ll_line, cxt->tty_name, sizeof(ll.ll_line));
        if (cxt->hostname)
                xstrncpy(ll.ll_host, cxt->hostname, sizeof(ll.ll_host));

        if (write_all(fd, (char *)&ll, sizeof(ll)))
                warn(_("write lastlog failed"));

        close(fd);
}

/*
 * Update wtmp and utmp logs
 */
static void log_utmp(struct login_context *cxt)
{
        struct utmp ut;
        struct utmp *utp;
        struct timeval tv;

        utmpname(_PATH_UTMP);
        setutent();

        /* Find pid in utmp.
         *
         * login sometimes overwrites the runlevel entry in /var/run/utmp,
         * confusing sysvinit. I added a test for the entry type, and the
         * problem was gone. (In a runlevel entry, st_pid is not really a pid
         * but some number calculated from the previous and current runlevel).
         * -- Michael Riepe <michael@stud.uni-hannover.de>
         */
        while ((utp = getutent()))
                if (utp->ut_pid == cxt->pid
                    && utp->ut_type >= INIT_PROCESS
                    && utp->ut_type <= DEAD_PROCESS)
                        break;

        /* If we can't find a pre-existing entry by pid, try by line.
         * BSD network daemons may rely on this.
         */
        if (utp == NULL) {
                setutent();
                ut.ut_type = LOGIN_PROCESS;
                strncpy(ut.ut_line, cxt->tty_name, sizeof(ut.ut_line));
                utp = getutline(&ut);
        }

        if (utp)
                memcpy(&ut, utp, sizeof(ut));
        else
                /* some gettys/telnetds don't initialize utmp... */
                memset(&ut, 0, sizeof(ut));

        if (ut.ut_id[0] == 0)
                strncpy(ut.ut_id, cxt->tty_number, sizeof(ut.ut_id));

        strncpy(ut.ut_user, cxt->username, sizeof(ut.ut_user));
        xstrncpy(ut.ut_line, cxt->tty_name, sizeof(ut.ut_line));

#ifdef _HAVE_UT_TV              /* in <utmpbits.h> included by <utmp.h> */
        gettimeofday(&tv, NULL);
        ut.ut_tv.tv_sec = tv.tv_sec;
        ut.ut_tv.tv_usec = tv.tv_usec;
#else
        {
                time_t t;
                time(&t);
                ut.ut_time = t; /* ut_time is not always a time_t */
                                /* glibc2 #defines it as ut_tv.tv_sec */
        }
#endif
        ut.ut_type = USER_PROCESS;
        ut.ut_pid = cxt->pid;
        if (cxt->hostname) {
                xstrncpy(ut.ut_host, cxt->hostname, sizeof(ut.ut_host));
                if (*cxt->hostaddress)
                        memcpy(&ut.ut_addr_v6, cxt->hostaddress,
                               sizeof(ut.ut_addr_v6));
        }

        pututline(&ut);
        endutent();

        updwtmp(_PATH_WTMP, &ut);
}

static void log_syslog(struct login_context *cxt)
{
        struct passwd *pwd = cxt->pwd;

        if (!strncmp(cxt->tty_name, "ttyS", 4))
                syslog(LOG_INFO, _("DIALUP AT %s BY %s"),
                       cxt->tty_name, pwd->pw_name);

        if (!pwd->pw_uid) {
                if (cxt->hostname)
                        syslog(LOG_NOTICE, _("ROOT LOGIN ON %s FROM %s"),
                               cxt->tty_name, cxt->hostname);
                else
                        syslog(LOG_NOTICE, _("ROOT LOGIN ON %s"), cxt->tty_name);
        } else {
                if (cxt->hostname)
                        syslog(LOG_INFO, _("LOGIN ON %s BY %s FROM %s"),
                               cxt->tty_name, pwd->pw_name, cxt->hostname);
                else
                        syslog(LOG_INFO, _("LOGIN ON %s BY %s"), cxt->tty_name,
                               pwd->pw_name);
        }
}

static struct passwd *get_passwd_entry(const char *username,
                                         char **pwdbuf,
                                         struct passwd *pwd)
{
        struct passwd *res = NULL;
        size_t sz = 16384;
        int x;

        if (!pwdbuf || !username)
                return NULL;

#ifdef _SC_GETPW_R_SIZE_MAX
        {
                long xsz = sysconf(_SC_GETPW_R_SIZE_MAX);
                if (xsz > 0)
                        sz = (size_t) xsz;
        }
#endif
        *pwdbuf = xrealloc(*pwdbuf, sz);

        x = getpwnam_r(username, pwd, *pwdbuf, sz, &res);
        if (!res) {
                errno = x;
                return NULL;
        }
        return res;
}

/* encapsulate stupid "void **" pam_get_item() API */
static int loginpam_get_username(pam_handle_t *pamh, char **name)
{
        const void *item = (void *)*name;
        int rc;
        rc = pam_get_item(pamh, PAM_USER, &item);
        *name = (char *)item;
        return rc;
}

static void loginpam_err(pam_handle_t *pamh, int retcode)
{
        const char *msg = pam_strerror(pamh, retcode);

        if (msg) {
                fprintf(stderr, "\n%s\n", msg);
                syslog(LOG_ERR, "%s", msg);
        }
        pam_end(pamh, retcode);
        sleepexit(EXIT_FAILURE);
}

/*
 * Composes "<host> login: " string; or returns "login: " is -H is given
 */
static const char *loginpam_get_prompt(struct login_context *cxt)
{
        const char *host;
        char *prompt, *dflt_prompt = _("login: ");
        size_t sz;

        if (cxt->nohost || !(host = get_thishost(cxt, NULL)))
                return dflt_prompt;

        sz = strlen(host) + 1 + strlen(dflt_prompt) + 1;

        prompt = xmalloc(sz);
        snprintf(prompt, sz, "%s %s", host, dflt_prompt);

        return prompt;
}

static pam_handle_t *init_loginpam(struct login_context *cxt)
{
        pam_handle_t *pamh = NULL;
        int rc;

        /*
         * username is initialized to NULL and if specified on the command line
         * it is set.  Therefore, we are safe not setting it to anything
         */
        rc = pam_start(cxt->remote ? "remote" : "login",
                       cxt->username, &cxt->conv, &pamh);
        if (rc != PAM_SUCCESS) {
                warnx(_("PAM failure, aborting: %s"), pam_strerror(pamh, rc));
                syslog(LOG_ERR, _("Couldn't initialize PAM: %s"),
                       pam_strerror(pamh, rc));
                sleepexit(EXIT_FAILURE);
        }

        /* hostname & tty are either set to NULL or their correct values,
         * depending on how much we know
         */
        rc = pam_set_item(pamh, PAM_RHOST, cxt->hostname);
        if (is_pam_failure(rc))
                loginpam_err(pamh, rc);

        rc = pam_set_item(pamh, PAM_TTY, cxt->tty_name);
        if (is_pam_failure(rc))
                loginpam_err(pamh, rc);

        /*
         * Andrew.Taylor@cal.montage.ca: Provide a user prompt to PAM so that
         * the "login: " prompt gets localized. Unfortunately, PAM doesn't have
         * an interface to specify the "Password: " string (yet).
         */
        rc = pam_set_item(pamh, PAM_USER_PROMPT, loginpam_get_prompt(cxt));
        if (is_pam_failure(rc))
                loginpam_err(pamh, rc);

        /* we need't the original username. We have to follow PAM. */
        free(cxt->username);
        cxt->username = NULL;
        cxt->pamh = pamh;

        return pamh;
}

static void loginpam_auth(struct login_context *cxt)
{
        int rc, failcount = 0, show_unknown, retries;
        const char *hostname = cxt->hostname ? cxt->hostname :
                               cxt->tty_name ? cxt->tty_name : "<unknown>";
        pam_handle_t *pamh = cxt->pamh;

        /* if we didn't get a user on the command line, set it to NULL */
        loginpam_get_username(pamh, &cxt->username);

        show_unknown = getlogindefs_bool("LOG_UNKFAIL_ENAB", 0);
        retries = getlogindefs_num("LOGIN_RETRIES", LOGIN_MAX_TRIES);

        /*
         * There may be better ways to deal with some of these conditions, but
         * at least this way I don't think we'll be giving away information...
         *
         * Perhaps someday we can trust that all PAM modules will pay attention
         * to failure count and get rid of LOGIN_MAX_TRIES?
         */
        rc = pam_authenticate(pamh, 0);

        while ((++failcount < retries) &&
               ((rc == PAM_AUTH_ERR) ||
                (rc == PAM_USER_UNKNOWN) ||
                (rc == PAM_CRED_INSUFFICIENT) ||
                (rc == PAM_AUTHINFO_UNAVAIL))) {

                if (rc == PAM_USER_UNKNOWN && !show_unknown)
                        /*
                         * logging unknown usernames may be a security issue if
                         * an user enter her password instead of her login name
                         */
                        cxt->username = NULL;
                else
                        loginpam_get_username(pamh, &cxt->username);

                syslog(LOG_NOTICE,
                       _("FAILED LOGIN %d FROM %s FOR %s, %s"),
                       failcount, hostname,
                       cxt->username ? cxt->username : "(unknown)",
                       pam_strerror(pamh, rc));

                log_btmp(cxt);
                log_audit(cxt, 0);

                fprintf(stderr, _("Login incorrect\n\n"));

                pam_set_item(pamh, PAM_USER, NULL);
                rc = pam_authenticate(pamh, 0);
        }

        if (is_pam_failure(rc)) {

                if (rc == PAM_USER_UNKNOWN && !show_unknown)
                        cxt->username = NULL;
                else
                        loginpam_get_username(pamh, &cxt->username);

                if (rc == PAM_MAXTRIES)
                        syslog(LOG_NOTICE,
                               _("TOO MANY LOGIN TRIES (%d) FROM %s FOR %s, %s"),
                               failcount, hostname,
                               cxt->username ? cxt->username : "(unknown)",
                               pam_strerror(pamh, rc));
                else
                        syslog(LOG_NOTICE,
                               _("FAILED LOGIN SESSION FROM %s FOR %s, %s"),
                               hostname,
                               cxt->username ? cxt->username : "(unknown)",
                               pam_strerror(pamh, rc));

                log_btmp(cxt);
                log_audit(cxt, 0);

                fprintf(stderr, _("\nLogin incorrect\n"));
                pam_end(pamh, rc);
                sleepexit(EXIT_SUCCESS);
        }
}

static void loginpam_acct(struct login_context *cxt)
{
        int rc;
        pam_handle_t *pamh = cxt->pamh;

        rc = pam_acct_mgmt(pamh, 0);

        if (rc == PAM_NEW_AUTHTOK_REQD)
                rc = pam_chauthtok(pamh, PAM_CHANGE_EXPIRED_AUTHTOK);

        if (is_pam_failure(rc))
                loginpam_err(pamh, rc);

        /*
         * Grab the user information out of the password file for future usage
         * First get the username that we are actually using, though.
         */
        rc = loginpam_get_username(pamh, &cxt->username);
        if (is_pam_failure(rc))
                loginpam_err(pamh, rc);

        if (!cxt->username || !*cxt->username) {
                warnx(_("\nSession setup problem, abort."));
                syslog(LOG_ERR, _("NULL user name in %s:%d. Abort."),
                       __FUNCTION__, __LINE__);
                pam_end(pamh, PAM_SYSTEM_ERR);
                sleepexit(EXIT_FAILURE);
        }
}

/*
 * Note that position of the pam_setcred() call is discussable:
 *
 *  - the PAM docs recommends pam_setcred() before pam_open_session()
 *  - but the original RFC http://www.opengroup.org/rfc/mirror-rfc/rfc86.0.txt
 *    uses pam_setcred() after pam_open_session()
 *
 * The old login versions (before year 2011) followed the RFC. This is probably
 * not optimal, because there could be dependence between some session modules
 * and user's credentials.
 *
 * The best is probably to follow openssh and call pam_setcred() before and
 * after pam_open_session().                -- kzak@redhat.com (18-Nov-2011)
 *
 */
static void loginpam_session(struct login_context *cxt)
{
        int rc;
        pam_handle_t *pamh = cxt->pamh;

        rc = pam_setcred(pamh, PAM_ESTABLISH_CRED);
        if (is_pam_failure(rc))
                loginpam_err(pamh, rc);

        rc = pam_open_session(pamh, 0);
        if (is_pam_failure(rc)) {
                pam_setcred(cxt->pamh, PAM_DELETE_CRED);
                loginpam_err(pamh, rc);
        }

        rc = pam_setcred(pamh, PAM_REINITIALIZE_CRED);
        if (is_pam_failure(rc)) {
                pam_close_session(pamh, 0);
                loginpam_err(pamh, rc);
        }
}

/*
 * We need to check effective UID/GID. For example $HOME could be on root
 * squashed NFS or on NFS with UID mapping and access(2) uses real UID/GID.
 * The open(2) seems as the surest solution.
 * -- kzak@redhat.com (10-Apr-2009)
 */
static int effective_access(const char *path, int mode)
{
        int fd = open(path, mode);
        if (fd != -1)
                close(fd);
        return fd == -1 ? -1 : 0;
}

/*
 * Check per accout or global hush-login setting.
 *
 * Hushed mode is enabled:
 *
 * a) if global (e.g. /etc/hushlogins) hush file exists:
 *     1) for ALL ACCOUNTS if the file is empty
 *     2) for the current user if the username or shell are found in the file
 *
 * b) if ~/.hushlogin file exists
 *
 * The ~/.hushlogin is ignored if the global hush file exists.
 *
 * The HUSHLOGIN_FILE login.def variable overwrites the default hush filename.
 *
 * Note that shadow-utils login(1) does not support "a1)". The "a1)" is
 * necessary if you want to use PAM for "Last login" message.
 *
 * -- Karel Zak <kzak@redhat.com> (26-Aug-2011)
 *
 *
 * Per-account check requires some explanation: As root we may not be able to
 * read the directory of the user if it is on an NFS mounted filesystem. We
 * temporarily set our effective uid to the user-uid making sure that we keep
 * root privs. in the real uid.
 *
 * A portable solution would require a fork(), but we rely on Linux having the
 * BSD setreuid()
 */
static int get_hushlogin_status(struct passwd *pwd)
{
        const char *files[] = { _PATH_HUSHLOGINS, _PATH_HUSHLOGIN, NULL };
        const char *file;
        char buf[BUFSIZ];
        int i;

        file = getlogindefs_str("HUSHLOGIN_FILE", NULL);
        if (file) {
                if (!*file)
                        return 0;       /* empty HUSHLOGIN_FILE defined */

                files[0] = file;
                files[1] = NULL;
        }

        for (i = 0; files[i]; i++) {
                int ok = 0;

                file = files[i];

                /* Global hush-file*/
                if (*file == '/') {
                        struct stat st;
                        FILE *f;

                        if (stat(file, &st) != 0)
                                continue;       /* file does not exist */

                        if (st.st_size == 0)
                                return 1;       /* for all accounts */

                        f = fopen(file, "r");
                        if (!f)
                                continue;       /* ignore errors... */

                        while (ok == 0 && fgets(buf, sizeof(buf), f)) {
                                buf[strlen(buf) - 1] = '\0';
                                ok = !strcmp(buf, *buf == '/' ? pwd->pw_shell :
                                                                pwd->pw_name);
                        }
                        fclose(f);
                        if (ok)
                                return 1;       /* found username/shell */

                        return 0;               /* ignore per-account files */
                }

                /* Per-account setting */
                if (strlen(pwd->pw_dir) + sizeof(file) + 2 > sizeof(buf))
                        continue;
                else {
                        uid_t ruid = getuid();
                        gid_t egid = getegid();

                        sprintf(buf, "%s/%s", pwd->pw_dir, file);
                        setregid(-1, pwd->pw_gid);
                        setreuid(0, pwd->pw_uid);
                        ok = effective_access(buf, O_RDONLY) == 0;
                        setuid(0);      /* setreuid doesn't do it alone! */
                        setreuid(ruid, 0);
                        setregid(-1, egid);

                        if (ok)
                                return 1;       /* enabled by user */
                }
        }

        return 0;
}

/*
 * Detach the controlling terminal, fork, restore syslog stuff and create a new
 * session.
 */
static void fork_session(struct login_context *cxt)
{
        struct sigaction sa, oldsa_hup, oldsa_term;

        signal(SIGALRM, SIG_DFL);
        signal(SIGQUIT, SIG_DFL);
        signal(SIGTSTP, SIG_IGN);

        memset(&sa, 0, sizeof(sa));
        sa.sa_handler = SIG_IGN;
        sigaction(SIGINT, &sa, NULL);

        sigaction(SIGHUP, &sa, &oldsa_hup);     /* ignore when TIOCNOTTY */

        /*
         * detach the controlling tty
         * -- we needn't the tty in parent who waits for child only.
         *    The child calls setsid() that detach from the tty as well.
         */
        ioctl(0, TIOCNOTTY, NULL);

        /*
         * We have care about SIGTERM, because leave PAM session without
         * pam_close_session() is pretty bad thing.
         */
        sa.sa_handler = sig_handler;
        sigaction(SIGHUP, &sa, NULL);
        sigaction(SIGTERM, &sa, &oldsa_term);

        closelog();

        /*
         * We must fork before setuid() because we need to call
         * pam_close_session() as root.
         */
        child_pid = fork();
        if (child_pid < 0) {
                /*
                 * fork() error
                 */
                warn(_("fork failed"));

                pam_setcred(cxt->pamh, PAM_DELETE_CRED);
                pam_end(cxt->pamh, pam_close_session(cxt->pamh, 0));
                sleepexit(EXIT_FAILURE);
        }

        if (child_pid) {
                /*
                 * parent - wait for child to finish, then cleanup session
                 */
                close(0);
                close(1);
                close(2);
                sa.sa_handler = SIG_IGN;
                sigaction(SIGQUIT, &sa, NULL);
                sigaction(SIGINT, &sa, NULL);

                /* wait as long as any child is there */
                while (wait(NULL) == -1 && errno == EINTR) ;
                openlog("login", LOG_ODELAY, LOG_AUTHPRIV);

                pam_setcred(cxt->pamh, PAM_DELETE_CRED);
                pam_end(cxt->pamh, pam_close_session(cxt->pamh, 0));
                exit(EXIT_SUCCESS);
        }

        /*
         * child
         */
        sigaction(SIGHUP, &oldsa_hup, NULL);            /* restore old state */
        sigaction(SIGTERM, &oldsa_term, NULL);
        if (got_sig)
                exit(EXIT_FAILURE);

        /*
         * Problem: if the user's shell is a shell like ash that doesn't do
         * setsid() or setpgrp(), then a ctrl-\, sending SIGQUIT to every
         * process in the pgrp, will kill us.
         */

        /* start new session */
        setsid();

        /* make sure we have a controlling tty */
        open_tty(cxt->tty_path);
        openlog("login", LOG_ODELAY, LOG_AUTHPRIV);     /* reopen */

        /*
         * TIOCSCTTY: steal tty from other process group.
         */
        if (ioctl(0, TIOCSCTTY, 1))
                syslog(LOG_ERR, _("TIOCSCTTY failed: %m"));
        signal(SIGINT, SIG_DFL);
}

/*
 * Initialize $TERM, $HOME, ...
 */
static void init_environ(struct login_context *cxt)
{
        struct passwd *pwd = cxt->pwd;
        char *termenv = NULL, **env;
        char tmp[PATH_MAX];
        int len, i;

        termenv = getenv("TERM");
        termenv = termenv ? xstrdup(termenv) : "dumb";

        /* destroy environment unless user has requested preservation (-p) */
        if (!cxt->keep_env) {
                environ = (char **) xmalloc(sizeof(char *));
                memset(environ, 0, sizeof(char *));
        }

        setenv("HOME", pwd->pw_dir, 0); /* legal to override */
        setenv("USER", pwd->pw_name, 1);
        setenv("SHELL", pwd->pw_shell, 1);
        setenv("TERM", termenv, 1);

        if (pwd->pw_uid)
                logindefs_setenv("PATH", "ENV_PATH", _PATH_DEFPATH);

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

        /* mailx will give a funny error msg if you forget this one */
        len = snprintf(tmp, sizeof(tmp), "%s/%s", _PATH_MAILDIR, pwd->pw_name);
        if (len > 0 && (size_t) len + 1 <= sizeof(tmp))
                setenv("MAIL", tmp, 0);

        /* LOGNAME is not documented in login(1) but HP-UX 6.5 does it. We'll
         * not allow modifying it.
         */
        setenv("LOGNAME", pwd->pw_name, 1);

        env = pam_getenvlist(cxt->pamh);
        for (i = 0; env && env[i]; i++)
                putenv(env[i]);
}

/*
 * Called for -h option, initialize cxt->{hostname,hostaddress}
 */
static void init_remote_info(struct login_context *cxt, char *remotehost)
{
        const char *domain;
        char *p;
        struct addrinfo hints, *info = NULL;

        cxt->remote = 1;

        get_thishost(cxt, &domain);

        if (domain && (p = strchr(remotehost, '.')) &&
            strcasecmp(p + 1, domain) == 0)
                *p = '\0';

        cxt->hostname = xstrdup(remotehost);

        memset(&hints, 0, sizeof(hints));
        hints.ai_flags = AI_ADDRCONFIG;
        cxt->hostaddress[0] = 0;

        if (getaddrinfo(cxt->hostname, NULL, &hints, &info) == 0 && info) {
                if (info->ai_family == AF_INET) {
                        struct sockaddr_in *sa =
                                    (struct sockaddr_in *) info->ai_addr;

                        memcpy(cxt->hostaddress, &(sa->sin_addr), sizeof(sa->sin_addr));

                } else if (info->ai_family == AF_INET6) {
                        struct sockaddr_in6 *sa =
                                     (struct sockaddr_in6 *) info->ai_addr;

                        memcpy(cxt->hostaddress, &(sa->sin6_addr), sizeof(sa->sin6_addr));
                }
                freeaddrinfo(info);
        }
}

int main(int argc, char **argv)
{
        int c;
        int cnt;
        char *childArgv[10];
        char *buff;
        int childArgc = 0;
        int retcode;

        char *pwdbuf = NULL;
        struct passwd *pwd = NULL, _pwd;

        struct login_context cxt = {
                .tty_mode = TTY_MODE,           /* tty chmod() */
                .pid = getpid(),                /* PID */
                .conv = { misc_conv, NULL }     /* PAM conversation function */
        };

        timeout = getlogindefs_num("LOGIN_TIMEOUT", LOGIN_TIMEOUT);

        signal(SIGALRM, timedout);
        siginterrupt(SIGALRM, 1);       /* we have to interrupt syscalls like ioclt() */
        alarm((unsigned int)timeout);
        signal(SIGQUIT, SIG_IGN);
        signal(SIGINT, SIG_IGN);

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

        setpriority(PRIO_PROCESS, 0, 0);
        initproctitle(argc, argv);

        /*
         * -p is used by getty to tell login not to destroy the environment
         * -f is used to skip a second login authentication
         * -h is used by other servers to pass the name of the remote
         *    host to login so that it may be placed in utmp and wtmp
         */
        while ((c = getopt(argc, argv, "fHh:pV")) != -1)
                switch (c) {
                case 'f':
                        cxt.noauth = 1;
                        break;

                case 'H':
                        cxt.nohost = 1;
                        break;

                case 'h':
                        if (getuid()) {
                                fprintf(stderr,
                                        _("login: -h for super-user only.\n"));
                                exit(EXIT_FAILURE);
                        }
                        init_remote_info(&cxt, optarg);
                        break;

                case 'p':
                        cxt.keep_env = 1;
                        break;

                case 'V':
                        printf(UTIL_LINUX_VERSION);
                        return EXIT_SUCCESS;
                case '?':
                default:
                        fprintf(stderr, _("usage: login [ -p ] [ -h host ] [ -H ] [ -f username | username ]\n"));
                        exit(EXIT_FAILURE);
                }
        argc -= optind;
        argv += optind;

        if (*argv) {
                char *p = *argv;
                cxt.username = xstrdup(p);

                /* wipe name - some people mistype their password here */
                /* (of course we are too late, but perhaps this helps a little ..) */
                while (*p)
                        *p++ = ' ';
        }

        for (cnt = get_fd_tabsize() - 1; cnt > 2; cnt--)
                close(cnt);

        setpgrp();       /* set pgid to pid this means that setsid() will fail */

        openlog("login", LOG_ODELAY, LOG_AUTHPRIV);

        init_tty(&cxt);
        init_loginpam(&cxt);

        /* login -f, then the user has already been authenticated */
        cxt.noauth = cxt.noauth && getuid() == 0 ? 1 : 0;

        if (!cxt.noauth)
                loginpam_auth(&cxt);

        /*
         * Authentication may be skipped (for example, during krlogin, rlogin,
         * etc...), but it doesn't mean that we can skip other account checks.
         * The account could be disabled or password expired (althought
         * kerberos ticket is valid).         -- kzak@redhat.com (22-Feb-2006)
         */
        loginpam_acct(&cxt);

        if (!(cxt.pwd = get_passwd_entry(cxt.username, &pwdbuf, &_pwd))) {
                warnx(_("\nSession setup problem, abort."));
                syslog(LOG_ERR, _("Invalid user name \"%s\" in %s:%d. Abort."),
                       cxt.username, __FUNCTION__, __LINE__);
                pam_end(cxt.pamh, PAM_SYSTEM_ERR);
                sleepexit(EXIT_FAILURE);
        }

        pwd = cxt.pwd;
        cxt.username = pwd->pw_name;

        /*
         * Initialize the supplementary group list. This should be done before
         * pam_setcred because the PAM modules might add groups during
         * pam_setcred.
         *
         * For root we don't call initgroups, instead we call setgroups with
         * group 0. This avoids the need to step through the whole group file,
         * which can cause problems if NIS, NIS+, LDAP or something similar
         * is used and the machine has network problems.
         */
        retcode = pwd->pw_uid ? initgroups(cxt.username, pwd->pw_gid) : /* user */
                                setgroups(0, NULL);                     /* root */
        if (retcode < 0) {
                syslog(LOG_ERR, _("groups initialization failed: %m"));
                warnx(_("\nSession setup problem, abort."));
                pam_end(cxt.pamh, PAM_SYSTEM_ERR);
                sleepexit(EXIT_FAILURE);
        }

        /*
         * Open PAM session (after successful authentication and account check)
         */
        loginpam_session(&cxt);

        /* committed to login -- turn off timeout */
        alarm((unsigned int)0);

        endpwent();

        cxt.quiet = get_hushlogin_status(pwd);

        log_utmp(&cxt);
        log_audit(&cxt, 1);
        log_lastlog(&cxt);

        chown_tty(&cxt);

        if (setgid(pwd->pw_gid) < 0 && pwd->pw_gid) {
                syslog(LOG_ALERT, _("setgid() failed"));
                exit(EXIT_FAILURE);
        }

        if (pwd->pw_shell == NULL || *pwd->pw_shell == '\0')
                pwd->pw_shell = _PATH_BSHELL;

        init_environ(&cxt);             /* init $HOME, $TERM ... */

        setproctitle("login", cxt.username);

        log_syslog(&cxt);

        if (!cxt.quiet) {
                motd();

#ifdef LOGIN_STAT_MAIL
                /*
                 * This turns out to be a bad idea: when the mail spool
                 * is NFS mounted, and the NFS connection hangs, the
                 * login hangs, even root cannot login.
                 * Checking for mail should be done from the shell.
                 */
                {
                        struct stat st;
                        char *mail;

                        mail = getenv("MAIL");
                        if (mail && stat(mail, &st) == 0 && st.st_size != 0) {
                                if (st.st_mtime > st.st_atime)
                                        printf(_("You have new mail.\n"));
                                else
                                        printf(_("You have mail.\n"));
                        }
                }
#endif
        }

        /*
         * Detach the controlling terminal, fork() and create, new session
         * and reinilizalize syslog stuff.
         */
        fork_session(&cxt);

        /* discard permissions last so can't get killed and drop core */
        if (setuid(pwd->pw_uid) < 0 && pwd->pw_uid) {
                syslog(LOG_ALERT, _("setuid() failed"));
                exit(EXIT_FAILURE);
        }

        /* wait until here to change directory! */
        if (chdir(pwd->pw_dir) < 0) {
                warn(_("%s: change directory failed"), pwd->pw_dir);

                if (!getlogindefs_bool("DEFAULT_HOME", 1))
                        exit(0);
                if (chdir("/"))
                        exit(EXIT_FAILURE);
                pwd->pw_dir = "/";
                printf(_("Logging in with home = \"/\".\n"));
        }

        /* if the shell field has a space: treat it like a shell script */
        if (strchr(pwd->pw_shell, ' ')) {
                buff = xmalloc(strlen(pwd->pw_shell) + 6);

                strcpy(buff, "exec ");
                strcat(buff, pwd->pw_shell);
                childArgv[childArgc++] = "/bin/sh";
                childArgv[childArgc++] = "-sh";
                childArgv[childArgc++] = "-c";
                childArgv[childArgc++] = buff;
        } else {
                char tbuf[PATH_MAX + 2], *p;

                tbuf[0] = '-';
                xstrncpy(tbuf + 1, ((p = strrchr(pwd->pw_shell, '/')) ?
                                    p + 1 : pwd->pw_shell), sizeof(tbuf) - 1);

                childArgv[childArgc++] = pwd->pw_shell;
                childArgv[childArgc++] = xstrdup(tbuf);
        }

        childArgv[childArgc++] = NULL;

        execvp(childArgv[0], childArgv + 1);

        if (!strcmp(childArgv[0], "/bin/sh"))
                warn(_("couldn't exec shell script"));
        else
                warn(_("no shell"));

        exit(EXIT_SUCCESS);
}