source: MondoRescue/branches/stable/mindi-busybox/loginutils/login.c@ 1770

/* vi: set sw=4 ts=4: */
/*
 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
 */

#include "libbb.h"
#include <utmp.h>
#include <sys/resource.h>
#include <syslog.h>

#if ENABLE_SELINUX
#include <selinux/selinux.h>  /* for is_selinux_enabled()  */
#include <selinux/get_context_list.h> /* for get_default_context() */
#include <selinux/flask.h> /* for security class definitions  */
#endif

#if ENABLE_PAM
/* PAM may include <locale.h>. We may need to undefine bbox's stub define: */
#undef setlocale
/* For some obscure reason, PAM is not in pam/xxx, but in security/xxx.
 * Apparently they like to confuse people. */
#include <security/pam_appl.h>
#include <security/pam_misc.h>
static const struct pam_conv conv = {
    misc_conv,
    NULL
};
#endif

enum {
    TIMEOUT = 60,
    EMPTY_USERNAME_COUNT = 10,
    USERNAME_SIZE = 32,
    TTYNAME_SIZE = 32,
};

static char* short_tty;

#if ENABLE_FEATURE_UTMP
/* vv  Taken from tinylogin utmp.c  vv */
/*
 * read_or_build_utent - see if utmp file is correct for this process
 *
 *  System V is very picky about the contents of the utmp file
 *  and requires that a slot for the current process exist.
 *  The utmp file is scanned for an entry with the same process
 *  ID.  If no entry exists the process exits with a message.
 *
 *  The "picky" flag is for network and other logins that may
 *  use special flags.  It allows the pid checks to be overridden.
 *  This means that getty should never invoke login with any
 *  command line flags.
 */

static void read_or_build_utent(struct utmp *utptr, int picky)
{
    struct utmp *ut;
    pid_t pid = getpid();

    setutent();

    /* First, try to find a valid utmp entry for this process.  */
    while ((ut = getutent()))
        if (ut->ut_pid == pid && ut->ut_line[0] && ut->ut_id[0] &&
        (ut->ut_type == LOGIN_PROCESS || ut->ut_type == USER_PROCESS))
            break;

    /* If there is one, just use it, otherwise create a new one.  */
    if (ut) {
        *utptr = *ut;
    } else {
        if (picky)
            bb_error_msg_and_die("no utmp entry found");

        memset(utptr, 0, sizeof(*utptr));
        utptr->ut_type = LOGIN_PROCESS;
        utptr->ut_pid = pid;
        strncpy(utptr->ut_line, short_tty, sizeof(utptr->ut_line));
        /* This one is only 4 chars wide. Try to fit something
         * remotely meaningful by skipping "tty"... */
        strncpy(utptr->ut_id, short_tty + 3, sizeof(utptr->ut_id));
        strncpy(utptr->ut_user, "LOGIN", sizeof(utptr->ut_user));
        utptr->ut_time = time(NULL);
    }
    if (!picky) /* root login */
        memset(utptr->ut_host, 0, sizeof(utptr->ut_host));
}

/*
 * write_utent - put a USER_PROCESS entry in the utmp file
 *
 *  write_utent changes the type of the current utmp entry to
 *  USER_PROCESS.  the wtmp file will be updated as well.
 */
static void write_utent(struct utmp *utptr, const char *username)
{
    utptr->ut_type = USER_PROCESS;
    strncpy(utptr->ut_user, username, sizeof(utptr->ut_user));
    utptr->ut_time = time(NULL);
    /* other fields already filled in by read_or_build_utent above */
    setutent();
    pututline(utptr);
    endutent();
#if ENABLE_FEATURE_WTMP
    if (access(bb_path_wtmp_file, R_OK|W_OK) == -1) {
        close(creat(bb_path_wtmp_file, 0664));
    }
    updwtmp(bb_path_wtmp_file, utptr);
#endif
}
#else /* !ENABLE_FEATURE_UTMP */
#define read_or_build_utent(utptr, picky) ((void)0)
#define write_utent(utptr, username) ((void)0)
#endif /* !ENABLE_FEATURE_UTMP */

#if ENABLE_FEATURE_NOLOGIN
static void die_if_nologin_and_non_root(int amroot)
{
    FILE *fp;
    int c;

    if (access("/etc/nologin", F_OK))
        return;

    fp = fopen("/etc/nologin", "r");
    if (fp) {
        while ((c = getc(fp)) != EOF)
            putchar((c=='\n') ? '\r' : c);
        fflush(stdout);
        fclose(fp);
    } else
        puts("\r\nSystem closed for routine maintenance\r");
    if (!amroot)
        exit(1);
    puts("\r\n[Disconnect bypassed -- root login allowed]\r");
}
#else
static ALWAYS_INLINE void die_if_nologin_and_non_root(int amroot) {}
#endif

#if ENABLE_FEATURE_SECURETTY && !ENABLE_PAM
static int check_securetty(void)
{
    FILE *fp;
    int i;
    char buf[256];

    fp = fopen("/etc/securetty", "r");
    if (!fp) {
        /* A missing securetty file is not an error. */
        return 1;
    }
    while (fgets(buf, sizeof(buf)-1, fp)) {
        for (i = strlen(buf)-1; i >= 0; --i) {
            if (!isspace(buf[i]))
                break;
        }
        buf[++i] = '\0';
        if (!buf[0] || (buf[0] == '#'))
            continue;
        if (strcmp(buf, short_tty) == 0) {
            fclose(fp);
            return 1;
        }
    }
    fclose(fp);
    return 0;
}
#else
static ALWAYS_INLINE int check_securetty(void) { return 1; }
#endif

static void get_username_or_die(char *buf, int size_buf)
{
    int c, cntdown;

    cntdown = EMPTY_USERNAME_COUNT;
 prompt:
    print_login_prompt();
    /* skip whitespace */
    do {
        c = getchar();
        if (c == EOF) exit(1);
        if (c == '\n') {
            if (!--cntdown) exit(1);
            goto prompt;
        }
    } while (isspace(c));

    *buf++ = c;
    if (!fgets(buf, size_buf-2, stdin))
        exit(1);
    if (!strchr(buf, '\n'))
        exit(1);
    while (isgraph(*buf)) buf++;
    *buf = '\0';
}

static void motd(void)
{
    int fd;

    fd = open(bb_path_motd_file, O_RDONLY);
    if (fd) {
        fflush(stdout);
        bb_copyfd_eof(fd, STDOUT_FILENO);
        close(fd);
    }
}

static void alarm_handler(int sig ATTRIBUTE_UNUSED)
{
    /* This is the escape hatch!  Poor serial line users and the like
     * arrive here when their connection is broken.
     * We don't want to block here */
    ndelay_on(1);
    ndelay_on(2);
    printf("\r\nLogin timed out after %d seconds\r\n", TIMEOUT);
    exit(EXIT_SUCCESS);
}

int login_main(int argc, char **argv);
int login_main(int argc, char **argv)
{
    enum {
        LOGIN_OPT_f = (1<<0),
        LOGIN_OPT_h = (1<<1),
        LOGIN_OPT_p = (1<<2),
    };
    char *fromhost;
    char username[USERNAME_SIZE];
    const char *tmp;
    int amroot;
    unsigned opt;
    int count = 0;
    struct passwd *pw;
    char *opt_host = NULL;
    char *opt_user = NULL;
    char full_tty[TTYNAME_SIZE];
    USE_SELINUX(security_context_t user_sid = NULL;)
    USE_FEATURE_UTMP(struct utmp utent;)
    USE_PAM(pam_handle_t *pamh;)
    USE_PAM(int pamret;)
    USE_PAM(const char *failed_msg;)

    short_tty = full_tty;
    username[0] = '\0';
    amroot = (getuid() == 0);
    signal(SIGALRM, alarm_handler);
    alarm(TIMEOUT);

    /* Mandatory paranoia for suid applet:
     * ensure that fd# 0,1,2 are opened (at least to /dev/null)
     * and any extra open fd's are closed.
     * (The name of the function is misleading. Not daemonizing here.) */
    bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE | DAEMON_CLOSE_EXTRA_FDS, NULL);

    opt = getopt32(argv, "f:h:p", &opt_user, &opt_host);
    if (opt & LOGIN_OPT_f) {
        if (!amroot)
            bb_error_msg_and_die("-f is for root only");
        safe_strncpy(username, opt_user, sizeof(username));
    }
    if (optind < argc) /* user from command line (getty) */
        safe_strncpy(username, argv[optind], sizeof(username));

    /* Let's find out and memorize our tty */
    if (!isatty(0) || !isatty(1) || !isatty(2))
        return EXIT_FAILURE;        /* Must be a terminal */
    safe_strncpy(full_tty, "UNKNOWN", sizeof(full_tty));
    tmp = ttyname(0);
    if (tmp) {
        safe_strncpy(full_tty, tmp, sizeof(full_tty));
        if (strncmp(full_tty, "/dev/", 5) == 0)
            short_tty = full_tty + 5;
    }

    read_or_build_utent(&utent, !amroot);

    if (opt_host) {
        USE_FEATURE_UTMP(
            safe_strncpy(utent.ut_host, opt_host, sizeof(utent.ut_host));
        )
        fromhost = xasprintf(" on '%s' from '%s'", short_tty, opt_host);
    } else
        fromhost = xasprintf(" on '%s'", short_tty);

    /* Was breaking "login <username>" from shell command line: */
    /*bb_setpgrp();*/

    openlog(applet_name, LOG_PID | LOG_CONS | LOG_NOWAIT, LOG_AUTH);

    while (1) {
        if (!username[0])
            get_username_or_die(username, sizeof(username));

#if ENABLE_PAM
        pamret = pam_start("login", username, &conv, &pamh);
        if (pamret != PAM_SUCCESS) {
            failed_msg = "pam_start";
            goto pam_auth_failed;
        }
        /* set TTY (so things like securetty work) */
        pamret = pam_set_item(pamh, PAM_TTY, short_tty);
        if (pamret != PAM_SUCCESS) {
            failed_msg = "pam_set_item(TTY)";
            goto pam_auth_failed;
        }
        pamret = pam_authenticate(pamh, 0);
        if (pamret != PAM_SUCCESS) {
            failed_msg = "pam_authenticate";
            goto pam_auth_failed;
            /* TODO: or just "goto auth_failed"
             * since user seems to enter wrong password
             * (in this case pamret == 7)
             */
        }
        /* check that the account is healthy */
        pamret = pam_acct_mgmt(pamh, 0);
        if (pamret != PAM_SUCCESS) {
            failed_msg = "account setup";
            goto pam_auth_failed;
        }
        /* read user back */
        {
            const char *pamuser;
            /* gcc: "dereferencing type-punned pointer breaks aliasing rules..."
             * thus we cast to (void*) */
            if (pam_get_item(pamh, PAM_USER, (void*)&pamuser) != PAM_SUCCESS) {
                failed_msg = "pam_get_item(USER)";
                goto pam_auth_failed;
            }
            safe_strncpy(username, pamuser, sizeof(username));
        }
        /* If we get here, the user was authenticated, and is
         * granted access. */
        pw = getpwnam(username);
        if (pw)
            break;
        goto auth_failed;
 pam_auth_failed:
        bb_error_msg("%s failed: %s (%d)", failed_msg, pam_strerror(pamh, pamret), pamret);
        safe_strncpy(username, "UNKNOWN", sizeof(username));
#else /* not PAM */
        pw = getpwnam(username);
        if (!pw) {
            strcpy(username, "UNKNOWN");
            goto fake_it;
        }

        if (pw->pw_passwd[0] == '!' || pw->pw_passwd[0] == '*')
            goto auth_failed;

        if (opt & LOGIN_OPT_f)
            break; /* -f USER: success without asking passwd */

        if (pw->pw_uid == 0 && !check_securetty())
            goto auth_failed;

        /* Don't check the password if password entry is empty (!) */
        if (!pw->pw_passwd[0])
            break;
 fake_it:
        /* authorization takes place here */
        if (correct_password(pw))
            break;
#endif /* ENABLE_PAM */
 auth_failed:
        opt &= ~LOGIN_OPT_f;
        bb_do_delay(FAIL_DELAY);
        /* TODO: doesn't sound like correct English phrase to me */
        puts("Login incorrect");
        if (++count == 3) {
            syslog(LOG_WARNING, "invalid password for '%s'%s",
                        username, fromhost);
            return EXIT_FAILURE;
        }
        username[0] = '\0';
    }

    alarm(0);
    die_if_nologin_and_non_root(pw->pw_uid == 0);

    write_utent(&utent, username);

#if ENABLE_SELINUX
    if (is_selinux_enabled()) {
        security_context_t old_tty_sid, new_tty_sid;

        if (get_default_context(username, NULL, &user_sid)) {
            bb_error_msg_and_die("cannot get SID for %s",
                    username);
        }
        if (getfilecon(full_tty, &old_tty_sid) < 0) {
            bb_perror_msg_and_die("getfilecon(%s) failed",
                    full_tty);
        }
        if (security_compute_relabel(user_sid, old_tty_sid,
                    SECCLASS_CHR_FILE, &new_tty_sid) != 0) {
            bb_perror_msg_and_die("security_change_sid(%s) failed",
                    full_tty);
        }
        if (setfilecon(full_tty, new_tty_sid) != 0) {
            bb_perror_msg_and_die("chsid(%s, %s) failed",
                    full_tty, new_tty_sid);
        }
    }
#endif
    /* Try these, but don't complain if they fail.
     * _f_chown is safe wrt race t=ttyname(0);...;chown(t); */
    fchown(0, pw->pw_uid, pw->pw_gid);
    fchmod(0, 0600);

    if (ENABLE_LOGIN_SCRIPTS) {
        char *t_argv[2];

        t_argv[0] = getenv("LOGIN_PRE_SUID_SCRIPT");
        if (t_argv[0]) {
            t_argv[1] = NULL;
            xsetenv("LOGIN_TTY", full_tty);
            xsetenv("LOGIN_USER", pw->pw_name);
            xsetenv("LOGIN_UID", utoa(pw->pw_uid));
            xsetenv("LOGIN_GID", utoa(pw->pw_gid));
            xsetenv("LOGIN_SHELL", pw->pw_shell);
            xspawn(t_argv); /* NOMMU-friendly */
            /* All variables are unset by setup_environment */
            wait(NULL);
        }
    }

    change_identity(pw);
    tmp = pw->pw_shell;
    if (!tmp || !*tmp)
        tmp = DEFAULT_SHELL;
    /* setup_environment params: shell, loginshell, changeenv, pw */
    setup_environment(tmp, 1, !(opt & LOGIN_OPT_p), pw);
    /* FIXME: login shell = 1 -> 3rd parameter is ignored! */

    motd();

    if (pw->pw_uid == 0)
        syslog(LOG_INFO, "root login%s", fromhost);
#if ENABLE_SELINUX
    /* well, a simple setexeccon() here would do the job as well,
     * but let's play the game for now */
    set_current_security_context(user_sid);
#endif

    // util-linux login also does:
    // /* start new session */
    // setsid();
    // /* TIOCSCTTY: steal tty from other process group */
    // if (ioctl(0, TIOCSCTTY, 1)) error_msg...
    // BBox login used to do this (see above):
    // bb_setpgrp();
    // If this stuff is really needed, add it and explain why!

    /* set signals to defaults */
    signal(SIGALRM, SIG_DFL);
    /* Is this correct? This way user can ctrl-c out of /etc/profile,
     * potentially creating security breach (tested with bash 3.0).
     * But without this, bash 3.0 will not enable ctrl-c either.
     * Maybe bash is buggy?
     * Need to find out what standards say about /bin/login -
     * should it leave SIGINT etc enabled or disabled? */
    signal(SIGINT, SIG_DFL);

    /* Exec login shell with no additional parameters */
    run_shell(tmp, 1, NULL, NULL);

    /* return EXIT_FAILURE; - not reached */
}