source: MondoRescue/branches/3.3/mindi-busybox/loginutils/login.c@ 3803

/* vi: set sw=4 ts=4: */
/*
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */
//config:config LOGIN
//config:   bool "login"
//config:   default y
//config:   select FEATURE_SYSLOG
//config:   help
//config:     login is used when signing onto a system.
//config:
//config:     Note that Busybox binary must be setuid root for this applet to
//config:     work properly.
//config:
//config:config LOGIN_SESSION_AS_CHILD
//config:   bool "Run logged in session in a child process"
//config:   default y if PAM
//config:   depends on LOGIN
//config:   help
//config:     Run the logged in session in a child process.  This allows
//config:     login to clean up things such as utmp entries or PAM sessions
//config:     when the login session is complete.  If you use PAM, you
//config:     almost always would want this to be set to Y, else PAM session
//config:     will not be cleaned up.
//config:
//config:config LOGIN_SCRIPTS
//config:   bool "Support for login scripts"
//config:   depends on LOGIN
//config:   default y
//config:   help
//config:     Enable this if you want login to execute $LOGIN_PRE_SUID_SCRIPT
//config:     just prior to switching from root to logged-in user.
//config:
//config:config FEATURE_NOLOGIN
//config:   bool "Support for /etc/nologin"
//config:   default y
//config:   depends on LOGIN
//config:   help
//config:     The file /etc/nologin is used by (some versions of) login(1).
//config:     If it exists, non-root logins are prohibited.
//config:
//config:config FEATURE_SECURETTY
//config:   bool "Support for /etc/securetty"
//config:   default y
//config:   depends on LOGIN
//config:   help
//config:     The file /etc/securetty is used by (some versions of) login(1).
//config:     The file contains the device names of tty lines (one per line,
//config:     without leading /dev/) on which root is allowed to login.

//applet:/* Needs to be run by root or be suid root - needs to change uid and gid: */
//applet:IF_LOGIN(APPLET(login, BB_DIR_BIN, BB_SUID_REQUIRE))

//kbuild:lib-$(CONFIG_LOGIN) += login.o

//usage:#define login_trivial_usage
//usage:       "[-p] [-h HOST] [[-f] USER]"
//usage:#define login_full_usage "\n\n"
//usage:       "Begin a new session on the system\n"
//usage:     "\n    -f  Don't authenticate (user already authenticated)"
//usage:     "\n    -h HOST Host user came from (for network logins)"
//usage:     "\n    -p  Preserve environment"

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

# if 0
/* This supposedly can be used to avoid double password prompt,
 * if used instead of standard misc_conv():
 *
 * "When we want to authenticate first with local method and then with tacacs for example,
 *  the password is asked for local method and if not good is asked a second time for tacacs.
 *  So if we want to authenticate a user with tacacs, and the user exists localy, the password is
 *  asked two times before authentication is accepted."
 *
 * However, code looks shaky. For example, why misc_conv() return value is ignored?
 * Are msg[i] and resp[i] indexes handled correctly?
 */
static char *passwd = NULL;
static int my_conv(int num_msg, const struct pam_message **msg,
        struct pam_response **resp, void *data)
{
    int i;
    for (i = 0; i < num_msg; i++) {
        switch (msg[i]->msg_style) {
        case PAM_PROMPT_ECHO_OFF:
            if (passwd == NULL) {
                misc_conv(num_msg, msg, resp, data);
                passwd = xstrdup(resp[i]->resp);
                return PAM_SUCCESS;
            }

            resp[0] = xzalloc(sizeof(struct pam_response));
            resp[0]->resp = passwd;
            passwd = NULL;
            resp[0]->resp_retcode = PAM_SUCCESS;
            resp[1] = NULL;
            return PAM_SUCCESS;

        default:
            break;
        }
    }

    return PAM_SUCCESS;
}
# endif

static const struct pam_conv conv = {
    misc_conv,
    NULL
};
#endif

enum {
    TIMEOUT = 60,
    EMPTY_USERNAME_COUNT = 10,
    /* Some users found 32 chars limit to be too low: */
    USERNAME_SIZE = 64,
    TTYNAME_SIZE = 32,
};

struct globals {
    struct termios tty_attrs;
} FIX_ALIASING;
#define G (*(struct globals*)bb_common_bufsiz1)
#define INIT_G() do { setup_common_bufsiz(); } while (0)


#if ENABLE_FEATURE_NOLOGIN
static void die_if_nologin(void)
{
    FILE *fp;
    int c;
    int empty = 1;

    fp = fopen_for_read("/etc/nologin");
    if (!fp) /* assuming it does not exist */
        return;

    while ((c = getc(fp)) != EOF) {
        if (c == '\n')
            bb_putchar('\r');
        bb_putchar(c);
        empty = 0;
    }
    if (empty)
        puts("\r\nSystem closed for routine maintenance\r");

    fclose(fp);
    fflush_all();
    /* Users say that they do need this prior to exit: */
    tcdrain(STDOUT_FILENO);
    exit(EXIT_FAILURE);
}
#else
# define die_if_nologin() ((void)0)
#endif

#if ENABLE_FEATURE_SECURETTY && !ENABLE_PAM
static int check_securetty(const char *short_tty)
{
    char *buf = (char*)"/etc/securetty"; /* any non-NULL is ok */
    parser_t *parser = config_open2("/etc/securetty", fopen_for_read);
    while (config_read(parser, &buf, 1, 1, "# \t", PARSE_NORMAL)) {
        if (strcmp(buf, short_tty) == 0)
            break;
        buf = NULL;
    }
    config_close(parser);
    /* buf != NULL here if config file was not found, empty
     * or line was found which equals short_tty */
    return buf != NULL;
}
#else
static ALWAYS_INLINE int check_securetty(const char *short_tty UNUSED_PARAM) { return 1; }
#endif

#if ENABLE_SELINUX
static void initselinux(char *username, char *full_tty,
                        security_context_t *user_sid)
{
    security_context_t old_tty_sid, new_tty_sid;

    if (!is_selinux_enabled())
        return;

    if (get_default_context(username, NULL, user_sid)) {
        bb_error_msg_and_die("can't 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

#if ENABLE_LOGIN_SCRIPTS
static void run_login_script(struct passwd *pw, char *full_tty)
{
    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);
        spawn_and_wait(t_argv); /* NOMMU-friendly */
        unsetenv("LOGIN_TTY");
        unsetenv("LOGIN_USER");
        unsetenv("LOGIN_UID");
        unsetenv("LOGIN_GID");
        unsetenv("LOGIN_SHELL");
    }
}
#else
void run_login_script(struct passwd *pw, char *full_tty);
#endif

#if ENABLE_LOGIN_SESSION_AS_CHILD && ENABLE_PAM
static void login_pam_end(pam_handle_t *pamh)
{
    int pamret;

    pamret = pam_setcred(pamh, PAM_DELETE_CRED);
    if (pamret != PAM_SUCCESS) {
        bb_error_msg("pam_%s failed: %s (%d)", "setcred",
            pam_strerror(pamh, pamret), pamret);
    }
    pamret = pam_close_session(pamh, 0);
    if (pamret != PAM_SUCCESS) {
        bb_error_msg("pam_%s failed: %s (%d)", "close_session",
            pam_strerror(pamh, pamret), pamret);
    }
    pamret = pam_end(pamh, pamret);
    if (pamret != PAM_SUCCESS) {
        bb_error_msg("pam_%s failed: %s (%d)", "end",
            pam_strerror(pamh, pamret), pamret);
    }
}
#endif /* ENABLE_PAM */

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(EXIT_FAILURE);
        if (c == '\n') {
            if (!--cntdown)
                exit(EXIT_FAILURE);
            goto prompt;
        }
    } while (isspace(c)); /* maybe isblank? */

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

static void motd(void)
{
    int fd;

    fd = open(bb_path_motd_file, O_RDONLY);
    if (fd >= 0) {
        fflush_all();
        bb_copyfd_eof(fd, STDOUT_FILENO);
        close(fd);
    }
}

static void alarm_handler(int sig UNUSED_PARAM)
{
    /* 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(STDOUT_FILENO);
    /* Test for correct attr restoring:
     * run "getty 0 -" from a shell, enter bogus username, stop at
     * password prompt, let it time out. Without the tcsetattr below,
     * when you are back at shell prompt, echo will be still off.
     */
    tcsetattr_stdin_TCSANOW(&G.tty_attrs);
    printf("\r\nLogin timed out after %u seconds\r\n", TIMEOUT);
    fflush_all();
    /* unix API is brain damaged regarding O_NONBLOCK,
     * we should undo it, or else we can affect other processes */
    ndelay_off(STDOUT_FILENO);
    _exit(EXIT_SUCCESS);
}

int login_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int login_main(int argc UNUSED_PARAM, char **argv)
{
    enum {
        LOGIN_OPT_f = (1<<0),
        LOGIN_OPT_h = (1<<1),
        LOGIN_OPT_p = (1<<2),
    };
    char *fromhost;
    char username[USERNAME_SIZE];
    int run_by_root;
    unsigned opt;
    int count = 0;
    struct passwd *pw;
    char *opt_host = NULL;
    char *opt_user = opt_user; /* for compiler */
    char *full_tty;
    char *short_tty;
    IF_SELINUX(security_context_t user_sid = NULL;)
#if ENABLE_PAM
    int pamret;
    pam_handle_t *pamh;
    const char *pamuser;
    const char *failed_msg;
    struct passwd pwdstruct;
    char pwdbuf[256];
    char **pamenv;
#endif
#if ENABLE_LOGIN_SESSION_AS_CHILD
    pid_t child_pid;
#endif

    INIT_G();

    /* More of suid paranoia if called by non-root: */
    /* Clear dangerous stuff, set PATH */
    run_by_root = !sanitize_env_if_suid();

    /* 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);

    username[0] = '\0';
    opt = getopt32(argv, "f:h:p", &opt_user, &opt_host);
    if (opt & LOGIN_OPT_f) {
        if (!run_by_root)
            bb_error_msg_and_die("-f is for root only");
        safe_strncpy(username, opt_user, sizeof(username));
    }
    argv += optind;
    if (argv[0]) /* user from command line (getty) */
        safe_strncpy(username, argv[0], sizeof(username));

    /* Save tty attributes - and by doing it, check that it's indeed a tty */
    if (tcgetattr(STDIN_FILENO, &G.tty_attrs) < 0
     || !isatty(STDOUT_FILENO)
     /*|| !isatty(STDERR_FILENO) - no, guess some people might want to redirect this */
    ) {
        return EXIT_FAILURE;  /* Must be a terminal */
    }

    /* We install timeout handler only _after_ we saved G.tty_attrs */
    signal(SIGALRM, alarm_handler);
    alarm(TIMEOUT);

    /* Find out and memorize our tty name */
    full_tty = xmalloc_ttyname(STDIN_FILENO);
    if (!full_tty)
        full_tty = xstrdup("UNKNOWN");
    short_tty = skip_dev_pfx(full_tty);

    if (opt_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_AUTH);

    while (1) {
        /* flush away any type-ahead (as getty does) */
        tcflush(0, TCIFLUSH);

        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 = "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 = "set_item(TTY)";
            goto pam_auth_failed;
        }
        /* set RHOST */
        if (opt_host) {
            pamret = pam_set_item(pamh, PAM_RHOST, opt_host);
            if (pamret != PAM_SUCCESS) {
                failed_msg = "set_item(RHOST)";
                goto pam_auth_failed;
            }
        }
        if (!(opt & LOGIN_OPT_f)) {
            pamret = pam_authenticate(pamh, 0);
            if (pamret != PAM_SUCCESS) {
                failed_msg = "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 = "acct_mgmt";
            goto pam_auth_failed;
        }
        /* read user back */
        pamuser = NULL;
        /* 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 = "get_item(USER)";
            goto pam_auth_failed;
        }
        if (!pamuser || !pamuser[0])
            goto auth_failed;
        safe_strncpy(username, pamuser, sizeof(username));
        /* Don't use "pw = getpwnam(username);",
         * PAM is said to be capable of destroying static storage
         * used by getpwnam(). We are using safe(r) function */
        pw = NULL;
        getpwnam_r(username, &pwdstruct, pwdbuf, sizeof(pwdbuf), &pw);
        if (!pw)
            goto auth_failed;
        pamret = pam_open_session(pamh, 0);
        if (pamret != PAM_SUCCESS) {
            failed_msg = "open_session";
            goto pam_auth_failed;
        }
        pamret = pam_setcred(pamh, PAM_ESTABLISH_CRED);
        if (pamret != PAM_SUCCESS) {
            failed_msg = "setcred";
            goto pam_auth_failed;
        }
        break; /* success, continue login process */

 pam_auth_failed:
        /* syslog, because we don't want potential attacker
         * to know _why_ login failed */
        syslog(LOG_WARNING, "pam_%s call 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(short_tty))
            goto auth_failed;

        /* Don't check the password if password entry is empty (!) */
        if (!pw->pw_passwd[0])
            break;
 fake_it:
        /* Password reading and authorization takes place here.
         * Note that reads (in no-echo mode) trash tty attributes.
         * If we get interrupted by SIGALRM, we need to restore attrs.
         */
        if (ask_and_check_password(pw) > 0)
            break;
#endif /* ENABLE_PAM */
 auth_failed:
        opt &= ~LOGIN_OPT_f;
        bb_do_delay(LOGIN_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);

            if (ENABLE_FEATURE_CLEAN_UP)
                free(fromhost);

            return EXIT_FAILURE;
        }
        username[0] = '\0';
    } /* while (1) */

    alarm(0);
    /* We can ignore /etc/nologin if we are logging in as root,
     * it doesn't matter whether we are run by root or not */
    if (pw->pw_uid != 0)
        die_if_nologin();

#if ENABLE_LOGIN_SESSION_AS_CHILD
    child_pid = vfork();
    if (child_pid != 0) {
        if (child_pid < 0)
            bb_perror_msg("vfork");
        else {
            if (safe_waitpid(child_pid, NULL, 0) == -1)
                bb_perror_msg("waitpid");
            update_utmp_DEAD_PROCESS(child_pid);
        }
        IF_PAM(login_pam_end(pamh);)
        return 0;
    }
#endif

    IF_SELINUX(initselinux(username, full_tty, &user_sid);)

    /* 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);

    update_utmp(getpid(), USER_PROCESS, short_tty, username, run_by_root ? opt_host : NULL);

    /* We trust environment only if we run by root */
    if (ENABLE_LOGIN_SCRIPTS && run_by_root)
        run_login_script(pw, full_tty);

    change_identity(pw);
    setup_environment(pw->pw_shell,
            (!(opt & LOGIN_OPT_p) * SETUP_ENV_CLEARENV) + SETUP_ENV_CHANGEENV,
            pw);

#if ENABLE_PAM
    /* Modules such as pam_env will setup the PAM environment,
     * which should be copied into the new environment. */
    pamenv = pam_getenvlist(pamh);
    if (pamenv) while (*pamenv) {
        putenv(*pamenv);
        pamenv++;
    }
#endif

    if (access(".hushlogin", F_OK) != 0)
        motd();

    if (pw->pw_uid == 0)
        syslog(LOG_INFO, "root login%s", fromhost);

    if (ENABLE_FEATURE_CLEAN_UP)
        free(fromhost);

    /* well, a simple setexeccon() here would do the job as well,
     * but let's play the game for now */
    IF_SELINUX(set_current_security_context(user_sid);)

    // 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 */
    /* Non-ignored signals revert to SIG_DFL on exec anyway */
    /*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 we leave SIGINT etc enabled or disabled? */
    signal(SIGINT, SIG_DFL);

    /* Exec login shell with no additional parameters */
    run_shell(pw->pw_shell, 1, NULL, NULL);

    /* return EXIT_FAILURE; - not reached */
}