/* vi: set sw=4 ts=4: */
/*
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */
//config:config LOGIN
//config:       bool "login (24 kb)"
//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 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 /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 /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"
//usage:     "\n"
//usage:     "\n$LOGIN_TIMEOUT          Seconds (default 60, 0 - disable)"
//usage:        IF_LOGIN_SCRIPTS(
//usage:     "\n$LOGIN_PRE_SUID_SCRIPT  Execute before user ID change"
//usage:        )

#include "libbb.h"
#include "common_bufsiz.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() */
# /* from deprecated <selinux/flask.h>: */
# undef  SECCLASS_CHR_FILE
# define SECCLASS_CHR_FILE 10
#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 {
        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;
        int timeout;
} 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_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);
        }
}
#else
# define login_pam_end(pamh) ((void)0)
#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(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", G.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
        IF_FEATURE_UTMP(pid_t my_pid;)

        INIT_G();

        G.timeout = xatoi_positive(getenv("LOGIN_TIMEOUT") ? : "60");

        /* 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.
         */
        bb_daemon_helper(DAEMON_CLOSE_EXTRA_FDS);

        username[0] = '\0';
        opt = getopt32(argv, "f:h:p", &opt_user, &opt_host);
        if (opt & LOGIN_OPT_f) {
                if (!run_by_root)
                        bb_simple_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(G.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_NEW_AUTHTOK_REQD) {
                        pamret = pam_chauthtok(pamh, PAM_CHANGE_EXPIRED_AUTHTOK);
                }
                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);
                login_pam_end(pamh);
                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 && !is_tty_secure(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;
                pause_after_failed_login();
                /* TODO: doesn't sound like correct English phrase to me */
                puts("Login incorrect");
                syslog(LOG_WARNING, "invalid password for '%s'%s",
                                        username, fromhost);
                if (++count == 3) {
                        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_FEATURE_UTMP(my_pid = getpid();)
        update_utmp(my_pid, USER_PROCESS, short_tty, username, run_by_root ? opt_host : NULL);

#if ENABLE_LOGIN_SESSION_AS_CHILD
        child_pid = vfork();
        if (child_pid != 0) {
                if (child_pid < 0)
                        bb_simple_perror_msg("vfork");
                else {
                        wait_for_exitstatus(child_pid);
                }
                update_utmp_DEAD_PROCESS(my_pid);
                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);

        /* 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 */
        exec_login_shell(pw->pw_shell);

        /* return EXIT_FAILURE; - not reached */
}