source: MondoRescue/branches/2.2.9/mindi-busybox/miscutils/crontab.c@ 2725

/* vi: set sw=4 ts=4: */
/*
 * CRONTAB
 *
 * usually setuid root, -c option only works if getuid() == geteuid()
 *
 * Copyright 1994 Matthew Dillon (dillon@apollo.west.oic.com)
 * Vladimir Oleynik <dzo@simtreas.ru> (C) 2002
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */

#include "libbb.h"

#define CRONTABS        CONFIG_FEATURE_CROND_DIR "/crontabs"
#ifndef CRONUPDATE
#define CRONUPDATE      "cron.update"
#endif

static void edit_file(const struct passwd *pas, const char *file)
{
    const char *ptr;
    int pid = xvfork();

    if (pid) { /* parent */
        wait4pid(pid);
        return;
    }

    /* CHILD - change user and run editor */
    /* initgroups, setgid, setuid */
    change_identity(pas);
    setup_environment(DEFAULT_SHELL,
            SETUP_ENV_CHANGEENV | SETUP_ENV_TO_TMP,
            pas);
    ptr = getenv("VISUAL");
    if (!ptr) {
        ptr = getenv("EDITOR");
        if (!ptr)
            ptr = "vi";
    }

    BB_EXECLP(ptr, ptr, file, NULL);
    bb_perror_msg_and_die("exec %s", ptr);
}

static int open_as_user(const struct passwd *pas, const char *file)
{
    pid_t pid;
    char c;

    pid = xvfork();
    if (pid) { /* PARENT */
        if (wait4pid(pid) == 0) {
            /* exitcode 0: child says it can read */
            return open(file, O_RDONLY);
        }
        return -1;
    }

    /* CHILD */
    /* initgroups, setgid, setuid */
    change_identity(pas);
    /* We just try to read one byte. If it works, file is readable
     * under this user. We signal that by exiting with 0. */
    _exit(safe_read(xopen(file, O_RDONLY), &c, 1) < 0);
}

int crontab_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int crontab_main(int argc UNUSED_PARAM, char **argv)
{
    const struct passwd *pas;
    const char *crontab_dir = CRONTABS;
    char *tmp_fname;
    char *new_fname;
    char *user_name;  /* -u USER */
    int fd;
    int src_fd;
    int opt_ler;

    /* file [opts]     Replace crontab from file
     * - [opts]        Replace crontab from stdin
     * -u user         User
     * -c dir          Crontab directory
     * -l              List crontab for user
     * -e              Edit crontab for user
     * -r              Delete crontab for user
     * bbox also supports -d == -r, but most other crontab
     * implementations do not. Deprecated.
     */
    enum {
        OPT_u = (1 << 0),
        OPT_c = (1 << 1),
        OPT_l = (1 << 2),
        OPT_e = (1 << 3),
        OPT_r = (1 << 4),
        OPT_ler = OPT_l + OPT_e + OPT_r,
    };

    opt_complementary = "?1:dr"; /* max one argument; -d implies -r */
    opt_ler = getopt32(argv, "u:c:lerd", &user_name, &crontab_dir);
    argv += optind;

    if (sanitize_env_if_suid()) { /* Clears dangerous stuff, sets PATH */
        /* Run by non-root */
        if (opt_ler & (OPT_u|OPT_c))
            bb_error_msg_and_die(bb_msg_you_must_be_root);
    }

    if (opt_ler & OPT_u) {
        pas = xgetpwnam(user_name);
    } else {
        pas = xgetpwuid(getuid());
    }

#define user_name DONT_USE_ME_BEYOND_THIS_POINT

    /* From now on, keep only -l, -e, -r bits */
    opt_ler &= OPT_ler;
    if ((opt_ler - 1) & opt_ler) /* more than one bit set? */
        bb_show_usage();

    /* Read replacement file under user's UID/GID/group vector */
    src_fd = STDIN_FILENO;
    if (!opt_ler) { /* Replace? */
        if (!argv[0])
            bb_show_usage();
        if (NOT_LONE_DASH(argv[0])) {
            src_fd = open_as_user(pas, argv[0]);
            if (src_fd < 0)
                bb_error_msg_and_die("user %s cannot read %s",
                        pas->pw_name, argv[0]);
        }
    }

    /* cd to our crontab directory */
    xchdir(crontab_dir);

    tmp_fname = NULL;

    /* Handle requested operation */
    switch (opt_ler) {

    default: /* case OPT_r: Delete */
        unlink(pas->pw_name);
        break;

    case OPT_l: /* List */
        {
            char *args[2] = { pas->pw_name, NULL };
            return bb_cat(args);
            /* list exits,
             * the rest go play with cron update file */
        }

    case OPT_e: /* Edit */
        tmp_fname = xasprintf("%s.%u", crontab_dir, (unsigned)getpid());
        /* No O_EXCL: we don't want to be stuck if earlier crontabs
         * were killed, leaving stale temp file behind */
        src_fd = xopen3(tmp_fname, O_RDWR|O_CREAT|O_TRUNC, 0600);
        fchown(src_fd, pas->pw_uid, pas->pw_gid);
        fd = open(pas->pw_name, O_RDONLY);
        if (fd >= 0) {
            bb_copyfd_eof(fd, src_fd);
            close(fd);
            xlseek(src_fd, 0, SEEK_SET);
        }
        close_on_exec_on(src_fd); /* don't want editor to see this fd */
        edit_file(pas, tmp_fname);
        /* fall through */

    case 0: /* Replace (no -l, -e, or -r were given) */
        new_fname = xasprintf("%s.new", pas->pw_name);
        fd = open(new_fname, O_WRONLY|O_CREAT|O_TRUNC|O_APPEND, 0600);
        if (fd >= 0) {
            bb_copyfd_eof(src_fd, fd);
            close(fd);
            xrename(new_fname, pas->pw_name);
        } else {
            bb_error_msg("can't create %s/%s",
                    crontab_dir, new_fname);
        }
        if (tmp_fname)
            unlink(tmp_fname);
        /*free(tmp_fname);*/
        /*free(new_fname);*/

    } /* switch */

    /* Bump notification file.  Handle window where crond picks file up
     * before we can write our entry out.
     */
    while ((fd = open(CRONUPDATE, O_WRONLY|O_CREAT|O_APPEND, 0600)) >= 0) {
        struct stat st;

        fdprintf(fd, "%s\n", pas->pw_name);
        if (fstat(fd, &st) != 0 || st.st_nlink != 0) {
            /*close(fd);*/
            break;
        }
        /* st.st_nlink == 0:
         * file was deleted, maybe crond missed our notification */
        close(fd);
        /* loop */
    }
    if (fd < 0) {
        bb_error_msg("can't append to %s/%s",
                crontab_dir, CRONUPDATE);
    }
    return 0;
}