/* 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 the GPL v2 or later, see the file LICENSE in this tarball.
 */

#include "libbb.h"

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

static void change_user(const struct passwd *pas)
{
        xsetenv("USER", pas->pw_name);
        xsetenv("HOME", pas->pw_dir);
        xsetenv("SHELL", DEFAULT_SHELL);

        /* initgroups, setgid, setuid */
        change_identity(pas);

        if (chdir(pas->pw_dir) < 0) {
                bb_perror_msg("chdir(%s) by %s failed",
                                pas->pw_dir, pas->pw_name);
                xchdir("/tmp");
        }
}

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

        if (pid < 0) /* failure */
                bb_perror_msg_and_die("vfork");
        if (pid) { /* parent */
                wait4pid(pid);
                return;
        }

        /* CHILD - change user and run editor */
        change_user(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 = vfork();
        if (pid < 0) /* ERROR */
                bb_perror_msg_and_die("vfork");
        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("only root can use -c or -u");
        }

        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("cannot 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("cannot append to %s/%s",
                                crontab_dir, CRONUPDATE);
        }
        return 0;
}