/* 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.
 */
//config:config CRONTAB
//config:       bool "crontab (10 kb)"
//config:       default y
//config:       help
//config:       Crontab manipulates the crontab for a particular user. Only
//config:       the superuser may specify a different user and/or crontab directory.
//config:       Note that busybox binary must be setuid root for this applet to
//config:       work properly.

/* Needs to be run by root or be suid root - needs to change /var/spool/cron* files: */
//applet:IF_CRONTAB(APPLET(crontab, BB_DIR_USR_BIN, BB_SUID_REQUIRE))

//kbuild:lib-$(CONFIG_CRONTAB) += crontab.o

//usage:#define crontab_trivial_usage
//usage:       "[-c DIR] [-u USER] [-ler]|[FILE]"
//usage:#define crontab_full_usage "\n\n"
//usage:       "        -c      Crontab directory"
//usage:     "\n        -u      User"
//usage:     "\n        -l      List crontab"
//usage:     "\n        -e      Edit crontab"
//usage:     "\n        -r      Delete crontab"
//usage:     "\n        FILE    Replace crontab by FILE ('-': stdin)"

#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;
        pid_t pid;

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

        /* CHILD - change user and run editor */
        /* initgroups, setgid, setuid */
        change_identity(pas);
        setup_environment(pas->pw_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("can't execute '%s'", ptr);
}

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_ler = getopt32(argv, "^" "u:c:lerd" "\0" "?1:dr"/*max one arg; -d implies -r*/,
                                &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_simple_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 = xopen_as_uid_gid(argv[0], O_RDONLY, pas->pw_uid, pas->pw_gid);
                }
        }

        /* 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(src_fd);
                edit_file(pas, tmp_fname);
                /* The src_fd needs to be reopened to handle editors that do
                 * save the buffer as new file and rename it to tmp_fname (so
                 * for example vim). */
                src_fd = xopen3(tmp_fname, O_RDONLY, 0600);
                /* 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;
}