source: MondoRescue/branches/stable/mindi-busybox/miscutils/crontab.c@ 1770

/* 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"

#ifndef CRONTABS
#define CRONTABS        "/var/spool/cron/crontabs"
#endif
#ifndef TMPDIR
#define TMPDIR          "/var/spool/cron"
#endif
#ifndef CRONUPDATE
#define CRONUPDATE      "cron.update"
#endif
#ifndef PATH_VI
#define PATH_VI         "/bin/vi"   /* location of vi */
#endif

static const char *CDir = CRONTABS;

static void EditFile(const char *user, const char *file);
static int GetReplaceStream(const char *user, const char *file);
static int ChangeUser(const char *user, short dochdir);

int crontab_main(int ac, char **av);
int crontab_main(int ac, char **av)
{
    enum { NONE, EDIT, LIST, REPLACE, DELETE } option = NONE;
    const struct passwd *pas;
    const char *repFile = NULL;
    int repFd = 0;
    int i;
    char caller[256];           /* user that ran program */
    char buf[1024];
    int UserId;

    UserId = getuid();
    pas = getpwuid(UserId);
    if (pas == NULL)
        bb_perror_msg_and_die("getpwuid");

    safe_strncpy(caller, pas->pw_name, sizeof(caller));

    i = 1;
    if (ac > 1) {
        if (LONE_DASH(av[1])) {
            option = REPLACE;
            ++i;
        } else if (av[1][0] != '-') {
            option = REPLACE;
            ++i;
            repFile = av[1];
        }
    }

    for (; i < ac; ++i) {
        char *ptr = av[i];

        if (*ptr != '-')
            break;
        ptr += 2;

        switch (ptr[-1]) {
        case 'l':
            if (ptr[-1] == 'l')
                option = LIST;
            /* fall through */
        case 'e':
            if (ptr[-1] == 'e')
                option = EDIT;
            /* fall through */
        case 'd':
            if (ptr[-1] == 'd')
                option = DELETE;
            /* fall through */
        case 'u':
            if (i + 1 < ac && av[i+1][0] != '-') {
                ++i;
                if (getuid() == geteuid()) {
                    pas = getpwnam(av[i]);
                    if (pas) {
                        UserId = pas->pw_uid;
                    } else {
                        bb_error_msg_and_die("user %s unknown", av[i]);
                    }
                } else {
                    bb_error_msg_and_die("only the superuser may specify a user");
                }
            }
            break;
        case 'c':
            if (getuid() == geteuid()) {
                CDir = (*ptr) ? ptr : av[++i];
            } else {
                bb_error_msg_and_die("-c option: superuser only");
            }
            break;
        default:
            i = ac;
            break;
        }
    }
    if (i != ac || option == NONE)
        bb_show_usage();

    /*
     * Get password entry
     */

    pas = getpwuid(UserId);
    if (pas == NULL)
        bb_perror_msg_and_die("getpwuid");

    /*
     * If there is a replacement file, obtain a secure descriptor to it.
     */

    if (repFile) {
        repFd = GetReplaceStream(caller, repFile);
        if (repFd < 0)
            bb_error_msg_and_die("cannot read replacement file");
    }

    /*
     * Change directory to our crontab directory
     */

    xchdir(CDir);

    /*
     * Handle options as appropriate
     */

    switch (option) {
    case LIST:
        {
            FILE *fi;

            fi = fopen(pas->pw_name, "r");
            if (fi) {
                while (fgets(buf, sizeof(buf), fi) != NULL)
                    fputs(buf, stdout);
                fclose(fi);
            } else {
                bb_error_msg("no crontab for %s", pas->pw_name);
            }
        }
        break;
    case EDIT:
        {
/* FIXME: messy code here! we have file copying helpers for this! */
            FILE *fi;
            int fd;
            int n;
            char tmp[128];

            snprintf(tmp, sizeof(tmp), TMPDIR "/crontab.%d", getpid());
            fd = xopen3(tmp, O_RDWR|O_CREAT|O_TRUNC|O_EXCL, 0600);
/* race, use fchown */
            chown(tmp, getuid(), getgid());
            fi = fopen(pas->pw_name, "r");
            if (fi) {
                while ((n = fread(buf, 1, sizeof(buf), fi)) > 0)
                    full_write(fd, buf, n);
            }
            EditFile(caller, tmp);
            remove(tmp);
            lseek(fd, 0L, SEEK_SET);
            repFd = fd;
        }
        option = REPLACE;
        /* fall through */
    case REPLACE:
        {
/* same here */
            char path[1024];
            int fd;
            int n;

            snprintf(path, sizeof(path), "%s.new", pas->pw_name);
            fd = open(path, O_CREAT|O_TRUNC|O_APPEND|O_WRONLY, 0600);
            if (fd >= 0) {
                while ((n = read(repFd, buf, sizeof(buf))) > 0) {
                    full_write(fd, buf, n);
                }
                close(fd);
                rename(path, pas->pw_name);
            } else {
                bb_error_msg("cannot create %s/%s", CDir, path);
            }
            close(repFd);
        }
        break;
    case DELETE:
        remove(pas->pw_name);
        break;
    case NONE:
    default:
        break;
    }

    /*
     *  Bump notification file.  Handle window where crond picks file up
     *  before we can write our entry out.
     */

    if (option == REPLACE || option == DELETE) {
        FILE *fo;
        struct stat st;

        while ((fo = fopen(CRONUPDATE, "a"))) {
            fprintf(fo, "%s\n", pas->pw_name);
            fflush(fo);
            if (fstat(fileno(fo), &st) != 0 || st.st_nlink != 0) {
                fclose(fo);
                break;
            }
            fclose(fo);
            /* loop */
        }
        if (fo == NULL) {
            bb_error_msg("cannot append to %s/%s", CDir, CRONUPDATE);
        }
    }
    return 0;
}

static int GetReplaceStream(const char *user, const char *file)
{
    int filedes[2];
    int pid;
    int fd;
    int n;
    char buf[1024];

    if (pipe(filedes) < 0) {
        perror("pipe");
        return -1;
    }
    pid = fork();
    if (pid < 0) {
        perror("fork");
        return -1;
    }
    if (pid > 0) {
        /*
         * PARENT
         */

        close(filedes[1]);
        if (read(filedes[0], buf, 1) != 1) {
            close(filedes[0]);
            filedes[0] = -1;
        }
        return filedes[0];
    }

    /*
     * CHILD
     */

    close(filedes[0]);

    if (ChangeUser(user, 0) < 0)
        exit(0);

    xfunc_error_retval = 0;
    fd = xopen(file, O_RDONLY);
    buf[0] = 0;
    write(filedes[1], buf, 1);
    while ((n = read(fd, buf, sizeof(buf))) > 0) {
        write(filedes[1], buf, n);
    }
    exit(0);
}

static void EditFile(const char *user, const char *file)
{
    int pid = fork();

    if (pid == 0) {
        /*
         * CHILD - change user and run editor
         */
        const char *ptr;

        if (ChangeUser(user, 1) < 0)
            exit(0);
        ptr = getenv("VISUAL");
        if (ptr == NULL)
            ptr = getenv("EDITOR");
        if (ptr == NULL)
            ptr = PATH_VI;

        ptr = xasprintf("%s %s", ptr, file);
        execl(DEFAULT_SHELL, DEFAULT_SHELL, "-c", ptr, NULL);
        bb_perror_msg_and_die("exec");
    }
    if (pid < 0) {
        /*
         * PARENT - failure
         */
        bb_perror_msg_and_die("fork");
    }
    wait4(pid, NULL, 0, NULL);
}

static int ChangeUser(const char *user, short dochdir)
{
    struct passwd *pas;

    /*
     * Obtain password entry and change privileges
     */

    pas = getpwnam(user);
    if (pas == NULL) {
        bb_perror_msg_and_die("failed to get uid for %s", user);
    }
    setenv("USER", pas->pw_name, 1);
    setenv("HOME", pas->pw_dir, 1);
    setenv("SHELL", DEFAULT_SHELL, 1);

    /*
     * Change running state to the user in question
     */
    change_identity(pas);

    if (dochdir) {
        if (chdir(pas->pw_dir) < 0) {
            bb_perror_msg("chdir(%s) by %s failed", pas->pw_dir, user);
            xchdir(TMPDIR);
        }
    }
    return pas->pw_uid;
}