miscutils/crontab.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * CRONTAB
   4  *
   5  * usually setuid root, -c option only works if getuid() == geteuid()
   6  *
   7  * Copyright 1994 Matthew Dillon (dillon@apollo.west.oic.com)
   8  * Vladimir Oleynik <dzo@simtreas.ru> (C) 2002
   9  *
  10  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
  11  */
  12 //config:config CRONTAB
  13 //config:       bool "crontab (10 kb)"
  14 //config:       default y
  15 //config:       help
  16 //config:       Crontab manipulates the crontab for a particular user. Only
  17 //config:       the superuser may specify a different user and/or crontab directory.
  18 //config:       Note that busybox binary must be setuid root for this applet to
  19 //config:       work properly.
  20
  21 /* Needs to be run by root or be suid root - needs to change /var/spool/cron* files: */
  22 //applet:IF_CRONTAB(APPLET(crontab, BB_DIR_USR_BIN, BB_SUID_REQUIRE))
  23
  24 //kbuild:lib-$(CONFIG_CRONTAB) += crontab.o
  25
  26 //usage:#define crontab_trivial_usage
  27 //usage:       "[-c DIR] [-u USER] [-ler]|[FILE]"
  28 //usage:#define crontab_full_usage "\n\n"
  29 //usage:       "        -c      Crontab directory"
  30 //usage:     "\n        -u      User"
  31 //usage:     "\n        -l      List crontab"
  32 //usage:     "\n        -e      Edit crontab"
  33 //usage:     "\n        -r      Delete crontab"
  34 //usage:     "\n        FILE    Replace crontab by FILE ('-': stdin)"
  35
  36 #include "libbb.h"
  37
  38 #define CRONTABS        CONFIG_FEATURE_CROND_DIR "/crontabs"
  39 #ifndef CRONUPDATE
  40 #define CRONUPDATE      "cron.update"
  41 #endif
  42
  43 static void edit_file(const struct passwd *pas, const char *file)
  44 {
  45         const char *ptr;
  46         pid_t pid;
  47
  48         pid = xvfork();
  49         if (pid) { /* parent */
  50                 wait4pid(pid);
  51                 return;
  52         }
  53
  54         /* CHILD - change user and run editor */
  55         /* initgroups, setgid, setuid */
  56         change_identity(pas);
  57         setup_environment(pas->pw_shell,
  58                 SETUP_ENV_CHANGEENV | SETUP_ENV_TO_TMP | SETUP_ENV_CHDIR,
  59                 pas);
  60         ptr = getenv("VISUAL");
  61         if (!ptr) {
  62                 ptr = getenv("EDITOR");
  63                 if (!ptr)
  64                         ptr = "vi";
  65         }
  66
  67         BB_EXECLP(ptr, ptr, file, NULL);
  68         bb_perror_msg_and_die("can't execute '%s'", ptr);
  69 }
  70
  71 int crontab_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  72 int crontab_main(int argc UNUSED_PARAM, char **argv)
  73 {
  74         const struct passwd *pas;
  75         const char *crontab_dir = CRONTABS;
  76         char *tmp_fname;
  77         char *new_fname;
  78         char *user_name;  /* -u USER */
  79         int fd;
  80         int src_fd;
  81         int opt_ler;
  82
  83         /* file [opts]     Replace crontab from file
  84          * - [opts]        Replace crontab from stdin
  85          * -u user         User
  86          * -c dir          Crontab directory
  87          * -l              List crontab for user
  88          * -e              Edit crontab for user
  89          * -r              Delete crontab for user
  90          * bbox also supports -d == -r, but most other crontab
  91          * implementations do not. Deprecated.
  92          */
  93         enum {
  94                 OPT_u = (1 << 0),
  95                 OPT_c = (1 << 1),
  96                 OPT_l = (1 << 2),
  97                 OPT_e = (1 << 3),
  98                 OPT_r = (1 << 4),
  99                 OPT_ler = OPT_l + OPT_e + OPT_r,
 100         };
 101
 102         opt_ler = getopt32(argv, "^" "u:c:lerd" "\0" "?1:dr"/*max one arg; -d implies -r*/,
 103                                 &user_name, &crontab_dir
 104         );
 105         argv += optind;
 106
 107         if (sanitize_env_if_suid()) { /* Clears dangerous stuff, sets PATH */
 108                 /* Run by non-root */
 109                 if (opt_ler & (OPT_u|OPT_c))
 110                         bb_simple_error_msg_and_die(bb_msg_you_must_be_root);
 111         }
 112
 113         if (opt_ler & OPT_u) {
 114                 pas = xgetpwnam(user_name);
 115         } else {
 116                 pas = xgetpwuid(getuid());
 117         }
 118
 119 #define user_name DONT_USE_ME_BEYOND_THIS_POINT
 120
 121         /* From now on, keep only -l, -e, -r bits */
 122         opt_ler &= OPT_ler;
 123         if ((opt_ler - 1) & opt_ler) /* more than one bit set? */
 124                 bb_show_usage();
 125
 126         /* Read replacement file under user's UID/GID/group vector */
 127         src_fd = STDIN_FILENO;
 128         if (!opt_ler) { /* Replace? */
 129                 if (!argv[0])
 130                         bb_show_usage();
 131                 if (NOT_LONE_DASH(argv[0])) {
 132                         src_fd = xopen_as_uid_gid(argv[0], O_RDONLY, pas->pw_uid, pas->pw_gid);
 133                 }
 134         }
 135
 136         /* cd to our crontab directory */
 137         xchdir(crontab_dir);
 138
 139         tmp_fname = NULL;
 140
 141         /* Handle requested operation */
 142         switch (opt_ler) {
 143
 144         default: /* case OPT_r: Delete */
 145                 unlink(pas->pw_name);
 146                 break;
 147
 148         case OPT_l: /* List */
 149                 {
 150                         char *args[2] = { pas->pw_name, NULL };
 151                         return bb_cat(args);
 152                         /* list exits,
 153                          * the rest go play with cron update file */
 154                 }
 155
 156         case OPT_e: /* Edit */
 157                 tmp_fname = xasprintf("%s.%u", crontab_dir, (unsigned)getpid());
 158                 /* No O_EXCL: we don't want to be stuck if earlier crontabs
 159                  * were killed, leaving stale temp file behind */
 160                 src_fd = xopen3(tmp_fname, O_RDWR|O_CREAT|O_TRUNC, 0600);
 161                 fchown(src_fd, pas->pw_uid, pas->pw_gid);
 162                 fd = open(pas->pw_name, O_RDONLY);
 163                 if (fd >= 0) {
 164                         bb_copyfd_eof(fd, src_fd);
 165                         close(fd);
 166                         xlseek(src_fd, 0, SEEK_SET);
 167                 }
 168                 close(src_fd);
 169                 edit_file(pas, tmp_fname);
 170                 /* The src_fd needs to be reopened to handle editors that do
 171                  * save the buffer as new file and rename it to tmp_fname (so
 172                  * for example vim). */
 173                 src_fd = xopen3(tmp_fname, O_RDONLY, 0600);
 174                 /* fall through */
 175
 176         case 0: /* Replace (no -l, -e, or -r were given) */
 177                 new_fname = xasprintf("%s.new", pas->pw_name);
 178                 fd = open(new_fname, O_WRONLY|O_CREAT|O_TRUNC|O_APPEND, 0600);
 179                 if (fd >= 0) {
 180                         bb_copyfd_eof(src_fd, fd);
 181                         close(fd);
 182                         xrename(new_fname, pas->pw_name);
 183                 } else {
 184                         bb_error_msg("can't create %s/%s",
 185                                         crontab_dir, new_fname);
 186                 }
 187                 if (tmp_fname)
 188                         unlink(tmp_fname);
 189                 /*free(tmp_fname);*/
 190                 /*free(new_fname);*/
 191         } /* switch */
 192
 193         /* Bump notification file.  Handle window where crond picks file up
 194          * before we can write our entry out.
 195          */
 196         while ((fd = open(CRONUPDATE, O_WRONLY|O_CREAT|O_APPEND, 0600)) >= 0) {
 197                 struct stat st;
 198
 199                 fdprintf(fd, "%s\n", pas->pw_name);
 200                 if (fstat(fd, &st) != 0 || st.st_nlink != 0) {
 201                         /*close(fd);*/
 202                         break;
 203                 }
 204                 /* st.st_nlink == 0:
 205                  * file was deleted, maybe crond missed our notification */
 206                 close(fd);
 207                 /* loop */
 208         }
 209         if (fd < 0) {
 210                 bb_error_msg("can't append to %s/%s",
 211                                 crontab_dir, CRONUPDATE);
 212         }
 213         return 0;
 214 }