release/src/router/busybox/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
  13 //usage:#define crontab_trivial_usage
  14 //usage:       "[-c DIR] [-u USER] [-ler]|[FILE]"
  15 //usage:#define crontab_full_usage "\n\n"
  16 //usage:       "        -c      Crontab directory"
  17 //usage:     "\n        -u      User"
  18 //usage:     "\n        -l      List crontab"
  19 //usage:     "\n        -e      Edit crontab"
  20 //usage:     "\n        -r      Delete crontab"
  21 //usage:     "\n        FILE    Replace crontab by FILE ('-': stdin)"
  22
  23 #include "libbb.h"
  24
  25 #define CRONTABS        CONFIG_FEATURE_CROND_DIR "/crontabs"
  26 #ifndef CRONUPDATE
  27 #define CRONUPDATE      "cron.update"
  28 #endif
  29
  30 static void edit_file(const struct passwd *pas, const char *file)
  31 {
  32         const char *ptr;
  33         pid_t pid;
  34
  35         pid = xvfork();
  36         if (pid) { /* parent */
  37                 wait4pid(pid);
  38                 return;
  39         }
  40
  41         /* CHILD - change user and run editor */
  42         /* initgroups, setgid, setuid */
  43         change_identity(pas);
  44         setup_environment(pas->pw_shell,
  45                         SETUP_ENV_CHANGEENV | SETUP_ENV_TO_TMP,
  46                         pas);
  47         ptr = getenv("VISUAL");
  48         if (!ptr) {
  49                 ptr = getenv("EDITOR");
  50                 if (!ptr)
  51                         ptr = "vi";
  52         }
  53
  54         BB_EXECLP(ptr, ptr, file, NULL);
  55         bb_perror_msg_and_die("can't execute '%s'", ptr);
  56 }
  57
  58 static int open_as_user(const struct passwd *pas, const char *file)
  59 {
  60         pid_t pid;
  61         char c;
  62
  63         pid = xvfork();
  64         if (pid) { /* PARENT */
  65                 if (wait4pid(pid) == 0) {
  66                         /* exitcode 0: child says it can read */
  67                         return open(file, O_RDONLY);
  68                 }
  69                 return -1;
  70         }
  71
  72         /* CHILD */
  73         /* initgroups, setgid, setuid */
  74         change_identity(pas);
  75         /* We just try to read one byte. If it works, file is readable
  76          * under this user. We signal that by exiting with 0. */
  77         _exit(safe_read(xopen(file, O_RDONLY), &c, 1) < 0);
  78 }
  79
  80 int crontab_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  81 int crontab_main(int argc UNUSED_PARAM, char **argv)
  82 {
  83         const struct passwd *pas;
  84         const char *crontab_dir = CRONTABS;
  85         char *tmp_fname;
  86         char *new_fname;
  87         char *user_name;  /* -u USER */
  88         int fd;
  89         int src_fd;
  90         int opt_ler;
  91
  92         /* file [opts]     Replace crontab from file
  93          * - [opts]        Replace crontab from stdin
  94          * -u user         User
  95          * -c dir          Crontab directory
  96          * -l              List crontab for user
  97          * -e              Edit crontab for user
  98          * -r              Delete crontab for user
  99          * bbox also supports -d == -r, but most other crontab
 100          * implementations do not. Deprecated.
 101          */
 102         enum {
 103                 OPT_u = (1 << 0),
 104                 OPT_c = (1 << 1),
 105                 OPT_l = (1 << 2),
 106                 OPT_e = (1 << 3),
 107                 OPT_r = (1 << 4),
 108                 OPT_ler = OPT_l + OPT_e + OPT_r,
 109         };
 110
 111         opt_complementary = "?1:dr"; /* max one argument; -d implies -r */
 112         opt_ler = getopt32(argv, "u:c:lerd", &user_name, &crontab_dir);
 113         argv += optind;
 114
 115         if (sanitize_env_if_suid()) { /* Clears dangerous stuff, sets PATH */
 116                 /* Run by non-root */
 117                 if (opt_ler & (OPT_u|OPT_c))
 118                         bb_error_msg_and_die(bb_msg_you_must_be_root);
 119         }
 120
 121         if (opt_ler & OPT_u) {
 122                 pas = xgetpwnam(user_name);
 123         } else {
 124                 pas = xgetpwuid(getuid());
 125         }
 126
 127 #define user_name DONT_USE_ME_BEYOND_THIS_POINT
 128
 129         /* From now on, keep only -l, -e, -r bits */
 130         opt_ler &= OPT_ler;
 131         if ((opt_ler - 1) & opt_ler) /* more than one bit set? */
 132                 bb_show_usage();
 133
 134         /* Read replacement file under user's UID/GID/group vector */
 135         src_fd = STDIN_FILENO;
 136         if (!opt_ler) { /* Replace? */
 137                 if (!argv[0])
 138                         bb_show_usage();
 139                 if (NOT_LONE_DASH(argv[0])) {
 140                         src_fd = open_as_user(pas, argv[0]);
 141                         if (src_fd < 0)
 142                                 bb_error_msg_and_die("user %s cannot read %s",
 143                                                 pas->pw_name, argv[0]);
 144                 }
 145         }
 146
 147         /* cd to our crontab directory */
 148         xchdir(crontab_dir);
 149
 150         tmp_fname = NULL;
 151
 152         /* Handle requested operation */
 153         switch (opt_ler) {
 154
 155         default: /* case OPT_r: Delete */
 156                 unlink(pas->pw_name);
 157                 break;
 158
 159         case OPT_l: /* List */
 160                 {
 161                         char *args[2] = { pas->pw_name, NULL };
 162                         return bb_cat(args);
 163                         /* list exits,
 164                          * the rest go play with cron update file */
 165                 }
 166
 167         case OPT_e: /* Edit */
 168                 tmp_fname = xasprintf("%s.%u", crontab_dir, (unsigned)getpid());
 169                 /* No O_EXCL: we don't want to be stuck if earlier crontabs
 170                  * were killed, leaving stale temp file behind */
 171                 src_fd = xopen3(tmp_fname, O_RDWR|O_CREAT|O_TRUNC, 0600);
 172                 fchown(src_fd, pas->pw_uid, pas->pw_gid);
 173                 fd = open(pas->pw_name, O_RDONLY);
 174                 if (fd >= 0) {
 175                         bb_copyfd_eof(fd, src_fd);
 176                         close(fd);
 177                         xlseek(src_fd, 0, SEEK_SET);
 178                 }
 179                 close_on_exec_on(src_fd); /* don't want editor to see this fd */
 180                 edit_file(pas, tmp_fname);
 181                 /* fall through */
 182
 183         case 0: /* Replace (no -l, -e, or -r were given) */
 184                 new_fname = xasprintf("%s.new", pas->pw_name);
 185                 fd = open(new_fname, O_WRONLY|O_CREAT|O_TRUNC|O_APPEND, 0600);
 186                 if (fd >= 0) {
 187                         bb_copyfd_eof(src_fd, fd);
 188                         close(fd);
 189                         xrename(new_fname, pas->pw_name);
 190                 } else {
 191                         bb_error_msg("can't create %s/%s",
 192                                         crontab_dir, new_fname);
 193                 }
 194                 if (tmp_fname)
 195                         unlink(tmp_fname);
 196                 /*free(tmp_fname);*/
 197                 /*free(new_fname);*/
 198
 199         } /* switch */
 200
 201         /* Bump notification file.  Handle window where crond picks file up
 202          * before we can write our entry out.
 203          */
 204         while ((fd = open(CRONUPDATE, O_WRONLY|O_CREAT|O_APPEND, 0600)) >= 0) {
 205                 struct stat st;
 206
 207                 fdprintf(fd, "%s\n", pas->pw_name);
 208                 if (fstat(fd, &st) != 0 || st.st_nlink != 0) {
 209                         /*close(fd);*/
 210                         break;
 211                 }
 212                 /* st.st_nlink == 0:
 213                  * file was deleted, maybe crond missed our notification */
 214                 close(fd);
 215                 /* loop */
 216         }
 217         if (fd < 0) {
 218                 bb_error_msg("can't append to %s/%s",
 219                                 crontab_dir, CRONUPDATE);
 220         }
 221         return 0;
 222 }