release/src/router/busybox/init/mesg.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * mesg implementation for busybox
   4  *
   5  * Copyright (c) 2002 Manuel Novoa III  <mjn3@codepoet.org>
   6  *
   7  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
   8  */
   9
  10 //config:config MESG
  11 //config:       bool "mesg"
  12 //config:       default y
  13 //config:       help
  14 //config:         Mesg controls access to your terminal by others. It is typically
  15 //config:         used to allow or disallow other users to write to your terminal
  16 //config:
  17 //config:config FEATURE_MESG_ENABLE_ONLY_GROUP
  18 //config:       bool "Enable writing to tty only by group, not by everybody"
  19 //config:       default y
  20 //config:       depends on MESG
  21 //config:       help
  22 //config:         Usually, ttys are owned by group "tty", and "write" tool is
  23 //config:         setgid to this group. This way, "mesg y" only needs to enable
  24 //config:         "write by owning group" bit in tty mode.
  25 //config:
  26 //config:         If you set this option to N, "mesg y" will enable writing
  27 //config:         by anybody at all. This is not recommended.
  28
  29 //applet:IF_MESG(APPLET(mesg, BB_DIR_USR_BIN, BB_SUID_DROP))
  30
  31 //kbuild:lib-$(CONFIG_MESG) += mesg.o
  32
  33 //usage:#define mesg_trivial_usage
  34 //usage:       "[y|n]"
  35 //usage:#define mesg_full_usage "\n\n"
  36 //usage:       "Control write access to your terminal\n"
  37 //usage:       "        y       Allow write access to your terminal\n"
  38 //usage:       "        n       Disallow write access to your terminal"
  39
  40 #include "libbb.h"
  41
  42 #if ENABLE_FEATURE_MESG_ENABLE_ONLY_GROUP
  43 #define S_IWGRP_OR_S_IWOTH  S_IWGRP
  44 #else
  45 #define S_IWGRP_OR_S_IWOTH  (S_IWGRP | S_IWOTH)
  46 #endif
  47
  48 int mesg_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  49 int mesg_main(int argc UNUSED_PARAM, char **argv)
  50 {
  51         struct stat sb;
  52         mode_t m;
  53         char c = 0;
  54
  55         argv++;
  56
  57         if (argv[0]
  58          && (argv[1] || ((c = argv[0][0]) != 'y' && c != 'n'))
  59         ) {
  60                 bb_show_usage();
  61         }
  62
  63         if (!isatty(STDIN_FILENO))
  64                 bb_error_msg_and_die("not a tty");
  65
  66         xfstat(STDIN_FILENO, &sb, "stderr");
  67         if (c == 0) {
  68                 puts((sb.st_mode & (S_IWGRP|S_IWOTH)) ? "is y" : "is n");
  69                 return EXIT_SUCCESS;
  70         }
  71         m = (c == 'y') ? sb.st_mode | S_IWGRP_OR_S_IWOTH
  72                        : sb.st_mode & ~(S_IWGRP|S_IWOTH);
  73         if (fchmod(STDIN_FILENO, m) != 0)
  74                 bb_perror_nomsg_and_die();
  75         return EXIT_SUCCESS;
  76 }