LXR 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
  48int mesg_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  49int 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}
  77