LXR busybox/shell/cttyhack.c

   1/* vi: set sw=4 ts=4: */
   2/*
   3 * Copyright (c) 2007 Denys Vlasenko <vda.linux@googlemail.com>
   4 *
   5 * Licensed under GPLv2, see file LICENSE in this source tree.
   6 */
   7#include "libbb.h"
   8
   9//applet:IF_CTTYHACK(APPLET(cttyhack, _BB_DIR_BIN, _BB_SUID_DROP))
  10
  11//kbuild:lib-$(CONFIG_CTTYHACK) += cttyhack.o
  12
  13//config:config CTTYHACK
  14//config:       bool "cttyhack"
  15//config:       default y
  16//config:       help
  17//config:         One common problem reported on the mailing list is "can't access tty;
  18//config:         job control turned off" error message which typically appears when
  19//config:         one tries to use shell with stdin/stdout opened to /dev/console.
  20//config:         This device is special - it cannot be a controlling tty.
  21//config:
  22//config:         Proper solution is to use correct device instead of /dev/console.
  23//config:
  24//config:         cttyhack provides "quick and dirty" solution to this problem.
  25//config:         It analyzes stdin with various ioctls, trying to determine whether
  26//config:         it is a /dev/ttyN or /dev/ttySN (virtual terminal or serial line).
  27//config:         If it detects one, it closes stdin/out/err and reopens that device.
  28//config:         Then it executes given program. Opening the device will make
  29//config:         that device a controlling tty. This may require cttyhack
  30//config:         to be a session leader.
  31//config:
  32//config:         Example for /etc/inittab (for busybox init):
  33//config:
  34//config:         ::respawn:/bin/cttyhack /bin/sh
  35//config:
  36//config:         Starting an interactive shell from boot shell script:
  37//config:
  38//config:         setsid cttyhack sh
  39//config:
  40//config:         Giving controlling tty to shell running with PID 1:
  41//config:
  42//config:         # exec cttyhack sh
  43//config:
  44//config:         Without cttyhack, you need to know exact tty name,
  45//config:         and do something like this:
  46//config:
  47//config:         # exec setsid sh -c 'exec sh </dev/tty1 >/dev/tty1 2>&1'
  48//config:
  49
  50//usage:#define cttyhack_trivial_usage
  51//usage:       "PROG ARGS"
  52//usage:#define cttyhack_full_usage "\n\n"
  53//usage:       "Give PROG a controlling tty if possible."
  54//usage:     "\nExample for /etc/inittab (for busybox init):"
  55//usage:     "\n        ::respawn:/bin/cttyhack /bin/sh"
  56//usage:     "\nGiving controlling tty to shell running with PID 1:"
  57//usage:     "\n        $ exec cttyhack sh"
  58//usage:     "\nStarting interactive shell from boot shell script:"
  59//usage:     "\n        setsid cttyhack sh"
  60
  61#if !defined(__linux__) && !defined(TIOCGSERIAL) && !ENABLE_WERROR
  62# warning cttyhack will not be able to detect a controlling tty on this system
  63#endif
  64
  65/* From <linux/vt.h> */
  66struct vt_stat {
  67        unsigned short v_active;        /* active vt */
  68        unsigned short v_signal;        /* signal to send */
  69        unsigned short v_state;         /* vt bitmask */
  70};
  71enum { VT_GETSTATE = 0x5603 }; /* get global vt state info */
  72
  73/* From <linux/serial.h> */
  74struct serial_struct {
  75        int     type;
  76        int     line;
  77        unsigned int    port;
  78        int     irq;
  79        int     flags;
  80        int     xmit_fifo_size;
  81        int     custom_divisor;
  82        int     baud_base;
  83        unsigned short  close_delay;
  84        char    io_type;
  85        char    reserved_char[1];
  86        int     hub6;
  87        unsigned short  closing_wait;   /* time to wait before closing */
  88        unsigned short  closing_wait2;  /* no longer used... */
  89        unsigned char   *iomem_base;
  90        unsigned short  iomem_reg_shift;
  91        unsigned int    port_high;
  92        unsigned long   iomap_base;     /* cookie passed into ioremap */
  93        int     reserved[1];
  94};
  95
  96int cttyhack_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  97int cttyhack_main(int argc UNUSED_PARAM, char **argv)
  98{
  99        int fd;
 100        char console[sizeof(int)*3 + 16];
 101        union {
 102                struct vt_stat vt;
 103                struct serial_struct sr;
 104                char paranoia[sizeof(struct serial_struct) * 3];
 105        } u;
 106
 107        if (!*++argv) {
 108                bb_show_usage();
 109        }
 110
 111        strcpy(console, "/dev/tty");
 112        fd = open(console, O_RDWR);
 113        if (fd >= 0) {
 114                /* We already have ctty, nothing to do */
 115                close(fd);
 116        } else {
 117                /* We don't have ctty (or don't have "/dev/tty" node...) */
 118                if (0) {}
 119#ifdef TIOCGSERIAL
 120                else if (ioctl(0, TIOCGSERIAL, &u.sr) == 0) {
 121                        /* this is a serial console */
 122                        sprintf(console + 8, "S%d", u.sr.line);
 123                }
 124#endif
 125#ifdef __linux__
 126                else if (ioctl(0, VT_GETSTATE, &u.vt) == 0) {
 127                        /* this is linux virtual tty */
 128                        sprintf(console + 8, "S%d" + 1, u.vt.v_active);
 129                }
 130#endif
 131                if (console[8]) {
 132                        fd = xopen(console, O_RDWR);
 133                        //bb_error_msg("switching to '%s'", console);
 134                        dup2(fd, 0);
 135                        dup2(fd, 1);
 136                        dup2(fd, 2);
 137                        while (fd > 2)
 138                                close(fd--);
 139                        /* Some other session may have it as ctty,
 140                         * steal it from them:
 141                         */
 142                        ioctl(0, TIOCSCTTY, 1);
 143                }
 144        }
 145
 146        BB_EXECVP_or_die(argv);
 147}
 148