src/consaver/cons.saver.c

   1 /* This program should be setuid vcsa and /dev/vcsa* should be
   2    owned by the same user too.
   3    Partly rewritten by Jakub Jelinek <jakub@redhat.com>.  */
   4
   5 /* General purpose Linux console screen save/restore server
   6    Copyright (C) 1994, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
   7    2006, 2007 Free Software Foundation, Inc.
   8    Original idea from Unix Interactive Tools version 3.2b (tty.c)
   9    This code requires root privileges.
  10    You may want to make the cons.saver setuid root.
  11    The code should be safe even if it is setuid but who knows?
  12
  13    This program is free software; you can redistribute it and/or modify
  14    it under the terms of the GNU General Public License as published by
  15    the Free Software Foundation; either version 2 of the License, or
  16    (at your option) any later version.
  17
  18    This program is distributed in the hope that it will be useful,
  19    but WITHOUT ANY WARRANTY; without even the implied warranty of
  20    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  21    GNU General Public License for more details.
  22
  23    You should have received a copy of the GNU General Public License
  24    along with this program; if not, write to the Free Software
  25    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  26
  27 /* This code does _not_ need to be setuid root. However, it needs
  28    read/write access to /dev/vcsa* (which is priviledged
  29    operation). You should create user vcsa, make cons.saver setuid
  30    user vcsa, and make all vcsa's owned by user vcsa.
  31
  32    Seeing other peoples consoles is bad thing, but believe me, full
  33    root is even worse. */
  34
  35 /** \file cons.saver.c
  36  *  \brief Source: general purpose Linux console screen save/restore server
  37  *
  38  *  This code does _not_ need to be setuid root. However, it needs
  39  *  read/write access to /dev/vcsa* (which is priviledged
  40  *  operation). You should create user vcsa, make cons.saver setuid
  41  *  user vcsa, and make all vcsa's owned by user vcsa.
  42  *  Seeing other peoples consoles is bad thing, but believe me, full
  43  *  root is even worse.
  44  */
  45
  46 #include <config.h>
  47
  48 #ifndef _GNU_SOURCE
  49 #define _GNU_SOURCE
  50 #endif
  51
  52 #include <stdlib.h>
  53 #include <stdio.h>
  54 #include <string.h>
  55
  56 #include <sys/types.h>
  57 #include <sys/stat.h>
  58 #include <sys/ioctl.h>
  59 #include <fcntl.h>
  60 #include <termios.h>
  61 #include <unistd.h>
  62
  63 #define LINUX_CONS_SAVER_C
  64 #include "cons.saver.h"
  65
  66 /*** global variables ****************************************************************************/
  67
  68 /*** file scope macro definitions ****************************************************************/
  69
  70 /*** file scope type declarations ****************************************************************/
  71
  72 /*** file scope variables ************************************************************************/
  73
  74 /*** file scope functions ************************************************************************/
  75 /* --------------------------------------------------------------------------------------------- */
  76
  77 static void
  78 send_contents (char *buffer, unsigned int columns, unsigned int rows)
  79 {
  80     unsigned char begin_line = 0, end_line = 0;
  81     unsigned int lastline, lc_index, x;
  82     unsigned char message, outbuf[1024], *p;
  83     unsigned short bytes;
  84
  85     lc_index = 2 * rows * columns;
  86     for (lastline = rows; lastline > 0; lastline--)
  87         for (x = 0; x < columns; x++)
  88         {
  89             lc_index -= 2;
  90             if (buffer[lc_index] != ' ')
  91                 goto out;
  92         }
  93   out:
  94
  95     message = CONSOLE_CONTENTS;
  96     if (write (1, &message, 1) != 1)
  97         return;
  98     if (read (0, &begin_line, 1) != 1)
  99         return;
 100     if (read (0, &end_line, 1) != 1)
 101         return;
 102     if (begin_line > lastline)
 103         begin_line = lastline;
 104     if (end_line > lastline)
 105         end_line = lastline;
 106
 107     lc_index = (end_line - begin_line) * columns;
 108     bytes = lc_index;
 109
 110     if (write (1, &bytes, 2) != 2)
 111         return;
 112     if (bytes == 0)
 113         return;
 114
 115     p = outbuf;
 116     for (lc_index = 2 * begin_line * columns; lc_index < 2 * end_line * columns; lc_index += 2)
 117     {
 118         *p++ = buffer[lc_index];
 119         if (p == outbuf + sizeof (outbuf))
 120         {
 121             if (write (1, outbuf, sizeof (outbuf)) != sizeof (outbuf))
 122                 return;
 123             p = outbuf;
 124         }
 125     }
 126
 127     if (p != outbuf)
 128         if (write (1, outbuf, p - outbuf) < (p - outbuf))
 129             return;
 130 }
 131
 132 /* --------------------------------------------------------------------------------------------- */
 133
 134 static void __attribute__ ((noreturn)) die (void)
 135 {
 136     unsigned char zero = 0;
 137     ssize_t ret;
 138     ret = write (1, &zero, 1);
 139     exit (3);
 140 }
 141
 142 /* --------------------------------------------------------------------------------------------- */
 143 /*** public functions ****************************************************************************/
 144 /* --------------------------------------------------------------------------------------------- */
 145
 146 int
 147 main (int argc, char **argv)
 148 {
 149     unsigned char action = 0, console_flag = 3;
 150     int console_fd, vcsa_fd, console_minor, buffer_size;
 151     struct stat st;
 152     uid_t uid, euid;
 153     char *buffer, *tty_name, console_name[16], vcsa_name[16];
 154     const char *p, *q;
 155     struct winsize winsz;
 156
 157     close (2);
 158
 159     if (argc != 2)
 160         die ();
 161
 162     tty_name = argv[1];
 163     if (strnlen (tty_name, 15) == 15 || strncmp (tty_name, "/dev/", 5))
 164         die ();
 165
 166     setsid ();
 167     uid = getuid ();
 168     euid = geteuid ();
 169
 170     if (seteuid (uid) < 0)
 171         die ();
 172     console_fd = open (tty_name, O_RDONLY);
 173     if (console_fd < 0)
 174         die ();
 175     if (fstat (console_fd, &st) < 0 || !S_ISCHR (st.st_mode))
 176         die ();
 177     if ((st.st_rdev & 0xff00) != 0x0400)
 178         die ();
 179     console_minor = (int) (st.st_rdev & 0x00ff);
 180     if (console_minor < 1 || console_minor > 63)
 181         die ();
 182     if (st.st_uid != uid)
 183         die ();
 184
 185     switch (tty_name[5])
 186     {
 187         /* devfs */
 188     case 'v':
 189         p = "/dev/vc/%d";
 190         q = "/dev/vcc/a%d";
 191         break;
 192         /* /dev/ttyN */
 193     case 't':
 194         p = "/dev/tty%d";
 195         q = "/dev/vcsa%d";
 196         break;
 197     default:
 198         die ();
 199         break;
 200     }
 201
 202     snprintf (console_name, sizeof (console_name), p, console_minor);
 203     if (strncmp (console_name, tty_name, sizeof (console_name)) != 0)
 204         die ();
 205
 206     if (seteuid (euid) < 0)
 207         die ();
 208
 209     snprintf (vcsa_name, sizeof (vcsa_name), q, console_minor);
 210     vcsa_fd = open (vcsa_name, O_RDWR);
 211     if (vcsa_fd < 0)
 212         die ();
 213     if (fstat (vcsa_fd, &st) < 0 || !S_ISCHR (st.st_mode))
 214         die ();
 215
 216     if (seteuid (uid) < 0)
 217         die ();
 218
 219     winsz.ws_col = winsz.ws_row = 0;
 220     if (ioctl (console_fd, TIOCGWINSZ, &winsz) < 0
 221         || winsz.ws_col <= 0 || winsz.ws_row <= 0 || winsz.ws_col >= 256 || winsz.ws_row >= 256)
 222         die ();
 223
 224     buffer_size = 4 + 2 * winsz.ws_col * winsz.ws_row;
 225     buffer = calloc (buffer_size, 1);
 226     if (buffer == NULL)
 227         die ();
 228
 229     if (write (1, &console_flag, 1) != 1)
 230         die ();
 231
 232     while (console_flag && read (0, &action, 1) == 1)
 233     {
 234         switch (action)
 235         {
 236         case CONSOLE_DONE:
 237             console_flag = 0;
 238             continue;
 239         case CONSOLE_SAVE:
 240             if (seteuid (euid) < 0
 241                 || lseek (vcsa_fd, 0, 0) != 0
 242                 || fstat (console_fd, &st) < 0 || st.st_uid != uid
 243                 || read (vcsa_fd, buffer, buffer_size) != buffer_size
 244                 || fstat (console_fd, &st) < 0 || st.st_uid != uid)
 245                 memset (buffer, 0, buffer_size);
 246             if (seteuid (uid) < 0)
 247                 die ();
 248             break;
 249         case CONSOLE_RESTORE:
 250             if (seteuid (euid) >= 0
 251                 && lseek (vcsa_fd, 0, 0) == 0 && fstat (console_fd, &st) >= 0 && st.st_uid == uid)
 252                 if (write (vcsa_fd, buffer, buffer_size) != buffer_size)
 253                     die ();
 254             if (seteuid (uid) < 0)
 255                 die ();
 256             break;
 257         case CONSOLE_CONTENTS:
 258             send_contents (buffer + 4, winsz.ws_col, winsz.ws_row);
 259             break;
 260         }
 261
 262         if (write (1, &console_flag, 1) != 1)
 263             die ();
 264     }
 265
 266     exit (0);
 267 }
 268
 269 /* --------------------------------------------------------------------------------------------- */