src/consaver/cons.saver.c

   1 /*
   2    General purpose Linux console screen save/restore server
   3
   4    This program should be setuid vcsa and /dev/vcsa* should be
   5    owned by the same user too.
   6
   7    Original idea from Unix Interactive Tools version 3.2b (tty.c)
   8    This code requires root privileges.
   9    You may want to make the cons.saver setuid root.
  10    The code should be safe even if it is setuid but who knows?
  11
  12    Partly rewritten by Jakub Jelinek <jakub@redhat.com>.
  13
  14    Copyright (C) 1994, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
  15    2006, 2007, 2011
  16    The Free Software Foundation, Inc.
  17
  18    This file is part of the Midnight Commander.
  19
  20    The Midnight Commander is free software: you can redistribute it
  21    and/or modify it under the terms of the GNU General Public License as
  22    published by the Free Software Foundation, either version 3 of the License,
  23    or (at your option) any later version.
  24
  25    The Midnight Commander is distributed in the hope that it will be useful,
  26    but WITHOUT ANY WARRANTY; without even the implied warranty of
  27    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  28    GNU General Public License for more details.
  29
  30    You should have received a copy of the GNU General Public License
  31    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  32  */
  33
  34 /* This code does _not_ need to be setuid root. However, it needs
  35    read/write access to /dev/vcsa* (which is priviledged
  36    operation). You should create user vcsa, make cons.saver setuid
  37    user vcsa, and make all vcsa's owned by user vcsa.
  38
  39    Seeing other peoples consoles is bad thing, but believe me, full
  40    root is even worse. */
  41
  42 /** \file cons.saver.c
  43  *  \brief Source: general purpose Linux console screen save/restore server
  44  *
  45  *  This code does _not_ need to be setuid root. However, it needs
  46  *  read/write access to /dev/vcsa* (which is priviledged
  47  *  operation). You should create user vcsa, make cons.saver setuid
  48  *  user vcsa, and make all vcsa's owned by user vcsa.
  49  *  Seeing other peoples consoles is bad thing, but believe me, full
  50  *  root is even worse.
  51  */
  52
  53 #include <config.h>
  54
  55 #ifndef _GNU_SOURCE
  56 #define _GNU_SOURCE
  57 #endif
  58
  59 #include <stdlib.h>
  60 #include <stdio.h>
  61 #include <string.h>
  62
  63 #include <sys/types.h>
  64 #include <sys/stat.h>
  65 #ifdef HAVE_SYS_IOCTL_H
  66 #include <sys/ioctl.h>
  67 #endif
  68 #include <fcntl.h>
  69 #include <termios.h>
  70 #include <unistd.h>
  71
  72 #define LINUX_CONS_SAVER_C
  73 #include "cons.saver.h"
  74
  75 /*** global variables ****************************************************************************/
  76
  77 /*** file scope macro definitions ****************************************************************/
  78
  79 /*** file scope type declarations ****************************************************************/
  80
  81 /*** file scope variables ************************************************************************/
  82
  83 /*** file scope functions ************************************************************************/
  84 /* --------------------------------------------------------------------------------------------- */
  85
  86 static void
  87 send_contents (char *buffer, unsigned int columns, unsigned int rows)
  88 {
  89     unsigned char begin_line = 0, end_line = 0;
  90     unsigned int lastline, lc_index, x;
  91     unsigned char message, outbuf[1024], *p;
  92     unsigned short bytes;
  93
  94     lc_index = 2 * rows * columns;
  95     for (lastline = rows; lastline > 0; lastline--)
  96         for (x = 0; x < columns; x++)
  97         {
  98             lc_index -= 2;
  99             if (buffer[lc_index] != ' ')
 100                 goto out;
 101         }
 102   out:
 103
 104     message = CONSOLE_CONTENTS;
 105     if (write (1, &message, 1) != 1)
 106         return;
 107     if (read (0, &begin_line, 1) != 1)
 108         return;
 109     if (read (0, &end_line, 1) != 1)
 110         return;
 111     if (begin_line > lastline)
 112         begin_line = lastline;
 113     if (end_line > lastline)
 114         end_line = lastline;
 115
 116     lc_index = (end_line - begin_line) * columns;
 117     bytes = lc_index;
 118
 119     if (write (1, &bytes, 2) != 2)
 120         return;
 121     if (bytes == 0)
 122         return;
 123
 124     p = outbuf;
 125     for (lc_index = 2 * begin_line * columns; lc_index < 2 * end_line * columns; lc_index += 2)
 126     {
 127         *p++ = buffer[lc_index];
 128         if (p == outbuf + sizeof (outbuf))
 129         {
 130             if (write (1, outbuf, sizeof (outbuf)) != sizeof (outbuf))
 131                 return;
 132             p = outbuf;
 133         }
 134     }
 135
 136     if (p != outbuf)
 137         if (write (1, outbuf, p - outbuf) < (p - outbuf))
 138             return;
 139 }
 140
 141 /* --------------------------------------------------------------------------------------------- */
 142
 143 static void __attribute__ ((noreturn)) die (void)
 144 {
 145     unsigned char zero = 0;
 146     (void) write (1, &zero, 1);
 147     exit (3);
 148 }
 149
 150 /* --------------------------------------------------------------------------------------------- */
 151 /*** public functions ****************************************************************************/
 152 /* --------------------------------------------------------------------------------------------- */
 153
 154 int
 155 main (int argc, char **argv)
 156 {
 157     unsigned char action = 0, console_flag = 3;
 158     int console_fd, vcsa_fd, console_minor, buffer_size;
 159     struct stat st;
 160     uid_t uid, euid;
 161     char *buffer, *tty_name, console_name[16], vcsa_name[16];
 162     const char *p, *q;
 163     struct winsize winsz;
 164
 165     close (2);
 166
 167     if (argc != 2)
 168         die ();
 169
 170     tty_name = argv[1];
 171     if (strnlen (tty_name, 15) == 15 || strncmp (tty_name, "/dev/", 5))
 172         die ();
 173
 174     setsid ();
 175     uid = getuid ();
 176     euid = geteuid ();
 177
 178     if (seteuid (uid) < 0)
 179         die ();
 180     console_fd = open (tty_name, O_RDONLY);
 181     if (console_fd < 0)
 182         die ();
 183     if (fstat (console_fd, &st) < 0 || !S_ISCHR (st.st_mode))
 184         die ();
 185     if ((st.st_rdev & 0xff00) != 0x0400)
 186         die ();
 187     console_minor = (int) (st.st_rdev & 0x00ff);
 188     if (console_minor < 1 || console_minor > 63)
 189         die ();
 190     if (st.st_uid != uid)
 191         die ();
 192
 193     switch (tty_name[5])
 194     {
 195         /* devfs */
 196     case 'v':
 197         p = "/dev/vc/%d";
 198         q = "/dev/vcc/a%d";
 199         break;
 200         /* /dev/ttyN */
 201     case 't':
 202         p = "/dev/tty%d";
 203         q = "/dev/vcsa%d";
 204         break;
 205     default:
 206         die ();
 207         break;
 208     }
 209
 210     snprintf (console_name, sizeof (console_name), p, console_minor);
 211     if (strncmp (console_name, tty_name, sizeof (console_name)) != 0)
 212         die ();
 213
 214     if (seteuid (euid) < 0)
 215         die ();
 216
 217     snprintf (vcsa_name, sizeof (vcsa_name), q, console_minor);
 218     vcsa_fd = open (vcsa_name, O_RDWR);
 219     if (vcsa_fd < 0)
 220         die ();
 221     if (fstat (vcsa_fd, &st) < 0 || !S_ISCHR (st.st_mode))
 222         die ();
 223
 224     if (seteuid (uid) < 0)
 225         die ();
 226
 227     winsz.ws_col = winsz.ws_row = 0;
 228     if (ioctl (console_fd, TIOCGWINSZ, &winsz) < 0
 229         || winsz.ws_col <= 0 || winsz.ws_row <= 0 || winsz.ws_col >= 256 || winsz.ws_row >= 256)
 230         die ();
 231
 232     buffer_size = 4 + 2 * winsz.ws_col * winsz.ws_row;
 233     buffer = calloc (buffer_size, 1);
 234     if (buffer == NULL)
 235         die ();
 236
 237     if (write (1, &console_flag, 1) != 1)
 238         die ();
 239
 240     while (console_flag && read (0, &action, 1) == 1)
 241     {
 242         switch (action)
 243         {
 244         case CONSOLE_DONE:
 245             console_flag = 0;
 246             continue;
 247         case CONSOLE_SAVE:
 248             if (seteuid (euid) < 0
 249                 || lseek (vcsa_fd, 0, 0) != 0
 250                 || fstat (console_fd, &st) < 0 || st.st_uid != uid
 251                 || read (vcsa_fd, buffer, buffer_size) != buffer_size
 252                 || fstat (console_fd, &st) < 0 || st.st_uid != uid)
 253                 memset (buffer, 0, buffer_size);
 254             if (seteuid (uid) < 0)
 255                 die ();
 256             break;
 257         case CONSOLE_RESTORE:
 258             if (seteuid (euid) >= 0
 259                 && lseek (vcsa_fd, 0, 0) == 0 && fstat (console_fd, &st) >= 0 && st.st_uid == uid)
 260                 if (write (vcsa_fd, buffer, buffer_size) != buffer_size)
 261                     die ();
 262             if (seteuid (uid) < 0)
 263                 die ();
 264             break;
 265         case CONSOLE_CONTENTS:
 266             send_contents (buffer + 4, winsz.ws_col, winsz.ws_row);
 267             break;
 268         }
 269
 270         if (write (1, &console_flag, 1) != 1)
 271             die ();
 272     }
 273
 274     exit (0);
 275 }
 276
 277 /* --------------------------------------------------------------------------------------------- */