/* General purpose Linux console screen save/restore server This program should be setuid vcsa and /dev/vcsa* should be owned by the same user too. Original idea from Unix Interactive Tools version 3.2b (tty.c) This code requires root privileges. You may want to make the cons.saver setuid root. The code should be safe even if it is setuid but who knows? Partly rewritten by Jakub Jelinek . Copyright (C) 1994-2023 Free Software Foundation, Inc. This file is part of the Midnight Commander. The Midnight Commander is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. The Midnight Commander is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see . */ /* This code does _not_ need to be setuid root. However, it needs read/write access to /dev/vcsa* (which is privileged operation). You should create user vcsa, make cons.saver setuid user vcsa, and make all vcsa's owned by user vcsa. Seeing other peoples consoles is bad thing, but believe me, full root is even worse. */ /** \file cons.saver.c * \brief Source: general purpose Linux console screen save/restore server * * This code does _not_ need to be setuid root. However, it needs * read/write access to /dev/vcsa* (which is privileged * operation). You should create user vcsa, make cons.saver setuid * user vcsa, and make all vcsa's owned by user vcsa. * Seeing other peoples consoles is bad thing, but believe me, full * root is even worse. */ #include #ifndef _GNU_SOURCE #define _GNU_SOURCE #endif #include #include #include #include #include #ifdef HAVE_SYS_IOCTL_H #include #endif #ifdef HAVE_FCNTL_H #include #endif #include #include "lib/unixcompat.h" /* STDERR_FILENO */ #define LINUX_CONS_SAVER_C #include "cons.saver.h" /*** global variables ****************************************************************************/ /*** file scope macro definitions ****************************************************************/ /*** file scope type declarations ****************************************************************/ /*** forward declarations (file scope functions) *************************************************/ /*** file scope variables ************************************************************************/ /* --------------------------------------------------------------------------------------------- */ /*** file scope functions ************************************************************************/ /* --------------------------------------------------------------------------------------------- */ static void send_contents (char *buffer, unsigned int columns, unsigned int rows) { unsigned char begin_line = 0, end_line = 0; unsigned int lastline, lc_index, x; unsigned char message, outbuf[1024], *p; unsigned short bytes; lc_index = 2 * rows * columns; for (lastline = rows; lastline > 0; lastline--) for (x = 0; x < columns; x++) { lc_index -= 2; if (buffer[lc_index] != ' ') goto out; } out: message = CONSOLE_CONTENTS; if (write (1, &message, 1) != 1) return; if (read (0, &begin_line, 1) != 1) return; if (read (0, &end_line, 1) != 1) return; if (begin_line > lastline) begin_line = lastline; if (end_line > lastline) end_line = lastline; lc_index = (end_line - begin_line) * columns; bytes = lc_index; if (write (1, &bytes, 2) != 2) return; if (bytes == 0) return; p = outbuf; for (lc_index = 2 * begin_line * columns; lc_index < 2 * end_line * columns; lc_index += 2) { *p++ = buffer[lc_index]; if (p == outbuf + sizeof (outbuf)) { if (write (1, outbuf, sizeof (outbuf)) != sizeof (outbuf)) return; p = outbuf; } } if (p != outbuf) if (write (1, outbuf, p - outbuf) < (p - outbuf)) return; } /* --------------------------------------------------------------------------------------------- */ static void __attribute__ ((noreturn)) die (void) { unsigned char zero = 0; ssize_t ret; ret = write (1, &zero, 1); (void) ret; exit (3); } /* --------------------------------------------------------------------------------------------- */ /*** public functions ****************************************************************************/ /* --------------------------------------------------------------------------------------------- */ int main (int argc, char **argv) { unsigned char action = 0, console_flag = 3; int console_fd, vcsa_fd, console_minor, buffer_size; struct stat st; uid_t uid, euid; char *buffer, *tty_name, console_name[16], vcsa_name[16]; const char *p, *q; struct winsize winsz; close (STDERR_FILENO); if (argc != 2) die (); tty_name = argv[1]; if (strnlen (tty_name, 15) == 15 || strncmp (tty_name, "/dev/", 5)) die (); setsid (); uid = getuid (); euid = geteuid (); if (seteuid (uid) < 0) die (); console_fd = open (tty_name, O_RDONLY); if (console_fd < 0) die (); if (fstat (console_fd, &st) < 0 || !S_ISCHR (st.st_mode)) die (); #ifdef HAVE_STRUCT_STAT_ST_RDEV if ((st.st_rdev & 0xff00) != 0x0400) die (); console_minor = (int) (st.st_rdev & 0x00ff); #else console_minor = 1; /* FIXME */ #endif if (console_minor < 1 || console_minor > 63) die (); if (st.st_uid != uid) die (); switch (tty_name[5]) { /* devfs */ case 'v': p = "/dev/vc/%d"; q = "/dev/vcc/a%d"; break; /* /dev/ttyN */ case 't': p = "/dev/tty%d"; q = "/dev/vcsa%d"; break; default: die (); } snprintf (console_name, sizeof (console_name), p, console_minor); if (strncmp (console_name, tty_name, sizeof (console_name)) != 0) die (); if (seteuid (euid) < 0) die (); snprintf (vcsa_name, sizeof (vcsa_name), q, console_minor); vcsa_fd = open (vcsa_name, O_RDWR); if (vcsa_fd < 0) die (); if (fstat (vcsa_fd, &st) < 0 || !S_ISCHR (st.st_mode)) die (); if (seteuid (uid) < 0) die (); winsz.ws_col = winsz.ws_row = 0; if (ioctl (console_fd, TIOCGWINSZ, &winsz) < 0 || winsz.ws_col <= 0 || winsz.ws_row <= 0 || winsz.ws_col >= 256 || winsz.ws_row >= 256) die (); buffer_size = 4 + 2 * winsz.ws_col * winsz.ws_row; buffer = calloc (buffer_size, 1); if (buffer == NULL) die (); if (write (1, &console_flag, 1) != 1) die (); while (console_flag && read (0, &action, 1) == 1) { switch (action) { case CONSOLE_DONE: console_flag = 0; continue; case CONSOLE_SAVE: if (seteuid (euid) < 0 || lseek (vcsa_fd, 0, 0) != 0 || fstat (console_fd, &st) < 0 || st.st_uid != uid || read (vcsa_fd, buffer, buffer_size) != buffer_size || fstat (console_fd, &st) < 0 || st.st_uid != uid) memset (buffer, 0, buffer_size); if (seteuid (uid) < 0) die (); break; case CONSOLE_RESTORE: if (seteuid (euid) >= 0 && lseek (vcsa_fd, 0, 0) == 0 && fstat (console_fd, &st) >= 0 && st.st_uid == uid) if (write (vcsa_fd, buffer, buffer_size) != buffer_size) die (); if (seteuid (uid) < 0) die (); break; case CONSOLE_CONTENTS: send_contents (buffer + 4, winsz.ws_col, winsz.ws_row); break; default: break; } if (write (1, &console_flag, 1) != 1) die (); } exit (0); } /* --------------------------------------------------------------------------------------------- */