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Diffstat (limited to '')
-rw-r--r-- | src/consaver/cons.saver.c | 289 |
1 files changed, 289 insertions, 0 deletions
diff --git a/src/consaver/cons.saver.c b/src/consaver/cons.saver.c new file mode 100644 index 0000000..4867ab6 --- /dev/null +++ b/src/consaver/cons.saver.c @@ -0,0 +1,289 @@ +/* + 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 <jakub@redhat.com>. + + 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 <http://www.gnu.org/licenses/>. + */ + +/* 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 <config.h> + +#ifndef _GNU_SOURCE +#define _GNU_SOURCE +#endif + +#include <stdlib.h> +#include <stdio.h> +#include <string.h> + +#include <sys/types.h> +#include <sys/stat.h> +#ifdef HAVE_SYS_IOCTL_H +#include <sys/ioctl.h> +#endif +#ifdef HAVE_FCNTL_H +#include <fcntl.h> +#endif +#include <termios.h> + +#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); +} + +/* --------------------------------------------------------------------------------------------- */ |