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-rw-r--r--src/consaver/cons.saver.c286
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diff --git a/src/consaver/cons.saver.c b/src/consaver/cons.saver.c
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+/*
+ 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) 1994-2022
+ 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 priviledged
+ 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 priviledged
+ * 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 ****************************************************************/
+
+/*** 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);
+}
+
+/* --------------------------------------------------------------------------------------------- */
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