tdebase/tsak/main.cpp

/*
Copyright 2010 Adam Marchetti
Copyright 2011-2013 Timothy Pearson <kb9vqf@pearsoncomputing.net>

This file is part of tsak, the TDE Secure Attention Key daemon

tsak 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.

tsak 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 tsak. If not, see http://www.gnu.org/licenses/.

*/

#include <stdio.h>
#include <stdlib.h>
#include <exception>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <dirent.h>
#include <linux/input.h>
#include <linux/uinput.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/select.h>
#include <sys/time.h>
#include <termios.h>
#include <signal.h>
extern "C" {
#include <libudev.h>
}
#include <libgen.h>

using namespace std;

#define FIFO_DIR "/tmp/tdesocket-global"
#define FIFO_FILE_OUT "/tmp/tdesocket-global/tsak"
#define FIFO_LOCKFILE_OUT "/tmp/tdesocket-global/tsak.lock"

// WARNING
// MAX_KEYBOARDS must be greater than or equal to MAX_INPUT_NODE
#define MAX_KEYBOARDS 128
#define MAX_INPUT_NODE 128

#define TestBit(bit, array) (array[(bit) / 8] & (1 << ((bit) % 8)))

typedef unsigned char byte;

bool        mPipeOpen_out = false;
int         mPipe_fd_out = -1;

int         mPipe_lockfd_out = -1;

char filename[32];
char key_bitmask[(KEY_MAX + 7) / 8];

struct sigaction usr_action;
sigset_t block_mask;

int keyboard_fd_num;
int keyboard_fds[MAX_KEYBOARDS];
int child_pids[MAX_KEYBOARDS];
int child_led_pids[MAX_KEYBOARDS];

const char *keycode[256] =
{
	"", "<esc>", "1", "2", "3", "4", "5", "6", "7", "8",
	"9", "0", "−", "=", "<backspace>", "<tab>", "q", "w", "e", "r",
	"t", "y", "u", "i", "o", "p", "[", "]", "\n", "<control>",
	"a", "s", "d", "f", "g", "h", "j", "k", "l", ";",
	"'", "", "<shift>", "\\", "z", "x", "c", "v", "b", "n",
	"m", ",", ".", "/", "<shift>", "", "<alt>", " ", "<capslock>",
	"<f1>", "<f2>", "<f3>", "<f4>", "<f5>", "<f6>", "<f7>", "<f8>", "<f9>", "<f10>",
	"<numlock>", "<scrolllock>", "", "", "", "", "", "", "", "",
	"", "", "\\", "f11", "f12", "", "", "", "", "",
	"", "", "", "<control>", "", "<sysrq>", "", "", "<control>", "", "",
	"<alt>", "", "", "", "", "", "", "", "", "",
	"", "<del>", "", "", "", "", "", "", "", "",
	"", "", "", "", "", "", "", "", "", "",
	"", "", "", "", "", "", "", "", "", "",
	"", "", "", "", "", "", "", "", "", "",
	"", "", "", "", "", "", "", "", "", "",
	"", "", "", "", "", "", "", "", "", "",
	"", "", "", "", "", "", "", "", "", "",
	"", "", "", "", "", "", "", "", "", "",
	"", "", "", "", "", "", "", "", "", ""
};

/* returns 1 if bit number i is set, otherwise returns 0 */
int bit_set(size_t i, const byte* a)
{
  return a[i/CHAR_BIT] & (1 << i%CHAR_BIT);
}

/* exception handling */
struct exit_exception {
	int c;
	exit_exception(int c):c(c) { }
};

/* signal handler */
void signal_callback_handler(int signum)
{
	// Terminate program
	throw exit_exception(signum);
}

/*  termination handler */
void tsak_friendly_termination() {
	int i;

	// Close down all child processes
	for (i=0; i<MAX_KEYBOARDS; i++) {
		if (child_pids[i] != 0) {
			kill(child_pids[i], SIGTERM);
		}
		if (child_led_pids[i] != 0) {
			kill(child_led_pids[i], SIGTERM);
		}
	}

	// Wait for process termination
	sleep(1);

	fprintf(stderr, "[tsak] tsak terminated by external request\n");
	exit(17);
}

// --------------------------------------------------------------------------------------
// Useful function from Stack Overflow
// http://stackoverflow.com/questions/874134/find-if-string-endswith-another-string-in-c
// --------------------------------------------------------------------------------------
/*  returns 1 iff str ends with suffix  */
int str_ends_with(const char * str, const char * suffix) {

  if( str == NULL || suffix == NULL )
    return 0;

  size_t str_len = strlen(str);
  size_t suffix_len = strlen(suffix);

  if(suffix_len > str_len)
    return 0;

  return 0 == strncmp( str + str_len - suffix_len, suffix, suffix_len );
}
// --------------------------------------------------------------------------------------

/*
 * Set a file descriptor to blocking or non-blocking mode.
 *
 * @param fd The file descriptor
 * @param blocking 0:non-blocking mode, 1:blocking mode
 *
 * @return 1:success, 0:failure.
 */
int fd_set_blocking(int fd, int blocking)
{
	/* Save the current flags */
	int flags = fcntl(fd, F_GETFL, 0);
	if (flags == -1) {
		return 0;
	}
	
	if (blocking) {
		flags &= ~O_NONBLOCK;
	}
	else {
		flags |= O_NONBLOCK;
	}
	return fcntl(fd, F_SETFL, flags) != -1;
}

/* Assign features (supported axes and keys) of the physical input device (devin)
 * to the virtual input device (devout) */
static void copy_features(int devin, int devout)
{
	byte evtypes[EV_MAX/CHAR_BIT + 1] = {0};
	byte codes[KEY_MAX/CHAR_BIT + 1];
	unsigned i,code;
	int op;
	if (ioctl(devin, EVIOCGBIT(0, sizeof(evtypes)), evtypes) < 0) return;
	for(i=0;i<EV_MAX;++i) {
		if (bit_set(i, evtypes)) {
			switch(i) {
				case EV_KEY: op = UI_SET_KEYBIT; break;
				case EV_REL: op = UI_SET_RELBIT; break;
				case EV_ABS: op = UI_SET_ABSBIT; break;
				case EV_MSC: op = UI_SET_MSCBIT; break;
				case EV_LED: op = UI_SET_LEDBIT; break;
				case EV_SND: op = UI_SET_SNDBIT; break;
				case EV_SW: op = UI_SET_SWBIT; break;
				default: op = -1;
			}
		}
		if (op == -1) continue;
		ioctl(devout, UI_SET_EVBIT, i);
		memset(codes,0,sizeof(codes));
		if (ioctl(devin, EVIOCGBIT(i, sizeof(codes)), codes) >= 0) {
			for(code=0;code<KEY_MAX;code++) {
				if (bit_set(code, codes)) ioctl(devout, op, code);
			}
		}
	}
}

int find_keyboards() {
	int i, j;
	int fd;
	char name[256] = "Unknown";

	keyboard_fd_num = 0;
	for (i=0; i<MAX_KEYBOARDS; i++) {
		keyboard_fds[i] = 0;
	}

	for (i=0; i<MAX_INPUT_NODE; i++) {
		snprintf(filename, sizeof(filename), "/dev/input/event%d", i);

		fd = open(filename, O_RDWR|O_SYNC);
		if (fd >= 0) {
			ioctl(fd, EVIOCGBIT(EV_KEY, sizeof(key_bitmask)), key_bitmask);
	
			// Ensure that we do not detect our own tsak faked keyboards
			ioctl (fd, EVIOCGNAME(sizeof(name)), name);
			if (str_ends_with(name, "+tsak") == 0) {
				/* We assume that anything that has an alphabetic key in the
					QWERTYUIOP range in it is the main keyboard. */
				for (j = KEY_Q; j <= KEY_P; j++) {
					if (TestBit(j, key_bitmask)) {
						keyboard_fds[keyboard_fd_num] = fd;
					}
				}
			}
	
			if (keyboard_fds[keyboard_fd_num] == 0) {
				close(fd);
			}
			else {
				keyboard_fd_num++;
			}
		}
	}
	return 0;
}

void tearDownPipe()
{
	if (mPipeOpen_out == true) {
		mPipeOpen_out = false;
		close(mPipe_fd_out);
		unlink(FIFO_FILE_OUT);
	}
}

void tearDownLockingPipe()
{
	close(mPipe_lockfd_out);
	unlink(FIFO_LOCKFILE_OUT);
}

bool setFileLock(int fd, bool close_on_failure)
{
	struct flock fl;

	fl.l_type = F_WRLCK;
	fl.l_whence = SEEK_SET;
	fl.l_start = 0;
	fl.l_len = 1;

	// Set the exclusive file lock
	if (fcntl(fd, F_SETLK, &fl) == -1) {
		close(fd);
		return false;
	}

	return true;
}

bool checkFileLock()
{
	struct flock fl;

	fl.l_type    = F_WRLCK;   /* Test for any lock on any part of file. */
	fl.l_start   = 0;
	fl.l_whence  = SEEK_SET;
	fl.l_len     = 0;

	int fd = open(FIFO_LOCKFILE_OUT, O_RDWR | O_NONBLOCK);
	fcntl(fd, F_GETLK, &fl);  /* Overwrites lock structure with preventors. */

	if (fd > -1) {
		if (fl.l_type == F_WRLCK) {
			return false;
		}
		return true;
	}

	return true;
}

bool setupPipe()
{
	/* Create the FIFOs if they do not exist */
	umask(0);
	mkdir(FIFO_DIR,0644);

	mknod(FIFO_FILE_OUT, S_IFIFO|0600, 0);
	chmod(FIFO_FILE_OUT, 0600);

	mPipe_fd_out = open(FIFO_FILE_OUT, O_RDWR | O_NONBLOCK);
	if (mPipe_fd_out > -1) {
		mPipeOpen_out = true;
	}

	// Set the exclusive file lock
	return setFileLock(mPipe_fd_out, true);
}

bool setupLockingPipe(bool writepid)
{
	/* Create the FIFOs if they do not exist */
	umask(0);
	mkdir(FIFO_DIR,0644);

	mknod(FIFO_LOCKFILE_OUT, 0600, 0);
	chmod(FIFO_LOCKFILE_OUT, 0600);

	mPipe_lockfd_out = open(FIFO_LOCKFILE_OUT, O_RDWR | O_NONBLOCK);
	if (mPipe_lockfd_out > -1) {
		if (writepid) {
			// Write my PID to the file
			pid_t tsakpid = getpid();
			char pidstring[1024];
			sprintf(pidstring, "%d", tsakpid);
			write(mPipe_lockfd_out, pidstring, strlen(pidstring));
		}
		// Set the exclusive file lock
		return setFileLock(mPipe_lockfd_out, true);
	}

	return false;
}

void broadcast_sak()
{
	// Let anyone listening to our interface know that an SAK keypress was received
	// I highly doubt there are more than 255 VTs active at once...
	int i;
	for (i=0;i<255;i++) {
		if (write(mPipe_fd_out, "SAK\n\r", 6) < 0) {
			fprintf(stderr, "[tsak] Unable to send SAK signal to clients\n");
		}
	}
}

void restart_tsak()
{
	int i;

	fprintf(stderr, "[tsak] Forcibly terminating...\n");

	// Close down all child processes
	for (i=0; i<MAX_KEYBOARDS; i++) {
		if (child_pids[i] != 0) {
			kill(child_pids[i], SIGKILL);
		}
		if (child_led_pids[i] != 0) {
			kill(child_led_pids[i], SIGKILL);
		}
	}

	// Wait for process termination
	sleep(1);

	// Release all exclusive keyboard locks
	for (int current_keyboard=0;current_keyboard<keyboard_fd_num;current_keyboard++) {
		if(ioctl(keyboard_fds[current_keyboard], EVIOCGRAB, 0) < 0) {
			fprintf(stderr, "[tsak] Failed to release exclusive input device lock\n");
		}
		close(keyboard_fds[current_keyboard]);
	}

	// Unset the exclusive file lock
	if (mPipe_fd_out != -1) {
		struct flock fl;
		if (fcntl(mPipe_fd_out, F_UNLCK, &fl) == -1) {
			fprintf(stderr, "[tsak] Failed to release exclusive pipe lock\n");
		}
		close(mPipe_fd_out);
	}

#if 1
	// Restart now
	// Note that the execl function never returns
	char me[2048];
	int chars = readlink("/proc/self/exe", me, sizeof(me));
	me[chars] = 0;
	me[2047] = 0;
	execl(me, basename(me), (char*)NULL);
#else
	_exit(0);
#endif
}

class PipeHandler
{
public:
	PipeHandler();
	~PipeHandler();

	bool active;
};

PipeHandler::PipeHandler()
{
	active = false;
}

PipeHandler::~PipeHandler()
{
	if (active) {
		tearDownPipe();
		tearDownLockingPipe();
	}
}

int main (int argc, char *argv[])
{
	struct input_event ev[64];
	struct input_event event;
	struct input_event revev;
	struct uinput_user_dev devinfo={{0},{0}};
	int devout[MAX_KEYBOARDS];
	int rd;
	int i;
	int size = sizeof (struct input_event);
	char name[256] = "Unknown";
	bool ctrl_down = false;
	bool alt_down = false;
	bool hide_event = false;
	bool established = false;
	bool testrun = false;
	bool depcheck = false;
	int current_keyboard;
	bool can_proceed;

	// Ignore SIGPIPE
	signal(SIGPIPE, SIG_IGN);

	// Register signal handlers
	// Register signal and signal handler
	signal(SIGINT, signal_callback_handler);
	signal(SIGTERM, signal_callback_handler);

	set_terminate(tsak_friendly_termination);

	try {
		for (i=0; i<MAX_KEYBOARDS; i++) {
			child_pids[i] = 0;
			child_led_pids[i] = 0;
		}

		if (argc == 2) {
			if (strcmp(argv[1], "checkactive") == 0) {
				testrun = true;
			}
			if (strcmp(argv[1], "checkdeps") == 0) {
				depcheck = true;
			}
		}

		if (depcheck == false) {
			// Check for existing file locks
			if (!checkFileLock()) {
				fprintf(stderr, "[tsak] Another instance of this program is already running [1]\n");
				return 8;
			}
			if (!setupLockingPipe(true)) {
				fprintf(stderr, "[tsak] Another instance of this program is already running [2]\n");
				return 8;
			}
		}

		// Create the output pipe
		PipeHandler controlpipe;
		if (depcheck == false) {
			if (!setupPipe()) {
				fprintf(stderr, "[tsak] Another instance of this program is already running\n");
				return 8;
			}
		}

		while (1) {
			if (depcheck == false) {
				controlpipe.active = true;
			}

			if ((getuid ()) != 0) {
				printf ("[tsak] You are not root! This WILL NOT WORK!\nDO NOT attempt to bypass security restrictions, e.g. by changing keyboard permissions or owner, if you want the SAK system to remain secure...\n");
				return 5;
			}

			// Find keyboards
			find_keyboards();
			if (keyboard_fd_num == 0) {
				printf ("[tsak] Could not find any usable keyboard(s)!\n");
				if (depcheck == true) {
					return 50;
				}
				// Make sure everyone knows we physically can't detect a SAK
				// Before we do this we broadcast one so that active dialogs are updated appropriately
				// Also, we keep watching for a keyboard to be added via a forked child process...
				broadcast_sak();
				if (established)
					sleep(1);
				else {
					int i=fork();
					if (i<0) {
						return 12; // fork failed
					}
					if (i>0) {
						return 4;
					}
					sleep(1);
					restart_tsak();
				}
			}
			else {
				fprintf(stderr, "[tsak] Found %d keyboard(s)\n", keyboard_fd_num);

				can_proceed = true;
				for (current_keyboard=0;current_keyboard<keyboard_fd_num;current_keyboard++) {
					// Print Device Name
					ioctl (keyboard_fds[current_keyboard], EVIOCGNAME (sizeof (name)), name);
					fprintf(stderr, "[tsak] Reading from keyboard: (%s)\n", name);

					// Create filtered virtual output device
					devout[current_keyboard]=open("/dev/misc/uinput",O_RDWR|O_NONBLOCK);
					if (devout[current_keyboard]<0) {
						devout[current_keyboard]=open("/dev/uinput",O_RDWR|O_NONBLOCK);
						if (devout[current_keyboard]<0) {
							perror("open(\"/dev/misc/uinput\")");
						}
					}
					if (devout[current_keyboard]<0) {
						can_proceed = false;
						fprintf(stderr, "[tsak] Unable to open /dev/uinput or /dev/misc/uinput (char device 10:223).\nPossible causes:\n 1) Device node does not exist\n 2) Kernel not compiled with evdev [INPUT_EVDEV] and uinput [INPUT_UINPUT] user level driver support\n 3) Permission denied.\n");
						perror("open(\"/dev/uinput\")");
						if (established)
							sleep(1);
						else
							return 3;
					}
					fd_set_blocking(devout[current_keyboard], true);
				}
				if (depcheck == true) {
					return 0;
				}

				if (can_proceed == true) {
					for (current_keyboard=0;current_keyboard<keyboard_fd_num;current_keyboard++) {
						if(ioctl(keyboard_fds[current_keyboard], EVIOCGRAB, 2) < 0) {
							close(keyboard_fds[current_keyboard]);
							fprintf(stderr, "[tsak] Failed to grab exclusive input device lock");
							if (established) {
								sleep(1);
							}
							else {
								return 1;
							}
						}
						else {
							ioctl(keyboard_fds[current_keyboard], EVIOCGNAME(UINPUT_MAX_NAME_SIZE), devinfo.name);
							strncat(devinfo.name, "+tsak", UINPUT_MAX_NAME_SIZE-1);
							fprintf(stderr, "[tsak] %s\n", devinfo.name);
							ioctl(keyboard_fds[current_keyboard], EVIOCGID, &devinfo.id);

							copy_features(keyboard_fds[current_keyboard], devout[current_keyboard]);
							if (write(devout[current_keyboard],&devinfo,sizeof(devinfo)) < 0) {
								fprintf(stderr, "[tsak] Unable to write to output device\n");
							}
							if (ioctl(devout[current_keyboard],UI_DEV_CREATE)<0) {
								fprintf(stderr, "[tsak] Unable to create input device with UI_DEV_CREATE\n");
								if (established)
									sleep(1);
								else
									return 2;
							}
							else {
								fprintf(stderr, "[tsak] Device created.\n");

								if (established == false) {
									int i=fork();
									if (i<0) return 9; // fork failed
									if (i>0) {
										child_pids[current_keyboard] = i;

										int i=fork();
										if (i<0) return 9; // fork failed
										if (i>0) {
											child_led_pids[current_keyboard] = i;
											continue;
										}

										if (testrun == true) {
											return 0;
										}

										while (1) {
											// Replicate LED events from the virtual keyboard to the physical keyboard
											int rrd = read(devout[current_keyboard], &revev, size);
											if (rrd >= size) {
												if ((revev.type == EV_LED) || (revev.type == EV_MSC)) {
													if (write(keyboard_fds[current_keyboard], &revev, sizeof(revev)) < 0) {
														fprintf(stderr, "[tsak] Unable to replicate LED event\n");
													}
												}
											}
										}
										return 0;
									}
									setupLockingPipe(false);
								}

								established = true;

								if (testrun == true) {
									return 0;
								}

								while (1) {
									if ((rd = read(keyboard_fds[current_keyboard], ev, size)) < size) {
										fprintf(stderr, "[tsak] Read failed.\n");
										break;
									}

									if (ev[0].value == 0 && ev[0].type == 1) { // Read the key release event
										if (keycode[(ev[0].code)]) {
											if (strcmp(keycode[(ev[0].code)], "<control>") == 0) ctrl_down = false;
											if (strcmp(keycode[(ev[0].code)], "<alt>") == 0) alt_down = false;
										}
									}
									if (ev[0].value == 1 && ev[0].type == 1) { // Read the key press event
										if (keycode[(ev[0].code)]) {
											if (strcmp(keycode[(ev[0].code)], "<control>") == 0) ctrl_down = true;
											if (strcmp(keycode[(ev[0].code)], "<alt>") == 0) alt_down = true;
										}
									}

									hide_event = false;
									if (ev[0].value == 1 && ev[0].type == 1) { // Read the key press event
										if (keycode[(ev[0].code)]) {
											if (alt_down && ctrl_down && (strcmp(keycode[(ev[0].code)], "<del>") == 0)) {
												hide_event = true;
											}
										}
									}

									if ((hide_event == false) && (ev[0].type != EV_LED) && (ev[0].type != EV_MSC)) {
										// Pass the event on...
										event = ev[0];
										if (write(devout[current_keyboard], &event, sizeof(event)) < 0) {
											fprintf(stderr, "[tsak] Unable to replicate keyboard event!\n");
										}
									}
									if (hide_event == true) {
										// Let anyone listening to our interface know that an SAK keypress was received
										broadcast_sak();
									}
								}
							}
						}
					}

					// fork udev monitor process
					int i=fork();
					if (i<0) {
						return 10; // fork failed
					}
					if (i>0) {
						// Terminate parent
						controlpipe.active = false;
						return 0;
					}

					// Prevent multiple process instances from starting
					setupLockingPipe(true);

					// Wait a little bit so that udev hotplug can stabilize before we start monitoring
					sleep(1);

					fprintf(stderr, "[tsak] Hotplug monitoring process started\n");

					// Monitor for hotplugged keyboards
					int j;
					int hotplug_fd;
					bool is_new_keyboard;
					struct udev *udev;
					struct udev_device *dev;
					struct udev_monitor *mon;

					// Create the udev object
					udev = udev_new();
					if (!udev) {
						fprintf(stderr, "[tsak] Cannot connect to udev interface\n");
						return 11;
					}

					// Set up a udev monitor to monitor input devices
					mon = udev_monitor_new_from_netlink(udev, "udev");
					udev_monitor_filter_add_match_subsystem_devtype(mon, "input", NULL);
					udev_monitor_enable_receiving(mon);

					while (1) {
						// Watch for input from the monitoring process
						fd_set readfds;
						FD_ZERO(&readfds);
						FD_SET(udev_monitor_get_fd(mon), &readfds);
						int fdcount = select(udev_monitor_get_fd(mon)+1, &readfds, NULL, NULL, NULL);
						if (fdcount < 0) {
							if (errno == EINTR) {
								fprintf(stderr, "[tsak] Signal caught in hotplug monitoring process; ignoring\n");
							}
							else {
								fprintf(stderr, "[tsak] Select failed on udev file descriptor in hotplug monitoring process\n");
							}
							usleep(1000);
							continue;
						}

						dev = udev_monitor_receive_device(mon);
						if (dev) {
							// If a keyboard was removed we need to restart...
							if (strcmp(udev_device_get_action(dev), "remove") == 0) {
								udev_device_unref(dev);
								udev_unref(udev);
								restart_tsak();
							}

							is_new_keyboard = false;
							snprintf(filename,sizeof(filename), "%s", udev_device_get_devnode(dev));
							udev_device_unref(dev);

							// Print name of keyboard
							hotplug_fd = open(filename, O_RDWR|O_SYNC);
							ioctl(hotplug_fd, EVIOCGBIT(EV_KEY, sizeof(key_bitmask)), key_bitmask);

							/* We assume that anything that has an alphabetic key in the
								QWERTYUIOP range in it is the main keyboard. */
							for (j = KEY_Q; j <= KEY_P; j++) {
								if (TestBit(j, key_bitmask)) {
									is_new_keyboard = true;
								}
							}
							ioctl (hotplug_fd, EVIOCGNAME (sizeof (name)), name);
							close(hotplug_fd);

							// Ensure that we do not detect our own tsak faked keyboards
							if (str_ends_with(name, "+tsak") == 1) {
								is_new_keyboard = false;
							}

							// If a keyboard was added we need to restart...
							if (is_new_keyboard == true) {
								fprintf(stderr, "[tsak] Hotplugged new keyboard: (%s)\n", name);
								udev_unref(udev);
								restart_tsak();
							}
						}
						else {
							fprintf(stderr, "[tsak] No device from receive_device().  A udev error has occurred; terminating hotplug monitoring process.\n");
							return 12;
						}
					}

					udev_unref(udev);

					fprintf(stderr, "[tsak] Hotplug monitoring process terminated\n");
				}
			}
		}
	}
	catch(exit_exception& e) {
		tsak_friendly_termination();
	}

	return 6;
}