Ubuntu RFID Screensaver lock-unlock

Question

So, I have this el-cheapo RFID scanner and some RFID tags.

I thought to myself, You know what would be neat? Enabling and disabling the lock screen with this thing.

So the package arrived and I tore it apart and hooked it up.

This device emulates a USB keyboard (that explains the driver-less thing they were pushing) and essentially types out the card ID and hits enter.

I thought I could just open a constant stream from /dev/stdin (a la keylogger) and watch for when the card I want was punched in. Thats what lead me to creating this stupid simple script:

#!/bin/bash  

cat /dev/stdin | while read line  
do  
  if [ "$line" == "0000996716" ]  
     then echo "Correct!"  
  fi  
done  

Which worked!

I then changed the THEN statement to the gnome-screensaver unlock command, gnome-screensaver-command -d.

And locked my screen manually (Ctrl-Alt-L) Swiped my card aaand.... nothing. The scanner had just typed the card # in the password field and hit enter, resulting in a 'password incorrect' to show up on the lock screen.

So I unlocked my screen via the password and noticed there was nothing on the terminal screen.

So I opened a direct pipe to /dev/stdin and locked my screen. Unlocked it with my password and... nothing again.

Why isn't this doing what I expect? Does /dev/stdin not contain information that is being typed during the lock screen? If not, what does?

Answer 1

Well you guys suck :P It was kinda specific and niche but I wont hold it against you ;)

Anywho, for the full run down.

I had bought this neat little unit which describes itself as 'driverless' like in the original post. This means it acts like a USB keyboard (and registeres itself as such in /dev/input/event*). This made it almost useless to me as I couldn’t interact with the device any way when the lock screen was active, I needed to read the keystrokes from the device as they were being 'input' by the reader Cat-ing /dev/input/event3 (my reader) gave me garbage, or so I though.

Then I ran into this piece of code here: http://itech-planet.net/content/reading-device-input-directly-fromto-devinputeventx-ubuntu-c with no? author that I can see, but most of the credit for the legwork in this application goes to him/her. Thanks! Simplifying this code I was able to read the raw input from my own keyboard, with the secret phrase being 'secret' and proceeded to capture the keystrokes into a variable and look for when 'enter' was hit to check the string against the stored value for the code.

This code is essentially a glorified keylogger pointing to a different 'keyboard' and scanning what it 'types' to a matching phrase. Much like how the FBI sifts though millions of AOL IM's from a 13-yo girl looking for terrorists!

When it hits the matching phrase, it triggers the if statement and runs the rest of the corresponding code. I've commented it the best I can, if you have any issues, email/pm/im/yell loudly at me.

Not like you read any of that, you just want the code! Well, here it is!

Usage:

sudo ./[file] -u [your username] -d [location to device] -t [tag id]

So I, being Tyler, with my device at /dev/input/event3 and my tag being 0000996716 would have:

sudo ./input -u tyler -d /dev/input/event3 -t 0000996716

CODE:

#include <linux/input.h>  
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
int getStatus(){
  FILE *fp;
  char path[128];
  fp = popen("sudo -u tyler gnome-screensaver-command -q", "r");

  fgets(path, sizeof(path)-1, fp);
  pclose(fp);
  printf("%s\n",path);
  if(strcmp("The screensaver is inactive\n",path)==0) 
    return 1;//if screensaver is disabled
  else if(strcmp("The screensaver is active\n",path)==0) 
    return 0;//if screensaver is enabled
  else
    return -1;//wat
}

int main(int argc, char **argv)
{
//char array that stores the keys in order up to like 40 something, DO NOT MESS WITH THE ORDER OF THIS ARRAY. ITS IMPORTANT.
    char arr[]={' ',' ','1','2','3','4','5','6','7','8','9','0','-','=','\b','\t','q','w','e','r','t','y','u','i','o','p','[',']','\n',' ','a','s','d','f','g','h','j','k','l',';',',','`',' ','\\','z','x','c','v','b','n','m',',','.','/',' ','*',' ',' '};
    char inp[256];//input string to check what you type.
    int fd;//file pointer to the /dev/input device
char usr[32];//stores your username to run screensaver command as you. Root user (sudo) can NOT lock the screen.
char tag[32];//stores the tag ID for the RFID
char dev[32];//stores the device location, /dev/input/eventX
char lcom[96];//locking command builder string
char ucom[96];//unlocking command builder string
//processes arguments, dont ask.
   int idx = 0;
   for (idx = 1; idx < argc;  idx++) {
       if (strcmp(argv[idx], "-u") == 0) {
      strcpy(usr,argv[idx+1]);
          printf("User = %s\n", usr);
       } else if (strcmp(argv[idx], "-t") == 0) {
      strcpy(tag,argv[idx+1]);
          printf("Tag = %s\n", tag);
       } else if (strcmp(argv[idx], "-d") == 0) {
      strcpy(dev,argv[idx+1]);
          printf("Device = %s\n", dev);
      fd = open(dev, O_RDONLY);
       } else {}
    }
    //build commands
    strcpy(lcom,"sudo -u ");
    strcat(lcom,usr);
    strcat(lcom," gnome-screensaver-command -l");
    strcpy(ucom,"sudo -u ");
    strcat(ucom,usr);
    strcat(ucom," gnome-screensaver-command -d");
    struct input_event ev;
    int cursor=0;
    while (1)
    {
        read(fd, &ev, sizeof(struct input_event));
        if(ev.type == 1)//only key ID event
            if(ev.value == 0)//only not repeat
        if(ev.code== 28||ev.code==14){//if code is enter or bsp, reset the counter and compare
            inp[cursor]='\0';//terminate string
            cursor=0;
            if(strcmp(inp,tag)==0){//if input string equals tag, strcmp works funny lol
                int status=getStatus();//find out what the screensaver is doing
                if(status==1){//screensaver is unlocked, so lock it
                    printf("Locking...");
                    system(lcom);}
                else if(status==0){//screensaver is locked, so unlock it!
                    printf("Unlocking...");
                    system(ucom);}
                else printf("Wat happened");//???
            }
        }
            else{//if not enter or bsp, log it      
            inp[cursor]=arr[ev.code];
            cursor++;
        }
    //fflush(stdout);this was here for debug purposes, since apparently I dont know how STDOUT works lol
    }
}