static int grub_username_get (char buf[], unsigned buf_size)
 {
   unsigned cur_len = 0;
   int key;

   while (1)
     {
       key = grub_getkey ();
       if (key == '\n' || key == '\r')
         break;

       if (key == '\e')
         {
           cur_len = 0;
           break;
         }

       if (key == '\b')  //keine Kontrolle auf Underflows
         {
           cur_len--;   //Integer Underflow
           grub_printf ("\b");
           continue;
         }

       if (!grub_isprint (key))
         continue;

       if (cur_len + 2 < buf_size)
         {
           buf[cur_len++] = key; //Off-by-Two Fehler
           grub_printf ("%c", key);
         }
     }
 [...]