[![CI Status](https://github.com/rickhull/device_input/actions/workflows/ci.yaml/badge.svg)](https://github.com/rickhull/device_input/actions/workflows/ci.yaml) [![Gem Version](https://badge.fury.io/rb/device_input.svg)](http://badge.fury.io/rb/device_input) [![Code Climate](https://codeclimate.com/github/rickhull/device_input/badges/gpa.svg)](https://codeclimate.com/github/rickhull/device_input) # Device Input *for the Linux kernel* This is a very basic tool for reading device input events from e.g. `/dev/input/event0` in Ruby. For example, in order to see what's happening "on the wire" when a special laptop function key is pressed. While this tool can plausibly be used for the purpose of malicious keystroke logging, it is not well suited for it and does not provide the root privileges in order to read `/dev/input`. Once you've given up the privilege to read `/dev/input` it's *game over* anyway. ## Rationale `/dev/input/eventX` is just a character device. Can't we read it with simple Unix tooling? Yes and no. First of all, a character device just means that it passes bytes (not necessarily characters or strings) from userspace into the kernel. Secondarily, the messages (defined as C structs) are in fact binary and not strings or conventional characters. Since these are C structs (analagous to a binary message), we need to be able to delimit individual messages and decode them. We can't simply read a byte at a time and try to make sense of it. In fact, on my system, `/dev/input/event0` refuses any read that is not a multiple of the struct / message size, so we need to know the message size before even attempting a `read()`, let alone a `decode()`. To determine the message size, we need to know the data structure. For a long time, it was pretty simple: events are 16 bytes: * timestamp - 8 bytes * type - 2 bytes * code - 2 bytes * value - 4 bytes However, this is only true for 32-bit platforms. On 64-bit platforms, event timestamps became 16 bytes, increasing the size of events from 16 to 24 bytes. This is because a timestamp is defined (ultimately) as two `long`s, which are bigger on 64-bit platforms. It's easy to remember: * 32-bit platform: 32-bit `long` (4 bytes) * 64-bit platform: 64-bit `long` (8 bytes) `read(/dev/input/event0, 16)` will fail on a 64-bit machine. Your tooling must be aware of this distinction and choose the correct underlying data types just to be able to delimit messages and perform a successful read. This software does that, decodes the message, maps the encoded values to friendly strings for display, and provides both library and executable code to assist in examining kernel input events. # Installation **REQUIREMENTS** * Ruby >= 2.0 **DEPENDENCIES** * none Install the gem: ```shell $ gem install device_input ``` Or, if using [Bundler](http://bundler.io/), add to your `Gemfile`: ```ruby gem 'device_input', '~> 0.3' ``` # Usage ## Executable ```shell $ evdump /dev/input/event0 # sudo as necessary ``` When the `f` key is pressed: ``` EV_MSC:ScanCode:33 EV_KEY:F:1 EV_SYN:SYN_REPORT:0 ``` And released immediately (1=pressed, 0=released): ``` EV_MSC:ScanCode:33 EV_KEY:F:1 EV_SYN:SYN_REPORT:0 EV_MSC:ScanCode:33 EV_KEY:F:0 EV_SYN:SYN_REPORT:0 ``` How about pretty mode? ```shell $ sudo cat /dev/input/event0 | evdump --print pretty # f 2017-01-24 05:29:43.923 Misc:ScanCode:33 2017-01-24 05:29:43.923 Key:F:1 2017-01-24 05:29:43.923 Sync:Report:0 2017-01-24 05:29:44.012 Misc:ScanCode:33 2017-01-24 05:29:44.012 Key:F:0 2017-01-24 05:29:44.012 Sync:Report:0 ``` We can pull off the labels and go raw: ```shell $ sudo cat /dev/input/event0 | evdump --print raw # f 4:4:33 1:33:1 0:0:0 4:4:33 1:33:0 0:0:0 ``` Fulfill your hacker-matrix fantasies: ```shell $ sudo cat /dev/input/event0 | evdump --print hex # f 00000000588757bd 00000000000046ca 0004 0004 00000021 00000000588757bd 00000000000046ca 0001 0021 00000001 00000000588757bd 00000000000046ca 0000 0000 00000000 00000000588757bd 000000000001a298 0004 0004 00000021 00000000588757bd 000000000001a298 0001 0021 00000000 00000000588757bd 000000000001a298 0000 0000 00000000 ``` ## Library ```ruby require 'device_input' File.open('/dev/input/event0', 'r') do |dev| # this loops forever and blocks waiting for input DeviceInput.read_loop(dev) do |event| puts event # break if event.time > start + 30 end end ``` An event has: * `#data`: Struct of ints (class name Data) * `#time`: Time, accurate to usecs * `#type`: String label, possibly `UNK-X` where X is the integer from `#data` * `#code`: String label, possibly `UNK-X-Y` where X and Y are from `#data` * `#value`: Fixnum (signed) from `#data` You will probably want to write your own read loop for your own project. [`DeviceInput.read_loop`](lib/device_input.rb#L98) is very simple and can easily be rewritten outside of this project's namespace and adapted for your needs. # Background ## Kernel docs * https://www.kernel.org/doc/Documentation/input/input.txt * https://www.kernel.org/doc/Documentation/input/event-codes.txt ### Kernel structs from https://www.kernel.org/doc/Documentation/input/input.txt ``` struct input_event { struct timeval time; unsigned short type; unsigned short code; unsigned int value; }; ``` from https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/input.h#n25 ``` struct input_event { struct timeval time; __u16 type; __u16 code; __s32 value; }; ``` What's a [`timeval`](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/time.h#n15)? ``` struct timeval { __kernel_time_t tv_sec; /* seconds */ __kernel_suseconds_t tv_usec; /* microseconds */ }; ``` What's a [`__kernel_time_t`](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/include/uapi/asm-generic/posix_types.h#n88)? ``` typedef long __kernel_long_t; # ... typedef __kernel_long_t __kernel_suseconds_t; # ... typedef __kernel_long_t __kernel_time_t; ``` What's a [`__u16`](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/include/uapi/asm-generic/int-l64.h#n23)? We're pretty sure it's an unsigned 16 bit integer. Likewise `__s32` should be a signed 32-bit integer: ``` typedef unsigned short __u16; typedef __signed__ int __s32; ``` Why is the value signed? It's meant to be able to communicate an "analog" range, say -127 to +127 as determined by the position of a joystick. ## Review `input_event` * time (timeval) - tv_sec (long) - tv_usec (long) * type (__u16) * code (__u16) * value (__s32) Flattened: `SEC` `USEC` `TYPE` `CODE` `VALUE` How many bytes is a `long`? Well, it's platform-dependent. On a 32-bit platform, you get 32 bits (4 bytes). On a 64-bit platform you get 64 bits (8 bytes). This means that the event is 16 bytes on a 32-bit machine and 24 bytes on a 64-bit machine. Software will need to accommodate. ## Ruby tools We can use [`RbConfig::SIZEOF`](http://idiosyncratic-ruby.com/42-ruby-config.html#rbconfigsizeof) and `Array#pack`/`String#unpack` to help us read these binary structs: ``` FIELD C RbConfig Pack --- --- --- --- tv_sec long long l! tv_usec long long l! type __u16 uint16_t S code __u16 uint16_t S value __s32 int32_t l ``` # Acknowledgments * Inspired by https://github.com/prullmann/libdevinput (don't use it) - also the source of an early version of the [event code labels](lib/device_input/labels.rb) * Thanks to al2o3-cr from #ruby on Freenode for feedback