keysniffer
A Linux kernel module to grab keys pressed in the keyboard, or a keylogger.
keysniffer was initially written with the US keyboard (and conforming laptops) in mind. By default it shows human-readable strings for the keys pressed. Optionally, the keycode shift_mask pair can be printed in hex or decimal. You can lookup the keycodes in /usr/include/linux/input-event-codes.h.
The keypress logs are recorded in debugfs as long as the module is loaded. Only root or sudoers can read the log. The module name has been camouflaged to blend-in with other kernel modules.
You can, however, execute a script at shutdown or reboot (the procedure would be distro-specific) to save the keys to a file.
DISCLAIMER: keysniffer is intended to track your own devices and NOT to trespass on others. The author has never used it to compromise any third-party device and is not responsible for any unethical application.
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Table of contents
Compilation
Build
Clone the repository and run:
# make
Note that you need to have the linux kernel headers installed for your running kernel version.
To insert the module into the kernel, run:
# insmod kisni.ko
OR
# make load
To unload the module (and clear the logs), run:
# rmmod kisni
DKMS support
If you have DKMS installed, you can install keysniffer in such a way that it survives kernel upgrades. It is recommended to remove older versions of keysniffer by running dkms remove -m kisni -v OLDVERSION --all as root. To install the new version, run:
# make -f Makefile.dkms
To uninstall it, run:
# make -f Makefile.dkms uninstall
Usage
To view the pressed keys, run:
# cat /sys/kernel/debug/kisni/keys
modinfo kisni.ko
cat /sys/kernel/debug/kisni/keys
#
To log generic hex keycodes in the format keycode shift_mask, run:
# insmod kisni.ko codes=1
// Type something
# cat /sys/kernel/debug/kisni/keys
23 0
12 0
26 0
26 0
18 0
39 0
2a 0
2a 1
2a 1
11 1
18 0
13 0
26 0
20 0
2a 0
2a 1
2a 1
2 1
1c 0
1f 0
16 0
20 0
18 0
39 0
2e 0
1e 0
14 0
6a 0
1c 0
To log the keycodes in decimal, run:
# insmod kisni.ko codes=2
To check the module details:
# modinfo kisni.ko
filename: kisni.ko
description: Sniff and log keys pressed in the system to debugfs
version: 1.7
author: Arun Prakash Jana <engineerarun@gmail.com>
license: GPL v2
srcversion: 26381298B8DB375C50B04EA
depends:
name: kisni
vermagic: 4.13.0-32-generic SMP mod_unload
parm: codes:log format (0:US keys (default), 1:hex keycodes, 2:dec keycodes) (int)
License
Developer
Copyright © 2015 Arun Prakash Jana
Links
- http://www.gadgetweb.de/programming/39-how-to-building-your-own-kernel-space-keylogger.html
- https://wiki.archlinux.org/index.php/Xmodmap
- http://www.osdever.net/bkerndev/Docs/keyboard.htm
- http://arjunsreedharan.org/post/99370248137/kernel-201-lets-write-a-kernel-with-keyboard
- http://www.linuxquestions.org/questions/slackware-14/how-to-match-x-keyboard-layout-with-the-the-kernel-keyboard-map-4175455061/
- http://www.tldp.org/LDP/lkmpg/2.4/html/x1210.html