Basic Knowledge :
A rootkit is a collection of computer software, typically malicious, designed to enable access to a computer or areas of its software that would not otherwise be allowed (for example, to an unauthorized user) while at the same time masking its existence or the existence of other software.
a) Use printk to perform any output. This output should use the KERN_INFO log level.
b) Your module should output welcome and goodbye messages when mod.ko is loaded and unloaded, respectively.
c) Your module should contain a function print_nr_procs(). This function should out- put the number of processes in the system. Use the for_each_process macro (sched.h) to get the number of processes.
d) After the welcome message,this module should call print_nr_procs() when loaded.
git clone https://github.com/huangzonghao/rootkit
Note: u can use those module for Buffer Overflow/Stack Overflow (if you Know).
Source : https://github.com/huangzonghao