trying out kernel module

0-README.MD

practice-kernel

gist

An example kernel plugin using C on the Linux kernel.

It is a corny Rickroll demo.

• The initial rickroll.c script was taken from the following Youtube walkthrough tutorial.

hello.c

#include <linux/module.h>

#if defined(CONFIG_SMP)
#define __SMP__
#endif

#if defined(CONFIG_MODVERSIONS)
#define MODVERSIONS
#include <linux/modversions.h>
#endif

#include <linux/kernel.h>

static __init int init_module(void) {
	printk(KERN_DEBUG "Hello, kernel!\n");
	return 0;
}

static __init void cleanup_module(void) {
	print(KERN_DEBUG "Good-bye, kernel!\n");
}

Makefile

obj-m += rickroll.o

# sudo apt-get install linux-headers-$(uname -r)
# compile rickroll.c
# sudo insmod rickroll.ko
#	sudo tail -f /var/log/kern.log
# moduleNumber=$(sudo grep 'Rickoll module has been loaded:' /var/log/kern.log | tail -n1 | awk '{printf $13}')
# cd /dev/
# sudo mknod rickroll c $moduleNumber 0
# sudo cat /dev/rickroll

all:
	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

linuxheaders:
	sudo apt install linux-headers-$(uname -r)

insertmod:
	sudo insmod rickroll.ko
	sudo tail -f /var/log/kern.log

removemod:
	sudo rmmod rickroll

makenode:
	#cd /dev/
	sudo mknod rickroll c $(sudo grep 'Rickoll module has been loaded:' /var/log/kern.log | tail -n1 | awk '{printf $13}') 0

run:
	sudo cat /dev/rickroll

clean:
	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

rickroll.c

/*
 * https://github.com/engineer-man/youtube/blob/master/062/rickroll.c
 * */

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/uaccess.h>

#define DEVICE_NAME "rickroll"

static int dev_open(struct inode*, struct file*);
static int dev_release(struct inode*, struct file*);
static ssize_t dev_read(struct file*, char*, size_t, loff_t*);
static ssize_t dev_write(struct file*, const char*, size_t, loff_t*);

static struct file_operations fops = {
   .open = dev_open,
   .read = dev_read,
   .write = dev_write,
   .release = dev_release,
};

static int major;

static int __init rickroll_init(void) {
    major = register_chrdev(0, DEVICE_NAME, &fops);

    if (major < 0) {
        printk(KERN_ALERT "Rickroll load failed\n");
        return major;
    }

    printk(KERN_INFO "Rickroll module has been loaded: %d\n", major);
    return 0;
}

static void __exit rickroll_exit(void) {
    unregister_chrdev(major, DEVICE_NAME);
    printk(KERN_INFO "Rickroll module has been unloaded\n");
}

static int dev_open(struct inode *inodep, struct file *filep) {
   printk(KERN_INFO "Rickroll device opened\n");
   return 0;
}

static ssize_t dev_write(struct file *filep, const char *buffer,
                         size_t len, loff_t *offset) {

   printk(KERN_INFO "Sorry, rickroll is read only\n");
   return -EFAULT;
}

static int dev_release(struct inode *inodep, struct file *filep) {
   printk(KERN_INFO "Rickroll device closed\n");
   return 0;
}

static ssize_t dev_read(struct file *filep, char *buffer, size_t len, loff_t *offset) {
    int errors = 0;
    char *message = "never gonna give you up, never gonna let you down... ";
    int message_len = strlen(message);

    errors = copy_to_user(buffer, message, message_len);

    return errors == 0 ? message_len : -EFAULT;
}

module_init(rickroll_init);
module_exit(rickroll_exit);