linux device driver that grants arbitary memory access in a broken way

benarydev.c

#include <linux/module.h>
#include <linux/version.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/kdev_t.h>
#include <linux/fs.h>
#include <linux/device.h>
#include <linux/cdev.h>

static dev_t first;
static struct cdev c_dev;
static struct class *cl;

static int dopen(struct inode *i,struct file *f)
{
	printk(KERN_INFO "Driver: open()\n");
	return 0;
}

static int dclose(struct inode *i,struct file *f)
{
	printk(KERN_INFO "Driver: close()\n");
	return 0;
}

static ssize_t dread(struct file *f,char __user *buf,size_t len,loff_t *off)
{
	printk(KERN_INFO "Driver: read()\n");
	memcpy(buf,off,len);
	return len;
}

static ssize_t dwrite(struct file *f,const char __user *buf,size_t len,loff_t *off)
{
	printk(KERN_INFO "Driver: write()\n");
	memcpy(off,buf,len);
	return len;
}

static int duevent(struct device *dev,struct kobj_uevent_env *env)
{
	printk(KERN_INFO "Driver: uevent()\n");
	add_uevent_var(env,"DEVMODE=%#o",0666);
	return 0;
}

static struct file_operations pugs_fops=
{
	.owner=THIS_MODULE,
	.open=dopen,
	.release=dclose,
	.read=dread,
	.write=dwrite,
};

static int __init benarydev_init(void)
{
	printk(KERN_INFO "benarydev: starting");
	if(alloc_chrdev_region(&first,0,1,"benarydev")<0)
	{
		return -1;
	}
	if ((cl = class_create(THIS_MODULE,"chardrv")) == NULL)
	{
		unregister_chrdev_region(first,1);
		return -1;
	}
	cl->dev_uevent=duevent;
	if (device_create(cl,NULL,first,NULL,"benarydevnull") == NULL)
	{
		class_destroy(cl);
		unregister_chrdev_region(first,1);
		return -1;
	}
	cdev_init(&c_dev,&pugs_fops);
	if (cdev_add(&c_dev,first,1) == -1)
	{
		device_destroy(cl,first);
		class_destroy(cl);
		unregister_chrdev_region(first,1);
		return -1;
	}
	printk(KERN_INFO "benarydev: started");
	return 0;
}

static void __exit benarydev_exit(void)
{
	printk(KERN_INFO "benarydev: stopping");
	cdev_del(&c_dev);
	device_destroy(cl, first);
	class_destroy(cl);
	unregister_chrdev_region(first, 1);
	printk(KERN_INFO "benarydev: stopped");
}

module_init(benarydev_init);
module_exit(benarydev_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("benaryorg <binary at benary dot org>");
MODULE_DESCRIPTION("benaryorg's device driver (do not use)");