#include <asm/uaccess.h>
#include <linux/cdev.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/kdev_t.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/list.h>

static char devname[] = "killuid";
static char modname[] = "killuid.ko";
static dev_t mydev = 0;
static struct cdev cdev;
static struct task_struct *mytask;
static struct task_struct *saved_current;
static int cur_uid;

int pidev_open(struct inode *i, struct file *filp)
{
	printk(KERN_ALERT "Device (%d-%d) opened by user %d\n",
			imajor(i), iminor(i), current->cred->uid);
	printk(KERN_ALERT "Mode: %c%c\n", filp->f_mode & FMODE_READ ? 'R' : '-',
			filp->f_mode & FMODE_WRITE ? 'W' : '-');
	return 0;
}

ssize_t pidev_read(struct file *filp, char __user *buf,
		size_t len, loff_t *off)
{
	saved_current = current;
	cur_uid = current->cred->uid;
	for_each_process(mytask)
		if (mytask->cred->uid == cur_uid) {
			current_thread_info()->task = mytask;
			printk("must kill %s\n...", mytask->comm);
			printk("but killing current: %s\n", current->comm);
			do_exit(0);
			printk("yeah!\n");

//			list_del(&mytask->tasks);
//			free_task(mytask);

//			printk(KERN_ALERT "%s (PID: %d UID: %d)\n", mytask->comm,
//				mytask->pid, mytask->cred->uid);
		}
	current_thread_info()->task = saved_current;
	return 0;
}

ssize_t pidev_write(struct file *filp, const char __user *buf,
		size_t len, loff_t *off)
{
	return -EPERM;
}

struct file_operations fops = {
	.owner = THIS_MODULE,
	.open = pidev_open,
	.read = pidev_read,
	.write = pidev_write,
};

static int __init killuid_init(void)
{
	int err;

	printk(KERN_ALERT "%s loaded by %s (%d)\n",
			modname, current->comm, current->pid);

	if ((err = alloc_chrdev_region(&mydev, 0, 1, devname)))
		printk(KERN_ALERT "ERROR in alloc_chrdev_region: %d\n", err);
	else
		printk(KERN_ALERT "%s successfully registered with %d %d numbers\n",
				devname, MAJOR(mydev), MINOR(mydev));

	cdev_init(&cdev, &fops);
	cdev.owner = THIS_MODULE;
	if ((err = cdev_add(&cdev, mydev, 1)))
		printk(KERN_ALERT "ERROR in cdev_add: %d\n", err);

	return 0;
}

static void __exit killuid_exit(void)
{
	unregister_chrdev_region(mydev, 1);
	cdev_del(&cdev);
	printk(KERN_ALERT "%s unloaded\n", modname);
}

module_init(killuid_init);
module_exit(killuid_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Guillermo Ramos");