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

MODULE_LICENSE("GPL");
MODULE_AUTHOR("ptr-yudai");
MODULE_DESCRIPTION("Holstein v1 - Vulnerable Kernel Driver for Pawnyable");

#define DEVICE_NAME "holstein"
#define BUFFER_SIZE 0x400

char *g_buf = NULL;

static int module_open(struct inode *inode, struct file *file) {
  printk(KERN_INFO "module_open called\n");

  g_buf = kmalloc(BUFFER_SIZE, GFP_KERNEL);
  if (!g_buf) {
    printk(KERN_INFO "kmalloc failed");
    return -ENOMEM;
  }

  return 0;
}

static ssize_t module_read(struct file *file, char __user *buf, size_t count,
                           loff_t *f_pos) {
  char kbuf[BUFFER_SIZE] = {0};

  printk(KERN_INFO "module_read called\n");

  memcpy(kbuf, g_buf, BUFFER_SIZE);
  if (_copy_to_user(buf, kbuf, count)) {
    printk(KERN_INFO "copy_to_user failed\n");
    return -EINVAL;
  }

  return count;
}

static ssize_t module_write(struct file *file, const char __user *buf,
                            size_t count, loff_t *f_pos) {
  char kbuf[BUFFER_SIZE] = {0};

  printk(KERN_INFO "module_write called\n");

  if (_copy_from_user(kbuf, buf, count)) {
    printk(KERN_INFO "copy_from_user failed\n");
    return -EINVAL;
  }
  memcpy(g_buf, kbuf, BUFFER_SIZE);

  return count;
}

static int module_close(struct inode *inode, struct file *file) {
  printk(KERN_INFO "module_close called\n");
  kfree(g_buf);
  return 0;
}

static struct file_operations module_fops = {
    .owner = THIS_MODULE,
    .read = module_read,
    .write = module_write,
    .open = module_open,
    .release = module_close,
};

static dev_t dev_id;
static struct cdev c_dev;

static int __init module_initialize(void) {
  if (alloc_chrdev_region(&dev_id, 0, 1, DEVICE_NAME)) {
    printk(KERN_WARNING "Failed to register device\n");
    return -EBUSY;
  }

  cdev_init(&c_dev, &module_fops);
  c_dev.owner = THIS_MODULE;

  if (cdev_add(&c_dev, dev_id, 1)) {
    printk(KERN_WARNING "Failed to add cdev\n");
    unregister_chrdev_region(dev_id, 1);
    return -EBUSY;
  }

  return 0;
}

static void __exit module_cleanup(void) {
  cdev_del(&c_dev);
  unregister_chrdev_region(dev_id, 1);
}

module_init(module_initialize);
module_exit(module_cleanup);