// SPDX-License-Identifier: GPL-2.0

  #include <linux/kernel.h>
  #include <linux/syscalls.h>
  #include <linux/fdtable.h>
  #include <linux/string.h>
  #include <linux/random.h>
  #include <linux/module.h>

  #include <linux/ptrace.h>

  #include <linux/init.h>
  #include <linux/errno.h>
  #include <linux/cache.h>
  #include <linux/bug.h>
  #include <linux/err.h>
  #include <linux/kcmp.h>

  #include <linux/capability.h>
  #include <linux/list.h>
  #include <linux/eventpoll.h>
  #include <linux/file.h>

  
  #include <asm/unistd.h>
  
  /*
   * We don't expose the real in-memory order of objects for security reasons.
   * But still the comparison results should be suitable for sorting. So we
   * obfuscate kernel pointers values and compare the production instead.
   *
   * The obfuscation is done in two steps. First we xor the kernel pointer with
   * a random value, which puts pointer into a new position in a reordered space.
   * Secondly we multiply the xor production with a large odd random number to
   * permute its bits even more (the odd multiplier guarantees that the product
   * is unique ever after the high bits are truncated, since any odd number is
   * relative prime to 2^n).
   *
   * Note also that the obfuscation itself is invisible to userspace and if needed
   * it can be changed to an alternate scheme.
   */
  static unsigned long cookies[KCMP_TYPES][2] __read_mostly;
  
  static long kptr_obfuscate(long v, int type)
  {
  	return (v ^ cookies[type][0]) * cookies[type][1];
  }
  
  /*
   * 0 - equal, i.e. v1 = v2
   * 1 - less than, i.e. v1 < v2
   * 2 - greater than, i.e. v1 > v2
   * 3 - not equal but ordering unavailable (reserved for future)
   */
  static int kcmp_ptr(void *v1, void *v2, enum kcmp_type type)
  {

  	long t1, t2;

  	t1 = kptr_obfuscate((long)v1, type);
  	t2 = kptr_obfuscate((long)v2, type);

  	return (t1 < t2) | ((t1 > t2) << 1);

  }
  
  /* The caller must have pinned the task */
  static struct file *
  get_file_raw_ptr(struct task_struct *task, unsigned int idx)
  {
  	struct file *file = NULL;
  
  	task_lock(task);
  	rcu_read_lock();
  
  	if (task->files)
  		file = fcheck_files(task->files, idx);
  
  	rcu_read_unlock();
  	task_unlock(task);
  
  	return file;
  }

  static void kcmp_unlock(struct rw_semaphore *l1, struct rw_semaphore *l2)

  {

  	if (likely(l2 != l1))
  		up_read(l2);
  	up_read(l1);

  }

  static int kcmp_lock(struct rw_semaphore *l1, struct rw_semaphore *l2)

  {
  	int err;

  	if (l2 > l1)
  		swap(l1, l2);

  	err = down_read_killable(l1);
  	if (!err && likely(l1 != l2)) {
  		err = down_read_killable_nested(l2, SINGLE_DEPTH_NESTING);

  		if (err)

  			up_read(l1);

  	}
  
  	return err;
  }

  #ifdef CONFIG_EPOLL
  static int kcmp_epoll_target(struct task_struct *task1,
  			     struct task_struct *task2,
  			     unsigned long idx1,
  			     struct kcmp_epoll_slot __user *uslot)
  {
  	struct file *filp, *filp_epoll, *filp_tgt;
  	struct kcmp_epoll_slot slot;
  	struct files_struct *files;
  
  	if (copy_from_user(&slot, uslot, sizeof(slot)))
  		return -EFAULT;
  
  	filp = get_file_raw_ptr(task1, idx1);
  	if (!filp)
  		return -EBADF;
  
  	files = get_files_struct(task2);
  	if (!files)
  		return -EBADF;
  
  	spin_lock(&files->file_lock);
  	filp_epoll = fcheck_files(files, slot.efd);
  	if (filp_epoll)
  		get_file(filp_epoll);
  	else
  		filp_tgt = ERR_PTR(-EBADF);
  	spin_unlock(&files->file_lock);
  	put_files_struct(files);
  
  	if (filp_epoll) {
  		filp_tgt = get_epoll_tfile_raw_ptr(filp_epoll, slot.tfd, slot.toff);
  		fput(filp_epoll);

  	}

  
  	if (IS_ERR(filp_tgt))
  		return PTR_ERR(filp_tgt);
  
  	return kcmp_ptr(filp, filp_tgt, KCMP_FILE);
  }
  #else
  static int kcmp_epoll_target(struct task_struct *task1,
  			     struct task_struct *task2,
  			     unsigned long idx1,
  			     struct kcmp_epoll_slot __user *uslot)
  {
  	return -EOPNOTSUPP;
  }
  #endif

  SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
  		unsigned long, idx1, unsigned long, idx2)
  {
  	struct task_struct *task1, *task2;
  	int ret;
  
  	rcu_read_lock();
  
  	/*
  	 * Tasks are looked up in caller's PID namespace only.
  	 */
  	task1 = find_task_by_vpid(pid1);
  	task2 = find_task_by_vpid(pid2);
  	if (!task1 || !task2)
  		goto err_no_task;
  
  	get_task_struct(task1);
  	get_task_struct(task2);
  
  	rcu_read_unlock();
  
  	/*
  	 * One should have enough rights to inspect task details.
  	 */

  	ret = kcmp_lock(&task1->signal->exec_update_lock,
  			&task2->signal->exec_update_lock);

  	if (ret)
  		goto err;

  	if (!ptrace_may_access(task1, PTRACE_MODE_READ_REALCREDS) ||
  	    !ptrace_may_access(task2, PTRACE_MODE_READ_REALCREDS)) {

  		ret = -EPERM;
  		goto err_unlock;
  	}
  
  	switch (type) {
  	case KCMP_FILE: {
  		struct file *filp1, *filp2;
  
  		filp1 = get_file_raw_ptr(task1, idx1);
  		filp2 = get_file_raw_ptr(task2, idx2);
  
  		if (filp1 && filp2)
  			ret = kcmp_ptr(filp1, filp2, KCMP_FILE);
  		else
  			ret = -EBADF;
  		break;
  	}
  	case KCMP_VM:
  		ret = kcmp_ptr(task1->mm, task2->mm, KCMP_VM);
  		break;
  	case KCMP_FILES:
  		ret = kcmp_ptr(task1->files, task2->files, KCMP_FILES);
  		break;
  	case KCMP_FS:
  		ret = kcmp_ptr(task1->fs, task2->fs, KCMP_FS);
  		break;
  	case KCMP_SIGHAND:
  		ret = kcmp_ptr(task1->sighand, task2->sighand, KCMP_SIGHAND);
  		break;
  	case KCMP_IO:
  		ret = kcmp_ptr(task1->io_context, task2->io_context, KCMP_IO);
  		break;
  	case KCMP_SYSVSEM:
  #ifdef CONFIG_SYSVIPC
  		ret = kcmp_ptr(task1->sysvsem.undo_list,
  			       task2->sysvsem.undo_list,
  			       KCMP_SYSVSEM);
  #else
  		ret = -EOPNOTSUPP;
  #endif
  		break;

  	case KCMP_EPOLL_TFD:
  		ret = kcmp_epoll_target(task1, task2, idx1, (void *)idx2);
  		break;

  	default:
  		ret = -EINVAL;
  		break;
  	}
  
  err_unlock:

  	kcmp_unlock(&task1->signal->exec_update_lock,
  		    &task2->signal->exec_update_lock);

  err:
  	put_task_struct(task1);
  	put_task_struct(task2);
  
  	return ret;
  
  err_no_task:
  	rcu_read_unlock();
  	return -ESRCH;
  }
  
  static __init int kcmp_cookies_init(void)
  {
  	int i;
  
  	get_random_bytes(cookies, sizeof(cookies));
  
  	for (i = 0; i < KCMP_TYPES; i++)
  		cookies[i][1] |= (~(~0UL >>  1) | 1);
  
  	return 0;
  }
  arch_initcall(kcmp_cookies_init);