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// 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 mutex *m1, struct mutex *m2)
	if (likely(m2 != m1))
		mutex_unlock(m2);
	mutex_unlock(m1);
static int kcmp_lock(struct mutex *m1, struct mutex *m2)
	if (m2 > m1)
		swap(m1, m2);
	err = mutex_lock_killable(m1);
	if (!err && likely(m1 != m2)) {
		err = mutex_lock_killable_nested(m2, SINGLE_DEPTH_NESTING);
			mutex_unlock(m1);
	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);
		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);
static int kcmp_epoll_target(struct task_struct *task1,
			     struct task_struct *task2,
			     unsigned long idx1,
			     struct kcmp_epoll_slot __user *uslot)
	return -EOPNOTSUPP;
SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
		unsigned long, idx1, unsigned long, idx2)
	struct task_struct *task1, *task2;
	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->cred_guard_mutex,
			&task2->signal->cred_guard_mutex);
		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);
			ret = -EBADF;
	case KCMP_VM:
		ret = kcmp_ptr(task1->mm, task2->mm, KCMP_VM);
	case KCMP_FILES:
		ret = kcmp_ptr(task1->files, task2->files, KCMP_FILES);
	case KCMP_FS:
		ret = kcmp_ptr(task1->fs, task2->fs, KCMP_FS);
	case KCMP_SIGHAND:
		ret = kcmp_ptr(task1->sighand, task2->sighand, KCMP_SIGHAND);
	case KCMP_IO:
		ret = kcmp_ptr(task1->io_context, task2->io_context, KCMP_IO);
	case KCMP_SYSVSEM:
#ifdef CONFIG_SYSVIPC
		ret = kcmp_ptr(task1->sysvsem.undo_list,
			       task2->sysvsem.undo_list,
			       KCMP_SYSVSEM);
		ret = -EOPNOTSUPP;
	case KCMP_EPOLL_TFD:
		ret = kcmp_epoll_target(task1, task2, idx1, (void *)idx2);
		ret = -EINVAL;
err_unlock:
	kcmp_unlock(&task1->signal->cred_guard_mutex,
		    &task2->signal->cred_guard_mutex);
	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)
	get_random_bytes(cookies, sizeof(cookies));
	for (i = 0; i < KCMP_TYPES; i++)
		cookies[i][1] |= (~(~0UL >>  1) | 1);
arch_initcall(kcmp_cookies_init);
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