SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
		int, newdfd, const char __user *, newname, int, flags)
{
	struct dentry *new_dentry;
	struct nameidata nd;
	struct path old_path;
	int error;
	char *to;

	if ((flags & ~AT_SYMLINK_FOLLOW) != 0)
		return -EINVAL;

	error = user_path_at(olddfd, oldname,
			     flags & AT_SYMLINK_FOLLOW ? LOOKUP_FOLLOW : 0,
			     &old_path);
	if (error)
		return error;

	error = user_path_parent(newdfd, newname, &nd, &to);
	if (error)
		goto out;
	error = -EXDEV;
	if (old_path.mnt != nd.path.mnt)
		goto out_release;
	new_dentry = lookup_create(&nd, 0);
	error = PTR_ERR(new_dentry);
	if (IS_ERR(new_dentry))
		goto out_unlock;
	error = mnt_want_write(nd.path.mnt);
	if (error)
		goto out_dput;
	error = security_path_link(old_path.dentry, &nd.path, new_dentry);
	if (error)
		goto out_drop_write;
	error = vfs_link(old_path.dentry, nd.path.dentry->d_inode, new_dentry);
out_drop_write:
	mnt_drop_write(nd.path.mnt);
out_dput:
	dput(new_dentry);
out_unlock:
	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
out_release:
	path_put(&nd.path);
	putname(to);
out:
	path_put(&old_path);

	return error;
}

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.