From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753944Ab2A0SiW (ORCPT <rfc822;w@1wt.eu>);
	Fri, 27 Jan 2012 13:38:22 -0500
Received: from out02.mta.xmission.com ([166.70.13.232]:46417 "EHLO
	out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1753157Ab2A0SiV (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Fri, 27 Jan 2012 13:38:21 -0500
From: ebiederm@xmission.com (Eric W. Biederman)
To: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Pavel Emelyanov <xemul@openvz.org>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Pavel Emelyanov <xemul@parallels.com>,
        Andrey Vagin <avagin@openvz.org>,
        KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
        Ingo Molnar <mingo@elte.hu>, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Glauber Costa <glommer@parallels.com>,
        Andi Kleen <andi@firstfloor.org>, Tejun Heo <tj@kernel.org>,
        Matt Helsley <matthltc@us.ibm.com>, Pekka Enberg <penberg@kernel.org>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        Vasiliy Kulikov <segoon@openwall.com>,
        Alexey Dobriyan <adobriyan@gmail.com>, Valdis.Kletnieks@vt.edu
Subject: Re: [RFC c/r 2/4] [RFC] syscalls, x86: Add __NR_kcmp syscall v7
References: <20120127175342.273260614@openvz.org>
	<20120127175939.795551339@openvz.org>
Date: Fri, 27 Jan 2012 10:40:54 -0800
In-Reply-To: <20120127175939.795551339@openvz.org> (Cyrill Gorcunov's message
	of "Fri, 27 Jan 2012 21:53:44 +0400")
Message-ID: <m1zkd92dl5.fsf@fess.ebiederm.org>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.2 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
X-XM-SPF: eid=;;;mid=;;;hst=in02.mta.xmission.com;;;ip=98.207.153.68;;;frm=ebiederm@xmission.com;;;spf=neutral
X-XM-AID: U2FsdGVkX18bpz7X8HV4bne6im+yFbTOBBum2DnGB2U=
X-SA-Exim-Connect-IP: 98.207.153.68
X-SA-Exim-Mail-From: ebiederm@xmission.com
X-SA-Exim-Scanned: No (on in02.mta.xmission.com); SAEximRunCond expanded to false
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Cyrill Gorcunov <gorcunov@openvz.org> writes:

> +/*
> + * We don't expose real in-memory order of objects for security
> + * reasons, still the comparision results should be suitable for
> + * sorting. Thus, we obfuscate kernel pointers values (using random
> + * cookies obtaned at early boot stage) and compare the production
> + * instead.
> + */
> +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
> + * 1 - less than
> + * 2 - greater than
> + * 3 - not equal but ordering unavailable (reserved for future)
> + */
> +static int kcmp_ptr(long v1, long v2, enum kcmp_type type)
> +{

Can you make the prototype:
static int kcmp_ptr(void *v1, void *v2, enum kcmp_type type)

So the caller does not need to have casts?

> +	long ret;
> +
> +	ret = kptr_obfuscate(v1, type) - kptr_obfuscate(v2, type);
> +
> +	return (ret < 0) | ((ret > 0) << 1);
> +}
> +
> +/* The caller must have pinned the task */
> +static struct file *
> +get_file_raw_ptr(struct task_struct *task, unsigned int idx)
> +{
> +	struct fdtable *fdt;
> +	struct file *file;
> +
> +	spin_lock(&task->files->file_lock);
> +	fdt = files_fdtable(task->files);
> +	if (idx < fdt->max_fds)
> +		file = fdt->fd[idx];
> +	else
> +		file = NULL;
> +	spin_unlock(&task->files->file_lock);

I believe I commented on this earlier but it looks like it got lost in
the noise.

file == NULL != file == NULL.

When you can't lookup the file kcmp should return -EBADF.

Eric