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 S1751556AbdGZQzs (ORCPT <rfc822;w@1wt.eu>);
        Wed, 26 Jul 2017 12:55:48 -0400
Received: from resqmta-ch2-04v.sys.comcast.net ([69.252.207.36]:45594 "EHLO
        resqmta-ch2-04v.sys.comcast.net" rhost-flags-OK-OK-OK-OK)
        by vger.kernel.org with ESMTP id S1750882AbdGZQzq (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 26 Jul 2017 12:55:46 -0400
Date: Wed, 26 Jul 2017 11:55:44 -0500 (CDT)
From: Christopher Lameter <cl@linux.com>
X-X-Sender: cl@nuc-kabylake
To: Kees Cook <keescook@chromium.org>
cc: Alexander Popov <alex.popov@linux.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Ingo Molnar <mingo@kernel.org>, Josh Triplett <josh@joshtriplett.org>,
        Andy Lutomirski <luto@kernel.org>,
        Nicolas Pitre <nicolas.pitre@linaro.org>, Tejun Heo <tj@kernel.org>,
        Daniel Mack <daniel@zonque.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Helge Deller <deller@gmx.de>, Rik van Riel <riel@redhat.com>,
        Linux-MM <linux-mm@kvack.org>, Tycho Andersen <tycho@docker.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "kernel-hardening@lists.openwall.com" 
        <kernel-hardening@lists.openwall.com>
Subject: Re: [v3] mm: Add SLUB free list pointer obfuscation
In-Reply-To: <CAGXu5jLkOjDKSZ48jOyh2voP17xXMeEnqzV_=8dGSvFmqdCZCA@mail.gmail.com>
Message-ID: <alpine.DEB.2.20.1707261154140.9167@nuc-kabylake>
References: <20170706002718.GA102852@beast> <cdd42a1b-ce15-df8c-6bd1-b0943275986f@linux.com> <CAGXu5jKRDhvqj0TU10W10hsdixN2P+hHzpYfSVvOFZy=hW72Mg@mail.gmail.com> <alpine.DEB.2.20.1707260906230.6341@nuc-kabylake>
 <CAGXu5jLkOjDKSZ48jOyh2voP17xXMeEnqzV_=8dGSvFmqdCZCA@mail.gmail.com>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
X-CMAE-Envelope: MS4wfO4queTxloZvolwVMjFg+pXPPRsbhXZ5R1P73Za+JProkAfv9sfRm6S4CqKNdz9ScwUuEh8BMvz9DH/g8ti2Dsrm59ig7PBMgZBHSWhRYge+Y2vGrUjy
 Ny+dC0/JCQ8ALdHkrq7UjlzhzJ32OlaWqNmsnOTiYgnkvZv+qd0jB61hhJat17RHngXQBOaNd3vKF6FXe9mhOzigwFD6y60BpVZXDWPTPBqWULhAn9SUmgBf
 rV/avxNwsiFeu4K7IXT3Vr/iVkqjyrr6eWw7NLOx0/OCCuuFBvQE0wVygf5CcPZisNXx3mAGzV+LuuEVwV/1Kp3k+REt0/7L8OVorGnRZVCPTGzhoJQZLnXY
 5o7+albv1zj/NkvRYFakm3N8da+ij6fe8AFiFquUx4IFasWpXainUltLU5hdxCAHrOnDGycGLpDkGw7DAlK5HCXIAItVKlBGXjCLHfCmA7UYAIyQjTn9RrtD
 wsQQnJuJf0VljKDBZVT3JnOpkrEuJVaxEt+heWqL2WVfvbXu9d7VcfJIwiDLRTDW/hL8vaDfAZhnV6F8NP2IqMHcd5jqnUvfxVptJOhVt44pnunNh56d9Fys
 u9Lr+g+mh9a+Xabm5NNVUEUuhLT0ZCy7XHuEh6U9UMJ9mSoy4delIJemNrYJ1+jaBrL2jUjWQOO5Y3AWX+GVk6rX+FFjB+o8e46sk7IuyQgtqjekAGHOSaZH
 smwHM8QhTxFWkNhqPWigTM5vhbMlC0aDy9xykPx19ln3VwLNynCqQ52w6BwDRGS7grDS/okaEYeBgT0nqFCP/8Neif9L02UL
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, 26 Jul 2017, Kees Cook wrote:

> >> What happens if, instead of BUG_ON, we do:
> >>
> >> if (unlikely(WARN_RATELIMIT(object == fp, "double-free detected"))
> >>         return;
> >
> > This may work for the free fastpath but the set_freepointer function is
> > use in multiple other locations. Maybe just add this to the fastpath
> > instead of to this fucnction?
>
> Do you mean do_slab_free()?

Yes inserting these lines into do_slab_free() would simple ignore the
double free operation in the fast path and that would be safe.

Although in either case we are adding code to the fastpath...