Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752635Ab1CFBJs (ORCPT ); Sat, 5 Mar 2011 20:09:48 -0500 Received: from waste.org ([173.11.57.241]:41547 "EHLO waste.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751175Ab1CFBJq (ORCPT ); Sat, 5 Mar 2011 20:09:46 -0500 Subject: Re: [PATCH] Make /proc/slabinfo 0400 From: Matt Mackall To: Jesper Juhl Cc: Dan Rosenberg , Pekka Enberg , Linus Torvalds , Dave Hansen , Theodore Tso , cl@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton In-Reply-To: References: <1299174652.2071.12.camel@dan> <1299185882.3062.233.camel@calx> <1299186986.2071.90.camel@dan> <1299188667.3062.259.camel@calx> <1299191400.2071.203.camel@dan> <2DD7330B-2FED-4E58-A76D-93794A877A00@mit.edu> <1299260164.8493.4071.camel@nimitz> <1299262495.3062.298.camel@calx> <1299271041.2071.1398.camel@dan> <1299273034.2071.1417.camel@dan> Content-Type: text/plain; charset="UTF-8" Date: Sat, 05 Mar 2011 19:09:41 -0600 Message-ID: <1299373781.3062.374.camel@calx> Mime-Version: 1.0 X-Mailer: Evolution 2.32.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2047 Lines: 45 On Sun, 2011-03-06 at 01:42 +0100, Jesper Juhl wrote: > On Fri, 4 Mar 2011, Dan Rosenberg wrote: > > > On Fri, 2011-03-04 at 22:58 +0200, Pekka Enberg wrote: > > > On Fri, Mar 4, 2011 at 10:37 PM, Dan Rosenberg wrote: > > > > This patch makes these techniques more difficult by making it hard to > > > > know whether the last attacker-allocated object resides before a free or > > > > allocated object. Especially with vulnerabilities that only allow one > > > > attempt at exploitation before recovery is needed to avoid trashing too > > > > much heap state and causing a crash, this could go a long way. I'd > > > > still argue in favor of removing the ability to know how many objects > > > > are used in a given slab, since randomizing objects doesn't help if you > > > > know every object is allocated. > > > > > > So if the attacker knows every object is allocated, how does that help > > > if we're randomizing the initial freelist? > > > > If you know you've got a slab completely full of your objects, then it > > doesn't matter that they happened to be allocated in a random fashion - > > they're still all allocated, and by freeing one of them and > > reallocating, you'll still be next to your target. > > > > But still, if randomizing allocations makes life just a little harder for > attackers in some scenarios, why not just do it? Lemme guess, you work for the TSA? As far as I can tell neither of the patches under discussion do anything that couldn't be worked around by an exploit writer in the time it takes to write this email. And the second attacker, of course, will have even less trouble. Putting trivial obstacles in the way of attackers accomplishes little beyond annoying users. -- Mathematics is the supreme nostalgia of our time. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/