Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760139Ab1CDUb6 (ORCPT ); Fri, 4 Mar 2011 15:31:58 -0500 Received: from waste.org ([173.11.57.241]:37787 "EHLO waste.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751746Ab1CDUb5 (ORCPT ); Fri, 4 Mar 2011 15:31:57 -0500 Subject: Re: [PATCH] Make /proc/slabinfo 0400 From: Matt Mackall To: Pekka Enberg Cc: Linus Torvalds , Dave Hansen , Theodore Tso , Dan Rosenberg , 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> Content-Type: text/plain; charset="UTF-8" Date: Fri, 04 Mar 2011 14:31:49 -0600 Message-ID: <1299270709.3062.313.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: 1528 Lines: 34 On Fri, 2011-03-04 at 22:02 +0200, Pekka Enberg wrote: > On Fri, Mar 4, 2011 at 8:14 PM, Matt Mackall wrote: > >> Of course, as you say, '/proc/meminfo' still does give you the trigger > >> for "oh, now somebody actually allocated a new page". That's totally > >> independent of slabinfo, though (and knowing the number of active > >> slabs would neither help nor hurt somebody who uses meminfo - you > >> might as well allocate new sockets in a loop, and use _only_ meminfo > >> to see when that allocated a new page). > > > > I think lying to the user is much worse than changing the permissions. > > The cost of the resulting confusion is WAY higher. > > Yeah, maybe. I've attached a proof of concept patch that attempts to > randomize object layout in individual slabs. I'm don't completely > understand the attack vector so I don't make any claims if the patch > helps or not. In general, the attack relies on getting an object A (vulnerable to overrun) immediately beneath an object B (that can be exploited when overrun). I'm not sure how much randomization helps, though. Allocate 1000 objects of type B, deallocate the 800th, then allocate an object of type A. It's almost certainly next to a B. -- 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/