Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753004Ab2BRQkw (ORCPT ); Sat, 18 Feb 2012 11:40:52 -0500 Received: from mail-bk0-f46.google.com ([209.85.214.46]:41479 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752730Ab2BRQkv (ORCPT ); Sat, 18 Feb 2012 11:40:51 -0500 Authentication-Results: mr.google.com; spf=pass (google.com: domain of segooon@gmail.com designates 10.204.129.86 as permitted sender) smtp.mail=segooon@gmail.com; dkim=pass header.i=segooon@gmail.com Date: Sat, 18 Feb 2012 20:35:56 +0400 From: Vasiliy Kulikov To: kernel-hardening@lists.openwall.com Cc: Roland Dreier , Djalal Harouni , Kees Cook , Ubuntu security discussion , linux-kernel@vger.kernel.org, pageexec@freemail.hu, spender@grsecurity.net, gregkh@linuxfoundation.org Subject: Re: [kernel-hardening] Re: Add overflow protection to kref Message-ID: <20120218163556.GA11640@albatros> References: <20120216204515.GH20420@outflux.net> <20120217002405.GB7746@kroah.com> <20120217075945.GA2831@albatros> <20120217175445.GC29902@kroah.com> <20120217193719.GA4187@albatros> <20120217233908.GA24047@dztty> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1880 Lines: 51 On Sat, Feb 18, 2012 at 11:15 -0500, David Windsor wrote: > On Fri, Feb 17, 2012 at 8:44 PM, Roland Dreier wrote: > > On Fri, Feb 17, 2012 at 3:39 PM, Djalal Harouni wrote: > >>> 2) what to do with architectures-loosers? > >> There is lib/atomic64.c but with a static hashed array of raw_spinlocks. > > > > Even leaving aside performance impact of atomic64_t (and probably > > in most cases the performance of kref is not important at all), it is > > unfortunate to bloat the size from 4 bytes to 8 bytes. > > > > It seems much better to have some out-of-line code for overflow > > checking rather than increasing the size of every data structure > > that embeds a kref. > > > > kref is mostly a set of operations (init, get, sub, put) to be > performed on an atomic_t object. > > >From linux/kref.h: > > struct kref { > atomic_t refcount; > }; > > Moving overflow protection into kref amounts to placing some > procedural code into kref_get and kref_sub, adding a rather small > constant factor of time, not space, to users of kref. Introducing > overflow protection doesn't necessitate adding anything to kref for > greater state tracking. > > Did you have something else in mind when you suggested a potential > increase in the size of kref? 4 bytes => 8 bytes of atomic_t => atomic64_t in case we increase the refcounter range to make it impossible to overflow the refcounter compared to add checks into kref_get()/atomic_inc*() without changing refcounter ranges. Thanks, -- Vasiliy Kulikov http://www.openwall.com - bringing security into open computing environments -- 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/