From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with SMTP id 2E8E45F0003 for ; Wed, 3 Jun 2009 12:22:32 -0400 (EDT) Received: by wa-out-1112.google.com with SMTP id m34so23507wag.22 for ; Wed, 03 Jun 2009 09:22:17 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <20090530192829.GK6535@oblivion.subreption.com> <20090530230022.GO6535@oblivion.subreption.com> <20090531022158.GA9033@oblivion.subreption.com> <20090602203405.GC6701@oblivion.subreption.com> Date: Wed, 3 Jun 2009 12:22:16 -0400 Message-ID: <7e0fb38c0906030922u3af8c2abi8a2cfdcd66151a5a@mail.gmail.com> Subject: Re: Security fix for remapping of page 0 (was [PATCH] Change ZERO_SIZE_PTR to point at unmapped space) From: Eric Paris Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Linus Torvalds Cc: Christoph Lameter , "Larry H." , linux-mm@kvack.org, Alan Cox , Rik van Riel , linux-kernel@vger.kernel.org, pageexec@freemail.hu List-ID: On Wed, Jun 3, 2009 at 11:38 AM, Linus Torvalds wrote: > > > On Wed, 3 Jun 2009, Christoph Lameter wrote: > >> On Wed, 3 Jun 2009, Linus Torvalds wrote: >> >> > The point being that we do need to support mmap at zero. Not necessarily >> > universally, but it can't be some fixed "we don't allow that". >> >> Hmmm... Depend on some capability? CAP_SYS_PTRACE may be something >> remotely related? > > But as mentioned several times, we do have the system-wide setting in > 'mmap_min_addr' (that then can be overridden by CAP_SYS_RAWIO, so in that > sense a capability already exists). > > It defaults to 64kB in at least the x86 defconfig files, but to 0 in the > Kconfig defaults. Also, for some reason it has a "depends on SECURITY", > which means that if you just default to the old-style unix security you'll > lose it. > > So there are several ways to disable it by mistake. I don't know what > distros do. Fedora has it on. As I recall the only need for CONFIG_SECURITY is for the ability to override the check. I think I could probably pretty cleanly change it to use CAP_SYS_RAWIO/SELinux permissions if CONFIG_SECURITY and just allow it for uid=0 in the non-security case? Deny it for everyone in the non-security case and make them change the /proc tunable if they need it? -Eric -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org