From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751641Ab0JTNL2 (ORCPT ); Wed, 20 Oct 2010 09:11:28 -0400 Received: from Mycroft.westnet.com ([216.187.52.7]:60386 "EHLO mycroft.westnet.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751044Ab0JTNL1 (ORCPT ); Wed, 20 Oct 2010 09:11:27 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <19646.59971.76978.642955@quad.stoffel.home> Date: Wed, 20 Oct 2010 09:10:27 -0400 From: "John Stoffel" To: Mimi Zohar Cc: Al Viro , Linus Torvalds , Eric Paris , linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org, hch@infradead.org, Mimi Zohar , warthog9@kernel.org, david@fromorbit.com, jmorris@namei.org, kyle@mcmartin.ca, hpa@zytor.com, akpm@linux-foundation.org, mingo@elte.hu Subject: Re: [PATCH 1/3] IMA: move read/write counters into struct inode In-Reply-To: <1287512182.3167.130.camel@localhost.localdomain> References: <20101019011650.25346.99614.stgit@paris.rdu.redhat.com> <1287506215.2530.187.camel@localhost.localdomain> <20101019165530.GT19804@ZenIV.linux.org.uk> <20101019172805.GU19804@ZenIV.linux.org.uk> <1287512182.3167.130.camel@localhost.localdomain> X-Mailer: VM 8.1.1 under 23.2.1 (x86_64-pc-linux-gnu) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>>>> "Mimi" == Mimi Zohar writes: Mimi> On Tue, 2010-10-19 at 18:28 +0100, Al Viro wrote: >> On Tue, Oct 19, 2010 at 10:03:48AM -0700, Linus Torvalds wrote: >> > On Tue, Oct 19, 2010 at 9:55 AM, Al Viro wrote: >> > > >> > > a) i_writecount is about VM_DENYWRITE, basically. ?Reusing it for ima could >> > > get unpleasant; when it's positive, we are fine, but it can get negative as >> > > well. ?IMA will have interesting time dealing with that. >> > > >> > > b) i_count is simply a refcount for struct inode. ?Not exactly the number >> > > of dentries, but that's the main contributor. ?Basically, that's "how many >> > > pointers outside of inode hash chains point that that struct inode at the >> > > moment". >> > >> > My question was deeper. More along the lines of "why would IMA care?" >> > >> > How/why could IMA ever care about the pointless and trivial >> > differences between its current private open/read/write counts and the >> > counts that we already maintain? >> > >> > Yes, yes, I realize that they have technical differences in what they >> > count. That's not the question. The question is "Why would IMA care?" Mimi> The filesystem prevents files being executed from being opened Mimi> for write. The same guarantees that the file won't change, Mimi> obviously, doesn't exist for files being opened for read. Thus Mimi> measuring a file opened for read that has already been open for Mimi> write, has no meaning. Unfortunately, since the inode counters Mimi> don't provide this information, IMA maintains a separate set of Mimi> counters. Does this mean I can't replace /bin/sh on a running system using IMA at all, even if just one process has it opened and is running? So how the hell am I supposed to do live upgrades on a system? Currently, /bin/sh gets replaced with the newer, better (for some value of better :-) version, while currently running users aren't impacted at all. New users pick up the new binary. Gah! The only way to upgrade such a system would look be via a reboot. Not very nice at all... or can the root user disable IMA, upgrade a binary, then re-start IMA on a system? So how does this improve security if root is compromised? John