From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Machek Subject: Re: [PATCH 0/3] dm-crypt: Adds support for wiping key when doing suspend/hibernation Date: Tue, 14 Apr 2015 08:41:48 +0200 Message-ID: <20150414064148.GA20597@amd> References: <1428254419-7334-1-git-send-email-pali.rohar@gmail.com> <20150406130045.GA18583@redhat.com> <201504061529.57299@pali> <20150409131208.GA9504@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <20150409131208.GA9504@redhat.com> Sender: linux-pm-owner@vger.kernel.org To: Mike Snitzer Cc: Pali =?iso-8859-1?Q?Roh=E1r?= , Alasdair Kergon , Neil Brown , "Rafael J. Wysocki" , Len Brown , dm-devel@redhat.com, linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org List-Id: linux-raid.ids On Thu 2015-04-09 09:12:08, Mike Snitzer wrote: > On Mon, Apr 06 2015 at 9:29am -0400, > Pali Roh=E1r wrote: >=20 > > On Monday 06 April 2015 15:00:46 Mike Snitzer wrote: > > > On Sun, Apr 05 2015 at 1:20pm -0400, > > >=20 > > > Pali Roh=E1r wrote: > > > > This patch series increase security of suspend and hibernate > > > > actions. It allows user to safely wipe crypto keys before > > > > suspend and hibernate actions starts without race > > > > conditions on userspace process with heavy I/O. > > > >=20 > > > > To automatically wipe cryto key for before > > > > hibernate action call: $ dmsetup message 0 key > > > > wipe_on_hibernation 1 > > > >=20 > > > > To automatically wipe cryto key for before suspend > > > > action call: $ dmsetup message 0 key > > > > wipe_on_suspend 1 > > > >=20 > > > > (Value 0 after wipe_* string reverts original behaviour - to > > > > not wipe key) > > >=20 > > > Can you elaborate on the attack vector your changes are meant > > > to protect against? The user already authorized access, why > > > is it inherently dangerous to _not_ wipe the associated key > > > across these events? > >=20 > > Hi, > >=20 > > yes, I will try to explain current problems with cryptsetup=20 > > luksSuspend command and hibernation. > >=20 > > First, sometimes it is needed to put machine into other hands.=20 > > You can still watch other person what is doing with machine, but=20 > > once if you let machine unlocked (e.g opened luks disk), she/he=20 > > can access encrypted data. > >=20 > > If you turn off machine, it could be safe, because luks disk=20 > > devices are locked. But if you enter machine into suspend or=20 > > hibernate state luks devices are still open. And my patches try=20 > > to achieve similar security as when machine is off (=3D no crypto=20 > > keys in RAM or on swap). > >=20 > > When doing hibernate on unencrypted swap it is to prevent leaking=20 > > crypto keys to hibernate image (which is stored in swap). > >=20 > > When doing suspend action it is again to prevent leaking crypto=20 > > keys. E.g when you suspend laptop and put it off (somebody can=20 > > remove RAMs and do some cold boot attack). > >=20 > > The most common situation is: > > You have mounted partition from dm-crypt device (e.g. /home/),=20 > > some userspace processes access it (e.g opened firefox which=20 > > still reads/writes to cache ~/.firefox/) and you want to drop=20 > > crypto keys from kernel for some time. > >=20 > > For that operation there is command cryptsetup luksSuspend, which=20 > > suspend dm device and then tell kernel to wipe crypto keys. All=20 > > I/O operations are then stopped and userspace processes which=20 > > want to do some those I/O operations are stopped too (until you=20 > > call cryptsetup luksResume and enter correct key). > >=20 > > Now if you want to suspend/hiberate your machine (when some of dm=20 > > devices are suspeneded and some processes are stopped due to=20 > > pending I/O) it is not possible. Kernel freeze_processes function=20 > > will fail because userspace processes are still stopped inside=20 > > some I/O syscall (read/write, etc,...). > >=20 > > My patches fixes this problem and do those operations (suspend dm=20 > > device, wipe crypto keys, enter suspend/hiberate) in correct=20 > > order and without race condition. > >=20 > > dm device is suspended *after* userspace processes are freezed=20 > > and after that are crypto keys wiped. And then computer/laptop=20 > > enters into suspend/hibernate state. >=20 > Wouldn't it be better to fix freeze_processes() to be tolerant of > processes that are hung as a side-effect of their backing storage bei= ng > suspended? A hibernate shouldn't fail simply because a user chose to > suspend a DM device. That would be nice, I agree. But that's non-trivial ammount of work and might be (close to) impossible. Pavel --=20 (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses= /blog.html