From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Snitzer Subject: Re: [PATCH 0/3] dm-crypt: Adds support for wiping key when doing suspend/hibernation Date: Thu, 9 Apr 2015 10:08:43 -0400 Message-ID: <20150409140842.GA9779@redhat.com> References: <1428254419-7334-1-git-send-email-pali.rohar@gmail.com> <20150406130045.GA18583@redhat.com> <201504061529.57299@pali> <20150409131208.GA9504@redhat.com> <20150409132836.GD12339@atrey.karlin.mff.cuni.cz> 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: <20150409132836.GD12339@atrey.karlin.mff.cuni.cz> Sender: linux-pm-owner@vger.kernel.org To: Pali =?iso-8859-1?Q?Roh=E1r?= Cc: Alasdair Kergon , Neil Brown , "Rafael J. Wysocki" , Len Brown , Pavel Machek , 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, Apr 09 2015 at 9:28am -0400, Pali Roh=E1r wrote: > On Thursday 09 April 2015 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 b= eing > > suspended? A hibernate shouldn't fail simply because a user chose = to > > suspend a DM device. > >=20 > > Then this entire problem goes away and the key can be wiped from > > userspace (like you said above). >=20 > Still there will be race condition. Before hibernation (and device > poweroff) we should have synced disks and filesystems to prevent data > lose (or other damage) as more as we can. And if there will be some > application which using lot of I/O (e.g normal firefox) then there > always will be race condtion. The DM suspend will take care of flushing any pending I/O. So I don't see where the supposed race is... Anything else that is trapped in userspace memory will be there when th= e machine resumes. > So proper way is to wipe luks crypto keys *after* userspace processes > are freezed. I know you believe that I'm just not accepting that at face value.