From: Mike Snitzer <snitzer@redhat.com>
To: "Pali Rohár" <pali.rohar@gmail.com>
Cc: Alasdair Kergon <agk@redhat.com>, Neil Brown <neilb@suse.de>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
dm-devel@redhat.com, linux-raid@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org
Subject: Re: [PATCH 0/3] dm-crypt: Adds support for wiping key when doing suspend/hibernation
Date: Thu, 9 Apr 2015 09:12:08 -0400 [thread overview]
Message-ID: <20150409131208.GA9504@redhat.com> (raw)
In-Reply-To: <201504061529.57299@pali>
On Mon, Apr 06 2015 at 9:29am -0400,
Pali Rohár <pali.rohar@gmail.com> wrote:
> On Monday 06 April 2015 15:00:46 Mike Snitzer wrote:
> > On Sun, Apr 05 2015 at 1:20pm -0400,
> >
> > Pali Rohár <pali.rohar@gmail.com> 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.
> > >
> > > To automatically wipe cryto key for <device> before
> > > hibernate action call: $ dmsetup message <device> 0 key
> > > wipe_on_hibernation 1
> > >
> > > To automatically wipe cryto key for <device> before suspend
> > > action call: $ dmsetup message <device> 0 key
> > > wipe_on_suspend 1
> > >
> > > (Value 0 after wipe_* string reverts original behaviour - to
> > > not wipe key)
> >
> > 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?
>
> Hi,
>
> yes, I will try to explain current problems with cryptsetup
> luksSuspend command and hibernation.
>
> First, sometimes it is needed to put machine into other hands.
> You can still watch other person what is doing with machine, but
> once if you let machine unlocked (e.g opened luks disk), she/he
> can access encrypted data.
>
> If you turn off machine, it could be safe, because luks disk
> devices are locked. But if you enter machine into suspend or
> hibernate state luks devices are still open. And my patches try
> to achieve similar security as when machine is off (= no crypto
> keys in RAM or on swap).
>
> When doing hibernate on unencrypted swap it is to prevent leaking
> crypto keys to hibernate image (which is stored in swap).
>
> When doing suspend action it is again to prevent leaking crypto
> keys. E.g when you suspend laptop and put it off (somebody can
> remove RAMs and do some cold boot attack).
>
> The most common situation is:
> You have mounted partition from dm-crypt device (e.g. /home/),
> some userspace processes access it (e.g opened firefox which
> still reads/writes to cache ~/.firefox/) and you want to drop
> crypto keys from kernel for some time.
>
> For that operation there is command cryptsetup luksSuspend, which
> suspend dm device and then tell kernel to wipe crypto keys. All
> I/O operations are then stopped and userspace processes which
> want to do some those I/O operations are stopped too (until you
> call cryptsetup luksResume and enter correct key).
>
> Now if you want to suspend/hiberate your machine (when some of dm
> devices are suspeneded and some processes are stopped due to
> pending I/O) it is not possible. Kernel freeze_processes function
> will fail because userspace processes are still stopped inside
> some I/O syscall (read/write, etc,...).
>
> My patches fixes this problem and do those operations (suspend dm
> device, wipe crypto keys, enter suspend/hiberate) in correct
> order and without race condition.
>
> dm device is suspended *after* userspace processes are freezed
> and after that are crypto keys wiped. And then computer/laptop
> enters into suspend/hibernate state.
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 being
suspended? A hibernate shouldn't fail simply because a user chose to
suspend a DM device.
Then this entire problem goes away and the key can be wiped from
userspace (like you said above).
next prev parent reply other threads:[~2015-04-09 13:12 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-05 17:20 [PATCH 0/3] dm-crypt: Adds support for wiping key when doing suspend/hibernation Pali Rohár
2015-04-05 17:20 ` [PATCH 1/3] PM suspend/hibernate: Call notifier after freezing processes Pali Rohár
2015-04-09 0:28 ` Rafael J. Wysocki
2015-04-09 6:36 ` Pali Rohár
2015-04-09 17:13 ` Rafael J. Wysocki
2015-04-09 16:55 ` Pali Rohár
2015-04-05 17:20 ` [PATCH 2/3] dm: Export function dm_suspend_md() Pali Rohár
2015-04-05 17:20 ` [PATCH 3/3] dm-crypt: Adds support for wiping key when doing suspend/hibernation Pali Rohár
2015-04-07 13:55 ` [dm-devel] " Alasdair G Kergon
2015-04-06 13:00 ` [PATCH 0/3] " Mike Snitzer
2015-04-06 13:25 ` Pavel Machek
2015-04-06 20:51 ` Mike Snitzer
2015-04-06 21:13 ` Why wipe crypto keys during suspend (was Re: [PATCH 0/3] dm-crypt: Adds support for wiping key when doing suspend/hibernation) Pavel Machek
2015-04-06 13:29 ` [PATCH 0/3] dm-crypt: Adds support for wiping key when doing suspend/hibernation Pali Rohár
2015-04-06 18:17 ` Pavel Machek
2015-04-06 21:27 ` Pali Rohár
2015-04-09 13:12 ` Mike Snitzer [this message]
2015-04-09 13:28 ` Pali Rohár
2015-04-09 14:08 ` Mike Snitzer
2015-04-09 14:16 ` Pali Rohár
2015-04-09 14:26 ` Mike Snitzer
2015-04-09 14:38 ` Pali Rohár
2015-04-14 6:50 ` Pavel Machek
2015-04-23 17:02 ` Pali Rohár
[not found] ` <mgnv2g$if5$2@ger.gmane.org>
2015-04-17 7:52 ` Mike Snitzer
2015-04-17 8:52 ` [dm-devel] " Ondrej Kozina
2015-04-17 15:53 ` Alex Elsayed
2015-04-14 6:41 ` Pavel Machek
2015-06-21 11:20 ` [PATCH v2 " Pali Rohár
2015-06-21 11:20 ` [PATCH v2 1/3] PM suspend/hibernate: Call notifier after freezing processes Pali Rohár
2015-07-16 1:02 ` Rafael J. Wysocki
2015-07-16 7:33 ` Pali Rohár
2015-07-17 23:27 ` Rafael J. Wysocki
2015-07-20 7:32 ` Pali Rohár
2015-07-20 21:46 ` Rafael J. Wysocki
2015-07-21 22:08 ` NeilBrown
2015-07-21 23:00 ` Rafael J. Wysocki
2015-07-21 23:03 ` Rafael J. Wysocki
2016-12-27 14:29 ` Pali Rohár
2015-06-21 11:20 ` [PATCH v2 2/3] dm: Export function dm_suspend_md() Pali Rohár
2015-07-17 14:04 ` Mike Snitzer
2015-07-17 14:22 ` Pali Rohár
2015-07-17 15:22 ` Mike Snitzer
2015-07-17 15:30 ` Mike Snitzer
2015-07-17 17:13 ` Pali Rohár
2015-07-17 17:31 ` Mike Snitzer
2015-06-21 11:20 ` [PATCH v2 3/3] dm-crypt: Adds support for wiping key when doing suspend/hibernation Pali Rohár
2015-07-28 14:44 ` Pavel Machek
2015-07-28 14:48 ` Pali Rohár
2015-07-07 7:59 ` [PATCH v2 0/3] " Pali Rohár
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