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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).

  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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