On Mon, Apr 06 2015 at 9:29am -0400, Pali Rohár <pali.rohar@xxxxxxxxx> 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@xxxxxxxxx> 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). -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
