On Thu, Apr 16 2015 at 5:23am -0400, Alex Elsayed <eternaleye@xxxxxxxxx> wrote: > Mike Snitzer wrote: > > > On Thu, Apr 09 2015 at 9:28am -0400, > > Pali Rohár <pali.rohar@xxxxxxxxx> wrote: > > > >> On Thursday 09 April 2015 09:12:08 Mike Snitzer wrote: > >> > 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). > >> > >> 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 the > > 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. > > Um, pardon me if I'm being naive, but what about the case of hibernation > where the swapdev and the root device are both LVs on the same dm_crypt > device? > > The kernel is writing to swap _after_ userspace processes are all frozen; > that seems to me like an ordering dependency entirely incompatible with > userspace dropping the key... Good point, definitely not compatible with the Pali's approach. (but is swap really configured ontop of the same dm-crypt device like this in practice? I've not heard of that being a common pattern but I could just be sheltered) -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
