On Thursday 09 April 2015 10:26:58 Mike Snitzer wrote: > On Thu, Apr 09 2015 at 10:16am -0400, > Pali Rohár <pali.rohar@xxxxxxxxx> wrote: > > > On Thursday 09 April 2015 10:08:43 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... > > > > > > > Any I/O operation after DM suspend is race condition and could cause > > data lost. > > > > > Anything else that is trapped in userspace memory will be there when the > > > machine resumes. > > > > > > > You are expecting that machine resumes always at 100% and correctly. But > > this is not truth in real world. There are planty of users who reported > > lot of random problems with suspend or hibernate... > > But the system was left in a crash consistent state. Properly written > apps will wait for I/O to ensure data loss (in the event of a failed > resume) isn't a problem. > I think you are too optimistic about ideal world... "Properly written apps" "ensure data loss" > > > > 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. > > > > If disks are synced before any DM suspend operation then we have higher > > chance of preventing data corruption. > > disks are already synced as part of the DM suspend operation! > Yes, but part of hibernate operation is also sync call. > But you're saying that all user processes are frozen (and associated > I/O flushed) before the DM suspend, that is different: > Yes, I want to ensure that. So processes wont be able to do any other I/O. > > I still think that correct order is only: > > > > * freeze processes (which doing continous I/O) > > * fs & disk sync > > * DM suspend > > * wipe crypto keys > > * enter hibernate > > I just don't think that extreme is _required_ to have a hibernate/resume > that incorporates dm-crypt key wiping. Ok, and what other developers think? I'm saying that if I want to wipe luks keys before suspend/hibernate and have system in consistant state as much as possible, keys must be wiped *after* userspace processes are freezed. Or do you have relevant or functional argument why not? Or is there any problem in my thinking? -- Pali Rohár pali.rohar@xxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
