Re: [PATCH] zero disk pages used by swsusp on resume

Andreas Steinmetz
2005-04-12T10:08:36Z

Rafael J. Wysocki wrote:
> Hi,
>
> On Monday, 11 of April 2005 19:02, Andreas Steinmetz wrote:
>
>>Rafael J. Wysocki wrote:
>>
>>>Hi,
>>>
>>>On Monday, 11 of April 2005 12:37, Oliver Neukum wrote:
>>>
>>>
>>>>Am Sonntag, 10. April 2005 22:14 schrieb Pavel Machek:
>>>>
>>>>
>>>>>Hi!
>>>>>
>>>>>
>>>>>
>>>>>>>Oliver Neukum wrote:
>>>>>>>
>>>>>>>
>>>>>>>>What is the point in doing so after they've rested on the disk for ages?
>>>>>>>
>>>>>>>The point is not physical access to the disk but data gathering after
>>>>>>>resume or reboot.
>>>>>>
>>>>>>After resume or reboot normal access control mechanisms will work
>>>>>>again. Those who can read a swap partition under normal circumstances
>>>>>>can also read /dev/kmem. It seems to me like you are putting an extra
>>>>>>lock on a window on the third floor while leaving the front door open.
>>>>>
>>>>>Andreas is right, his patches are needed.
>>>>>
>>>>>Currently, if your laptop is stolen after resume, they can still data
>>>>>in swsusp image.
>>>>>
>>>>>Zeroing the swsusp pages helps a lot here, because at least they are
>>>>>not getting swsusp image data without heavy tools. [Or think root
>>>>>compromise month after you used swsusp.]
>>>>>
>>>>>Encrypting swsusp image is of course even better, because you don't
>>>>>have to write large ammounts of zeros to your disks during resume ;-).
>>>>
>>>>Not only is it better, it completely supercedes wiping the image.
>>>>Your laptop being stolen after resume is very much a corner case.
>>>>You suspend your laptop while you are not around, don't you?
>>>
>>>
>>>Not necessarily. Some people use suspend instead of shutdown. :-)
>>
>>Now here's what I'm currently doing:
>>
>>I do usually suspend instead of shutdown. The suspend partition is the
>>only unencrypted swap partition and it is disabled during regular
>>operation so it is not used for regular swapping. Except for a small
>>boot partition without any valuable data all other partitions are encrypted.
>>
>>The key for dm-crypt setup is stored on an ide flash disk which isn't
>>inserted during travelling and which is transported separately.
>>
>>Now let's imagine the laptop gets stolen by an average thief which is
>>the most common case.Thief needs to know if the laptop is working
>>because thief wants to sell it so thief powers on the laptop.
>>
>>swsusp resumes and with the encryption patch renders the suspend image
>>worthless. The suspend/resume script immediately checks for the presence
>>of the ide flash disk with the correct key (match is done against the
>>in-kernel dm-crypt key). If the ide flash disk is not present or if
>>there is a key mismatch the script shuts the system immediately down, so
>>the in-kernel key is lost.
>>
>>The only way for the thief now to access any data on the disk is to come
>>back and steal the flash disk, too.
>
>
> Yes. And if you accidentally lose the flash disk, you are locked out of your
> own data. ;-) The same happens if the data on the flash disk is lost (which
> occurs, from time to time). You should be _really_ careful doing such things
> and IMO it's not to be tried by Joe User.

Right. But thats what this backup flash disk in some safe place is for.
No risk, no fun :-)

--
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