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Re: Securely erase files cached in memory (dm_crypt)

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On 01/09/2012 10:04 PM, bmearns wrote:
> On Jan 9, 6:02 am, Richard Kettlewell<r...@greenend.org.uk>  wrote:
>> bmearns<mearn...@gmail.com>  writes:
>>> I'm setting up a dm_crypt/LUKS volume and I want to make sure that
>>> when the volume is suspended/closed, all the decrypted data is
>>> securely removed from memory.
>>
>>> If I understand dm_crypt correctly, all data on the harddisk is
>>> encrypted, but pages will be decrypted into RAM on demand. The manpage
>>> for cryptsetup specifies that luksSuspend wipes the encryption key
>>> from the kernel, but doesn't say anything about data that's already
>>> been decrypted. Is this all taken care of by dm_crypt, or do I need to
>>> be proactive about removing it, and if so, how?
>>
>> I can't see anything in the kernel or the tools that would erase cached
>> decrypted data, but I may not be looking in the right places.
>>
>>> Also, do I need to worry about decrypte blocks being put in swap
>>> space?
>>
>> I think you're OK on this one; AFAIK the buffer cache is not swapped.
>> (It's hard to see what the point of doing so would be.)
>>
>> --http://www.greenend.org.uk/rjk/
>
> Thanks, Richard. I guess it makes sense that the data would not be
> swapped: as far as the kernel knows, any file data it's cached is
> already on disk, it would be pointless to put it on another disk by
> swapping.
>
> So now I just have to worry about anything cached in RAM, which is a
> bummer, because the whole point of this is to purge all the data
> without having to power cycle.
>
> -Brian

I'm no expert in this, but it would seem to me, that once the program is 
suspended, and the key removed, the program would also de-allocate any 
memory it is holding, and on any kind of reasonably busy machine, that 
memory is going to be fairly quickly re-allocted to something else and 
over written. But I'm really just guessing.

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Thread

Securely erase files cached in memory (dm_crypt) bmearns <mearns.b@gmail.com> - 2012-01-08 08:53 -0800
  Re: Securely erase files cached in memory (dm_crypt) Richard Kettlewell <rjk@greenend.org.uk> - 2012-01-09 11:02 +0000
    Re: Securely erase files cached in memory (dm_crypt) bmearns <mearns.b@gmail.com> - 2012-01-09 19:04 -0800
      Re: Securely erase files cached in memory (dm_crypt) William Colls <william.colls@rogers.com> - 2012-01-09 22:47 -0500
        Re: Securely erase files cached in memory (dm_crypt) bmearns <mearns.b@gmail.com> - 2012-01-11 13:51 -0800
          Re: Securely erase files cached in memory (dm_crypt) Richard Kettlewell <rjk@greenend.org.uk> - 2012-01-11 22:09 +0000
            Re: Securely erase files cached in memory (dm_crypt) bmearns <mearns.b@gmail.com> - 2012-01-11 14:23 -0800
          Re: Securely erase files cached in memory (dm_crypt) unruh <unruh@invalid.ca> - 2012-01-12 01:54 +0000
            Re: Securely erase files cached in memory (dm_crypt) bmearns <mearns.b@gmail.com> - 2012-01-13 10:21 -0800
              Re: Securely erase files cached in memory (dm_crypt) Jim Beard <jdbeard@patriot.net> - 2012-06-14 08:51 -0400
          Re: Securely erase files cached in memory (dm_crypt) Robert Nichols <SEE_SIGNATURE@localhost.localdomain.invalid> - 2012-01-12 10:35 -0600
    Re: Securely erase files cached in memory (dm_crypt) Alexander Schreiber <als@usenet.thangorodrim.de> - 2012-01-15 23:20 +0100
      Re: Securely erase files cached in memory (dm_crypt) Aragorn <stryder@telenet.be.invalid> - 2012-01-16 00:16 +0100

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