[dm-crypt] [Request] cryptsetup option to fix leftovers from old filesystems

[dm-crypt] [Request] cryptsetup option to fix leftovers from old filesystems

[Thomas Bächler]

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We have encountered a problem with blkid that is caused by cryptsetup 
not cleaning superblocks of old filesystems on luksFormat. The problem 
has been fixed in 1.0.7, however old LUKS volumes still suffer from this 
problem. Please read this thread for details:

http://thread.gmane.org/gmane.linux.utilities.util-linux-ng/2563

What I would request is an option to "clean" the unused area in the LUKS 
header up to the start of the payload, such that for example an old ext2 
magic is removed. All that without destroying the used areas in the LUKS 
header, of course.

I'm not very familiar with the LUKS code or on-disk format, so I would 
be greatful if anyone who is would implement such a feature. Thanks for 
your replies.

Thomas


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Re: [dm-crypt] [Request] cryptsetup option to fix leftovers from old filesystems

[Milan Broz]

Thomas Bächler wrote:
> We have encountered a problem with blkid that is caused by cryptsetup 
> not cleaning superblocks of old filesystems on luksFormat. The problem 
> has been fixed in 1.0.7, however old LUKS volumes still suffer from this 
> problem. Please read this thread for details:
> 
> http://thread.gmane.org/gmane.linux.utilities.util-linux-ng/2563
> 
> What I would request is an option to "clean" the unused area in the LUKS 
> header up to the start of the payload, such that for example an old ext2 
> magic is removed. All that without destroying the used areas in the LUKS 
> header, of course.
> 
> I'm not very familiar with the LUKS code or on-disk format, so I would 
> be greatful if anyone who is would implement such a feature. Thanks for 
> your replies.

Hi Thomas,

I don't think we need implement any clean function, new version already
wipes that area.

Because visible LUKS header is written in first 2 sectors and keyslot
area always begins on 4k offset, you can use this command to wipe unused area
with possible old signature (at least this works for swap/luks signature mismatch):

dd if=/dev/zero of=<device> bs=512 seek=2 count=6

But please create backup before trying this... ;-)

(btw mkswap should clean LUKS signature too - try mkswap over old LUKS
and then blkid:-)

Milan
--
mbroz@redhat.com

Re: [dm-crypt] [Request] cryptsetup option to fix leftovers from old filesystems

[Karel Zak]

 Hi Milan,

On Mon, Aug 31, 2009 at 09:13:08PM +0200, Milan Broz wrote:
> (btw mkswap should clean LUKS signature too - try mkswap over old LUKS
> and then blkid:-)

 this problem should be fixed, util-linux-ng 2.15 (May 2009):

        commit ff3bed806863d1c2075d0efda70b39ea6af9ecba
        Author: Karel Zak <kzak@redhat.com>
        Date:   Thu Mar 12 16:01:59 2009 +0100
        Subject: mkswap: zap bootbits

 
    Karel

-- 
 Karel Zak  <kzak@redhat.com>