[dm-crypt] exclusive flag trouble

Milan Broz mbroz at redhat.com
Mon Mar 12 23:54:57 CET 2012

On 03/11/2012 11:27 AM, Javier Juan Martínez Cabezón wrote:
> Hi until now I used a tool to make hidden partitions called scubed (is
> something like a partition tool that used cryptsetup to create the
> needed volumes (really old but worked fine)
> http://cube.dyndns.org/cgi-bin/viewvc.cgi/trunk/scubed.c?diff_format=l&sortdir=down&logsort=rev&sortby=log&view=markup&root=scubed
> - I get realized from this:
> http://code.google.com/p/cryptsetup/issues/detail?id=105
> With scubed you create five cryptsetup levels in the same device and
> with all unlocked you assign needed blocks to each of them with scubed)
> I haven't get troubles with this is able for example to create read only
> media (dvd+-r) with multiple ciphered layers.
> Here is the readme (with a mini tutorial):
> http://cube.dyndns.org/svn/scubed/trunk/README


# cryptsetup create scubed1 /dev/loop0
Enter passphrase:
# cryptsetup create scubed2 /dev/loop0
Enter passphrase:

This is exactly why exclusive checking is there - it is recipe
for data corruption if plaintext devices are wrongly accessed
(you write to one device but you will get data from cache for other).

Please can you add a new issue on cryptsetup project page to track that?
(I have currently no time to check it now but save it for later.)

I do not think I will reintroduce non-exclusive mode but I would like
to check how scubed works and possibly provide some workaround.
(IMHO if scubed creates private devices, it is fine, so maybe some patch
is the way to go.)


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