[dm-crypt] inconsistency in opening multiple mappers on the same device

Arno Wagner arno at wagner.name
Fri Jun 1 07:55:24 CEST 2012


Of course you cannot have two mappings on the same name.
The collision is not for the mapping, but for the name!
How would you even address a mapping if you had several on
the same /dev/mapper/<...> entry? That would be like
having several different files under the same file name.

Arno


On Thu, May 31, 2012 at 06:12:02PM -0400, .. ink .. wrote:
> I read the announcement of 1.4.3 and decided to do a simple test on
> opening multiple mappers on the same device and this is what i found
> out:
> 
> test using cryptsetup 1.4.3
> 
> [root at mtz ink]# echo -n xxx | cryptsetup create zzz xxx
> [root at mtz ink]# echo -n xxx | cryptsetup create zzz xxx
> Device zzz already exists.
> [root at mtz ink]# echo -n xxx | cryptsetup create yyy xxx
> 
> [root at mtz ink]# ls -l /dev/mapper/
> total 0
> crw------- 1 root root 10, 236 May 29 14:46 control
> lrwxrwxrwx 1 root root       7 May 31 18:01 yyy -> ../dm-1
> lrwxrwxrwx 1 root root       7 May 31 18:01 zzz -> ../dm-0
> 
> [root at mtz ink]# zuluCrypt-cli -P -d /dev/mapper/zzz
> /home/ink/xxx
> [root at mtz ink]# zuluCrypt-cli -P -d /dev/mapper/yyy
> /home/ink/xxx
> [root at mtz ink]#
> 
> It looks like by default, cryptsetup does not allow opening more than
> one mapper on the same device bu it only checks the mapper name, not
> the device behind the mapper and hence it allows opening of multiple
> mappers on the same device as long as they use a different mapper
> name.
> 
> The same behavior is there in luks based volume
> 
> Also,shouldnt  the error say mapper name since the check is on the
> mapper,not the device behind the mapper.
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> dm-crypt at saout.de
> http://www.saout.de/mailman/listinfo/dm-crypt
> 

-- 
Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno at wagner.name 
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----
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are stupid, and those with any imagination and understanding are filled 
with doubt and indecision. -- Bertrand Russell 


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