[dm-crypt] Offset/size issue during LUKS recovery.

Arno Wagner arno at wagner.name
Fri Jul 15 15:13:33 CEST 2016


On Fri, Jul 15, 2016 at 13:12:30 CEST, Milan Broz wrote:
> On 07/15/2016 11:13 AM, Arno Wagner wrote:
> > On Fri, Jul 15, 2016 at 02:52:35 CEST, Julio Cesar Faracco wrote:
> >> Hi,
> >>
> >> Since I moved to the version 1.6.7 of cryptsetup, I started to have some problems to recovery a LUKS partition
> >> using a LUKS header file and a valid passphrase.
> >>
> >> # cryptsetup luksDump my_header_file --debug
> >> # Detected kernel Linux 3.10.0-327.13.1.el7.x86_64 x86_64.
> >> # Reading LUKS header of size 1024 from device /tmp/my_header_file
> >> # Key length 64, device size 8192 sectors, header size 4036 sectors.
> > [...]
> >> # # cryptsetup luksOpen /dev/loop0 my_enc_partition <<EOF
> >> $(PASSWORD)
> >> EOF
> >> # Detected kernel Linux 3.10.0-327.13.1.el7.x86_64 x86_64.
> >> # Reading LUKS header of size 1024 from device /tmp/my_header_file
> >> # Key length 64, device size 4060 sectors, header size 4036 sectors.
> > 
> > I take it, the device is  8192 sectors, i.e. 4MB? 
> > 
> > If so, there seem to be a bug in device-size detection
> > as used by luksOpen.
> 
> libcryptsetup uses  BLKGETSIZE64 ioctl as all other tools, so more likely is that
> device-size is really 4MB :)
> 
> But if separate header is used then the debug output above mean device 
> (or file image) size for the header image,
> not the data device
> 
> I should probably change wording in this message...
> 
> Milan

Hmm, makes sense, from the file-names this is a detached header. 
But the data-offset should then be 0, should it not?
It was 
> Payload offset:    4096
from luksDump. 

@Julio: Did you manually split the header off from a file that 
was originally 8MB and is now 4MB header and 4MB data? 
If so, you probably need to adjust the data-offset field
manually.

Regards,
Arno
-- 
Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno at wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
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