[dm-crypt] Strange kind of corruption on a dm-crypt device

Oren Held oren.held at gmail.com
Sat May 14 19:01:21 CEST 2011


Alright. Problem solved.
As mentioned in Debian's
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=568008, default cipher was
changed from aes-cbc-plain to aes-cbc-essiv:sha256, while mine uses the
former.

(Still, crypttab should've enforced it, as I had a cipher=aes-cbc-plain
line. I'll update if I find any interesting finding on that)

10x

Oren

On 14 May 2011 18:58, Oren Held <oren.held at gmail.com> wrote:

> Uh; sorry for the messed message.. will re-paste with clean formatting.
> ----
>
> Hi,
>
> I'm using dm-crypt for 2 years now and it's rather stable. I'm not using
> luks but only 'cryptsetup create' method. Suddenly this morning, after an
> unclean shutdown, I've encountered a strange problem:
>
> When I use 'cryptsetup create homes /dev/mapper/myvg-homes' and enter the
> passphrase, instead of creating a new dm device with a proper ext4 fs as
> it used to, I get a bad device. But not *totally* bad.
>
> Fsck/mount fail to find the superblock. Also no backup superblocks are
> available. I did try the 'mkfs -n' for finding the backup superblocks, for
> fsck -b, but none of them works.
> ===================================================
> fsck from util-linux-ng 2.17.2
> e2fsck 1.41.12 (17-May-2010)
> fsck.ext4: Superblock invalid, trying backup blocks...
> fsck.ext4: The ext2 superblock is corrupt while trying to open
> /dev/mapper/homes
>
> The superblock could not be read or does not describe a correct ext2
> filesystem.  If the device is valid and it really contains an ext2
> filesystem (and not swap or ufs or something else), then the superblock
> is corrupt, and you might try running e2fsck with an alternate superblock:
>     e2fsck -b 8193 <device>
> ===================================================
>
> Why is this case strange? because when I read the device with my naked eye
> (or with 'strings' command) I can see lots of plain, *unencrypted* file
> content. so it seems like some kind of a limbo, decryption worked, but not
> so well...
>
> I'm using Debian unstable (kernel 2.6.38-2), which just got the upgrade
> package for cryptsetup 1.3.0 yesterday. I'm not sure if my problem has to do
> with the upgrade, but the timing makes me wonder. I did try downgrading to
> 1.2.0 and to 2.6.37, but it didn't help.
>
> Any suggestion on how to progress? anybody experienced something similar
> recently? I'm still not sure if it's a real bug in cryptsetup/dm/kernel, or
> something broken specifically in my place.
>
> 10x
>
> Oren
>
>
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