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

Oren Held oren.held at gmail.com
Sat May 14 17:58:54 CEST 2011

Uh; sorry for the messed message.. will re-paste with clean formatting.

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

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.


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