[dm-crypt] Initializing dm-crypt on Android results in "device lookup failed"

[Roman Schlegel <lists@ione.ch>]

Hello,

I am currently trying to track down an issue with dm-crypt on an Android
device (more specifically, I am building a CM 12.1 ROM), where
initializing device encryption fails with an error.

I have asked this question in a number of other places as well
(stackoverflow and xda), but have not gotten any responses. I therefore
decided to ask the question on a list more directly connected to
dm-crypt. It is if course entirely possible that the error lies
somewhere in the device-mapper, but in that case my hope is still that
somebody on this list is familiar enough with the device-mapper and its
interaction with dm-crypt to point me to a potential solution.

So here is the problem: when starting the device encryption, the
encryption itself fails with the following error:

01-01 03:20:02.631 I/Cryptfs (  254): Using scrypt for cryptfs KDF

01-01 03:20:03.592 I/Cryptfs (  254): Enabling support for
allow_discards in dmcrypt.

01-01 03:20:03.592 I/Cryptfs (  254): load_crypto_mapping_table:
target_type = crypt

01-01 03:20:03.592 I/Cryptfs (  254): load_crypto_mapping_table:
real_blk_name = /dev/block/platform/mtk-msdc.0/by-name/userdata,
extra_params = 1 allow_discards

01-01 03:20:03.592 I/Cryptfs (  254): load_crypto_mapping_table:
crypt_params = aes-cbc-essiv:sha256 0A66F89B0D3DFC0B05D9BD23B3453A70 0
/dev/block/platform/mtk-msdc.0/by-name/userdata 0 1 allow_discards 0

01-01 03:20:08.619 E/Cryptfs (  254): Cannot load dm-crypt mapping table.


at the same time, the kernel log prints the following messages:

<3>[  138.163773] (5)[327:vold]device-mapper: table: 253:0: crypt:
Device lookup failed
<4>[  138.163781] (5)[327:vold]device-mapper: ioctl: error adding target
to table

Unfortunately, the device I am testing this with has not had the kernel
sources released, so I only have a prebuilt kernel (3.10.61) that I
cannot recompile. However, another ROM using the same kernel (IIRC) can
successfully encrypt the device, so I don't think it is anything
inherent in the kernel itself. But I am at a loss what else could be the
problem.

I'd be happy to provide any additional information as needed.

Any help or pointers in solving this issue would be greatly appreciated.
Thanks!

Best regards,

Roman