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

Milan Broz gmazyland at gmail.com
Mon May 23 11:04:02 CEST 2016

On 05/22/2016 11:31 AM, Roman Schlegel wrote:
> 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.


> 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

I really hope Android does not log volume key such a way to system log...

> 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

This message seems to indicate that problem is with device specification:

Can you check, that such device node exists before calling this activation?

You can try to use "major:minor" pair instead (of the device above),
but it can sause problem if it is dynamic (it shouldn't be in this
environment though).


> 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.

The situation in Android world is really not good. Some major vendors even
reimplemented dm-crypt with hardcoded algorithms to speed up on their crappy hw.
Obviously without contact mainline kernel developers, and breaking all other
interfaces as a side effect etc.
So do not be surprised that we will ignore any support questions if someone
is doing such things, nobody really know what source code was used to compile
the kernel.

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