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

[Roman Schlegel <lists@ione.ch>]

Hi Ondrej,

Thanks a lot for your reply.

On 23.05.2016 10:17, Ondrej Kozina wrote:
> Hello Roman,
> 
> I'm no Android developer, so just according to what I can see in your logs:
> 
> On 05/22/2016 11:31 AM, Roman Schlegel wrote:
>>
>> 01-01 03:20:03.592 I/Cryptfs (  254): load_crypto_mapping_table:
>> crypt_params = aes-cbc-essiv:sha256 0A66F89B0D3DFC0B05D9BD23B3453A70 0
> 
> Don't post your volume key publicly! If it was just a test device it's
> not so big deal but it's generally good rule to follow so that you don't
> post your VK for real device accidentally.
> 
> </mentoring_mode>
> 

I was aware that the log contained the volume key (it is a test device),
but you're of course right that I should not get in the habit of posting
it :-).

>> /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
> 
> The kernel driver complaints that it can't access a block device
> referenced by path /dev/block/platform/mtk-msdc.0/by-name/userdata. Is
> it block device? If it's supposed to be a symlink does a referenced
> block device exist?
> 
> The thing is kernel accepts only limited set of paths as device
> identifier in DM table. Usually major:minor numbers, kernel path,
> part_uuid. The translation from arbitrary path '
> /dev/block/platform/mtk-msdc.0/by-name/userdata' to something DM driver
> is able to parse should be done in userspace. Usually, it's libdevmapper
> library what does that. Given that kernel complaints, it seems userspace
> haven't done the translation properly or there was a race maybe. Could
> you pass major:minor for /dev/block/platform/mtk-msdc.0/by-name/userdata
> directly in userspace utility that's supposed to establish device
> encryption?
> 

The device /dev/block/platform/mtk-msdc.0/by-name/userdata is actually a
symbolic link to another block device, but it seems to exist at the time
of encryption.

What exactly do you mean with that there might be a race?

Thanks and best regards,

Roman