[dm-devel] : suggestion needed for dm-verity data block corrupted issue

[Krishan Baveja]

Sending it again my query, after i subscribed to the mailing list.

> Hi,
>
> This is regarding the behavior of dm-verity on Android. Could you please
> provide your valuable suggestions?
>
> [Issue]:
> During development on android device after some usage of device , I could
> see the following logs from dm-verity driver
>
> https://android.googlesource.com/kernel/msm/+/android-6.0.1_r0.9/drivers/md/dm-verity.c#379
>
> [dmesg]:
> dm-verity: data block 77897 is corrupted
>
> I think this indicates that data block 77897 in partition on which
> dm-verity is enabled is corrupted. Means some hash mismatch occurred with
> the predefined hash.
>
> [Debugging]:
> The /dev/block/dm-0 is mounted successfully on ext4 partition.
>
> So I thought it could be a filesystem corruption issue, but it does not
> seems to be.
> I compared the system partition of the device in which the log is observed
> and compared it with the same S/W in which the issue is not observed.
>
> There seems to be no difference.
>
> I am suspecting that it can be due to OS corruption or some bug in
> dm-verity module.
>
> Could you please suggest how to proceed further?
>
> P.S.:
> In my understanding correct about dm-verity in above case. At runtime,
> dm-verity calculates the hash of each block when its read and verifies it
> by traversing the precalculated hash tree. As dm-verity depends on a
> precalculated hash tree over all blocks of a device, the underlying device
> must be mounted read-only in order for verification to be possible. In
> system partition dm-verity is enabled that hold system files, so system
> files can be changed during OS updates through OTA. Any other change
> indicates either OS(RAM) or disk(eMMC) corruption, or that a malicious
> program is trying to modify the OS or masquerade as a system file.
>
> Thanks in advance !
>
> Best Regards
> KK
>
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