linux-kernel - Re: New mode DM-Verity error handling

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Date:   Mon, 22 Jun 2020 09:58:37 +0200
From:   Milan Broz <gmazyland@...il.com>
To:     Mike Snitzer <snitzer@...hat.com>,
        Sami Tolvanen <samitolvanen@...gle.com>
Cc:     JeongHyeon Lee <jhs2.lee@...sung.com>, dm-devel@...hat.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        agk@...hat.com, corbet@....net
Subject: Re: New mode DM-Verity error handling

On 18/06/2020 19:09, Mike Snitzer wrote:
> On Thu, Jun 18 2020 at 12:50pm -0400,
> Sami Tolvanen <samitolvanen@...gle.com> wrote:
> 
>> On Thu, Jun 18, 2020 at 11:44:45AM -0400, Mike Snitzer wrote:
>>> I do not accept that panicing the system because of verity failure is
>>> reasonable.
>>>
>>> In fact, even rebooting (via DM_VERITY_MODE_RESTART) looks very wrong.
>>>
>>> The device should be put in a failed state and left for admin recovery.
>>
>> That's exactly how the restart mode works on some Android devices. The
>> bootloader sees the verification error and puts the device in recovery
>> mode. Using the restart mode on systems without firmware support won't
>> make sense, obviously.
> 
> OK, so I need further justification from Samsung why they are asking for
> this panic mode.

I think when we have reboot already, panic is not much better :-)

Just please note that dm-verity is used not only in Android world (with own tooling)
but in normal Linux distributions, and I need to modify userspace (veritysetup) to support
and recognize this flag.

Please *always* increase minor dm-verity target version when adding a new feature
- we can then provide some better hint if it is not supported.

Thanks,
Milan