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

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Date:   Tue, 23 Jun 2020 09:28:32 +0200
From:   Milan Broz <gmazyland@...il.com>
To:     JeongHyeon Lee <jhs2.lee@...sung.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Sami Tolvanen <samitolvanen@...gle.com>
Cc:     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 23/06/2020 01:53, JeongHyeon Lee wrote:
> 
> For what reason isn't panic better?

I did not say panic is better, I said that while we have restart already in mainline dm-verity code,
panic() is almost the same, so I see no problem in merging this patch.

Stopping system this way could create more damage if it is not configured properly,
but I think it is quite common to stop the system as fast as possible if data system integrity
is violated...

> If when i suggested new patch, i will send you a patch that increased 
> minor version.

I think Mike can fold-in version increase, if the patch is accepted.

But please include these version changes with every new feature.

Actually I am tracking it here for dm-verity as part of veritysetup userspace documentation:
  https://gitlab.com/cryptsetup/cryptsetup/-/wikis/DMVerity

Thanks,
Milan

> On 22/06/2020 16:58, Milan Broz wrote:
>> 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
>>
>>