linux-kernel - Re: MODSIGN without RTC?

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Message-ID: <51135137.4010003@ahsoftware.de>
Date:	Thu, 07 Feb 2013 08:01:11 +0100
From:	Alexander Holler <holler@...oftware.de>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
CC:	linux-kernel@...r.kernel.org
Subject: Re: MODSIGN without RTC?

Am 07.02.2013 07:42, schrieb Geert Uytterhoeven:
> On Thu, Feb 7, 2013 at 2:06 AM, Alexander Holler <holler@...oftware.de> wrote:
>> Am 07.02.2013 00:42, schrieb Alexander Holler:
>>> I wanted to try out MODSIGN with kernel 3.7.6 and I've just got hit by:
>>>
>>> [    1.346445] X.509: Cert 6a23533cec71c4c52a1618fb4d830e06aa90474e is
>>> not yet valid
>>>
>>> The reason is likely that the (ARM) device in question doesn't have a
>>> RTC (oh, that topic again ;) ) and gets it's time on boot through NTP.
>>>
>>> The used certificate was generated automatically. Having a look at it,
>>> the following is shown:
>>>
>>>         Validity
>>>              Not Before: Feb  6 02:56:46 2013 GMT
>>>              Not After : Jan 13 02:56:46 2113 GMT
>>>
>>> Without having thought about possible security problems, my first idea
>>> would be to let the validity start at 1970. As I never did such I never
>>> had thought about possible implications when doing such (e.g. I don't
>>> know if someone checks the start date for plausabilitiy)
>>>
>>> Another solution would be to retry loading of the certificate if the
>>> time gets set (and e.g. differs more than a year).
>>>
>>> Has someone already thought about how to solve that problem? Or did
>>> everyone use sane systems which have a (working) RTC?
>>
>>
>> Another option would be to make a configure option to just ignore the date.
> 
> Or an option to auto-advance the clock to the "Not Before" date if needed...
> 
>> I'm not sure if I would like to use MODSIGN when I have to fear that the
>> machine wouldn't start when the RTC fails or got set to a wrong date.
> 
> Hmm, nice failure mode...

And the dream of every vendor, finally a working expiration date. And a
nice TV-B-Gone, just feed a wrong date once. ;)

Regards,

Alexader

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