linux-kernel - Re: MODSIGN without RTC?

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Date:	Thu, 7 Feb 2013 07:42:29 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Alexander Holler <holler@...oftware.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: MODSIGN without RTC?

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...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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