Re: MODSIGN without RTC?

[Alexander Holler]

Am 07.02.2013 08:01, schrieb Alexander Holler:
> Am 07.02.2013 07:42, schrieb Geert Uytterhoeven:
> > On Thu, Feb 7, 2013 at 2:06 AM, Alexander Holler <holler@xxxxxxxxxxxxx> 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. ;)

I've digged a bit around about how to disable the date check, but then 
decided that I shouldn't try to implement that 
(CONFIG_MODSIGN_IGNORE_DATES) because of missing knowledge about the 
(usage of) crypto-api.

I think adding attributes to the key and the parsed key like bool 
ingore_dates and bool parsed_dates_invalid might be an option. Using 
such x509_key_preparse() could just set parsed_dates_invalid instead of 
returning with -EKEYREJECTED or -EKEYEXPIRED, if it encounters invalid 
dates.

Regards,

Alexander

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