linux-kernel - Re: Wrong system clock vs X.509 date specifiers

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Message-ID: <20120925163037.20ba3f3c@pyramind.ukuu.org.uk>
Date:	Tue, 25 Sep 2012 16:30:37 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	David Howells <dhowells@...hat.com>
Cc:	rusty@...tcorp.com.au, herbert@...dor.hengli.com.au,
	pjones@...hat.com, jwboyer@...hat.com,
	linux-crypto@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, keyrings@...ux-nfs.org
Subject: Re: Wrong system clock vs X.509 date specifiers

On Tue, 25 Sep 2012 16:09:54 +0100
David Howells <dhowells@...hat.com> wrote:

> 
> The X.509 certificate has a pair of times in it that delineate the valid
> period of the cert, and I'm checking that the system clock is within the
> bounds they define before permitting you to use the cert.  I've been setting
> the expiry date to be 100 years in the future - by which time hopefully I
> won't have to worry about it - but occasionally clock skew means a freshly
> built kernel won't boot because the machine trying to boot doesn't think that
> the start time has been reached yet.
> 
> Do we actually want to do this, however?  Or should we just ignore the times?
> Or just the start time?

Generate a certificate that is valid from a few minutes before the
wallclock time. It's a certificate policy question not a kernel hackery
one.

Be careful moving your system clock on 100 years and testing - ext4 gets
some timestamps wrong after 2038.

Alan


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