linux-kernel - Re: [PATCH v2] DRBG: fix maximum value checks on 32 bit systems

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Date:	Tue, 26 Aug 2014 16:58:53 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Stephan Mueller <smueller@...onox.de>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] DRBG: fix maximum value checks on 32 bit systems

On Tue, Aug 26, 2014 at 10:52:45AM +0200, Stephan Mueller wrote:
> Am Dienstag, 26. August 2014, 16:43:43 schrieb Herbert Xu:
> 
> Hi Herbert,
> 
> > On Tue, Aug 26, 2014 at 10:29:45AM +0200, Stephan Mueller wrote:
> > > The maximum values for additional input string or generated blocks is
> > > larger than 1<<32. To ensure a sensible value on 32 bit systems, return
> > > SIZE_MAX on 32 bit systems. This value is lower than the maximum
> > > allowed values defined in SP800-90A. The standard allow lower maximum
> > > values, but not larger values.
> > > 
> > > SIZE_MAX - 1 is used for drbg_max_addtl to allow
> > > drbg_healthcheck_sanity to check the enforcement of the variable
> > > without wrapping.
> > 
> > This is really ugly but OK.  However, I'm not sure how the sanity
> > check ever worked.  It would appear that the drbg_generate call in
> > drbg_healthcheck_sanity should always fail because you explicitly
> > set addtl->len to drbg_max_addtl + 1, which should trigger the
> > "DRBG: additional information string too long" error, no?
> 
> That is exactly what the test shall do: the test is intended to check whether 
> the maximum values are enforced. And it does that by checking whether an error 
> is returned.

OK that makes sense.  Patch applied.  Thanks!
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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