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

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Message-ID: <20140826084343.GA4417@gondor.apana.org.au>
Date:	Tue, 26 Aug 2014 16:43:43 +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 10:29:45AM +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?

Obviously it's working for you but I'd like to understand why
it's working and whether it'll continue to work.

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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