From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephan Mueller Subject: Re: [PATCH v2] DRBG: fix maximum value checks on 32 bit systems Date: Tue, 26 Aug 2014 10:52:45 +0200 Message-ID: <2049245.HpByroTSUp@myon.chronox.de> References: <20140826161456.7ad100e3@canb.auug.org.au> <2984929.nIbTCa5fhe@myon.chronox.de> <20140826084343.GA4417@gondor.apana.org.au> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: In-Reply-To: <20140826084343.GA4417@gondor.apana.org.au> Sender: linux-kernel-owner@vger.kernel.org To: Herbert Xu Cc: Stephen Rothwell , linux-next@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-next.vger.kernel.org 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. /* get the maximum value */ max_addtllen = drbg_max_addtl(drbg); /* add one to definitely overflow the maximum value */ drbg_string_fill(&addtl, buf, max_addtllen + 1); /* overflow addtllen with additonal info string */ len = drbg_generate(drbg, buf, OUTBUFLEN, &addtl); /* * check that the drbg_generate does not return a positive * value, i.e. check that drbg_generate does not generate anything */ BUG_ON(0 < len); > > Obviously it's working for you but I'd like to understand why > it's working and whether it'll continue to work. > > Thanks, -- Ciao Stephan