From: Stephan Mueller <smueller@chronox•de>
To: Herbert Xu <herbert@gondor•apana.org.au>
Cc: Stephen Rothwell <sfr@canb•auug.org.au>,
linux-next@vger•kernel.org, linux-kernel@vger•kernel.org
Subject: Re: [PATCH v2] DRBG: fix maximum value checks on 32 bit systems
Date: Tue, 26 Aug 2014 11:36:54 +0200 [thread overview]
Message-ID: <1471416.zGlxQVbHUr@myon.chronox.de> (raw)
In-Reply-To: <20140826085853.GA4646@gondor.apana.org.au>
Am Dienstag, 26. August 2014, 16:58:53 schrieb Herbert Xu:
Hi Herbert,
> 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!
I am wondering about the current code in Linus' tree though considering the
applied patch:
Linus' code contains:
static inline size_t drbg_max_addtl(struct drbg_state *drbg)
{
return (1UL<<(drbg->core->max_addtllen));
}
static inline size_t drbg_max_requests(struct drbg_state *drbg)
{
return (1UL<<(drbg->core->max_req));
}
The max_addtllen and max_req are defined in drbg_cores[] in crypto/drbg.c for
each DRBG type. As size_t on a 32 bit system is 32 bit the bit shifts would
not work either.
Thus, I am wondering whether the just applied patch would need to go to Linus
tree too? I would think that the following patch would be in order:
static inline size_t drbg_max_addtl(struct drbg_state *drbg)
{
#if (__BITS_PER_LONG == 32)
return (SIZE_MAX - 1);
#else
return (1UL<<(drbg->core->max_addtllen));
#endif
}
static inline size_t drbg_max_requests(struct drbg_state *drbg)
{
#if (__BITS_PER_LONG == 32)
return SIZE_MAX;
#else
return (1UL<<(drbg->core->max_req));
#endif
}
--
Ciao
Stephan
next prev parent reply other threads:[~2014-08-26 9:36 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-26 6:14 linux-next: build warnings after merge of the crypto tree Stephen Rothwell
2014-08-26 6:38 ` Herbert Xu
2014-08-26 7:00 ` Stephan Mueller
2014-08-26 7:31 ` [PATCH] DRBG: fix bit shifting on 32 bit systems Stephan Mueller
2014-08-26 7:32 ` Herbert Xu
2014-08-26 7:37 ` Stephan Mueller
2014-08-26 8:06 ` [PATCH] DRBG: fix maximum value checks " Stephan Mueller
2014-08-26 8:08 ` Herbert Xu
2014-08-26 8:29 ` [PATCH v2] " Stephan Mueller
2014-08-26 8:43 ` Herbert Xu
2014-08-26 8:52 ` Stephan Mueller
2014-08-26 8:58 ` Herbert Xu
2014-08-26 9:36 ` Stephan Mueller [this message]
2014-08-27 13:35 ` Herbert Xu
2014-08-27 13:40 ` Stephan Mueller
2014-08-28 7:13 ` Stephan Mueller
2014-08-28 7:17 ` DRBG: remove test for uninitialized DRBG handle Stephan Mueller
2014-09-01 5:11 ` [PATCH v2] DRBG: remove check " Stephan Mueller
2014-09-03 1:33 ` Stephan Mueller
2014-09-03 23:21 ` Herbert Xu
2014-09-03 23:50 ` Stephan Mueller
2014-09-05 7:55 ` Herbert Xu
2014-09-05 11:25 ` Stephan Mueller
2014-09-05 8:13 ` Herbert Xu
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