linux-kernel - Re: [RFC v2 1/7] integrity: added digest calculation function

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Message-ID: <CALLzPKZhDg0b7XF7A_MH1gtXafe2OfKr=c5hH-KGM7J_oXXCrQ@mail.gmail.com>
Date:	Wed, 22 Aug 2012 19:38:59 +0300
From:	"Kasatkin, Dmitry" <dmitry.kasatkin@...el.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	zohar@...ux.vnet.ibm.com, jmorris@...ei.org, dhowells@...hat.com,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC v2 1/7] integrity: added digest calculation function

On Mon, Aug 20, 2012 at 5:59 AM, Rusty Russell <rusty@...tcorp.com.au> wrote:
> On Wed, 15 Aug 2012 21:43:06 +0300, Dmitry Kasatkin <dmitry.kasatkin@...el.com> wrote:
>> +     } else {
>> +             struct {
>> +                     struct shash_desc shash;
>> +                     char ctx[crypto_shash_descsize(tfm)];
>> +             } desc;
>
> Linus had a rant a while ago about using variable-sized stack vars in
> the kernel (can't find a reference right now, sorry).
>
> The problem is that either you know there's a limit to
> crypto_shash_descsize(), in which case you can just use this here, or
> you don't know, in which case, this risks a stack oveflow.
>
> Cheers,
> Rusty.

Well... descriptor size is a algo specific but constant... just
sizeof(some struct).
So there is no possibility to force overflow unless someone implement
some algo driver which
uses too big descriptor size.

- Dmitry
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