linux-kernel - Re: [PATCH v2 11/11] crypto: skcipher: Remove VLA usage for SKCIPHER_REQUEST_ON

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Message-ID: <20180627143622.ntksjxsymo4yw6dz@gondor.apana.org.au>
Date:   Wed, 27 Jun 2018 22:36:22 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Kees Cook <keescook@...omium.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        linux-crypto <linux-crypto@...r.kernel.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Arnd Bergmann <arnd@...db.de>,
        Eric Biggers <ebiggers@...gle.com>,
        Alasdair Kergon <agk@...hat.com>,
        Giovanni Cabiddu <giovanni.cabiddu@...el.com>,
        Lars Persson <larper@...s.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Rabin Vincent <rabinv@...s.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>, qat-linux@...el.com,
        dm-devel@...hat.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 11/11] crypto: skcipher: Remove VLA usage for
 SKCIPHER_REQUEST_ON_STACK

On Tue, Jun 26, 2018 at 09:45:09AM -0700, Kees Cook wrote:
>
> Which are likely to be wrapped together? Should I take this to 512 or
> something else?

The situation is similar to ahash.  While they're using the same
skcipher interface, the underlying algorithms must all be
synchronous.  In fact, if they're not then they're buggy.

Therefore it makes no sense to use the general skcipher request
size as a threshold.  You should look at synchronous skcipher
algorithms only.

Cheers,
-- 
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