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

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Date:   Tue, 26 Jun 2018 09:45:09 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Herbert Xu <herbert@...dor.apana.org.au>
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 2:20 AM, Herbert Xu <herbert@...dor.apana.org.au> wrote:
> On Mon, Jun 25, 2018 at 02:10:26PM -0700, Kees Cook wrote:
>> In the quest to remove all stack VLA usage from the kernel[1], this
>> caps the skcipher request size similar to other limits and adds a
>> sanity check at registration. In a manual review of the callers of
>> crypto_skcipher_set_reqsize(), the largest was 384:
>>
>> 4     sun4i_cipher_req_ctx
>> 6     safexcel_cipher_req
>> 8     cryptd_skcipher_request_ctx
>> 80    cipher_req_ctx
>> 80    skcipher_request
>> 96    crypto_rfc3686_req_ctx
>> 104   nitrox_kcrypt_request
>> 144   mv_cesa_skcipher_std_req
>> 384   rctx
>>
>> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>>
>> Cc: Herbert Xu <herbert@...dor.apana.org.au>
>> Cc: "David S. Miller" <davem@...emloft.net>
>> Cc: linux-crypto@...r.kernel.org
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>
> This has the same issue as the ahash reqsize patch.

Which are likely to be wrapped together? Should I take this to 512 or
something else?

-Kees

-- 
Kees Cook
Pixel Security