linux-kernel - Re: [PATCH v2 2/4] crypto: skcipher - Enforce non-ASYNC for on-stack requests

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Message-ID: <20180907034242.zhm4dglzkldhvh3x@gondor.apana.org.au>
Date:   Fri, 7 Sep 2018 11:42:42 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Kees Cook <keescook@...omium.org>
Cc:     Eric Biggers <ebiggers@...gle.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Gilad Ben-Yossef <gilad@...yossef.com>,
        Alexander Stein <alexander.stein@...tec-electronic.com>,
        Antoine Tenart <antoine.tenart@...tlin.com>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Arnaud Ebalard <arno@...isbad.org>,
        Corentin Labbe <clabbe.montjoie@...il.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Christian Lamparter <chunkeey@...il.com>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/4] crypto: skcipher - Enforce non-ASYNC for on-stack
 requests

On Thu, Sep 06, 2018 at 03:58:52PM -0700, Kees Cook wrote:
>
> @@ -437,6 +442,12 @@ static inline struct crypto_skcipher *crypto_skcipher_reqtfm_check(
>  {
>  	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
>  
> +	if (req->__onstack) {
> +		if (WARN_ON(crypto_skcipher_alg(tfm)->base.cra_flags &
> +				CRYPTO_ALG_ASYNC))
> +			return ERR_PTR(-EINVAL);
> +	}

Sorry but I don't like imposing a run-time check on everybody when
stack-based requests are the odd ones out.  If we're going to make
this a run-time check (I'd much prefer a compile-time check, but I
understand that this may involve too much churn), then please do it
for stack-based request users only.

Thanks,
-- 
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