linux-kernel - Re: [PATCH v6 17/18] crypto: ccm: Remove VLA usage

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Message-ID: <CAKv+Gu-D9FrOrFU0EmkPA52vrywCGZkFP9vUsyEovdby9dLj0g@mail.gmail.com>
Date:   Tue, 24 Jul 2018 18:57:44 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        Arnd Bergmann <arnd@...db.de>,
        Eric Biggers <ebiggers@...gle.com>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Alasdair Kergon <agk@...hat.com>,
        Rabin Vincent <rabinv@...s.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Philipp Reisner <philipp.reisner@...bit.com>,
        Lars Ellenberg <lars.ellenberg@...bit.com>,
        Jens Axboe <axboe@...nel.dk>,
        Giovanni Cabiddu <giovanni.cabiddu@...el.com>,
        Mike Snitzer <snitzer@...hat.com>,
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        Andrew Morton <akpm@...ux-foundation.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Will Deacon <will.deacon@....com>,
        device-mapper development <dm-devel@...hat.com>,
        linux-pm <linux-pm@...r.kernel.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
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        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 17/18] crypto: ccm: Remove VLA usage

On 24 July 2018 at 18:49, Kees Cook <keescook@...omium.org> wrote:
> From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>
> In the quest to remove all stack VLA usage from the kernel[1], this
> drops AHASH_REQUEST_ON_STACK by preallocated the ahash request area
> with the skcipher area (which are not used at the same time).
>

-EGRAMMAR

> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  crypto/ccm.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/crypto/ccm.c b/crypto/ccm.c
> index 0a083342ec8c..b242fd0d3262 100644
> --- a/crypto/ccm.c
> +++ b/crypto/ccm.c
> @@ -50,7 +50,10 @@ struct crypto_ccm_req_priv_ctx {
>         u32 flags;
>         struct scatterlist src[3];
>         struct scatterlist dst[3];
> -       struct skcipher_request skreq;
> +       union {
> +               struct ahash_request ahreq;
> +               struct skcipher_request skreq;
> +       };
>  };
>
>  struct cbcmac_tfm_ctx {
> @@ -181,7 +184,7 @@ static int crypto_ccm_auth(struct aead_request *req, struct scatterlist *plain,
>         struct crypto_ccm_req_priv_ctx *pctx = crypto_ccm_reqctx(req);
>         struct crypto_aead *aead = crypto_aead_reqtfm(req);
>         struct crypto_ccm_ctx *ctx = crypto_aead_ctx(aead);
> -       AHASH_REQUEST_ON_STACK(ahreq, ctx->mac);
> +       struct ahash_request *ahreq = &pctx->ahreq;
>         unsigned int assoclen = req->assoclen;
>         struct scatterlist sg[3];
>         u8 *odata = pctx->odata;
> @@ -427,7 +430,7 @@ static int crypto_ccm_init_tfm(struct crypto_aead *tfm)
>         crypto_aead_set_reqsize(
>                 tfm,
>                 align + sizeof(struct crypto_ccm_req_priv_ctx) +
> -               crypto_skcipher_reqsize(ctr));
> +               max(crypto_ahash_reqsize(mac), crypto_skcipher_reqsize(ctr)));
>
>         return 0;
>
> --
> 2.17.1
>