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

Ard Biesheuvel
2018-07-24T16:57:44Z

On 24 July 2018 at 18:49, Kees Cook <keescook@chromium.org> wrote:
> From: Ard Biesheuvel <ard.biesheuvel@linaro.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@linaro.org>
> Signed-off-by: Kees Cook <keescook@chromium.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
>