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

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Message-Id: <20180724164936.37477-18-keescook@chromium.org>
Date:   Tue, 24 Jul 2018 09:49:35 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Kees Cook <keescook@...omium.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        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>, 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>,
        Paul Mackerras <paulus@...ba.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Howells <dhowells@...hat.com>,
        Johannes Berg <johannes@...solutions.net>,
        Tudor-Dan Ambarus <tudor.ambarus@...rochip.com>,
        Jia-Ju Bai <baijiaju1990@...il.com>,
        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>, dm-devel@...hat.com,
        linux-pm@...r.kernel.org, linux-crypto@...r.kernel.org,
        drbd-dev@...ts.linbit.com, linux-block@...r.kernel.org,
        qat-linux@...el.com, linux-ppp@...r.kernel.org,
        netdev@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-afs@...ts.infradead.org, linux-wireless@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v6 17/18] crypto: ccm: Remove VLA usage

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).

[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