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

Kees Cook
2018-07-24T16:49:35Z

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).

[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