crypto: ccm - Remove VLA usage

In the quest to remove all stack VLA usage from the kernel[1], this drops
AHASH_REQUEST_ON_STACK by preallocating the ahash request area combined
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>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files 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;