crypto: null - Remove VLA usage of skcipher

In the quest to remove all stack VLA usage from the kernel[1], this
replaces struct crypto_skcipher and SKCIPHER_REQUEST_ON_STACK() usage
with struct crypto_sync_skcipher and SYNC_SKCIPHER_REQUEST_ON_STACK(),
which uses a fixed stack size.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/crypto/authencesn.c b/crypto/authencesn.c
index 50b8047..80a25cc 100644
--- a/crypto/authencesn.c
+++ b/crypto/authencesn.c
@@ -36,7 +36,7 @@ struct crypto_authenc_esn_ctx {
 	unsigned int reqoff;
 	struct crypto_ahash *auth;
 	struct crypto_skcipher *enc;
-	struct crypto_skcipher *null;
+	struct crypto_sync_skcipher *null;
 };
 
 struct authenc_esn_request_ctx {
@@ -183,9 +183,9 @@ static int crypto_authenc_esn_copy(struct aead_request *req, unsigned int len)
 {
 	struct crypto_aead *authenc_esn = crypto_aead_reqtfm(req);
 	struct crypto_authenc_esn_ctx *ctx = crypto_aead_ctx(authenc_esn);
-	SKCIPHER_REQUEST_ON_STACK(skreq, ctx->null);
+	SYNC_SKCIPHER_REQUEST_ON_STACK(skreq, ctx->null);
 
-	skcipher_request_set_tfm(skreq, ctx->null);
+	skcipher_request_set_sync_tfm(skreq, ctx->null);
 	skcipher_request_set_callback(skreq, aead_request_flags(req),
 				      NULL, NULL);
 	skcipher_request_set_crypt(skreq, req->src, req->dst, len, NULL);
@@ -341,7 +341,7 @@ static int crypto_authenc_esn_init_tfm(struct crypto_aead *tfm)
 	struct crypto_authenc_esn_ctx *ctx = crypto_aead_ctx(tfm);
 	struct crypto_ahash *auth;
 	struct crypto_skcipher *enc;
-	struct crypto_skcipher *null;
+	struct crypto_sync_skcipher *null;
 	int err;
 
 	auth = crypto_spawn_ahash(&ictx->auth);