crypto: authenc - Find proper IV address in ablkcipher callback

When performing an asynchronous ablkcipher operation the authenc
completion callback routine is invoked, but it does not locate and use
the proper IV.

The callback routine, crypto_authenc_encrypt_done, is updated to use
the same method of calculating the address of the IV as is done in
crypto_authenc_encrypt function which sets up the callback.

Cc: stable@vger.kernel.org
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/authenc.c

@@ -380,9 +380,10 @@ static void crypto_authenc_encrypt_done(struct crypto_async_request *req,
 	if (!err) {
 		struct crypto_aead *authenc = crypto_aead_reqtfm(areq);
 		struct crypto_authenc_ctx *ctx = crypto_aead_ctx(authenc);
-		struct ablkcipher_request *abreq = aead_request_ctx(areq);
-		u8 *iv = (u8 *)(abreq + 1) +
-			 crypto_ablkcipher_reqsize(ctx->enc);
+		struct authenc_request_ctx *areq_ctx = aead_request_ctx(areq);
+		struct ablkcipher_request *abreq = (void *)(areq_ctx->tail
+							    + ctx->reqoff);
+		u8 *iv = (u8 *)abreq - crypto_ablkcipher_ivsize(ctx->enc);
 
 		err = crypto_authenc_genicv(areq, iv, 0);
 	}