crypto: authenc - Find proper IV address in ablkcipher callback

commit fc019c7122dfcd69c50142b57a735539aec5da95 upstream.

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.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/crypto/authenc.c b/crypto/authenc.c
index 5ef7ba6..d21da2f 100644
--- a/crypto/authenc.c
+++ b/crypto/authenc.c
@@ -368,9 +368,10 @@
 	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);
 	}