crypto: gcm - fix rfc4543 to handle async crypto correctly

If the gcm cipher used by rfc4543 does not complete request immediately,
the authentication tag is not copied to destination buffer. Patch adds
correct async logic for this case.
Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/gcm.c

@@ -1099,6 +1099,21 @@ static int crypto_rfc4543_setauthsize(struct crypto_aead *parent,
 	return crypto_aead_setauthsize(ctx->child, authsize);
 }
 
+static void crypto_rfc4543_done(struct crypto_async_request *areq, int err)
+{
+	struct aead_request *req = areq->data;
+	struct crypto_aead *aead = crypto_aead_reqtfm(req);
+	struct crypto_rfc4543_req_ctx *rctx = crypto_rfc4543_reqctx(req);
+
+	if (!err) {
+		scatterwalk_map_and_copy(rctx->auth_tag, req->dst,
+					 req->cryptlen,
+					 crypto_aead_authsize(aead), 1);
+	}
+
+	aead_request_complete(req, err);
+}
+
 static struct aead_request *crypto_rfc4543_crypt(struct aead_request *req,
 						 bool enc)
 {
@@ -1145,8 +1160,8 @@ static struct aead_request *crypto_rfc4543_crypt(struct aead_request *req,
 	scatterwalk_crypto_chain(assoc, payload, 0, 2);
 
 	aead_request_set_tfm(subreq, ctx->child);
-	aead_request_set_callback(subreq, req->base.flags, req->base.complete,
-				  req->base.data);
+	aead_request_set_callback(subreq, req->base.flags, crypto_rfc4543_done,
+				  req);
 	aead_request_set_crypt(subreq, cipher, cipher, enc ? 0 : authsize, iv);
 	aead_request_set_assoc(subreq, assoc, assoclen);