s390/qeth: fix error handling in checksum cmd callback

Make sure to check both return code fields before processing the
response. Otherwise we risk operating on invalid data.

Fixes: c9475369bd2b ("s390/qeth: rework RX/TX checksum offload")
Signed-off-by: Julian Wiedmann <jwi@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/s390/net/qeth_core_main.c

@@ -5386,6 +5386,13 @@ out:
 }
 EXPORT_SYMBOL_GPL(qeth_poll);
 
+static int qeth_setassparms_inspect_rc(struct qeth_ipa_cmd *cmd)
+{
+	if (!cmd->hdr.return_code)
+		cmd->hdr.return_code = cmd->data.setassparms.hdr.return_code;
+	return cmd->hdr.return_code;
+}
+
 int qeth_setassparms_cb(struct qeth_card *card,
 			struct qeth_reply *reply, unsigned long data)
 {
@@ -6242,7 +6249,7 @@ static int qeth_ipa_checksum_run_cmd_cb(struct qeth_card *card,
 				(struct qeth_checksum_cmd *)reply->param;
 
 	QETH_CARD_TEXT(card, 4, "chkdoccb");
-	if (cmd->hdr.return_code)
+	if (qeth_setassparms_inspect_rc(cmd))
 		return 0;
 
 	memset(chksum_cb, 0, sizeof(*chksum_cb));