hyperv: Fix page buffer handling in rndis_filter_send_request()

To prevent possible data corruption in RNDIS requests, add another
page buffer if the request message crossed page boundary.
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hyperv/rndis_filter.c

@@ -45,7 +45,8 @@ struct rndis_request {
 
 	/* Simplify allocation by having a netvsc packet inline */
 	struct hv_netvsc_packet	pkt;
-	struct hv_page_buffer buf;
+	/* Set 2 pages for rndis requests crossing page boundary */
+	struct hv_page_buffer buf[2];
 
 	struct rndis_message request_msg;
 	/*
@@ -227,6 +228,18 @@ static int rndis_filter_send_request(struct rndis_device *dev,
 	packet->page_buf[0].offset =
 		(unsigned long)&req->request_msg & (PAGE_SIZE - 1);
 
+	/* Add one page_buf when request_msg crossing page boundary */
+	if (packet->page_buf[0].offset + packet->page_buf[0].len > PAGE_SIZE) {
+		packet->page_buf_cnt++;
+		packet->page_buf[0].len = PAGE_SIZE -
+			packet->page_buf[0].offset;
+		packet->page_buf[1].pfn = virt_to_phys((void *)&req->request_msg
+			+ packet->page_buf[0].len) >> PAGE_SHIFT;
+		packet->page_buf[1].offset = 0;
+		packet->page_buf[1].len = req->request_msg.msg_len -
+			packet->page_buf[0].len;
+	}
+
 	packet->completion.send.send_completion_ctx = req;/* packet; */
 	packet->completion.send.send_completion =
 		rndis_filter_send_request_completion;