net/hyperv: Fix the page buffer when an RNDIS message goes beyond page boundary

There is a possible data corruption if an RNDIS message goes beyond page
boundary in the sending code path. This patch fixes the problem.
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hyperv/netvsc_drv.c

@@ -151,10 +151,10 @@ static int netvsc_start_xmit(struct sk_buff *skb, struct net_device *net)
 	int ret;
 	unsigned int i, num_pages, npg_data;
 
-	/* Add multipage for skb->data and additional one for RNDIS */
+	/* Add multipages for skb->data and additional 2 for RNDIS */
 	npg_data = (((unsigned long)skb->data + skb_headlen(skb) - 1)
 		>> PAGE_SHIFT) - ((unsigned long)skb->data >> PAGE_SHIFT) + 1;
-	num_pages = skb_shinfo(skb)->nr_frags + npg_data + 1;
+	num_pages = skb_shinfo(skb)->nr_frags + npg_data + 2;
 
 	/* Allocate a netvsc packet based on # of frags. */
 	packet = kzalloc(sizeof(struct hv_netvsc_packet) +
@@ -173,8 +173,8 @@ static int netvsc_start_xmit(struct sk_buff *skb, struct net_device *net)
 				sizeof(struct hv_netvsc_packet) +
 				    (num_pages * sizeof(struct hv_page_buffer));
 
-	/* Setup the rndis header */
-	packet->page_buf_cnt = num_pages;
+	/* If the rndis msg goes beyond 1 page, we will add 1 later */
+	packet->page_buf_cnt = num_pages - 1;
 
 	/* Initialize it from the skb */
 	packet->total_data_buflen = skb->len;

drivers/net/hyperv/rndis_filter.c

@@ -797,6 +797,19 @@ int rndis_filter_send(struct hv_device *dev,
 			(unsigned long)rndisMessage & (PAGE_SIZE-1);
 	pkt->page_buf[0].len = rndisMessageSize;
 
+	/* Add one page_buf if the rndis msg goes beyond page boundary */
+	if (pkt->page_buf[0].offset + rndisMessageSize > PAGE_SIZE) {
+		int i;
+		for (i = pkt->page_buf_cnt; i > 1; i--)
+			pkt->page_buf[i] = pkt->page_buf[i-1];
+		pkt->page_buf_cnt++;
+		pkt->page_buf[0].len = PAGE_SIZE - pkt->page_buf[0].offset;
+		pkt->page_buf[1].pfn = virt_to_phys((void *)((ulong)
+			rndisMessage + pkt->page_buf[0].len)) >> PAGE_SHIFT;
+		pkt->page_buf[1].offset = 0;
+		pkt->page_buf[1].len = rndisMessageSize - pkt->page_buf[0].len;
+	}
+
 	/* Save the packet send completion and context */
 	filterPacket->completion = pkt->completion.send.send_completion;
 	filterPacket->completion_ctx =

include/linux/hyperv.h

@@ -35,7 +35,7 @@
 #include <linux/mod_devicetable.h>
 
 
-#define MAX_PAGE_BUFFER_COUNT				18
+#define MAX_PAGE_BUFFER_COUNT				19
 #define MAX_MULTIPAGE_BUFFER_COUNT			32 /* 128K */
 
 #pragma pack(push, 1)