[PATCH 2/4] xen-netfront: drop skb when skb->len > 65535

[Wei Liu <wei.liu2@citrix.com>]

The `size' field of Xen network wire format is uint16_t, anything bigger than
65535 will cause overflow.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
---
 drivers/net/xen-netfront.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 5527663..8c3d065 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -547,6 +547,18 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	unsigned int len = skb_headlen(skb);
 	unsigned long flags;
 
+	/*
+	 * wire format of xen_netif_tx_request only supports skb->len
+	 * < 64K, because size field in xen_netif_tx_request is
+	 * uint16_t.
+	 */
+	if (unlikely(skb->len > (uint16_t)(~0))) {
+		net_alert_ratelimited(
+			"xennet: skb->len = %d, too big for wire format\n",
+			skb->len);
+		goto drop;
+	}
+
 	slots = DIV_ROUND_UP(offset + len, PAGE_SIZE) +
 		xennet_count_skb_frag_slots(skb);
 	if (unlikely(slots > MAX_SKB_FRAGS + 1)) {
-- 
1.7.10.4