[PATCH] sky2: make sure ethernet header is in transmit skb

[Stephen Hemminger <shemminger@linux-foundation.org>]

When DHCP sends a packet using AF_PACKET, it is possible for driver
to receive a transmit packet with the Ethernet header off in the
skb fragments.  The hardware doesn't handle 0 size DMA's well,
so it gets confused.

Other drivers may have same problem, I really think this ought
to be done at higher level.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>

---
Patch against net-2.6, but same patch applies to -stable as well
(with fuzz).

--- a/drivers/net/sky2.c	2009-12-26 13:39:34.289252942 -0800
+++ b/drivers/net/sky2.c	2009-12-26 13:59:44.548877690 -0800
@@ -1654,6 +1654,14 @@ static netdev_tx_t sky2_xmit_frame(struc
  	if (unlikely(tx_avail(sky2) < tx_le_req(skb)))
   		return NETDEV_TX_BUSY;
 
+	/* Make sure there is at least some data for first DMA */
+	if (!pskb_may_pull(skb, ETH_HLEN)) {
+		if (net_ratelimit())
+			pr_info(PFX "%s: packet missing ether header (%d)?",
+				dev->name, skb->len);
+		goto drop;
+	}
+
 	len = skb_headlen(skb);
 	mapping = pci_map_single(hw->pdev, skb->data, len, PCI_DMA_TODEVICE);
 
@@ -1799,6 +1807,7 @@ mapping_unwind:
 mapping_error:
 	if (net_ratelimit())
 		dev_warn(&hw->pdev->dev, "%s: tx mapping error\n", dev->name);
+drop:
 	dev_kfree_skb(skb);
 	return NETDEV_TX_OK;
 }