[PATCH net] net: dlink: handle copy_thresh allocation failure

[Yeounsu Moon <yyyynoom@gmail.com>]

The driver did not handle failure of `netdev_alloc_skb_ip_align()`.
If the allocation failed, dereferencing `skb->protocol` could lead to a
NULL pointer dereference.

This patch adds proper error handling by falling back to the `else` clause
when the allocation fails.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Tested-on: D-Link DGE-550T Rev-A3
Signed-off-by: Yeounsu Moon <yyyynoom@gmail.com>
---
 drivers/net/ethernet/dlink/dl2k.c | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/drivers/net/ethernet/dlink/dl2k.c b/drivers/net/ethernet/dlink/dl2k.c
index 6bbf6e5584e5..a82e1fd01b92 100644
--- a/drivers/net/ethernet/dlink/dl2k.c
+++ b/drivers/net/ethernet/dlink/dl2k.c
@@ -965,26 +965,31 @@ receive_packet (struct net_device *dev)
 			struct sk_buff *skb;
 
 			/* Small skbuffs for short packets */
-			if (pkt_len > copy_thresh) {
-				dma_unmap_single(&np->pdev->dev,
-						 desc_to_dma(desc),
-						 np->rx_buf_sz,
-						 DMA_FROM_DEVICE);
-				skb_put (skb = np->rx_skbuff[entry], pkt_len);
-				np->rx_skbuff[entry] = NULL;
-			} else if ((skb = netdev_alloc_skb_ip_align(dev, pkt_len))) {
+			if (pkt_len <= copy_thresh) {
+				skb = netdev_alloc_skb_ip_align(dev, pkt_len);
+				if (!skb)
+					goto reuse_skbuff;
+
 				dma_sync_single_for_cpu(&np->pdev->dev,
 							desc_to_dma(desc),
 							np->rx_buf_sz,
 							DMA_FROM_DEVICE);
-				skb_copy_to_linear_data (skb,
+				skb_copy_to_linear_data(skb,
 						  np->rx_skbuff[entry]->data,
 						  pkt_len);
-				skb_put (skb, pkt_len);
+				skb_put(skb, pkt_len);
 				dma_sync_single_for_device(&np->pdev->dev,
 							   desc_to_dma(desc),
 							   np->rx_buf_sz,
 							   DMA_FROM_DEVICE);
+			} else {
+reuse_skbuff:
+				dma_unmap_single(&np->pdev->dev,
+						 desc_to_dma(desc),
+						 np->rx_buf_sz,
+						 DMA_FROM_DEVICE);
+				skb_put(skb = np->rx_skbuff[entry], pkt_len);
+				np->rx_skbuff[entry] = NULL;
 			}
 			skb->protocol = eth_type_trans (skb, dev);
 #if 0
-- 
2.51.0