net: dlink: handle copy_thresh allocation failure

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 tries to allocate `skb`. If the allocation fails, it falls
back to the normal path.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Tested-on: D-Link DGE-550T Rev-A3
Signed-off-by: Yeounsu Moon <yyyynoom@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250928190124.1156-1-yyyynoom@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Cruzer-S

drivers/net/ethernet/dlink/dl2k.c

@@ -964,15 +964,18 @@ receive_packet (struct net_device *dev)
 		} else {
 			struct sk_buff *skb;
 
+			skb = NULL;
 			/* Small skbuffs for short packets */
-			if (pkt_len > copy_thresh) {
+			if (pkt_len <= copy_thresh)
+				skb = netdev_alloc_skb_ip_align(dev, pkt_len);
+			if (!skb) {
 				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))) {
+			} else {
 				dma_sync_single_for_cpu(&np->pdev->dev,
 							desc_to_dma(desc),
 							np->rx_buf_sz,