net: ethernet: nixge: fix NULL dereference

In function nixge_hw_dma_bd_release() dereference of NULL pointer
priv->rx_bd_v is possible for the case of its allocation failure in
nixge_hw_dma_bd_init().

Move for() loop with priv->rx_bd_v dereference under the check for
its validity.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 492caffa8a1a ("net: ethernet: nixge: Add support for National Instruments XGE netdev")
Signed-off-by: Yuri Karpov <[e-mail]>
Reviewed-by: Maciej Fijalkowski <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/ni/nixge.c

···
 	struct sk_buff *skb;
 	int i;
 
-	for (i = 0; i < RX_BD_NUM; i++) {
-		phys_addr = nixge_hw_dma_bd_get_addr(&priv->rx_bd_v[i],
-						     phys);
+	if (priv->rx_bd_v) {
+		for (i = 0; i < RX_BD_NUM; i++) {
+			phys_addr = nixge_hw_dma_bd_get_addr(&priv->rx_bd_v[i],
+							     phys);
 
-		dma_unmap_single(ndev->dev.parent, phys_addr,
-				 NIXGE_MAX_JUMBO_FRAME_SIZE,
-				 DMA_FROM_DEVICE);
+			dma_unmap_single(ndev->dev.parent, phys_addr,
+					 NIXGE_MAX_JUMBO_FRAME_SIZE,
+					 DMA_FROM_DEVICE);
 
-		skb = (struct sk_buff *)(uintptr_t)
-			nixge_hw_dma_bd_get_addr(&priv->rx_bd_v[i],
-						 sw_id_offset);
-		dev_kfree_skb(skb);
-	}
+			skb = (struct sk_buff *)(uintptr_t)
+				nixge_hw_dma_bd_get_addr(&priv->rx_bd_v[i],
+							 sw_id_offset);
+			dev_kfree_skb(skb);
+		}
 
-	if (priv->rx_bd_v)
 		dma_free_coherent(ndev->dev.parent,
 				  sizeof(*priv->rx_bd_v) * RX_BD_NUM,
 				  priv->rx_bd_v,
 				  priv->rx_bd_p);
+	}
 
 	if (priv->tx_skb)
 		devm_kfree(ndev->dev.parent, priv->tx_skb);