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: 492caffa ("net: ethernet: nixge: Add support for National Instruments XGE netdev")
Signed-off-by: Yuri Karpov <YKarpov@ispras.ru>
Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/ni/nixge.c

@@ -249,6 +249,7 @@ static void nixge_hw_dma_bd_release(struct net_device *ndev)
 	struct sk_buff *skb;
 	int i;
 
+	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);
@@ -263,11 +264,11 @@ static void nixge_hw_dma_bd_release(struct net_device *ndev)
 			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);