net: hns3: fix a use after free problem in hns3_nic_maybe_stop_tx()

Currently, hns3_nic_maybe_stop_tx() uses skb_copy() to linearize a
SKB if the BD num required by the SKB does not meet the hardware
limitation, and it linearizes the SKB by allocating a new linearized SKB
and freeing the old SKB, if hns3_nic_maybe_stop_tx() returns -EBUSY
because there are no enough space in the ring to send the linearized
skb to hardware, the sch_direct_xmit() still hold reference to old SKB
and try to retransmit the old SKB when dev_hard_start_xmit() return
TX_BUSY, which may cause use after freed problem.

This patch fixes it by using __skb_linearize() to linearize the
SKB in hns3_nic_maybe_stop_tx().

Fixes: 51e8439f ("net: hns3: add 8 BD limit for tx flow")
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/hisilicon/hns3/hns3_enet.c

@@ -1288,31 +1288,24 @@ static bool hns3_skb_need_linearized(struct sk_buff *skb, unsigned int *bd_size,
 
 static int hns3_nic_maybe_stop_tx(struct hns3_enet_ring *ring,
 				  struct net_device *netdev,
-				  struct sk_buff **out_skb)
+				  struct sk_buff *skb)
 {
 	struct hns3_nic_priv *priv = netdev_priv(netdev);
 	unsigned int bd_size[HNS3_MAX_TSO_BD_NUM + 1U];
-	struct sk_buff *skb = *out_skb;
 	unsigned int bd_num;
 
 	bd_num = hns3_tx_bd_num(skb, bd_size);
 	if (unlikely(bd_num > HNS3_MAX_NON_TSO_BD_NUM)) {
-		struct sk_buff *new_skb;
-
 		if (bd_num <= HNS3_MAX_TSO_BD_NUM && skb_is_gso(skb) &&
 		    !hns3_skb_need_linearized(skb, bd_size, bd_num))
 			goto out;
 
-		/* manual split the send packet */
-		new_skb = skb_copy(skb, GFP_ATOMIC);
-		if (!new_skb)
+		if (__skb_linearize(skb))
 			return -ENOMEM;
-		dev_kfree_skb_any(skb);
-		*out_skb = new_skb;
 
-		bd_num = hns3_tx_bd_count(new_skb->len);
-		if ((skb_is_gso(new_skb) && bd_num > HNS3_MAX_TSO_BD_NUM) ||
-		    (!skb_is_gso(new_skb) &&
+		bd_num = hns3_tx_bd_count(skb->len);
+		if ((skb_is_gso(skb) && bd_num > HNS3_MAX_TSO_BD_NUM) ||
+		    (!skb_is_gso(skb) &&
 		     bd_num > HNS3_MAX_NON_TSO_BD_NUM))
 			return -ENOMEM;
 
@@ -1415,7 +1408,7 @@ netdev_tx_t hns3_nic_net_xmit(struct sk_buff *skb, struct net_device *netdev)
 	/* Prefetch the data used later */
 	prefetch(skb->data);
 
-	ret = hns3_nic_maybe_stop_tx(ring, netdev, &skb);
+	ret = hns3_nic_maybe_stop_tx(ring, netdev, skb);
 	if (unlikely(ret <= 0)) {
 		if (ret == -EBUSY) {
 			u64_stats_update_begin(&ring->syncp);