Re: [PATCH net 2/3] net: hns3: fix a use after free problem in hns3_nic_maybe_stop_tx()

[David Miller]

From: Yunsheng Lin <linyunsheng@xxxxxxxxxx>
Date: Tue, 3 Dec 2019 12:22:11 +0800

> 2. When skb_copy() returns success, the hns3_nic_maybe_stop_tx()
> returns -EBUSY when there are not no enough space in the ring to
> send the skb to hardware, and hns3_nic_net_xmit() will return
> NETDEV_TX_BUSY to the upper layer, the upper layer will resend the old
> skb later when driver wakes up the queue, but the old skb has been freed
> by the hns3_nic_maybe_stop_tx(). Because when using the skb_copy() to
> linearize a skb, it will return a new linearized skb, and the old skb is
> freed, the upper layer does not have a reference to the new skb and resend
> using the old skb, which casues a use after freed problem.
> 
> This patch is trying to fixes the case 2.
> 
> Maybe I should mention why hns3_nic_maybe_stop_tx() returns -EBUSY to
> better describe the problem?

I think it would help understand the code path you are fixing, yes.