linux-kernel - Re: [PATCH net 2/3] net: hns3: fix a use after free problem in hns3_nic_maybe_stop

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Date:   Wed, 4 Dec 2019 09:33:05 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     David Miller <davem@...emloft.net>
CC:     <tanhuazhong@...wei.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <salil.mehta@...wei.com>,
        <yisen.zhuang@...wei.com>, <linuxarm@...wei.com>,
        <jakub.kicinski@...ronome.com>
Subject: Re: [PATCH net 2/3] net: hns3: fix a use after free problem in
 hns3_nic_maybe_stop_tx()

On 2019/12/4 3:57, David Miller wrote:
> From: Yunsheng Lin <linyunsheng@...wei.com>
> 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.

Will mention that in the next version, thanks.

> 
> .
>