netdev - Re: [PATCH v3] tun: fix use-after-free when register netdev failed

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Date:   Thu, 22 Aug 2019 10:13:11 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     David Miller <davem@...emloft.net>, yangyingliang@...wei.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        xiyou.wangcong@...il.com, weiyongjun1@...wei.com
Subject: Re: [PATCH v3] tun: fix use-after-free when register netdev failed


On 2019/8/20 上午10:28, Jason Wang wrote:
>
> On 2019/8/20 上午9:25, David Miller wrote:
>> From: Yang Yingliang <yangyingliang@...wei.com>
>> Date: Mon, 19 Aug 2019 21:31:19 +0800
>>
>>> Call tun_attach() after register_netdevice() to make sure tfile->tun
>>> is not published until the netdevice is registered. So the read/write
>>> thread can not use the tun pointer that may freed by free_netdev().
>>> (The tun and dev pointer are allocated by alloc_netdev_mqs(), they can
>>> be freed by netdev_freemem().)
>> register_netdevice() must always be the last operation in the order of
>> network device setup.
>>
>> At the point register_netdevice() is called, the device is visible 
>> globally
>> and therefore all of it's software state must be fully initialized and
>> ready for us.
>>
>> You're going to have to find another solution to these problems.
>
>
> The device is loosely coupled with sockets/queues. Each side is 
> allowed to be go away without caring the other side. So in this case, 
> there's a small window that network stack think the device has one 
> queue but actually not, the code can then safely drop them. Maybe it's 
> ok here with some comments?
>
> Or if not, we can try to hold the device before tun_attach and drop it 
> after register_netdevice().


Hi Yang:

I think maybe we can try to hold refcnt instead of playing real num 
queues here. Do you want to post a V4?

Thanks


>
> Thanks
>