netdev - Re: [PATCH v2] vxlan: remove the redundant gro_cells

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Date:   Sat, 16 Mar 2019 10:33:14 +0800
From:   Zhiqiang Liu <liuzhiqiang26@...wei.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        David Miller <davem@...emloft.net>
CC:     <sbrivio@...hat.com>, <petrm@...lanox.com>, <idosch@...lanox.com>,
        <sd@...asysnail.net>, <mousuanming@...wei.com>,
        <netdev@...r.kernel.org>, <mingfangsen@...wei.com>,
        <zhoukang7@...wei.com>, <wangxiaogang3@...wei.com>
Subject: Re: [PATCH v2] vxlan: remove the redundant gro_cells_destroy()
 calling.


>>> On 03/15/2019 08:28 AM, Stefano Brivio wrote:
>>>> On Fri, 15 Mar 2019 23:18:52 +0800
>>>> Zhiqiang Liu <liuzhiqiang26@...wei.com> wrote:
>>>>
>>>>
>>>> NACK, please read my and Eric's comments to v1 -- giving me more than 23
>>>> minutes to answer would have been a nice touch as well :)
>>>>
>>>
>>> Sorry for the confusion, I forgot to add the question marks to my sentences.
>>>
>>> In fact, this is a bug fix, that we missed in the previous fix.
>>>
>>> Technically the bug is older.
>>
>> Please elaborate.
>>
> 
> Commit ad6c9986bcb62
> ("vxlan: Fix GRO cells race condition between receive and link delete")
> 
> fixed a race condition for the typical case a vxlan device is dismantled from the
> current netns.
> 
> But if a netns is dismantled, we call vxlan_destroy_tunnels()
> to schedule a unregister_netdevice_queue() of all the vxlan tunnels
> that are related to this netns.
> 
> This means that the gro_cells_destroy() call is done too soon,
> for the same reasons explained in above commit .
> 
> We need to fully respect the RCU rules, and thus must remove the
> gro_cells_destroy() call or risk use after-free.
> 
> The bug is day-0 I think.
> 
> commit 58ce31cca1ffe057f4744c3f671e3e84606d3d4a
> Author: Tom Herbert <tom@...bertland.com>
> Date:   Wed Aug 19 17:07:33 2015 -0700
> 
>     vxlan: GRO support at tunnel layer
> 

Thank you for pointing out the real issueI will update the commit message and Fixes: tag as your explanation.