netdev - Re: [PATCH net-next 1/7] openvswitch: Use inverted tuple in ovs_ct_find

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Date:   Mon, 06 Feb 2017 12:15:12 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     pshelar@....org
Cc:     jarno@....org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 1/7] openvswitch: Use inverted tuple in
 ovs_ct_find_existing() if NATted.

From: Pravin Shelar <pshelar@....org>
Date: Mon, 6 Feb 2017 09:06:29 -0800

> On Sun, Feb 5, 2017 at 2:28 PM, David Miller <davem@...emloft.net> wrote:
>> From: Jarno Rajahalme <jarno@....org>
>> Date: Thu,  2 Feb 2017 17:10:00 -0800
>>
>>> This does not match either of the conntrack tuples above.  Normally
>>> this does not matter, as the conntrack lookup was already done using
>>> the tuple (B,A), but if the current packet does not match any flow in
>>> the OVS datapath, the packet is sent to userspace via an upcall,
>>> during which the packet's skb is freed, and the conntrack entry
>>> pointer in the skb is lost.
>>
>> This is the real bug.
>>
>> If the metadata for a packet is important, as it obviously is here,
>> then upcalls should preserve that metadata across the upcall.  This
>> is exactly how NF_QUEUE handles this problem and so should OVS.
> 
> OVS kernel datapath serializes skb context and sends it along with skb
> during upcall via genetlink parameters. userspace echoes same
> information back to kernel modules. This way OVS does maintains
> metadata across upcall.

Then the conntrack state looked up before the NAT operation done in
the upcall should be maintained and therefore this bug should not
exist.