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

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Message-ID: <CAOrHB_AOYrzDVZBST-TDZo2ZtrBqQiv6+0eHNDJuukGUDYGZFQ@mail.gmail.com>
Date:   Tue, 7 Feb 2017 09:14:26 -0800
From:   Pravin Shelar <pshelar@....org>
To:     David Miller <davem@...emloft.net>
Cc:     Jarno Rajahalme <jarno@....org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 1/7] openvswitch: Use inverted tuple in
 ovs_ct_find_existing() if NATted.

On Mon, Feb 6, 2017 at 9:15 AM, David Miller <davem@...emloft.net> wrote:
> 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.

I think it fails because after upcall OVS is performing lookup for
nonexistent conntrack entry. This is due to the fact that the packet
is already Nat-ed. So one could argue that there is already enough
context available in OVS to lookup original conntract entry after the
upcall as shown in this patch.
But I am also fine with using original context to lookup the conntract
entry as Joe has suggested.