netdev - Re: [PATCH 0/3] Check gso_size of packets when forwarding

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Date:   Thu, 18 Jan 2018 13:57:48 -0800
From:   Pravin Shelar <pshelar@....org>
To:     Daniel Axtens <dja@...ens.net>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Manish.Chopra@...ium.com, ovs dev <dev@...nvswitch.org>
Subject: Re: [PATCH 0/3] Check gso_size of packets when forwarding

On Thu, Jan 18, 2018 at 5:08 AM, Daniel Axtens <dja@...ens.net> wrote:
> Pravin Shelar <pshelar@....org> writes:
>
>> On Mon, Jan 15, 2018 at 6:09 PM, Daniel Axtens <dja@...ens.net> wrote:
>>> When regular packets are forwarded, we validate their size against the
>>> MTU of the destination device. However, when GSO packets are
>>> forwarded, we do not validate their size against the MTU. We
>>> implicitly assume that when they are segmented, the resultant packets
>>> will be correctly sized.
>>>
>>> This is not always the case.
>>>
>>> We observed a case where a packet received on an ibmveth device had a
>>> GSO size of around 10kB. This was forwarded by Open vSwitch to a bnx2x
>>> device, where it caused a firmware assert. This is described in detail
>>> at [0] and was the genesis of this series. Rather than fixing it in
>>> the driver, this series fixes the forwarding path.
>>>
>> Are there any other possible forwarding path in networking stack? TC
>> is one subsystem that could forward such a packet to the bnx2x device,
>> how is that handled ?
>
> So far I have only looked at bridges, openvswitch and macvlan. In
> general, if the code uses dev_forward_skb() it should automatically be
> fine as that invokes is_skb_forwardable(), which we patch.
>
But there are other ways to forward packets, e.g tc-mirred or bpf
redirect. We need to handle all these cases rather than fixing one at
a time. As Jason suggested netif_needs_gso() looks like good function
to validate if a device is capable of handling given GSO packet.