netdev - Re: [PATCH] virtio: Work around frames incorrectly marked as gso

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Date:   Tue, 11 Feb 2020 07:42:37 +0000
From:   Anton Ivanov <anton.ivanov@...bridgegreys.com>
To:     Jason Wang <jasowang@...hat.com>, netdev@...r.kernel.org
Cc:     linux-um@...ts.infradead.org, mst@...hat.com,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] virtio: Work around frames incorrectly marked as gso

On 11/02/2020 02:51, Jason Wang wrote:
> 
> On 2020/2/11 上午12:55, Anton Ivanov wrote:
>>
>>
>> On 09/12/2019 10:48, anton.ivanov@...bridgegreys.com wrote:
>>> From: Anton Ivanov <anton.ivanov@...bridgegreys.com>
>>>
>>> Some of the frames marked as GSO which arrive at
>>> virtio_net_hdr_from_skb() have no GSO_TYPE, no
>>> fragments (data_len = 0) and length significantly shorter
>>> than the MTU (752 in my experiments).
>>>
>>> This is observed on raw sockets reading off vEth interfaces
>>> in all 4.x and 5.x kernels I tested.
>>>
>>> These frames are reported as invalid while they are in fact
>>> gso-less frames.
>>>
>>> This patch marks the vnet header as no-GSO for them instead
>>> of reporting it as invalid.
>>>
>>> Signed-off-by: Anton Ivanov <anton.ivanov@...bridgegreys.com>
>>> ---
>>>   include/linux/virtio_net.h | 8 ++++++--
>>>   1 file changed, 6 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
>>> index 0d1fe9297ac6..d90d5cff1b9a 100644
>>> --- a/include/linux/virtio_net.h
>>> +++ b/include/linux/virtio_net.h
>>> @@ -112,8 +112,12 @@ static inline int virtio_net_hdr_from_skb(const 
>>> struct sk_buff *skb,
>>>               hdr->gso_type = VIRTIO_NET_HDR_GSO_TCPV4;
>>>           else if (sinfo->gso_type & SKB_GSO_TCPV6)
>>>               hdr->gso_type = VIRTIO_NET_HDR_GSO_TCPV6;
>>> -        else
>>> -            return -EINVAL;
>>> +        else {
>>> +            if (skb->data_len == 0)
>>> +                hdr->gso_type = VIRTIO_NET_HDR_GSO_NONE;
>>> +            else
>>> +                return -EINVAL;
>>> +        }
>>>           if (sinfo->gso_type & SKB_GSO_TCP_ECN)
>>>               hdr->gso_type |= VIRTIO_NET_HDR_GSO_ECN;
>>>       } else
>>>
>>
>> ping.
>>
> 
> Do you mean gso_size is set but gso_type is not? Looks like a bug 
> elsewhere.
> 
> Thanks
> 
> 
Yes.

I could not trace it where it is coming from.

I see it when doing recvmmsg on raw sockets in the UML vector network 
drivers.


-- 
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/