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

[Anton Ivanov <anton.ivanov@cambridgegreys.com>]

On 13/02/2020 10:00, Michael S. Tsirkin wrote:
> On Wed, Feb 12, 2020 at 05:38:09PM +0000, Anton Ivanov wrote:
>>
>>
>> On 11/02/2020 10:37, Michael S. Tsirkin wrote:
>>> On Tue, Feb 11, 2020 at 07:42:37AM +0000, Anton Ivanov wrote:
>>>> 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@cambridgegreys.com wrote:
>>>>>>> From: Anton Ivanov <anton.ivanov@cambridgegreys.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@cambridgegreys.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.
>>>>
>>>
>>> I think we need to find the culprit and fix it there, lots of other things
>>> can break otherwise.
>>> Just printing out skb->dev->name should do the trick, no?
>>
>> The printk in virtio_net_hdr_from_skb says NULL.
>>
>> That is probably normal for a locally originated frame.
>>
>> I cannot reproduce this with network traffic by the way - it happens only if the traffic is locally originated on the host.
>>
>> A,
> 
> OK so is it code in __tcp_transmit_skb that sets gso_size to non-null
> when gso_type is 0?

It does look like that, but I cannot see it when reading it :(


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

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