Linux Virtualization - Feb 2020 - [PATCH] virtio: Work around frames incorrectly marked as gso

From: Anton Ivanov <anton.ivanov at 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 at 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
-- 
2.20.1

>  		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;

maybe use "else if" like in the before? yes, it's a different type
of
condition, but braces look a bit unnatural here to me at least

johannes

On 09/12/2019 10:48, anton.ivanov at cambridgegreys.com
wrote:
> From: Anton Ivanov <anton.ivanov at 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 at 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.

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

On 2020/2/11 ??12:55, Anton Ivanov wrote:
>
>
> On 09/12/2019 10:48, anton.ivanov at cambridgegreys.com wrote:
>> From: Anton Ivanov <anton.ivanov at 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 at 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