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

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 ??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
> > > > 
> > > > 
> > > 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?

> > 
> > 
> > > -- 
> > > Anton R. Ivanov
> > > Cambridgegreys Limited. Registered in England. Company Number
10273661
> > > https://www.cambridgegreys.com/
> > 
> > 
> > _______________________________________________
> > linux-um mailing list
> > linux-um at lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-um
> > 
> 
> -- 
> Anton R. Ivanov
> Cambridgegreys Limited. Registered in England. Company Number 10273661
> https://www.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 ??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
>>>>>
>>>>>
>>>> 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/
>>>
>>>
>>> _______________________________________________
>>> linux-um mailing list
>>> linux-um at lists.infradead.org
>>> http://lists.infradead.org/mailman/listinfo/linux-um
>>>
>>
>> -- 
>> 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/

On Thu, Feb 13, 2020 at 11:12:45AM +0000, Anton Ivanov
wrote:
> 
> 
> 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 ??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
> > > > > > 
> > > > > > 
> > > > > 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 :(
dump skb pointer at the two locations and see whether it matches :)
> 
> > 
> > 
> > > > 
> > > > 
> > > > > -- 
> > > > > Anton R. Ivanov
> > > > > Cambridgegreys Limited. Registered in England. Company
Number 10273661
> > > > > https://www.cambridgegreys.com/
> > > > 
> > > > 
> > > > _______________________________________________
> > > > linux-um mailing list
> > > > linux-um at lists.infradead.org
> > > > http://lists.infradead.org/mailman/listinfo/linux-um
> > > > 
> > > 
> > > -- 
> > > 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/

On 2/13/20 2:00 AM, 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 ??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
>>>>>
>>>>>
>>>> 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?
>
Correct way to determine if a packet is a gso one is by looking at gso_size.
Then only it is legal looking at gso_type


static inline bool skb_is_gso(const struct sk_buff *skb)
{
    return skb_shinfo(skb)->gso_size;
}

/* Note: Should be called only if skb_is_gso(skb) is true */
static inline bool skb_is_gso_v6(const struct sk_buff *skb)
...


There is absolutely no relation between GSO and skb->data_len, skb can be
linearized
for various orthogonal reasons.

On Thu, Feb 13, 2020 at 07:44:06AM -0800, Eric Dumazet
wrote:
> 
> 
> On 2/13/20 2:00 AM, 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 ??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
> >>>>>
> >>>>>
> >>>> 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?
> >
> 
> Correct way to determine if a packet is a gso one is by looking at
gso_size.
> Then only it is legal looking at gso_type
> 
> 
> static inline bool skb_is_gso(const struct sk_buff *skb)
> {
>     return skb_shinfo(skb)->gso_size;
> }
> 
> /* Note: Should be called only if skb_is_gso(skb) is true */
> static inline bool skb_is_gso_v6(const struct sk_buff *skb)
> ...
> 
> 
> There is absolutely no relation between GSO and skb->data_len, skb can
be linearized
> for various orthogonal reasons.
The reported problem is that virtio gets a packet where gso_size
is !0 but gso_type is 0.

It currently drops these on the assumption that it's some type
of a gso packet it does not know how to handle.


So you are saying if skb_is_gso we can still have gso_type set to 0,
and that's an expected configuration?

So the patch should just be:


-        if (skb_is_gso(skb)) {
+        if (skb_is_gso(skb) && sinfo->gso_type) {



?