From: Anton Ivanov <anton.iva...@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.iva...@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

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