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

On Tue, Feb 11, 2020 at 07:42:37AM +0000, Anton Ivanov wrote:

On 11/02/2020 02:51, Jason Wang wrote:

quoted

On 2020/2/11 上午12:55, Anton Ivanov wrote:

quoted

On 09/12/2019 10:48, anton.ivanov@cambridgegreys.com wrote:

quoted

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?

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