[PATCH net 2/2] virtio-net: correct hdr_len handling for VIRTIO_NET_F_GUEST_HDRLEN

[Xuan Zhuo]

The commit be50da3e9d4a ("net: virtio_net: implement exact header length
guest feature") introduces support for the VIRTIO_NET_F_GUEST_HDRLEN
feature in virtio-net.

This feature requires virtio-net to set hdr_len to the actual header
length of the packet when transmitting, the number of
bytes from the start of the packet to the beginning of the
transport-layer payload.

However, in practice, hdr_len was being set using skb_headlen(skb),
which is clearly incorrect. This commit fixes that issue.

Fixes: be50da3e9d4a ("net: virtio_net: implement exact header length guest 
feature")
Signed-off-by: Xuan Zhuo <xuanz...@linux.alibaba.com>
---
 include/linux/virtio_net.h | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 20e0584db1dd..4273420a9ff9 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -217,20 +217,25 @@ static inline int virtio_net_hdr_from_skb(const struct 
sk_buff *skb,
 
        if (skb_is_gso(skb)) {
                struct skb_shared_info *sinfo = skb_shinfo(skb);
+               u16 hdr_len;
 
-               /* This is a hint as to how much should be linear. */
-               hdr->hdr_len = __cpu_to_virtio16(little_endian,
-                                                skb_headlen(skb));
+               hdr_len = skb_transport_offset(skb);
                hdr->gso_size = __cpu_to_virtio16(little_endian,
                                                  sinfo->gso_size);
-               if (sinfo->gso_type & SKB_GSO_TCPV4)
+               if (sinfo->gso_type & SKB_GSO_TCPV4) {
                        hdr->gso_type = VIRTIO_NET_HDR_GSO_TCPV4;
-               else if (sinfo->gso_type & SKB_GSO_TCPV6)
+                       hdr_len += tcp_hdrlen(skb);
+               } else if (sinfo->gso_type & SKB_GSO_TCPV6) {
                        hdr->gso_type = VIRTIO_NET_HDR_GSO_TCPV6;
-               else if (sinfo->gso_type & SKB_GSO_UDP_L4)
+                       hdr_len += tcp_hdrlen(skb);
+               } else if (sinfo->gso_type & SKB_GSO_UDP_L4) {
                        hdr->gso_type = VIRTIO_NET_HDR_GSO_UDP_L4;
-               else
+                       hdr_len += sizeof(struct udphdr);
+               } else {
                        return -EINVAL;
+               }
+
+               hdr->hdr_len = __cpu_to_virtio16(little_endian, hdr_len);
                if (sinfo->gso_type & SKB_GSO_TCP_ECN)
                        hdr->gso_type |= VIRTIO_NET_HDR_GSO_ECN;
        } else
-- 
2.32.0.3.g01195cf9f