virtio-net: correct hdr_len handling for tunnel gso

The commit a2fb4bc4e2a6a03 ("net: implement virtio helpers to handle UDP
GSO tunneling.") introduces support for the UDP GSO tunnel feature in
virtio-net.

The virtio spec says:

    If the \field{gso_type} has the VIRTIO_NET_HDR_GSO_UDP_TUNNEL_IPV4 bit or
    VIRTIO_NET_HDR_GSO_UDP_TUNNEL_IPV6 bit set, \field{hdr_len} accounts for
    all the headers up to and including the inner transport.

The commit did not update the hdr_len to include the inner transport.

I observed that the "hdr_len" is 116 for this packet:

    17:36:18.241105 52:55:00:d1:27:0a > 2e:2c:df:46:a9:e1, ethertype IPv4 (0x0800), length 2912: (tos 0x0, ttl 64, id 45197, offset 0, flags [none], proto UDP (17), length 2898)
        192.168.122.100.50613 > 192.168.122.1.4789: [bad udp cksum 0x8106 -> 0x26a0!] VXLAN, flags [I] (0x08), vni 1
    fa:c3:ba:82:05:ee > ce:85:0c:31:77:e5, ethertype IPv4 (0x0800), length 2862: (tos 0x0, ttl 64, id 14678, offset 0, flags [DF], proto TCP (6), length 2848)
        192.168.3.1.49880 > 192.168.3.2.9898: Flags [P.], cksum 0x9266 (incorrect -> 0xaa20), seq 515667:518463, ack 1, win 64, options [nop,nop,TS val 2990048824 ecr 2798801412], length 2796

116 = 14(mac) + 20(ip) + 8(udp) + 8(vxlan) + 14(inner mac) + 20(inner ip) + 32(innner tcp)

Fixes: a2fb4bc4e2a6a03 ("net: implement virtio helpers to handle UDP GSO tunneling.")
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Link: https://patch.msgid.link/20260320021818.111741-3-xuanzhuo@linux.alibaba.com
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 361b60c8be68029bf88fa3a1cb02caddb1dbcdfd..f36d21b5bc19e217f73f93538afc1bf55eadfcb6 100644 (file)
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -224,6 +224,22 @@ static inline void __virtio_net_set_hdrlen(const struct sk_buff *skb,
        hdr->hdr_len = __cpu_to_virtio16(little_endian, hdr_len);
 }
 
+/* This function must be called after virtio_net_hdr_from_skb(). */
+static inline void __virtio_net_set_tnl_hdrlen(const struct sk_buff *skb,
+                                              struct virtio_net_hdr *hdr)
+{
+       u16 hdr_len;
+
+       hdr_len = skb_inner_transport_offset(skb);
+
+       if (hdr->gso_type == VIRTIO_NET_HDR_GSO_UDP_L4)
+               hdr_len += sizeof(struct udphdr);
+       else
+               hdr_len += inner_tcp_hdrlen(skb);
+
+       hdr->hdr_len = __cpu_to_virtio16(true, hdr_len);
+}
+
 static inline int virtio_net_hdr_from_skb(const struct sk_buff *skb,
                                          struct virtio_net_hdr *hdr,
                                          bool little_endian,
@@ -440,6 +456,9 @@ virtio_net_hdr_tnl_from_skb(const struct sk_buff *skb,
        if (ret)
                return ret;
 
+       if (feature_hdrlen && hdr->hdr_len)
+               __virtio_net_set_tnl_hdrlen(skb, hdr);
+
        if (skb->protocol == htons(ETH_P_IPV6))
                hdr->gso_type |= VIRTIO_NET_HDR_GSO_UDP_TUNNEL_IPV6;
        else