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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>

authored by

Xuan Zhuo and committed by
Paolo Abeni 6c860dc0 38ec410b

+19
+19
include/linux/virtio_net.h
··· 224 224 hdr->hdr_len = __cpu_to_virtio16(little_endian, hdr_len); 225 225 } 226 226 227 + /* This function must be called after virtio_net_hdr_from_skb(). */ 228 + static inline void __virtio_net_set_tnl_hdrlen(const struct sk_buff *skb, 229 + struct virtio_net_hdr *hdr) 230 + { 231 + u16 hdr_len; 232 + 233 + hdr_len = skb_inner_transport_offset(skb); 234 + 235 + if (hdr->gso_type == VIRTIO_NET_HDR_GSO_UDP_L4) 236 + hdr_len += sizeof(struct udphdr); 237 + else 238 + hdr_len += inner_tcp_hdrlen(skb); 239 + 240 + hdr->hdr_len = __cpu_to_virtio16(true, hdr_len); 241 + } 242 + 227 243 static inline int virtio_net_hdr_from_skb(const struct sk_buff *skb, 228 244 struct virtio_net_hdr *hdr, 229 245 bool little_endian, ··· 455 439 skb_shinfo(skb)->gso_type |= tnl_gso_type; 456 440 if (ret) 457 441 return ret; 442 + 443 + if (feature_hdrlen && hdr->hdr_len) 444 + __virtio_net_set_tnl_hdrlen(skb, hdr); 458 445 459 446 if (skb->protocol == htons(ETH_P_IPV6)) 460 447 hdr->gso_type |= VIRTIO_NET_HDR_GSO_UDP_TUNNEL_IPV6;