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 <xuanzhuo@linux.alibaba.com>
---
 drivers/net/tun_vnet.h     |  2 +-
 drivers/net/virtio_net.c   |  8 +++--
 include/linux/virtio_net.h | 61 ++++++++++++++++++++++++++++++--------
 3 files changed, 56 insertions(+), 15 deletions(-)

diff --git a/drivers/net/tun_vnet.h b/drivers/net/tun_vnet.h
index a5f93b6c4482..fa5cab9d3e55 100644
--- a/drivers/net/tun_vnet.h
+++ b/drivers/net/tun_vnet.h

@@ -244,7 +244,7 @@ tun_vnet_hdr_tnl_from_skb(unsigned int flags,

        if (virtio_net_hdr_tnl_from_skb(skb, tnl_hdr, has_tnl_offload,
                                        tun_vnet_is_little_endian(flags),
-                                       vlan_hlen, true)) {
+                                       vlan_hlen, true, false)) {
                struct virtio_net_hdr_v1 *hdr = &tnl_hdr->hash_hdr.hdr;
                struct skb_shared_info *sinfo = skb_shinfo(skb);

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 72d6a9c6a5a2..1800058c8072 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -3265,9 +3265,13 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb, bool orphan)
        const unsigned char *dest = ((struct ethhdr *)skb->data)->h_dest;
        struct virtnet_info *vi = sq->vq->vdev->priv;
        struct virtio_net_hdr_v1_hash_tunnel *hdr;
-       int num_sg;
        unsigned hdr_len = vi->hdr_len;
+       bool feature_hdrlen;
        bool can_push;
+       int num_sg;

+
+       feature_hdrlen = virtio_has_feature(vi->vdev,
+                                           VIRTIO_NET_F_GUEST_HDRLEN);

        pr_debug("%s: xmit %p %pM\n", vi->dev->name, skb, dest);

@@ -3288,7 +3292,7 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb, bool orphan)

        if (virtio_net_hdr_tnl_from_skb(skb, hdr, vi->tx_tnl,
                                        virtio_is_little_endian(vi->vdev), 0,
-                                       false))
+                                       false, feature_hdrlen))
                return -EPROTO;

        if (vi->mergeable_rx_bufs)

diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 75dabb763c65..d31c9af1f3d6 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h

@@ -207,20 +207,40 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
        return __virtio_net_hdr_to_skb(skb, hdr, little_endian, hdr->gso_type);
 }

-static inline int virtio_net_hdr_from_skb(const struct sk_buff *skb,
-                                         struct virtio_net_hdr *hdr,
-                                         bool little_endian,
-                                         bool has_data_valid,
-                                         int vlan_hlen)
+static inline void virtio_net_set_hdrlen(const struct sk_buff *skb,
+                                        struct virtio_net_hdr *hdr,
+                                        bool little_endian,
+                                        bool feature_hdrlen)
+{
+       u16 hdr_len;
+
+       if (feature_hdrlen) {
+               hdr_len = skb_transport_offset(skb);
+
+               if (hdr->gso_type == VIRTIO_NET_HDR_GSO_UDP_L4)
+                       hdr_len += sizeof(struct udphdr);
+               else
+                       hdr_len += tcp_hdrlen(skb);
+       } else {
+               /* This is a hint as to how much should be linear. */
+               hdr_len = skb_headlen(skb);
+       }
+
+       hdr->hdr_len = __cpu_to_virtio16(little_endian, hdr_len);
+}
+
+static inline int __virtio_net_hdr_from_skb(const struct sk_buff *skb,
+                                           struct virtio_net_hdr *hdr,
+                                           bool little_endian,
+                                           bool has_data_valid,
+                                           bool feature_hdrlen,
+                                           int vlan_hlen)
 {
        memset(hdr, 0, sizeof(*hdr));   /* no info leak */

        if (skb_is_gso(skb)) {
                struct skb_shared_info *sinfo = skb_shinfo(skb);

-               /* This is a hint as to how much should be linear. */
-               hdr->hdr_len = __cpu_to_virtio16(little_endian,
-                                                skb_headlen(skb));
                hdr->gso_size = __cpu_to_virtio16(little_endian,
                                                  sinfo->gso_size);
                if (sinfo->gso_type & SKB_GSO_TCPV4)

@@ -231,6 +251,10 @@ static inline int virtio_net_hdr_from_skb(const struct sk_buff *skb,
                        hdr->gso_type = VIRTIO_NET_HDR_GSO_UDP_L4;
                else
                        return -EINVAL;
+
+               virtio_net_set_hdrlen(skb, hdr, little_endian,
+                                     feature_hdrlen);
+
                if (sinfo->gso_type & SKB_GSO_TCP_ECN)
                        hdr->gso_type |= VIRTIO_NET_HDR_GSO_ECN;
        } else

@@ -250,6 +274,16 @@ static inline int virtio_net_hdr_from_skb(const struct sk_buff *skb,
        return 0;
 }

+static inline int virtio_net_hdr_from_skb(const struct sk_buff *skb,
+                                         struct virtio_net_hdr *hdr,
+                                         bool little_endian,
+                                         bool has_data_valid,
+                                         int vlan_hlen)
+{
+       return __virtio_net_hdr_from_skb(skb, hdr, little_endian,
+                                        has_data_valid, false, vlan_hlen);
+}
+
 static inline unsigned int virtio_l3min(bool is_ipv6)
 {
        return is_ipv6 ? sizeof(struct ipv6hdr) : sizeof(struct iphdr);

@@ -385,7 +419,8 @@ virtio_net_hdr_tnl_from_skb(const struct sk_buff *skb,
                            bool tnl_hdr_negotiated,
                            bool little_endian,
                            int vlan_hlen,
-                           bool has_data_valid)
+                           bool has_data_valid,
+                           bool feature_hdrlen)
 {
        struct virtio_net_hdr *hdr = (struct virtio_net_hdr *)vhdr;
        unsigned int inner_nh, outer_th;

@@ -395,8 +430,9 @@ virtio_net_hdr_tnl_from_skb(const struct sk_buff *skb,
        tnl_gso_type = skb_shinfo(skb)->gso_type & (SKB_GSO_UDP_TUNNEL |
                                                    SKB_GSO_UDP_TUNNEL_CSUM);
        if (!tnl_gso_type)
-               return virtio_net_hdr_from_skb(skb, hdr, little_endian,
-                                              has_data_valid, vlan_hlen);
+               return __virtio_net_hdr_from_skb(skb, hdr, little_endian,
+                                                has_data_valid,
+                                                feature_hdrlen, vlan_hlen);

        /* Tunnel support not negotiated but skb ask for it. */
        if (!tnl_hdr_negotiated)

@@ -409,7 +445,8 @@ virtio_net_hdr_tnl_from_skb(const struct sk_buff *skb,

        /* Let the basic parsing deal with plain GSO features. */
        skb_shinfo(skb)->gso_type &= ~tnl_gso_type;
-       ret = virtio_net_hdr_from_skb(skb, hdr, true, false, vlan_hlen);
+       ret = __virtio_net_hdr_from_skb(skb, hdr, true, false,
+                                       feature_hdrlen, vlan_hlen);