virtio-net: correct hdr_len handling for VIRTIO_NET_F_GUEST_HDRLEN

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>
Link: https://patch.msgid.link/20260320021818.111741-2-xuanzhuo@linux.alibaba.com
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/drivers/net/tun_vnet.h b/drivers/net/tun_vnet.h
index a5f93b6c4482c318679a44dadbb2cc34b70bbd90..fa5cab9d3e55c5a6e70afe4c76582c8affe0b73c 100644 (file)
--- 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 72d6a9c6a5a24f56e03ee2a7488057078e0e645a..7106333ef90481fe169aa7f6982eb41454aa8fd5 100644 (file)
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3267,8 +3267,12 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb, bool orphan)
        struct virtio_net_hdr_v1_hash_tunnel *hdr;
        int num_sg;
        unsigned hdr_len = vi->hdr_len;
+       bool feature_hdrlen;
        bool can_push;
 
+       feature_hdrlen = virtio_has_feature(vi->vdev,
+                                           VIRTIO_NET_F_GUEST_HDRLEN);
+
        pr_debug("%s: xmit %p %pM\n", vi->dev->name, skb, dest);
 
        /* Make sure it's safe to cast between formats */
@@ -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 75dabb763c650478844950f9a8b92edcde48abf0..361b60c8be68029bf88fa3a1cb02caddb1dbcdfd 100644 (file)
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -207,6 +207,23 @@ 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);
 }
 
+/* This function must be called after virtio_net_hdr_from_skb(). */
+static inline void __virtio_net_set_hdrlen(const struct sk_buff *skb,
+                                          struct virtio_net_hdr *hdr,
+                                          bool little_endian)
+{
+       u16 hdr_len;
+
+       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);
+
+       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,
@@ -385,7 +402,8 @@ 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;
@@ -394,9 +412,17 @@ 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);
+       if (!tnl_gso_type) {
+               ret = virtio_net_hdr_from_skb(skb, hdr, little_endian,
+                                             has_data_valid, vlan_hlen);
+               if (ret)
+                       return ret;
+
+               if (feature_hdrlen && hdr->hdr_len)
+                       __virtio_net_set_hdrlen(skb, hdr, little_endian);
+
+               return ret;
+       }
 
        /* Tunnel support not negotiated but skb ask for it. */
        if (!tnl_hdr_negotiated)