Merge branch 'virtio-net-fix-for-virtio_net_f_guest_hdrlen'

Xuan Zhuo says:

====================
virtio-net: fix 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 path set fixes that issue.

As discussed in [0], this version checks the VIRTIO_NET_F_GUEST_HDRLEN is
negotiated.

[0]: http://lore.kernel.org/all/20251029030913.20423-1-xuanzhuo@linux.alibaba.com

v10: fix http://lore.kernel.org/all/202603122214.8Anoxrmq-lkp@intel.com
====================

Link: https://patch.msgid.link/20260320021818.111741-1-xuanzhuo@linux.alibaba.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

3 files changed, 55 insertions, 6 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..7106333ef904 100644
--- 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 75dabb763c65..f36d21b5bc19 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -207,6 +207,39 @@ 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);
+}
+
+/* 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,
@@ -385,7 +418,8 @@ 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 +428,17 @@ 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)
@@ -414,6 +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