[PATCH net v9 0/2] virtio-net: fix for VIRTIO_NET_F_GUEST_HDRLEN

[PATCH net v9 0/2] virtio-net: fix for VIRTIO_NET_F_GUEST_HDRLEN

[Xuan Zhuo]

v9:
  1. Introduce new helpers to set hdr len, and virtio_net_hdr_tnl_from_skb
  calls them directly.

v8:
  1. move changes of virtio_net_hdr_from_skb for udp tunnel to #2
  2. remove change for num_sg

v7:
  1. fix bug reported by robot
  2. Still splitting into two commits, as the issues fixed originate from
     different commits. This separation makes it easier to selectively revert to
     previous versions.

v6:
  1. rename to guest_hdrlen
  2. introduce a function virtio_net_set_hdrlen to set the 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





Xuan Zhuo (2):
  virtio-net: correct hdr_len handling for VIRTIO_NET_F_GUEST_HDRLEN
  virtio-net: correct hdr_len handling for tunnel gso

 drivers/net/tun_vnet.h     |  2 +-
 drivers/net/virtio_net.c   |  6 ++++-
 include/linux/virtio_net.h | 51 +++++++++++++++++++++++++++++++++++---
 3 files changed, 53 insertions(+), 6 deletions(-)

--
2.32.0.3.g01195cf9f

[PATCH net v9 1/2] virtio-net: correct hdr_len handling for VIRTIO_NET_F_GUEST_HDRLEN

[Xuan Zhuo]

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   |  6 +++++-
 include/linux/virtio_net.h | 33 +++++++++++++++++++++++++++++----
 3 files changed, 35 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..48de4a16a96a 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -207,6 +207,22 @@ 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 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 +401,8 @@ 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 +411,17 @@ 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)
-- 
2.32.0.3.g01195cf9f

[PATCH net v9 2/2] virtio-net: correct hdr_len handling for tunnel gso

[Xuan Zhuo]

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>
---
 include/linux/virtio_net.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 48de4a16a96a..0fe69876d839 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -223,6 +223,21 @@ static inline void virtio_net_set_hdrlen(const struct sk_buff *skb,
 	hdr->hdr_len = __cpu_to_virtio16(little_endian, hdr_len);
 }
 
+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_le16(hdr_len);
+}
+
 static inline int virtio_net_hdr_from_skb(const struct sk_buff *skb,
 					  struct virtio_net_hdr *hdr,
 					  bool little_endian,
@@ -439,6 +454,9 @@ 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
-- 
2.32.0.3.g01195cf9f

Re: [PATCH net v9 2/2] virtio-net: correct hdr_len handling for tunnel gso

[kernel test robot]

Hi Xuan,

kernel test robot noticed the following build warnings:

[auto build test WARNING on net/main]

url:    https://github.com/intel-lab-lkp/linux/commits/Xuan-Zhuo/virtio-net-correct-hdr_len-handling-for-VIRTIO_NET_F_GUEST_HDRLEN/20260311-200042
base:   net/main
patch link:    https://lore.kernel.org/r/20260311115414.31243-3-xuanzhuo%40linux.alibaba.com
patch subject: [PATCH net v9 2/2] virtio-net: correct hdr_len handling for tunnel gso
config: i386-randconfig-061-20260312 (https://download.01.org/0day-ci/archive/20260312/202603122214.8Anoxrmq-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
sparse: v0.6.5-rc1
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260312/202603122214.8Anoxrmq-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202603122214.8Anoxrmq-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
   drivers/net/virtio_net.c: note: in included file:
>> include/linux/virtio_net.h:238:22: sparse: sparse: incorrect type in assignment (different base types) @@     expected restricted __virtio16 [usertype] hdr_len @@     got restricted __le16 [usertype] @@
   include/linux/virtio_net.h:238:22: sparse:     expected restricted __virtio16 [usertype] hdr_len
   include/linux/virtio_net.h:238:22: sparse:     got restricted __le16 [usertype]

vim +238 include/linux/virtio_net.h

   225	
   226	static inline void virtio_net_set_tnl_hdrlen(const struct sk_buff *skb,
   227						     struct virtio_net_hdr *hdr)
   228	{
   229		u16 hdr_len;
   230	
   231		hdr_len = skb_inner_transport_offset(skb);
   232	
   233		if (hdr->gso_type == VIRTIO_NET_HDR_GSO_UDP_L4)
   234			hdr_len += sizeof(struct udphdr);
   235		else
   236			hdr_len += inner_tcp_hdrlen(skb);
   237	
 > 238		hdr->hdr_len = cpu_to_le16(hdr_len);
   239	}
   240	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki