Subject: [PATCH v2 nf] netfilter: nf_flow_table_ip: Introduce nf_flow_vlan_push()

From: Eric Woudstra <[email-masked]>
Date: Tue, 14 Apr 2026 13:21:20 +0200

Calling skb_reset_mac_header() before calling skb_vlan_push() does
remove the error:

"skb_vlan_push got skb with skb->data not at mac header (offset 18)"

But the inner vlan tag is still not inserted correctly.

skb_vlan_push() uses __vlan_insert_inner_tag() to insert the tag
at offset ETH_HLEN. But the inner tag should only be pushed, without
offset, similar to nf_flow_pppoe_push().

Fixes: c653d5a78f34 ("netfilter: flowtable: inline vlan encapsulation in xmit path")
Fixes: a3aca98aec9a ("netfilter: nf_flow_table_ip: reset mac header before vlan push")
Signed-off-by: Eric Woudstra <[email-masked]>

---

 net/netfilter/nf_flow_table_ip.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/nf_flow_table_ip.c b/net/netfilter/nf_flow_table_ip.c
index fd56d663cb5b..0086f8a1a0d6 100644
--- a/net/netfilter/nf_flow_table_ip.c
+++ b/net/netfilter/nf_flow_table_ip.c
@@ -544,6 +544,26 @@ static int nf_flow_offload_forward(struct nf_flowtable_ctx *ctx,
 	return 1;
 }
 
+static int nf_flow_vlan_push(struct sk_buff *skb, __be16 proto, u16 id)
+{
+	if (skb_vlan_tag_present(skb)) {
+		struct vlan_hdr *vhdr;
+
+		if (skb_cow_head(skb, VLAN_HLEN))
+			return -1;
+
+		__skb_push(skb, VLAN_HLEN);
+		skb_reset_network_header(skb);
+		vhdr = (struct vlan_hdr *)(skb->data);
+		vhdr->h_vlan_TCI = htons(id);
+		vhdr->h_vlan_encapsulated_proto = skb->protocol;
+		skb->protocol = proto;
+	} else {
+		__vlan_hwaccel_put_tag(skb, proto, id);
+	}
+	return 0;
+}
+
 static int nf_flow_pppoe_push(struct sk_buff *skb, u16 id)
 {
 	int data_len = skb->len + sizeof(__be16);
@@ -738,9 +758,8 @@ static int nf_flow_encap_push(struct sk_buff *skb,
 		switch (tuple->encap[i].proto) {
 		case htons(ETH_P_8021Q):
 		case htons(ETH_P_8021AD):
-			skb_reset_mac_header(skb);
-			if (skb_vlan_push(skb, tuple->encap[i].proto,
-					  tuple->encap[i].id) < 0)
+			if (nf_flow_vlan_push(skb, tuple->encap[i].proto,
+					      tuple->encap[i].id) < 0)
 				return -1;
 			break;
 		case htons(ETH_P_PPP_SES):
-- 
2.53.0