--- zzzz-none-000/linux-4.4.271/net/l2tp/l2tp_eth.c	2021-06-03 06:22:09.000000000 +0000
+++ hawkeye-5590-750/linux-4.4.271/net/l2tp/l2tp_eth.c	2023-04-19 10:22:30.000000000 +0000
@@ -87,7 +87,11 @@
 	struct l2tp_eth *priv = netdev_priv(dev);
 	struct l2tp_session *session = priv->session;
 	unsigned int len = skb->len;
-	int ret = l2tp_xmit_skb(session, skb, session->hdr_len);
+	int ret;
+
+	skb->skb_iif = dev->ifindex;
+
+	ret = l2tp_xmit_skb(session, skb, session->hdr_len);
 
 	if (likely(ret == NET_XMIT_SUCCESS)) {
 		atomic_long_add(len, &priv->tx_bytes);
@@ -125,6 +129,7 @@
 {
 	ether_setup(dev);
 	dev->priv_flags		&= ~IFF_TX_SKB_SHARING;
+	dev->priv_flags_ext	|= IFF_EXT_PPP_L2TPV3;
 	dev->features		|= NETIF_F_LLTX;
 	dev->netdev_ops		= &l2tp_eth_netdev_ops;
 	dev->destructor		= free_netdev;
@@ -156,13 +161,15 @@
 	skb->ip_summed = CHECKSUM_NONE;
 
 	skb_dst_drop(skb);
-	nf_reset(skb);
+	nf_reset_no_generic_ct(skb);
 
 	rcu_read_lock();
 	dev = rcu_dereference(spriv->dev);
 	if (!dev)
 		goto error_rcu;
 
+	skb->skb_iif = dev->ifindex;
+
 	priv = netdev_priv(dev);
 	if (dev_forward_skb(dev, skb) == NET_RX_SUCCESS) {
 		atomic_long_inc(&priv->rx_packets);