--- zzzz-none-000/linux-4.4.60/net/l2tp/l2tp_eth.c	2017-04-08 07:53:53.000000000 +0000
+++ hawkeye-5590-729/linux-4.4.60/net/l2tp/l2tp_eth.c	2022-03-30 14:21:53.000000000 +0000
@@ -95,7 +95,11 @@
 	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);
@@ -133,6 +137,7 @@
 {
 	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;
@@ -164,7 +169,9 @@
 	skb->ip_summed = CHECKSUM_NONE;
 
 	skb_dst_drop(skb);
-	nf_reset(skb);
+	nf_reset_no_generic_ct(skb);
+
+	skb->skb_iif = dev->ifindex;
 
 	if (dev_forward_skb(dev, skb) == NET_RX_SUCCESS) {
 		atomic_long_inc(&priv->rx_packets);
@@ -223,12 +230,6 @@
 		goto out;
 	}
 
-	session = l2tp_session_find(net, tunnel, session_id);
-	if (session) {
-		rc = -EEXIST;
-		goto out;
-	}
-
 	if (cfg->ifname) {
 		dev = dev_get_by_name(net, cfg->ifname);
 		if (dev) {
@@ -242,8 +243,8 @@
 
 	session = l2tp_session_create(sizeof(*spriv), tunnel, session_id,
 				      peer_session_id, cfg);
-	if (!session) {
-		rc = -ENOMEM;
+	if (IS_ERR(session)) {
+		rc = PTR_ERR(session);
 		goto out;
 	}