diff --git a/include/net/addrconf.h b/include/net/addrconf.h
index fb314de2b61ba228059b1f09cb916d7d275a6a9b..86505bfa5d2c4829698d21ce81ba47575b504941 100644
--- a/include/net/addrconf.h
+++ b/include/net/addrconf.h
@@ -67,6 +67,10 @@ int ipv6_chk_addr(struct net *net, const struct in6_addr *addr,
 int ipv6_chk_home_addr(struct net *net, const struct in6_addr *addr);
 #endif
 
+bool ipv6_chk_custom_prefix(const struct in6_addr *addr,
+				   const unsigned int prefix_len,
+				   struct net_device *dev);
+
 int ipv6_chk_prefix(const struct in6_addr *addr, struct net_device *dev);
 
 struct inet6_ifaddr *ipv6_get_ifaddr(struct net *net,
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index d6ff12617f36f9eabbf7c9744b3b8121a567c1bf..a0c3abe724612ffa6fed1d4b820e60a80b0f0a2f 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -1499,6 +1499,33 @@ static bool ipv6_chk_same_addr(struct net *net, const struct in6_addr *addr,
 	return false;
 }
 
+/* Compares an address/prefix_len with addresses on device @dev.
+ * If one is found it returns true.
+ */
+bool ipv6_chk_custom_prefix(const struct in6_addr *addr,
+	const unsigned int prefix_len, struct net_device *dev)
+{
+	struct inet6_dev *idev;
+	struct inet6_ifaddr *ifa;
+	bool ret = false;
+
+	rcu_read_lock();
+	idev = __in6_dev_get(dev);
+	if (idev) {
+		read_lock_bh(&idev->lock);
+		list_for_each_entry(ifa, &idev->addr_list, if_list) {
+			ret = ipv6_prefix_equal(addr, &ifa->addr, prefix_len);
+			if (ret)
+				break;
+		}
+		read_unlock_bh(&idev->lock);
+	}
+	rcu_read_unlock();
+
+	return ret;
+}
+EXPORT_SYMBOL(ipv6_chk_custom_prefix);
+
 int ipv6_chk_prefix(const struct in6_addr *addr, struct net_device *dev)
 {
 	struct inet6_dev *idev;
diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index 7ee5cb96db348ab5c75946e77d3068c3c447ba17..afd5605aea7c9aca5b373291b3f3a00bd2c85157 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -566,6 +566,70 @@ static inline bool is_spoofed_6rd(struct ip_tunnel *tunnel, const __be32 v4addr,
 	return false;
 }
 
+/* Checks if an address matches an address on the tunnel interface.
+ * Used to detect the NAT of proto 41 packets and let them pass spoofing test.
+ * Long story:
+ * This function is called after we considered the packet as spoofed
+ * in is_spoofed_6rd.
+ * We may have a router that is doing NAT for proto 41 packets
+ * for an internal station. Destination a.a.a.a/PREFIX:bbbb:bbbb
+ * will be translated to n.n.n.n/PREFIX:bbbb:bbbb. And is_spoofed_6rd
+ * function will return true, dropping the packet.
+ * But, we can still check if is spoofed against the IP
+ * addresses associated with the interface.
+ */
+static bool only_dnatted(const struct ip_tunnel *tunnel,
+	const struct in6_addr *v6dst)
+{
+	int prefix_len;
+
+#ifdef CONFIG_IPV6_SIT_6RD
+	prefix_len = tunnel->ip6rd.prefixlen + 32
+		- tunnel->ip6rd.relay_prefixlen;
+#else
+	prefix_len = 48;
+#endif
+	return ipv6_chk_custom_prefix(v6dst, prefix_len, tunnel->dev);
+}
+
+/* Returns true if a packet is spoofed */
+static bool packet_is_spoofed(struct sk_buff *skb,
+			      const struct iphdr *iph,
+			      struct ip_tunnel *tunnel)
+{
+	const struct ipv6hdr *ipv6h;
+
+	if (tunnel->dev->priv_flags & IFF_ISATAP) {
+		if (!isatap_chksrc(skb, iph, tunnel))
+			return true;
+
+		return false;
+	}
+
+	if (tunnel->dev->flags & IFF_POINTOPOINT)
+		return false;
+
+	ipv6h = ipv6_hdr(skb);
+
+	if (unlikely(is_spoofed_6rd(tunnel, iph->saddr, &ipv6h->saddr))) {
+		net_warn_ratelimited("Src spoofed %pI4/%pI6c -> %pI4/%pI6c\n",
+				     &iph->saddr, &ipv6h->saddr,
+				     &iph->daddr, &ipv6h->daddr);
+		return true;
+	}
+
+	if (likely(!is_spoofed_6rd(tunnel, iph->daddr, &ipv6h->daddr)))
+		return false;
+
+	if (only_dnatted(tunnel, &ipv6h->daddr))
+		return false;
+
+	net_warn_ratelimited("Dst spoofed %pI4/%pI6c -> %pI4/%pI6c\n",
+			     &iph->saddr, &ipv6h->saddr,
+			     &iph->daddr, &ipv6h->daddr);
+	return true;
+}
+
 static int ipip6_rcv(struct sk_buff *skb)
 {
 	const struct iphdr *iph = ip_hdr(skb);
@@ -586,19 +650,9 @@ static int ipip6_rcv(struct sk_buff *skb)
 		IPCB(skb)->flags = 0;
 		skb->protocol = htons(ETH_P_IPV6);
 
-		if (tunnel->dev->priv_flags & IFF_ISATAP) {
-			if (!isatap_chksrc(skb, iph, tunnel)) {
-				tunnel->dev->stats.rx_errors++;
-				goto out;
-			}
-		} else if (!(tunnel->dev->flags&IFF_POINTOPOINT)) {
-			if (is_spoofed_6rd(tunnel, iph->saddr,
-					   &ipv6_hdr(skb)->saddr) ||
-			    is_spoofed_6rd(tunnel, iph->daddr,
-					   &ipv6_hdr(skb)->daddr)) {
-				tunnel->dev->stats.rx_errors++;
-				goto out;
-			}
+		if (packet_is_spoofed(skb, iph, tunnel)) {
+			tunnel->dev->stats.rx_errors++;
+			goto out;
 		}
 
 		__skb_tunnel_rx(skb, tunnel->dev, tunnel->net);
@@ -748,7 +802,7 @@ static netdev_tx_t ipip6_tunnel_xmit(struct sk_buff *skb,
 			neigh = dst_neigh_lookup(skb_dst(skb), &iph6->daddr);
 
 		if (neigh == NULL) {
-			net_dbg_ratelimited("sit: nexthop == NULL\n");
+			net_dbg_ratelimited("nexthop == NULL\n");
 			goto tx_error;
 		}
 
@@ -777,7 +831,7 @@ static netdev_tx_t ipip6_tunnel_xmit(struct sk_buff *skb,
 			neigh = dst_neigh_lookup(skb_dst(skb), &iph6->daddr);
 
 		if (neigh == NULL) {
-			net_dbg_ratelimited("sit: nexthop == NULL\n");
+			net_dbg_ratelimited("nexthop == NULL\n");
 			goto tx_error;
 		}