041-ubnt-protection-from-routing-loops.patch

diff --git a/src/device.c b/src/device.c
index c673446..25aac06 100644
--- a/src/device.c
+++ b/src/device.c
@@ -127,14 +127,26 @@ static netdev_tx_t wg_xmit(struct sk_buff *skb, struct net_device *dev)
 	struct sk_buff_head packets;
 	struct wg_peer *peer;
 	struct sk_buff *next;
 	sa_family_t family;
 	u32 mtu;
 	int ret;
 
+	if (unlikely(skb->mark & wg->fwmark)) {
+		ret = -ENETDOWN;
+		net_crit_ratelimited("%s: loop detected, dropping skb of length %u\n", dev->name, skb->len);
+		goto err;
+	}
+
+	if (unlikely(skb_end_offset(skb) > 33000)) {
+		ret = -ENETDOWN;
+		net_crit_ratelimited("%s: possible loop detected, dropping skb of size %u\n", dev->name, skb_end_offset(skb));
+		goto err;
+	}
+
 	if (unlikely(!wg_check_packet_protocol(skb))) {
 		ret = -EPROTONOSUPPORT;
 		net_dbg_ratelimited("%s: Invalid IP packet\n", dev->name);
 		goto err;
 	}
 
 	peer = wg_allowedips_lookup_dst(&wg->peer_allowedips, skb);