[nrf fromtree] net: openthread: filter ipv6 fragments

If OPENTHREAD_IP6_FRAGM is enabled the IPv6 fragments are handled in
OpenThread stack but also forwarder unconditionally to the Zephyr
uplayers. It causes additional packets processing and leads to errors
like unrecognized next header type or duplicate ping reply. What more
these errors generate additional traffic which jam channel and decrease
latency for packets required fragmentation.
This commit add filtering IPv6 fragments when data fragmentation and
reassembling is enabled in OpenThread.

Signed-off-by: Lukasz Maciejonczyk <[email protected]>
(cherry picked from commit c9effd0)

Author: lmaciejonczyk

subsys/net/l2/openthread/openthread.c

@@ -297,8 +297,20 @@ static void openthread_process(struct k_work *work)
 	openthread_api_mutex_unlock(ot_context);
 }
 
-static enum net_verdict openthread_recv(struct net_if *iface,
-					struct net_pkt *pkt)
+static bool is_ipv6_frag(struct net_pkt *pkt)
+{
+	NET_PKT_DATA_ACCESS_CONTIGUOUS_DEFINE(ipv6_access, struct net_ipv6_hdr);
+	struct net_ipv6_hdr *hdr;
+
+	hdr = (struct net_ipv6_hdr *)net_pkt_get_data(pkt, &ipv6_access);
+	if (!hdr) {
+		return false;
+	}
+
+	return hdr->nexthdr == NET_IPV6_NEXTHDR_FRAG ? true : false;
+}
+
+static enum net_verdict openthread_recv(struct net_if *iface, struct net_pkt *pkt)
 {
 	struct openthread_context *ot_context = net_if_l2_data(iface);
 
@@ -310,6 +322,10 @@ static enum net_verdict openthread_recv(struct net_if *iface,
 			net_pkt_hexdump(pkt, "Injected IPv6 packet");
 		}
 
+		if (IS_ENABLED(CONFIG_OPENTHREAD_IP6_FRAGM) && is_ipv6_frag(pkt)) {
+			return NET_DROP;
+		}
+
 		return NET_CONTINUE;
 	}