net: arp: Use proper dest hw address after receiving a request

If a packet is received with Ethernet source address different
from ARP's sender hardware address field, then DUT must use the
latter address in response packets.

Fixes #16098

Signed-off-by: Jukka Rissanen <[email protected]>

Author: jukkar

subsys/net/l2/ethernet/arp.c

@@ -440,6 +440,23 @@ static void arp_update(struct net_if *iface,
 			if (entry) {
 				memcpy(&entry->eth, hwaddr,
 				       sizeof(struct net_eth_addr));
+			} else {
+				/* Add new entry as it was not found and force
+				 * was set.
+				 */
+				entry = arp_entry_get_free();
+				if (!entry) {
+					/* Then let's take one from table? */
+					entry = arp_entry_get_last_from_table();
+				}
+
+				if (entry) {
+					entry->req_start = k_uptime_get();
+					entry->iface = iface;
+					net_ipaddr_copy(&entry->ip, src);
+					memcpy(&entry->eth, hwaddr, sizeof(entry->eth));
+					sys_slist_prepend(&arp_table, &entry->node);
+				}
 			}
 		}
 
@@ -468,7 +485,8 @@ static void arp_update(struct net_if *iface,
 
 static inline struct net_pkt *arp_prepare_reply(struct net_if *iface,
 						struct net_pkt *req,
-						struct net_eth_hdr *eth_query)
+						struct net_eth_hdr *eth_query,
+						struct net_eth_addr *dst_addr)
 {
 	struct net_arp_hdr *hdr, *query;
 	struct net_pkt *pkt;
@@ -492,7 +510,7 @@ static inline struct net_pkt *arp_prepare_reply(struct net_if *iface,
 	hdr->protolen = sizeof(struct in_addr);
 	hdr->opcode = htons(NET_ARP_REPLY);
 
-	memcpy(&hdr->dst_hwaddr.addr, &eth_query->src.addr,
+	memcpy(&hdr->dst_hwaddr.addr, &dst_addr->addr,
 	       sizeof(struct net_eth_addr));
 	memcpy(&hdr->src_hwaddr.addr, net_if_get_link_addr(iface)->addr,
 	       sizeof(struct net_eth_addr));
@@ -526,6 +544,7 @@ static bool arp_hdr_check(struct net_arp_hdr *arp_hdr)
 enum net_verdict net_arp_input(struct net_pkt *pkt,
 			       struct net_eth_hdr *eth_hdr)
 {
+	struct net_eth_addr *dst_hw_addr;
 	struct net_arp_hdr *arp_hdr;
 	struct net_pkt *reply;
 	struct in_addr *addr;
@@ -594,9 +613,7 @@ enum net_verdict net_arp_input(struct net_pkt *pkt,
 		 * changed. In this case the target MAC address is all zeros
 		 * and the target IP address is our address.
 		 */
-		if (memcmp(&eth_hdr->src, &arp_hdr->src_hwaddr,
-			   sizeof(struct net_eth_addr)) == 0 &&
-		    net_eth_is_addr_unspecified(&arp_hdr->dst_hwaddr)) {
+		if (net_eth_is_addr_unspecified(&arp_hdr->dst_hwaddr)) {
 			NET_DBG("Updating ARP cache for %s [%s]",
 				log_strdup(net_sprint_ipv4_addr(
 						 &arp_hdr->src_ipaddr)),
@@ -608,10 +625,15 @@ enum net_verdict net_arp_input(struct net_pkt *pkt,
 				   &arp_hdr->src_ipaddr,
 				   &arp_hdr->src_hwaddr,
 				   false, true);
+
+			dst_hw_addr = &arp_hdr->src_hwaddr;
+		} else {
+			dst_hw_addr = &eth_hdr->src;
 		}
 
 		/* Send reply */
-		reply = arp_prepare_reply(net_pkt_iface(pkt), pkt, eth_hdr);
+		reply = arp_prepare_reply(net_pkt_iface(pkt), pkt, eth_hdr,
+					  dst_hw_addr);
 		if (reply) {
 			net_if_queue_tx(net_pkt_iface(reply), reply);
 		} else {