arp: Return ERR_MEM on ARP queue full

Root Cause:
When the ARP cache table is filled, when a new packet comes in, the ARP cache table will be emptied.
Solution:
If the ARP cache table is full, ERR_MEM is returned.

picked from 602d25c5
Ref IDF-4849

.github/workflows/ci-linux.yml

@@ -48,8 +48,9 @@ jobs:
       run: |
         cp ${CONTRIB}/examples/example_app/lwipcfg.h.example ${CONTRIB}/examples/example_app/lwipcfg.h
         cd ${CONTRIB}/ports/unix/example_app
-        export CFLAGS="-DESP_LWIP=LWIP_NETCONN_FULLDUPLEX -DESP_LWIP_IGMP_TIMERS_ONDEMAND=ESP_LWIP -DESP_LWIP_MLD6_TIMERS_ONDEMAND=ESP_LWIP -DESP_DNS=ESP_LWIP"
+        export CFLAGS="-DESP_LWIP=LWIP_NETCONN_FULLDUPLEX -DESP_LWIP_IGMP_TIMERS_ONDEMAND=ESP_LWIP -DESP_LWIP_MLD6_TIMERS_ONDEMAND=ESP_LWIP -DESP_DNS=ESP_LWIP -DESP_LWIP_ARP=ESP_LWIP"
         export LWIPDIR=../../../../src/
+        make TESTFLAGS="-Wno-documentation" -j 4
         chmod +x iteropts.sh && ./iteropts.sh
 
     - name: Build and run unit tests with cmake

src/core/ipv4/etharp.c

@@ -1037,12 +1037,12 @@ etharp_query(struct netif *netif, const ip4_addr_t *ipaddr, struct pbuf *q)
       /* allocate a new arp queue entry */
       new_entry = (struct etharp_q_entry *)memp_malloc(MEMP_ARP_QUEUE);
       if (new_entry != NULL) {
+        struct etharp_q_entry *r;
         unsigned int qlen = 0;
         new_entry->next = 0;
         new_entry->p = p;
         if (arp_table[i].q != NULL) {
           /* queue was already existent, append the new entry to the end */
-          struct etharp_q_entry *r;
           r = arp_table[i].q;
           qlen++;
           while (r->next != NULL) {
@@ -1056,11 +1056,19 @@ etharp_query(struct netif *netif, const ip4_addr_t *ipaddr, struct pbuf *q)
         }
 #if ARP_QUEUE_LEN
         if (qlen >= ARP_QUEUE_LEN) {
+#if ESP_LWIP_ARP 
+          r->next = NULL;
+          pbuf_free(new_entry->p);
+          memp_free(MEMP_ARP_QUEUE, new_entry);
+          LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: could not queue the packet %p (queue is full)\n", (void *)q));
+          return ERR_MEM;
+#else
           struct etharp_q_entry *old;
           old = arp_table[i].q;
           arp_table[i].q = arp_table[i].q->next;
           pbuf_free(old->p);
           memp_free(MEMP_ARP_QUEUE, old);
+#endif
         }
 #endif
         LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: queued packet %p on ARP entry %"U16_F"\n", (void *)q, i));