etharp.c

lwip-1.4.0

 * @param p The ARP packet that arrived on netif. Is freed by this function.
 *
 * @return NULL
 *
 * @see pbuf_free()
 */
static void
etharp_arp_input(struct netif *netif, struct eth_addr *ethaddr, struct pbuf *p)
{
  struct etharp_hdr *hdr;
  struct eth_hdr *ethhdr;
  /* these are aligned properly, whereas the ARP header fields might not be */
  ip_addr_t sipaddr, dipaddr;
  u8_t for_us;
#if LWIP_AUTOIP
  const u8_t * ethdst_hwaddr;
#endif /* LWIP_AUTOIP */

  LWIP_ERROR("netif != NULL", (netif != NULL), return;);

  /* drop short ARP packets: we have to check for p->len instead of p->tot_len here
     since a struct etharp_hdr is pointed to p->payload, so it musn't be chained! */
  if (p->len < SIZEOF_ETHARP_PACKET) {
    LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
      ("etharp_arp_input: packet dropped, too short (%"S16_F"/%"S16_F")\n", p->tot_len,
      (s16_t)SIZEOF_ETHARP_PACKET));
    ETHARP_STATS_INC(etharp.lenerr);
    ETHARP_STATS_INC(etharp.drop);
    pbuf_free(p);
    return;
  }

  ethhdr = (struct eth_hdr *)p->payload;
  hdr = (struct etharp_hdr *)((u8_t*)ethhdr + SIZEOF_ETH_HDR);
#if ETHARP_SUPPORT_VLAN
  if (ethhdr->type == PP_HTONS(ETHTYPE_VLAN)) {
    hdr = (struct etharp_hdr *)(((u8_t*)ethhdr) + SIZEOF_ETH_HDR + SIZEOF_VLAN_HDR);
  }
#endif /* ETHARP_SUPPORT_VLAN */

  /* RFC 826 "Packet Reception": */
  if ((hdr->hwtype != PP_HTONS(HWTYPE_ETHERNET)) ||
      (hdr->hwlen != ETHARP_HWADDR_LEN) ||
      (hdr->protolen != sizeof(ip_addr_t)) ||
      (hdr->proto != PP_HTONS(ETHTYPE_IP)))  {
    LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
      ("etharp_arp_input: packet dropped, wrong hw type, hwlen, proto, protolen or ethernet type (%"U16_F"/%"U16_F"/%"U16_F"/%"U16_F")\n",
      hdr->hwtype, hdr->hwlen, hdr->proto, hdr->protolen));
    ETHARP_STATS_INC(etharp.proterr);
    ETHARP_STATS_INC(etharp.drop);
    pbuf_free(p);
    return;
  }
  ETHARP_STATS_INC(etharp.recv);

#if LWIP_AUTOIP
  /* We have to check if a host already has configured our random
   * created link local address and continously check if there is
   * a host with this IP-address so we can detect collisions */
  autoip_arp_reply(netif, hdr);
#endif /* LWIP_AUTOIP */

  /* Copy struct ip_addr2 to aligned ip_addr, to support compilers without
   * structure packing (not using structure copy which breaks strict-aliasing rules). */
  IPADDR2_COPY(&sipaddr, &hdr->sipaddr);
  IPADDR2_COPY(&dipaddr, &hdr->dipaddr);

  /* this interface is not configured? */
  if (ip_addr_isany(&netif->ip_addr)) {
    for_us = 0;
  } else {
    /* ARP packet directed to us? */
    for_us = (u8_t)ip_addr_cmp(&dipaddr, &(netif->ip_addr));
  }

  /* ARP message directed to us?
      -> add IP address in ARP cache; assume requester wants to talk to us,
         can result in directly sending the queued packets for this host.
     ARP message not directed to us?
      ->  update the source IP address in the cache, if present */
  update_arp_entry(netif, &sipaddr, &(hdr->shwaddr),
                   for_us ? ETHARP_FLAG_TRY_HARD : ETHARP_FLAG_FIND_ONLY);

  /* now act on the message itself */
  switch (hdr->opcode) {
  /* ARP request? */
  case PP_HTONS(ARP_REQUEST):
    /* ARP request. If it asked for our address, we send out a
     * reply. In any case, we time-stamp any existing ARP entry,
     * and possiby send out an IP packet that was queued on it. */

    LWIP_DEBUGF (ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: incoming ARP request\n"));
    /* ARP request for our address? */
    if (for_us) {

      LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: replying to ARP request for our IP address\n"));
      /* Re-use pbuf to send ARP reply.
         Since we are re-using an existing pbuf, we can't call etharp_raw since
         that would allocate a new pbuf. */
      hdr->opcode = htons(ARP_REPLY);

      IPADDR2_COPY(&hdr->dipaddr, &hdr->sipaddr);
      IPADDR2_COPY(&hdr->sipaddr, &netif->ip_addr);

      LWIP_ASSERT("netif->hwaddr_len must be the same as ETHARP_HWADDR_LEN for etharp!",
                  (netif->hwaddr_len == ETHARP_HWADDR_LEN));
#if LWIP_AUTOIP
      /* If we are using Link-Local, all ARP packets that contain a Link-Local
       * 'sender IP address' MUST be sent using link-layer broadcast instead of
       * link-layer unicast. (See RFC3927 Section 2.5, last paragraph) */
      ethdst_hwaddr = ip_addr_islinklocal(&netif->ip_addr) ? (u8_t*)(ethbroadcast.addr) : hdr->shwaddr.addr;
#endif /* LWIP_AUTOIP */

      ETHADDR16_COPY(&hdr->dhwaddr, &hdr->shwaddr);
#if LWIP_AUTOIP
      ETHADDR16_COPY(&ethhdr->dest, ethdst_hwaddr);
#else  /* LWIP_AUTOIP */
      ETHADDR16_COPY(&ethhdr->dest, &hdr->shwaddr);
#endif /* LWIP_AUTOIP */
      ETHADDR16_COPY(&hdr->shwaddr, ethaddr);
      ETHADDR16_COPY(&ethhdr->src, ethaddr);

      /* hwtype, hwaddr_len, proto, protolen and the type in the ethernet header
         are already correct, we tested that before */

      /* return ARP reply */
      netif->linkoutput(netif, p);
    /* we are not configured? */
    } else if (ip_addr_isany(&netif->ip_addr)) {
      /* { for_us == 0 and netif->ip_addr.addr == 0 } */
      LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: we are unconfigured, ARP request ignored.\n"));
    /* request was not directed to us */
    } else {
      /* { for_us == 0 and netif->ip_addr.addr != 0 } */
      LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: ARP request was not for us.\n"));
    }
    break;
  case PP_HTONS(ARP_REPLY):
    /* ARP reply. We already updated the ARP cache earlier. */
    LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: incoming ARP reply\n"));
#if (LWIP_DHCP && DHCP_DOES_ARP_CHECK)
    /* DHCP wants to know about ARP replies from any host with an
     * IP address also offered to us by the DHCP server. We do not
     * want to take a duplicate IP address on a single network.
     * @todo How should we handle redundant (fail-over) interfaces? */
    dhcp_arp_reply(netif, &sipaddr);
#endif /* (LWIP_DHCP && DHCP_DOES_ARP_CHECK) */
    break;
  default:
    LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_arp_input: ARP unknown opcode type %"S16_F"\n", htons(hdr->opcode)));
    ETHARP_STATS_INC(etharp.err);
    break;
  }
  /* free ARP packet */
  pbuf_free(p);
}

/**
 * Resolve and fill-in Ethernet address header for outgoing IP packet.
 *
 * For IP multicast and broadcast, corresponding Ethernet addresses
 * are selected and the packet is transmitted on the link.
 *
 * For unicast addresses, the packet is submitted to etharp_query(). In
 * case the IP address is outside the local network, the IP address of
 * the gateway is used.
 *
 * @param netif The lwIP network interface which the IP packet will be sent on.
 * @param q The pbuf(s) containing the IP packet to be sent.
 * @param ipaddr The IP address of the packet destination.
 *
 * @return
 * - ERR_RTE No route to destination (no gateway to external networks),
 * or the return type of either etharp_query() or etharp_send_ip().
 */
err_t
etharp_output(struct netif *netif, struct pbuf *q, ip_addr_t *ipaddr)
{
  struct eth_addr *dest, mcastaddr;

  /* make room for Ethernet header - should not fail */
  if (pbuf_header(q, sizeof(struct eth_hdr)) != 0) {
    /* bail out */
    LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
      ("etharp_output: could not allocate room for header.\n"));
    LINK_STATS_INC(link.lenerr);
    return ERR_BUF;
  }

  /* assume unresolved Ethernet address */
  dest = NULL;
  /* Determine on destination hardware address. Broadcasts and multicasts
   * are special, other IP addresses are looked up in the ARP table. */

  /* broadcast destination IP address? */
  if (ip_addr_isbroadcast(ipaddr, netif)) {
    /* broadcast on Ethernet also */
    dest = (struct eth_addr *)&ethbroadcast;
  /* multicast destination IP address? */
  } else if (ip_addr_ismulticast(ipaddr)) {
    /* Hash IP multicast address to MAC address.*/
    mcastaddr.addr[0] = 0x01;
    mcastaddr.addr[1] = 0x00;
    mcastaddr.addr[2] = 0x5e;
    mcastaddr.addr[3] = ip4_addr2(ipaddr) & 0x7f;
    mcastaddr.addr[4] = ip4_addr3(ipaddr);
    mcastaddr.addr[5] = ip4_addr4(ipaddr);
    /* destination Ethernet address is multicast */
    dest = &mcastaddr;
  /* unicast destination IP address? */
  } else {
    /* outside local network? */
    if (!ip_addr_netcmp(ipaddr, &(netif->ip_addr), &(netif->netmask)) &&
        !ip_addr_islinklocal(ipaddr)) {
#if LWIP_AUTOIP
      struct ip_hdr *iphdr = (struct ip_hdr*)((u8_t*)q->payload +
        sizeof(struct eth_hdr));
      /* According to RFC 3297, chapter 2.6.2 (Forwarding Rules), a packet with
         a link-local source address must always be "directly to its destination
         on the same physical link. The host MUST NOT send the packet to any
         router for forwarding". */
      if (!ip_addr_islinklocal(&iphdr->src))
#endif /* LWIP_AUTOIP */
      {
        /* interface has default gateway? */
        if (!ip_addr_isany(&netif->gw)) {
          /* send to hardware address of default gateway IP address */
          ipaddr = &(netif->gw);
        /* no default gateway available */
        } else {
          /* no route to destination error (default gateway missing) */
          return ERR_RTE;
        }
      }
    }
#if LWIP_NETIF_HWADDRHINT
    if (netif->addr_hint != NULL) {
      /* per-pcb cached entry was given */
      u8_t etharp_cached_entry = *(netif->addr_hint);
      if (etharp_cached_entry < ARP_TABLE_SIZE) {
#endif /* LWIP_NETIF_HWADDRHINT */
        if ((arp_table[etharp_cached_entry].state == ETHARP_STATE_STABLE) &&
            (ip_addr_cmp(ipaddr, &arp_table[etharp_cached_entry].ipaddr))) {
          /* the per-pcb-cached entry is stable and the right one! */
          ETHARP_STATS_INC(etharp.cachehit);
          return etharp_send_ip(netif, q, (struct eth_addr*)(netif->hwaddr),
            &arp_table[etharp_cached_entry].ethaddr);
        }
#if LWIP_NETIF_HWADDRHINT
      }
    }
#endif /* LWIP_NETIF_HWADDRHINT */
    /* queue on destination Ethernet address belonging to ipaddr */
    return etharp_query(netif, ipaddr, q);
  }

  /* continuation for multicast/broadcast destinations */
  /* obtain source Ethernet address of the given interface */
  /* send packet directly on the link */
  return etharp_send_ip(netif, q, (struct eth_addr*)(netif->hwaddr), dest);
}

/**
 * Send an ARP request for the given IP address and/or queue a packet.
 *
 * If the IP address was not yet in the cache, a pending ARP cache entry
 * is added and an ARP request is sent for the given address. The packet
 * is queued on this entry.
 *
 * If the IP address was already pending in the cache, a new ARP request
 * is sent for the given address. The packet is queued on this entry.
 *
 * If the IP address was already stable in the cache, and a packet is
 * given, it is directly sent and no ARP request is sent out. 
 * 
 * If the IP address was already stable in the cache, and no packet is
 * given, an ARP request is sent out.
 * 
 * @param netif The lwIP network interface on which ipaddr
 * must be queried for.
 * @param ipaddr The IP address to be resolved.
 * @param q If non-NULL, a pbuf that must be delivered to the IP address.
 * q is not freed by this function.
 *
 * @note q must only be ONE packet, not a packet queue!
 *
 * @return
 * - ERR_BUF Could not make room for Ethernet header.
 * - ERR_MEM Hardware address unknown, and no more ARP entries available
 *   to query for address or queue the packet.
 * - ERR_MEM Could not queue packet due to memory shortage.
 * - ERR_RTE No route to destination (no gateway to external networks).
 * - ERR_ARG Non-unicast address given, those will not appear in ARP cache.
 *
 */
err_t
etharp_query(struct netif *netif, ip_addr_t *ipaddr, struct pbuf *q)
{
  struct eth_addr * srcaddr = (struct eth_addr *)netif->hwaddr;
  err_t result = ERR_MEM;
  s8_t i; /* ARP entry index */

  /* non-unicast address? */
  if (ip_addr_isbroadcast(ipaddr, netif) ||
      ip_addr_ismulticast(ipaddr) ||
      ip_addr_isany(ipaddr)) {
    LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: will not add non-unicast IP address to ARP cache\n"));
    return ERR_ARG;
  }

  /* find entry in ARP cache, ask to create entry if queueing packet */
  i = find_entry(ipaddr, ETHARP_FLAG_TRY_HARD);

  /* could not find or create entry? */
  if (i < 0) {
    LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: could not create ARP entry\n"));
    if (q) {
      LWIP_DEBUGF(ETHARP_DEBUG | LWIP_DBG_TRACE, ("etharp_query: packet dropped\n"));
      ETHARP_STATS_INC(etharp.memerr);
    }
    return (err_t)i;
  }

  /* mark a fresh entry as pending (we just sent a request) */
  if (arp_table[i].state == ETHARP_STATE_EMPTY) {
    arp_table[i].state = ETHARP_STATE_PENDING;
  }

  /* { i is either a STABLE or (new or existing) PENDING entry } */
  LWIP_ASSERT("arp_table[i].state == PENDING or STABLE",