arp.c

#include "netif.h"
#include "ether.h"
#include "arp.h"
#include "lib.h"

#define BRD_HWADDR ((unsigned char *)"\xff\xff\xff\xff\xff\xff")

void arp_request(struct arpentry *ae)
{
	struct pkbuf *pkb;
	struct ether *ehdr;
	struct arp *ahdr;

	pkb = alloc_pkb(ETH_HRD_SZ + ARP_HRD_SZ);
	ehdr = (struct ether *)pkb->pk_data;
	ahdr = (struct arp *)ehdr->eth_data;
	/* normal arp information */
	ahdr->arp_hrd = _htons(ARP_HRD_ETHER);
	ahdr->arp_pro = _htons(ETH_P_IP);
	ahdr->arp_hrdlen = ETH_ALEN;
	ahdr->arp_prolen = IP_ALEN;
	ahdr->arp_op = _htons(ARP_OP_REQUEST);
	/* address */
	ahdr->arp_sip = ae->ae_dev->net_ipaddr;
	hwacpy(ahdr->arp_sha, ae->ae_dev->net_hwaddr);
	ahdr->arp_tip = ae->ae_ipaddr;
	hwacpy(ahdr->arp_tha, BRD_HWADDR);

	arpdbg(IPFMT"("MACFMT")->"IPFMT"(request)",
				ipfmt(ahdr->arp_sip),
				macfmt(ahdr->arp_sha),
				ipfmt(ahdr->arp_tip));
	netdev_tx(ae->ae_dev, pkb, pkb->pk_len - ETH_HRD_SZ, ETH_P_ARP, BRD_HWADDR);
}

void arp_reply(struct netdev *dev, struct pkbuf *pkb)
{
	struct ether *ehdr = (struct ether *)pkb->pk_data;
	struct arp *ahdr = (struct arp *)ehdr->eth_data;
	arpdbg("replying arp request");
	/* arp field */
	ahdr->arp_op = ARP_OP_REPLY;
	hwacpy(ahdr->arp_tha, ahdr->arp_sha);
	ahdr->arp_tip = ahdr->arp_sip;
	hwacpy(ahdr->arp_sha, dev->net_hwaddr);
	ahdr->arp_sip = dev->net_ipaddr;
	arp_ntoh(ahdr);
	/* ether field */
	netdev_tx(dev, pkb, ARP_HRD_SZ, ETH_P_ARP, ehdr->eth_src);
}

void arp_recv(struct netdev *dev, struct pkbuf *pkb)
{
	struct ether *ehdr = (struct ether *)pkb->pk_data;
	struct arp *ahdr = (struct arp *)ehdr->eth_data;
	struct arpentry *ae;

	/* real arp process */
	arpdbg(IPFMT " -> " IPFMT, ipfmt(ahdr->arp_sip), ipfmt(ahdr->arp_tip));

	/* drop multi target ip(refer to linux) */
	if (MULTICAST(ahdr->arp_tip)) {
		arpdbg("multicast tip");
		goto free_pkb;
	}

	if (ahdr->arp_tip != dev->net_ipaddr) {
		arpdbg("not for us");
		goto free_pkb;
	}

	ae = arp_lookup(ahdr->arp_pro, ahdr->arp_sip);
	if (ae) {
		/* passive learning(REQUEST): update old arp entry in cache */
		hwacpy(ae->ae_hwaddr, ahdr->arp_sha);
		/* send waiting packet (maybe we receive arp reply) */
		if (ae->ae_state == ARP_WAITING)
			arp_queue_send(ae);
		ae->ae_state = ARP_RESOLVED;
		ae->ae_ttl = ARP_TIMEOUT;
	} else if (ahdr->arp_op == ARP_OP_REQUEST) {
		/* Unsolicited ARP reply is not accepted */
		arp_insert(dev, ahdr->arp_pro, ahdr->arp_sip, ahdr->arp_sha);
	}

	if (ahdr->arp_op == ARP_OP_REQUEST) {
		arp_reply(dev, pkb);
		return;
	}
free_pkb:
	free_pkb(pkb);
}

/*
 * The algorithm is strictly based on RFC 826 ( and referred to linux )
 * ARP Packet Reception
 */
void arp_in(struct netdev *dev, struct pkbuf *pkb)
{
	struct ether *ehdr = (struct ether *)pkb->pk_data;
	struct arp *ahdr = (struct arp *)ehdr->eth_data;

	if (pkb->pk_type == PKT_OTHERHOST) {
		arpdbg("arp(l2) packet is not for us");
		goto err_free_pkb;
	}

	if (pkb->pk_len < ETH_HRD_SZ + ARP_HRD_SZ) {
		arpdbg("arp packet is too small");
		goto err_free_pkb;
	}

	/* safe check for arp cheating */
	if (hwacmp(ahdr->arp_sha, ehdr->eth_src) != 0) {
		arpdbg("error sender hardware address");
		goto err_free_pkb;
	}
	arp_hton(ahdr);

#if defined(ARP_ETHERNET) && defined(ARP_IP)
	/* ethernet/ip arp only */
	if (ahdr->arp_hrd != ARP_HRD_ETHER || ahdr->arp_pro != ETH_P_IP ||
		ahdr->arp_hrdlen != ETH_ALEN || ahdr->arp_prolen != IP_ALEN) {
		arpdbg("unsupported L2/L3 protocol");
		goto err_free_pkb;
	}
#endif
	if (ahdr->arp_op != ARP_OP_REQUEST && ahdr->arp_op != ARP_OP_REPLY) {
		arpdbg("unknown arp operation");
		goto err_free_pkb;
	}

	arp_recv(dev, pkb);
	return;
err_free_pkb:
	free_pkb(pkb);
}