arp.c

linux 内核源代码

int arp_find(unsigned char *haddr, struct sk_buff *skb)
{
	struct net_device *dev = skb->dev;
	__be32 paddr;
	struct neighbour *n;

	if (!skb->dst) {
		printk(KERN_DEBUG "arp_find is called with dst==NULL\n");
		kfree_skb(skb);
		return 1;
	}

	paddr = ((struct rtable*)skb->dst)->rt_gateway;

	if (arp_set_predefined(inet_addr_type(paddr), haddr, paddr, dev))
		return 0;

	n = __neigh_lookup(&arp_tbl, &paddr, dev, 1);

	if (n) {
		n->used = jiffies;
		if (n->nud_state&NUD_VALID || neigh_event_send(n, skb) == 0) {
			read_lock_bh(&n->lock);
			memcpy(haddr, n->ha, dev->addr_len);
			read_unlock_bh(&n->lock);
			neigh_release(n);
			return 0;
		}
		neigh_release(n);
	} else
		kfree_skb(skb);
	return 1;
}

/* END OF OBSOLETE FUNCTIONS */

int arp_bind_neighbour(struct dst_entry *dst)
{
	struct net_device *dev = dst->dev;
	struct neighbour *n = dst->neighbour;

	if (dev == NULL)
		return -EINVAL;
	if (n == NULL) {
		__be32 nexthop = ((struct rtable*)dst)->rt_gateway;
		if (dev->flags&(IFF_LOOPBACK|IFF_POINTOPOINT))
			nexthop = 0;
		n = __neigh_lookup_errno(
#if defined(CONFIG_ATM_CLIP) || defined(CONFIG_ATM_CLIP_MODULE)
		    dev->type == ARPHRD_ATM ? clip_tbl_hook :
#endif
		    &arp_tbl, &nexthop, dev);
		if (IS_ERR(n))
			return PTR_ERR(n);
		dst->neighbour = n;
	}
	return 0;
}

/*
 * Check if we can use proxy ARP for this path
 */

static inline int arp_fwd_proxy(struct in_device *in_dev, struct rtable *rt)
{
	struct in_device *out_dev;
	int imi, omi = -1;

	if (!IN_DEV_PROXY_ARP(in_dev))
		return 0;

	if ((imi = IN_DEV_MEDIUM_ID(in_dev)) == 0)
		return 1;
	if (imi == -1)
		return 0;

	/* place to check for proxy_arp for routes */

	if ((out_dev = in_dev_get(rt->u.dst.dev)) != NULL) {
		omi = IN_DEV_MEDIUM_ID(out_dev);
		in_dev_put(out_dev);
	}
	return (omi != imi && omi != -1);
}

/*
 *	Interface to link layer: send routine and receive handler.
 */

/*
 *	Create an arp packet. If (dest_hw == NULL), we create a broadcast
 *	message.
 */
struct sk_buff *arp_create(int type, int ptype, __be32 dest_ip,
			   struct net_device *dev, __be32 src_ip,
			   unsigned char *dest_hw, unsigned char *src_hw,
			   unsigned char *target_hw)
{
	struct sk_buff *skb;
	struct arphdr *arp;
	unsigned char *arp_ptr;

	/*
	 *	Allocate a buffer
	 */

	skb = alloc_skb(sizeof(struct arphdr)+ 2*(dev->addr_len+4)
				+ LL_RESERVED_SPACE(dev), GFP_ATOMIC);
	if (skb == NULL)
		return NULL;

	skb_reserve(skb, LL_RESERVED_SPACE(dev));
	skb_reset_network_header(skb);
	arp = (struct arphdr *) skb_put(skb,sizeof(struct arphdr) + 2*(dev->addr_len+4));
	skb->dev = dev;
	skb->protocol = htons(ETH_P_ARP);
	if (src_hw == NULL)
		src_hw = dev->dev_addr;
	if (dest_hw == NULL)
		dest_hw = dev->broadcast;

	/*
	 *	Fill the device header for the ARP frame
	 */
	if (dev_hard_header(skb, dev, ptype, dest_hw, src_hw, skb->len) < 0)
		goto out;

	/*
	 * Fill out the arp protocol part.
	 *
	 * The arp hardware type should match the device type, except for FDDI,
	 * which (according to RFC 1390) should always equal 1 (Ethernet).
	 */
	/*
	 *	Exceptions everywhere. AX.25 uses the AX.25 PID value not the
	 *	DIX code for the protocol. Make these device structure fields.
	 */
	switch (dev->type) {
	default:
		arp->ar_hrd = htons(dev->type);
		arp->ar_pro = htons(ETH_P_IP);
		break;

#if defined(CONFIG_AX25) || defined(CONFIG_AX25_MODULE)
	case ARPHRD_AX25:
		arp->ar_hrd = htons(ARPHRD_AX25);
		arp->ar_pro = htons(AX25_P_IP);
		break;

#if defined(CONFIG_NETROM) || defined(CONFIG_NETROM_MODULE)
	case ARPHRD_NETROM:
		arp->ar_hrd = htons(ARPHRD_NETROM);
		arp->ar_pro = htons(AX25_P_IP);
		break;
#endif
#endif

#ifdef CONFIG_FDDI
	case ARPHRD_FDDI:
		arp->ar_hrd = htons(ARPHRD_ETHER);
		arp->ar_pro = htons(ETH_P_IP);
		break;
#endif
#ifdef CONFIG_TR
	case ARPHRD_IEEE802_TR:
		arp->ar_hrd = htons(ARPHRD_IEEE802);
		arp->ar_pro = htons(ETH_P_IP);
		break;
#endif
	}

	arp->ar_hln = dev->addr_len;
	arp->ar_pln = 4;
	arp->ar_op = htons(type);

	arp_ptr=(unsigned char *)(arp+1);

	memcpy(arp_ptr, src_hw, dev->addr_len);
	arp_ptr+=dev->addr_len;
	memcpy(arp_ptr, &src_ip,4);
	arp_ptr+=4;
	if (target_hw != NULL)
		memcpy(arp_ptr, target_hw, dev->addr_len);
	else
		memset(arp_ptr, 0, dev->addr_len);
	arp_ptr+=dev->addr_len;
	memcpy(arp_ptr, &dest_ip, 4);

	return skb;

out:
	kfree_skb(skb);
	return NULL;
}

/*
 *	Send an arp packet.
 */
void arp_xmit(struct sk_buff *skb)
{
	/* Send it off, maybe filter it using firewalling first.  */
	NF_HOOK(NF_ARP, NF_ARP_OUT, skb, NULL, skb->dev, dev_queue_xmit);
}

/*
 *	Create and send an arp packet.
 */
void arp_send(int type, int ptype, __be32 dest_ip,
	      struct net_device *dev, __be32 src_ip,
	      unsigned char *dest_hw, unsigned char *src_hw,
	      unsigned char *target_hw)
{
	struct sk_buff *skb;

	/*
	 *	No arp on this interface.
	 */

	if (dev->flags&IFF_NOARP)
		return;

	skb = arp_create(type, ptype, dest_ip, dev, src_ip,
			 dest_hw, src_hw, target_hw);
	if (skb == NULL) {
		return;
	}

	arp_xmit(skb);
}

/*
 *	Process an arp request.
 */

static int arp_process(struct sk_buff *skb)
{
	struct net_device *dev = skb->dev;
	struct in_device *in_dev = in_dev_get(dev);
	struct arphdr *arp;
	unsigned char *arp_ptr;
	struct rtable *rt;
	unsigned char *sha;
	__be32 sip, tip;
	u16 dev_type = dev->type;
	int addr_type;
	struct neighbour *n;

	/* arp_rcv below verifies the ARP header and verifies the device
	 * is ARP'able.
	 */

	if (in_dev == NULL)
		goto out;

	arp = arp_hdr(skb);

	switch (dev_type) {
	default:
		if (arp->ar_pro != htons(ETH_P_IP) ||
		    htons(dev_type) != arp->ar_hrd)
			goto out;
		break;
	case ARPHRD_ETHER:
	case ARPHRD_IEEE802_TR:
	case ARPHRD_FDDI:
	case ARPHRD_IEEE802:
		/*
		 * ETHERNET, Token Ring and Fibre Channel (which are IEEE 802
		 * devices, according to RFC 2625) devices will accept ARP
		 * hardware types of either 1 (Ethernet) or 6 (IEEE 802.2).
		 * This is the case also of FDDI, where the RFC 1390 says that
		 * FDDI devices should accept ARP hardware of (1) Ethernet,
		 * however, to be more robust, we'll accept both 1 (Ethernet)
		 * or 6 (IEEE 802.2)
		 */
		if ((arp->ar_hrd != htons(ARPHRD_ETHER) &&
		     arp->ar_hrd != htons(ARPHRD_IEEE802)) ||
		    arp->ar_pro != htons(ETH_P_IP))
			goto out;
		break;
	case ARPHRD_AX25:
		if (arp->ar_pro != htons(AX25_P_IP) ||
		    arp->ar_hrd != htons(ARPHRD_AX25))
			goto out;
		break;
	case ARPHRD_NETROM:
		if (arp->ar_pro != htons(AX25_P_IP) ||
		    arp->ar_hrd != htons(ARPHRD_NETROM))
			goto out;
		break;
	}

	/* Understand only these message types */

	if (arp->ar_op != htons(ARPOP_REPLY) &&
	    arp->ar_op != htons(ARPOP_REQUEST))
		goto out;

/*
 *	Extract fields
 */
	arp_ptr= (unsigned char *)(arp+1);
	sha	= arp_ptr;
	arp_ptr += dev->addr_len;
	memcpy(&sip, arp_ptr, 4);
	arp_ptr += 4;
	arp_ptr += dev->addr_len;
	memcpy(&tip, arp_ptr, 4);
/*
 *	Check for bad requests for 127.x.x.x and requests for multicast
 *	addresses.  If this is one such, delete it.
 */
	if (LOOPBACK(tip) || MULTICAST(tip))
		goto out;

/*
 *     Special case: We must set Frame Relay source Q.922 address
 */
	if (dev_type == ARPHRD_DLCI)
		sha = dev->broadcast;

/*
 *  Process entry.  The idea here is we want to send a reply if it is a
 *  request for us or if it is a request for someone else that we hold
 *  a proxy for.  We want to add an entry to our cache if it is a reply
 *  to us or if it is a request for our address.
 *  (The assumption for this last is that if someone is requesting our
 *  address, they are probably intending to talk to us, so it saves time
 *  if we cache their address.  Their address is also probably not in
 *  our cache, since ours is not in their cache.)
 *
 *  Putting this another way, we only care about replies if they are to
 *  us, in which case we add them to the cache.  For requests, we care
 *  about those for us and those for our proxies.  We reply to both,
 *  and in the case of requests for us we add the requester to the arp
 *  cache.
 */

	/* Special case: IPv4 duplicate address detection packet (RFC2131) */
	if (sip == 0) {
		if (arp->ar_op == htons(ARPOP_REQUEST) &&
		    inet_addr_type(tip) == RTN_LOCAL &&
		    !arp_ignore(in_dev,dev,sip,tip))
			arp_send(ARPOP_REPLY, ETH_P_ARP, sip, dev, tip, sha,
				 dev->dev_addr, sha);
		goto out;
	}

	if (arp->ar_op == htons(ARPOP_REQUEST) &&
	    ip_route_input(skb, tip, sip, 0, dev) == 0) {

		rt = (struct rtable*)skb->dst;
		addr_type = rt->rt_type;

		if (addr_type == RTN_LOCAL) {
			n = neigh_event_ns(&arp_tbl, sha, &sip, dev);
			if (n) {
				int dont_send = 0;

				if (!dont_send)
					dont_send |= arp_ignore(in_dev,dev,sip,tip);
				if (!dont_send && IN_DEV_ARPFILTER(in_dev))
					dont_send |= arp_filter(sip,tip,dev);
				if (!dont_send)
					arp_send(ARPOP_REPLY,ETH_P_ARP,sip,dev,tip,sha,dev->dev_addr,sha);

				neigh_release(n);
			}
			goto out;
		} else if (IN_DEV_FORWARD(in_dev)) {
			if ((rt->rt_flags&RTCF_DNAT) ||
			    (addr_type == RTN_UNICAST  && rt->u.dst.dev != dev &&
			     (arp_fwd_proxy(in_dev, rt) || pneigh_lookup(&arp_tbl, &tip, dev, 0)))) {
				n = neigh_event_ns(&arp_tbl, sha, &sip, dev);
				if (n)
					neigh_release(n);

				if (NEIGH_CB(skb)->flags & LOCALLY_ENQUEUED ||
				    skb->pkt_type == PACKET_HOST ||
				    in_dev->arp_parms->proxy_delay == 0) {
					arp_send(ARPOP_REPLY,ETH_P_ARP,sip,dev,tip,sha,dev->dev_addr,sha);
				} else {
					pneigh_enqueue(&arp_tbl, in_dev->arp_parms, skb);
					in_dev_put(in_dev);
					return 0;
				}
				goto out;
			}
		}
	}

	/* Update our ARP tables */

	n = __neigh_lookup(&arp_tbl, &sip, dev, 0);

	if (IPV4_DEVCONF_ALL(ARP_ACCEPT)) {
		/* Unsolicited ARP is not accepted by default.
		   It is possible, that this option should be enabled for some
		   devices (strip is candidate)
		 */
		if (n == NULL &&
		    arp->ar_op == htons(ARPOP_REPLY) &&
		    inet_addr_type(sip) == RTN_UNICAST)
			n = __neigh_lookup(&arp_tbl, &sip, dev, 1);
	}

	if (n) {
		int state = NUD_REACHABLE;
		int override;

		/* If several different ARP replies follows back-to-back,
		   use the FIRST one. It is possible, if several proxy
		   agents are active. Taking the first reply prevents
		   arp trashing and chooses the fastest router.
		 */
		override = time_after(jiffies, n->updated + n->parms->locktime);

		/* Broadcast replies and request packets
		   do not assert neighbour reachability.
		 */
		if (arp->ar_op != htons(ARPOP_REPLY) ||
		    skb->pkt_type != PACKET_HOST)
			state = NUD_STALE;
		neigh_update(n, sha, state, override ? NEIGH_UPDATE_F_OVERRIDE : 0);
		neigh_release(n);
	}

out:
	if (in_dev)
		in_dev_put(in_dev);
	kfree_skb(skb);
	return 0;
}

static void parp_redo(struct sk_buff *skb)
{
	arp_process(skb);
}


/*
 *	Receive an arp request from the device layer.
 */

static int arp_rcv(struct sk_buff *skb, struct net_device *dev,
		   struct packet_type *pt, struct net_device *orig_dev)
{
	struct arphdr *arp;

	if (dev->nd_net != &init_net)
		goto freeskb;

	/* ARP header, plus 2 device addresses, plus 2 IP addresses.  */
	if (!pskb_may_pull(skb, (sizeof(struct arphdr) +
				 (2 * dev->addr_len) +
				 (2 * sizeof(u32)))))
		goto freeskb;

	arp = arp_hdr(skb);
	if (arp->ar_hln != dev->addr_len ||
	    dev->flags & IFF_NOARP ||
	    skb->pkt_type == PACKET_OTHERHOST ||
	    skb->pkt_type == PACKET_LOOPBACK ||
	    arp->ar_pln != 4)
		goto freeskb;

	if ((skb = skb_share_check(skb, GFP_ATOMIC)) == NULL)