arp.c

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/* linux/net/inet/arp.c
 *
 * Version:     $Id: arp.c,v 1.99 2001/08/30 22:55:42 davem Exp $
 *
 * Copyright (C) 1994 by Florian  La Roche
 *
 * This module implements the Address Resolution Protocol ARP (RFC 826),
 * which is used to convert IP addresses (or in the future maybe other
 * high-level addresses) into a low-level hardware address (like an Ethernet
 * address).
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 *
 * Fixes:
 *              Alan Cox        :       Removed the Ethernet assumptions in 
 *                                      Florian's code
 *              Alan Cox        :       Fixed some small errors in the ARP 
 *                                      logic
 *              Alan Cox        :       Allow >4K in /proc
 *              Alan Cox        :       Make ARP add its own protocol entry
 *              Ross Martin     :       Rewrote arp_rcv() and arp_get_info()
 *              Stephen Henson  :       Add AX25 support to arp_get_info()
 *              Alan Cox        :       Drop data when a device is downed.
 *              Alan Cox        :       Use init_timer().
 *              Alan Cox        :       Double lock fixes.
 *              Martin Seine    :       Move the arphdr structure
 *                                      to if_arp.h for compatibility.
 *                                      with BSD based programs.
 *              Andrew Tridgell :       Added ARP netmask code and
 *                                      re-arranged proxy handling.
 *              Alan Cox        :       Changed to use notifiers.
 *              Niibe Yutaka    :       Reply for this device or proxies only.
 *              Alan Cox        :       Don't proxy across hardware types!
 *              Jonathan Naylor :       Added support for NET/ROM.
 *              Mike Shaver     :       RFC1122 checks.
 *              Jonathan Naylor :       Only lookup the hardware address for
 *                                      the correct hardware type.
 *              Germano Caronni :       Assorted subtle races.
 *              Craig Schlenter :       Don't modify permanent entry 
 *                                      during arp_rcv.
 *              Russ Nelson     :       Tidied up a few bits.
 *              Alexey Kuznetsov:       Major changes to caching and behaviour,
 *                                      eg intelligent arp probing and 
 *                                      generation
 *                                      of host down events.
 *              Alan Cox        :       Missing unlock in device events.
 *              Eckes           :       ARP ioctl control errors.
 *              Alexey Kuznetsov:       Arp free fix.
 *              Manuel Rodriguez:       Gratuitous ARP.
 *              Jonathan Layes  :       Added arpd support through kerneld 
 *                                      message queue (960314)
 *              Mike Shaver     :       /proc/sys/net/ipv4/arp_* support
 *              Mike McLagan    :       Routing by source
 *              Stuart Cheshire :       Metricom and grat arp fixes
 *                                      *** FOR 2.1 clean this up ***
 *              Lawrence V. Stefani: (08/12/96) Added FDDI support.
 *              Alan Cox        :       Took the AP1000 nasty FDDI hack and
 *                                      folded into the mainstream FDDI code.
 *                                      Ack spit, Linus how did you allow that
 *                                      one in...
 *              Jes Sorensen    :       Make FDDI work again in 2.1.x and
 *                                      clean up the APFDDI & gen. FDDI bits.
 *              Alexey Kuznetsov:       new arp state machine;
 *                                      now it is in net/core/neighbour.c.
 *              Krzysztof Halasa:       Added Frame Relay ARP support.
 */

#include <linux/types.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/config.h>
#include <linux/socket.h>
#include <linux/sockios.h>
#include <linux/errno.h>
#include <linux/in.h>
#include <linux/mm.h>
#include <linux/inet.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/fddidevice.h>
#include <linux/if_arp.h>
#include <linux/trdevice.h>
#include <linux/skbuff.h>
#include <linux/proc_fs.h>
#include <linux/stat.h>
#include <linux/init.h>
#ifdef CONFIG_SYSCTL
#include <linux/sysctl.h>
#endif

#include <net/ip.h>
#include <net/icmp.h>
#include <net/route.h>
#include <net/protocol.h>
#include <net/tcp.h>
#include <net/sock.h>
#include <net/arp.h>
#if defined(CONFIG_AX25) || defined(CONFIG_AX25_MODULE)
#include <net/ax25.h>
#if defined(CONFIG_NETROM) || defined(CONFIG_NETROM_MODULE)
#include <net/netrom.h>
#endif
#endif
#if defined(CONFIG_ATM_CLIP) || defined(CONFIG_ATM_CLIP_MODULE)
#include <net/atmclip.h>
struct neigh_table *clip_tbl_hook;
#endif

#include <asm/system.h>
#include <asm/uaccess.h>

#include <linux/netfilter_arp.h>

/*
 *      Interface to generic neighbour cache.
 */
static u32 arp_hash(const void *pkey, const struct net_device *dev);
static int arp_constructor(struct neighbour *neigh);
static void arp_solicit(struct neighbour *neigh, struct sk_buff *skb);
static void arp_error_report(struct neighbour *neigh, struct sk_buff *skb);
static void parp_redo(struct sk_buff *skb);

static struct neigh_ops arp_generic_ops = {
        family:                 AF_INET,
        solicit:                arp_solicit,
        error_report:           arp_error_report,
        output:                 neigh_resolve_output,
        connected_output:       neigh_connected_output,
        hh_output:              dev_queue_xmit,
        queue_xmit:             dev_queue_xmit,
};

static struct neigh_ops arp_hh_ops = {
        family:                 AF_INET,
        solicit:                arp_solicit,
        error_report:           arp_error_report,
        output:                 neigh_resolve_output,
        connected_output:       neigh_resolve_output,
        hh_output:              dev_queue_xmit,
        queue_xmit:             dev_queue_xmit,
};

static struct neigh_ops arp_direct_ops = {
        family:                 AF_INET,
        output:                 dev_queue_xmit,
        connected_output:       dev_queue_xmit,
        hh_output:              dev_queue_xmit,
        queue_xmit:             dev_queue_xmit,
};

struct neigh_ops arp_broken_ops = {
        family:                 AF_INET,
        solicit:                arp_solicit,
        error_report:           arp_error_report,
        output:                 neigh_compat_output,
        connected_output:       neigh_compat_output,
        hh_output:              dev_queue_xmit,
        queue_xmit:             dev_queue_xmit,
};

struct neigh_table arp_tbl = {
        family:         AF_INET,
        entry_size:     sizeof(struct neighbour) + 4,
        key_len:        4,
        hash:           arp_hash,
        constructor:    arp_constructor,
        proxy_redo:     parp_redo,
        id:             "arp_cache",
        parms: {
                tbl:                    &arp_tbl,
                base_reachable_time:    30 * HZ,
                retrans_time:           1 * HZ,
                gc_staletime:           60 * HZ,
                reachable_time:         30 * HZ,
                delay_probe_time:       5 * HZ,
                queue_len:              3,
                ucast_probes:           3,
                mcast_probes:           3,
                anycast_delay:          1 * HZ,
                proxy_delay:            (8 * HZ) / 10,
                proxy_qlen:             64,
                locktime:               1 * HZ,
        },
        gc_interval:    30 * HZ,
        gc_thresh1:     128,
        gc_thresh2:     512,
        gc_thresh3:     1024,
};

int arp_mc_map(u32 addr, u8 *haddr, struct net_device *dev, int dir)
{
        switch (dev->type) {
        case ARPHRD_ETHER:
        case ARPHRD_FDDI:
        case ARPHRD_IEEE802:
                ip_eth_mc_map(addr, haddr);
                return 0; 
        case ARPHRD_IEEE802_TR:
                ip_tr_mc_map(addr, haddr);
                return 0;
        default:
                if (dir) {
                        memcpy(haddr, dev->broadcast, dev->addr_len);
                        return 0;
                }
        }
        return -EINVAL;
}


static u32 arp_hash(const void *pkey, const struct net_device *dev)
{
        u32 hash_val;

        hash_val = *(u32*)pkey;
        hash_val ^= (hash_val>>16);
        hash_val ^= hash_val>>8;
        hash_val ^= hash_val>>3;
        hash_val = (hash_val^dev->ifindex)&NEIGH_HASHMASK;

        return hash_val;
}

static int arp_constructor(struct neighbour *neigh)
{
        u32 addr = *(u32*)neigh->primary_key;
        struct net_device *dev = neigh->dev;
        struct in_device *in_dev = in_dev_get(dev);

        if (in_dev == NULL)
                return -EINVAL;

        neigh->type = inet_addr_type(addr);
        if (in_dev->arp_parms)
                neigh->parms = in_dev->arp_parms;

        in_dev_put(in_dev);

        if (dev->hard_header == NULL) {
                neigh->nud_state = NUD_NOARP;
                neigh->ops = &arp_direct_ops;
                neigh->output = neigh->ops->queue_xmit;
        } else {
                /* Good devices (checked by reading texts, but only Ethernet is
                   tested)

                   ARPHRD_ETHER: (ethernet, apfddi)
                   ARPHRD_FDDI: (fddi)
                   ARPHRD_IEEE802: (tr)
                   ARPHRD_METRICOM: (strip)
                   ARPHRD_ARCNET:
                   etc. etc. etc.

                   ARPHRD_IPDDP will also work, if author repairs it.
                   I did not it, because this driver does not work even
                   in old paradigm.
                 */

#if 1
                /* So... these "amateur" devices are hopeless.
                   The only thing, that I can say now:
                   It is very sad that we need to keep ugly obsolete
                   code to make them happy.

                   They should be moved to more reasonable state, now
                   they use rebuild_header INSTEAD OF hard_start_xmit!!!
                   Besides that, they are sort of out of date
                   (a lot of redundant clones/copies, useless in 2.1),
                   I wonder why people believe that they work.
                 */
                switch (dev->type) {
                default:
                        break;
                case ARPHRD_ROSE:       
#if defined(CONFIG_AX25) || defined(CONFIG_AX25_MODULE)
                case ARPHRD_AX25:
#if defined(CONFIG_NETROM) || defined(CONFIG_NETROM_MODULE)
                case ARPHRD_NETROM:
#endif
                        neigh->ops = &arp_broken_ops;
                        neigh->output = neigh->ops->output;
                        return 0;
#endif
                ;}
#endif
                if (neigh->type == RTN_MULTICAST) {
                        neigh->nud_state = NUD_NOARP;
                        arp_mc_map(addr, neigh->ha, dev, 1);
                } else if (dev->flags&(IFF_NOARP|IFF_LOOPBACK)) {
                        neigh->nud_state = NUD_NOARP;
                        memcpy(neigh->ha, dev->dev_addr, dev->addr_len);
                } else if (neigh->type == RTN_BROADCAST || dev->flags&IFF_POINTOPOINT) {
                        neigh->nud_state = NUD_NOARP;
                        memcpy(neigh->ha, dev->broadcast, dev->addr_len);
                }
                if (dev->hard_header_cache)
                        neigh->ops = &arp_hh_ops;
                else
                        neigh->ops = &arp_generic_ops;
                if (neigh->nud_state&NUD_VALID)
                        neigh->output = neigh->ops->connected_output;
                else
                        neigh->output = neigh->ops->output;
        }
        return 0;
}

static void arp_error_report(struct neighbour *neigh, struct sk_buff *skb)
{
        dst_link_failure(skb);
        kfree_skb(skb);
}

static void arp_solicit(struct neighbour *neigh, struct sk_buff *skb)
{
        u32 saddr;
        u8  *dst_ha = NULL;
        struct net_device *dev = neigh->dev;
        u32 target = *(u32*)neigh->primary_key;
        int probes = atomic_read(&neigh->probes);

        if (skb && inet_addr_type(skb->nh.iph->saddr) == RTN_LOCAL)
                saddr = skb->nh.iph->saddr;
        else
                saddr = inet_select_addr(dev, target, RT_SCOPE_LINK);

        if ((probes -= neigh->parms->ucast_probes) < 0) {
                if (!(neigh->nud_state&NUD_VALID))
                        printk(KERN_DEBUG "trying to ucast probe in NUD_INVALID\n");
                dst_ha = neigh->ha;
                read_lock_bh(&neigh->lock);
        } else if ((probes -= neigh->parms->app_probes) < 0) {
#ifdef CONFIG_ARPD
                neigh_app_ns(neigh);
#endif
                return;
        }

        arp_send(ARPOP_REQUEST, ETH_P_ARP, target, dev, saddr,
                 dst_ha, dev->dev_addr, NULL);
        if (dst_ha)
                read_unlock_bh(&neigh->lock);
}

static int arp_filter(__u32 sip, __u32 tip, struct net_device *dev)
{
        struct rtable *rt;
        int flag = 0; 
        /*unsigned long now; */

        if (ip_route_output(&rt, sip, tip, 0, 0) < 0) 
                return 1;
        if (rt->u.dst.dev != dev) { 
                NET_INC_STATS_BH(ArpFilter);
                flag = 1;
        } 
        ip_rt_put(rt); 
        return flag; 
} 

/* OBSOLETE FUNCTIONS */

/*
 *      Find an arp mapping in the cache. If not found, post a request.
 *
 *      It is very UGLY routine: it DOES NOT use skb->dst->neighbour,
 *      even if it exists. It is supposed that skb->dev was mangled
 *      by a virtual device (eql, shaper). Nobody but broken devices
 *      is allowed to use this function, it is scheduled to be removed. --ANK
 */

static int arp_set_predefined(int addr_hint, unsigned char * haddr, u32 paddr, struct net_device * dev)
{
        switch (addr_hint) {
        case RTN_LOCAL:
                printk(KERN_DEBUG "ARP: arp called for own IP address\n");
                memcpy(haddr, dev->dev_addr, dev->addr_len);
                return 1;
        case RTN_MULTICAST:
                arp_mc_map(paddr, haddr, dev, 1);
                return 1;
        case RTN_BROADCAST:
                memcpy(haddr, dev->broadcast, dev->addr_len);
                return 1;
        }
        return 0;
}


int arp_find(unsigned char *haddr, struct sk_buff *skb)
{
        struct net_device *dev = skb->dev;
        u32 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) {
                u32 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 and send an arp packet. If (dest_hw == NULL), we create a broadcast
 *      message.
 */

void arp_send(int type, int ptype, u32 dest_ip, 
              struct net_device *dev, u32 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;

        /*
         *      No arp on this interface.
         */
        
        if (dev->flags&IFF_NOARP)
                return;

        /*
         *      Allocate a buffer
         */
        
        skb = alloc_skb(sizeof(struct arphdr)+ 2*(dev->addr_len+4)
                                + dev->hard_header_len + 15, GFP_ATOMIC);
        if (skb == NULL)
                return;

        skb_reserve(skb, (dev->hard_header_len+15)&~15);
        skb->nh.raw = skb->data;
        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 &&
            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);

        /* Send it off, maybe filter it using firewalling first.  */
        NF_HOOK(NF_ARP, NF_ARP_OUT, skb, NULL, dev, dev_queue_xmit);
        return;

out:
        kfree_skb(skb);
}

static void parp_redo(struct sk_buff *skb)
{
        arp_rcv(skb, skb->dev, NULL);
}

/*
 *      Process an arp request.
 */

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, *tha;
        u32 sip, tip;
        u16 dev_type = dev->type;
        int addr_type;
        struct neighbour *n;

        /* arp_rcv below verifies the ARP header, verifies the device
         * is ARP'able, and linearizes the SKB (if needed).
         */

        if (in_dev == NULL)
                goto out;

        arp = skb->nh.arph;
        arp_ptr= (unsigned char *)(arp+1);

        switch (dev_type) {
        default:        
                if (arp->ar_pro != htons(ETH_P_IP))
                        goto out;
                if (htons(dev_type) != arp->ar_hrd)
                        goto out;
                break;
#ifdef CONFIG_NET_ETHERNET
        case ARPHRD_ETHER:
                /*
                 * ETHERNET devices will accept ARP hardware types of either
                 * 1 (Ethernet) or 6 (IEEE 802.2).
                 */
                if (arp->ar_hrd != htons(ARPHRD_ETHER) &&
                    arp->ar_hrd != htons(ARPHRD_IEEE802))
                        goto out;
                if (arp->ar_pro != htons(ETH_P_IP))
                        goto out;
                break;
#endif
#ifdef CONFIG_TR
        case ARPHRD_IEEE802_TR:
                /*
                 * Token ring devices will accept ARP hardware types of either
                 * 1 (Ethernet) or 6 (IEEE 802.2).
                 */
                if (arp->ar_hrd != htons(ARPHRD_ETHER) &&
                    arp->ar_hrd != htons(ARPHRD_IEEE802))
                        goto out;
                if (arp->ar_pro != htons(ETH_P_IP))
                        goto out;
                break;
#endif
#ifdef CONFIG_FDDI
        case ARPHRD_FDDI:
                /*
                 * According to RFC 1390, FDDI devices should accept ARP hardware types
                 * of 1 (Ethernet).  However, to be more robust, we'll accept hardware
                 * types of either 1 (Ethernet) or 6 (IEEE 802.2).
                 */
                if (arp->ar_hrd != htons(ARPHRD_ETHER) &&
                    arp->ar_hrd != htons(ARPHRD_IEEE802))
                        goto out;
                if (arp->ar_pro != htons(ETH_P_IP))
                        goto out;
                break;
#endif
#ifdef CONFIG_NET_FC
        case ARPHRD_IEEE802:
                /*
                 * According to RFC 2625, Fibre Channel devices (which are IEEE
                 * 802 devices) should accept ARP hardware types of 6 (IEEE 802)
                 * and 1 (Ethernet).
                 */
                if (arp->ar_hrd != htons(ARPHRD_ETHER) &&
                    arp->ar_hrd != htons(ARPHRD_IEEE802))
                        goto out;
                if (arp->ar_pro != htons(ETH_P_IP))
                        goto out;
                break;
#endif
#if defined(CONFIG_AX25) || defined(CONFIG_AX25_MODULE)
        case ARPHRD_AX25:
                if (arp->ar_pro != htons(AX25_P_IP))
                        goto out;
                if (arp->ar_hrd != htons(ARPHRD_AX25))
                        goto out;
                break;
#if defined(CONFIG_NETROM) || defined(CONFIG_NETROM_MODULE)
        case ARPHRD_NETROM:
                if (arp->ar_pro != htons(AX25_P_IP))
                        goto out;
                if (arp->ar_hrd != htons(ARPHRD_NETROM))
                        goto out;
                break;
#endif
#endif
        }

        /* Understand only these message types */

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

/*
 *      Extract fields
 */
        sha=arp_ptr;
        arp_ptr += dev->addr_len;
        memcpy(&sip, arp_ptr, 4);
        arp_ptr += 4;
        tha=arp_ptr;
        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_send(ARPOP_REPLY,ETH_P_ARP,tip,dev,tip,sha,dev->dev_addr,dev->dev_addr);
                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 (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 (skb->stamp.tv_sec == 0 ||
                                    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);

#ifdef CONFIG_IP_ACCEPT_UNSOLICITED_ARP
        /* 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);
#endif

        if (n) {
                int state = NUD_REACHABLE;
                int override = 0;

                /* 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.
                 */
                if (jiffies - n->updated >= n->parms->locktime)
                        override = 1;

                /* 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, 1);
                neigh_release(n);
        }

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


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

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

        /* 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 = skb->nh.arph;
        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)
                goto out_of_mem;

        return NF_HOOK(NF_ARP, NF_ARP_IN, skb, dev, NULL, arp_process);

freeskb:
        kfree_skb(skb);
out_of_mem:
        return 0;
}

/*
 *      User level interface (ioctl, /proc)
 */

/*
 *      Set (create) an ARP cache entry.
 */

int arp_req_set(struct arpreq *r, struct net_device * dev)
{
        u32 ip = ((struct sockaddr_in *) &r->arp_pa)->sin_addr.s_addr;
        struct neighbour *neigh;
        int err;

        if (r->arp_flags&ATF_PUBL) {
                u32 mask = ((struct sockaddr_in *) &r->arp_netmask)->sin_addr.s_addr;
                if (mask && mask != 0xFFFFFFFF)
                        return -EINVAL;
                if (!dev && (r->arp_flags & ATF_COM)) {
                        dev = dev_getbyhwaddr(r->arp_ha.sa_family, r->arp_ha.sa_data);
                        if (!dev)
                                return -ENODEV;
                }
                if (mask) {
                        if (pneigh_lookup(&arp_tbl, &ip, dev, 1) == NULL)
                                return -ENOBUFS;
                        return 0;
                }
                if (dev == NULL) {
                        ipv4_devconf.proxy_arp = 1;
                        return 0;
                }
                if (__in_dev_get(dev)) {
                        __in_dev_get(dev)->cnf.proxy_arp = 1;
                        return 0;
                }
                return -ENXIO;
        }

        if (r->arp_flags & ATF_PERM)
                r->arp_flags |= ATF_COM;
        if (dev == NULL) {
                struct rtable * rt;
                if ((err = ip_route_output(&rt, ip, 0, RTO_ONLINK, 0)) != 0)
                        return err;
                dev = rt->u.dst.dev;
                ip_rt_put(rt);
                if (!dev)
                        return -EINVAL;
        }
        if (r->arp_ha.sa_family != dev->type)   
                return -EINVAL;

        neigh = __neigh_lookup_errno(&arp_tbl, &ip, dev);
        err = PTR_ERR(neigh);
        if (!IS_ERR(neigh)) {
                unsigned state = NUD_STALE;
                if (r->arp_flags & ATF_PERM)
                        state = NUD_PERMANENT;
                err = neigh_update(neigh, (r->arp_flags&ATF_COM) ?
                                   r->arp_ha.sa_data : NULL, state, 1, 0);
                neigh_release(neigh);
        }
        return err;
}

static unsigned arp_state_to_flags(struct neighbour *neigh)
{
        unsigned flags = 0;
        if (neigh->nud_state&NUD_PERMANENT)
                flags = ATF_PERM|ATF_COM;
        else if (neigh->nud_state&NUD_VALID)
                flags = ATF_COM;
        return flags;
}

/*
 *      Get an ARP cache entry.
 */

static int arp_req_get(struct arpreq *r, struct net_device *dev)
{
        u32 ip = ((struct sockaddr_in *) &r->arp_pa)->sin_addr.s_addr;
        struct neighbour *neigh;
        int err = -ENXIO;

        neigh = neigh_lookup(&arp_tbl, &ip, dev);
        if (neigh) {
                read_lock_bh(&neigh->lock);
                memcpy(r->arp_ha.sa_data, neigh->ha, dev->addr_len);
                r->arp_flags = arp_state_to_flags(neigh);
                read_unlock_bh(&neigh->lock);
                r->arp_ha.sa_family = dev->type;
                strncpy(r->arp_dev, dev->name, sizeof(r->arp_dev));
                neigh_release(neigh);
                err = 0;
        }
        return err;
}

int arp_req_delete(struct arpreq *r, struct net_device * dev)
{
        int err;
        u32 ip = ((struct sockaddr_in *)&r->arp_pa)->sin_addr.s_addr;
        struct neighbour *neigh;

        if (r->arp_flags & ATF_PUBL) {
                u32 mask = ((struct sockaddr_in *) &r->arp_netmask)->sin_addr.s_addr;
                if (mask == 0xFFFFFFFF)
                        return pneigh_delete(&arp_tbl, &ip, dev);
                if (mask == 0) {
                        if (dev == NULL) {
                                ipv4_devconf.proxy_arp = 0;
                                return 0;
                        }
                        if (__in_dev_get(dev)) {
                                __in_dev_get(dev)->cnf.proxy_arp = 0;
                                return 0;
                        }
                        return -ENXIO;
                }
                return -EINVAL;
        }

        if (dev == NULL) {
                struct rtable * rt;
                if ((err = ip_route_output(&rt, ip, 0, RTO_ONLINK, 0)) != 0)
                        return err;
                dev = rt->u.dst.dev;
                ip_rt_put(rt);
                if (!dev)
                        return -EINVAL;
        }
        err = -ENXIO;
        neigh = neigh_lookup(&arp_tbl, &ip, dev);
        if (neigh) {
                if (neigh->nud_state&~NUD_NOARP)
                        err = neigh_update(neigh, NULL, NUD_FAILED, 1, 0);
                neigh_release(neigh);
        }
        return err;
}

/*
 *      Handle an ARP layer I/O control request.
 */

int arp_ioctl(unsigned int cmd, void *arg)
{
        int err;
        struct arpreq r;
        struct net_device * dev = NULL;

        switch(cmd) {
                case SIOCDARP:
                case SIOCSARP:
                        if (!capable(CAP_NET_ADMIN))
                                return -EPERM;
                case SIOCGARP:
                        err = copy_from_user(&r, arg, sizeof(struct arpreq));
                        if (err)
                                return -EFAULT;
                        break;
                default:
                        return -EINVAL;
        }

        if (r.arp_pa.sa_family != AF_INET)
                return -EPFNOSUPPORT;

        if (!(r.arp_flags & ATF_PUBL) &&
            (r.arp_flags & (ATF_NETMASK|ATF_DONTPUB)))
                return -EINVAL;
        if (!(r.arp_flags & ATF_NETMASK))
                ((struct sockaddr_in *)&r.arp_netmask)->sin_addr.s_addr=htonl(0xFFFFFFFFUL);

        rtnl_lock();
        if (r.arp_dev[0]) {
                err = -ENODEV;
                if ((dev = __dev_get_by_name(r.arp_dev)) == NULL)
                        goto out;

                /* Mmmm... It is wrong... ARPHRD_NETROM==0 */
                if (!r.arp_ha.sa_family)
                        r.arp_ha.sa_family = dev->type;
                err = -EINVAL;
                if ((r.arp_flags & ATF_COM) && r.arp_ha.sa_family != dev->type)
                        goto out;
        } else if (cmd == SIOCGARP) {
                err = -ENODEV;
                goto out;
        }

        switch(cmd) {
        case SIOCDARP:
                err = arp_req_delete(&r, dev);
                break;
        case SIOCSARP:
                err = arp_req_set(&r, dev);
                break;
        case SIOCGARP:
                err = arp_req_get(&r, dev);
                if (!err && copy_to_user(arg, &r, sizeof(r)))
                        err = -EFAULT;
                break;
        }
out:
        rtnl_unlock();
        return err;
}

/*
 *      Write the contents of the ARP cache to a PROCfs file.
 */
#ifndef CONFIG_PROC_FS
static int arp_get_info(char *buffer, char **start, off_t offset, int length) { return 0; }
#else
#if defined(CONFIG_AX25) || defined(CONFIG_AX25_MODULE)
static char *ax2asc2(ax25_address *a, char *buf);
#endif
#define HBUFFERLEN 30

static int arp_get_info(char *buffer, char **start, off_t offset, int length)
{
        int len=0;
        off_t pos=0;
        int size;
        char hbuffer[HBUFFERLEN];
        int i,j,k;
        const char hexbuf[] =  "0123456789ABCDEF";

        size = sprintf(buffer,"IP address       HW type     Flags       HW address            Mask     Device\n");

        pos+=size;
        len+=size;

        for(i=0; i<=NEIGH_HASHMASK; i++) {
                struct neighbour *n;
                read_lock_bh(&arp_tbl.lock);
                for (n=arp_tbl.hash_buckets[i]; n; n=n->next) {
                        struct net_device *dev = n->dev;
                        int hatype = dev->type;

                        /* Do not confuse users "arp -a" with magic entries */
                        if (!(n->nud_state&~NUD_NOARP))
                                continue;

                        read_lock(&n->lock);

/*
 *      Convert hardware address to XX:XX:XX:XX ... form.
 */
#if defined(CONFIG_AX25) || defined(CONFIG_AX25_MODULE)
                        if (hatype == ARPHRD_AX25 || hatype == ARPHRD_NETROM)
                                ax2asc2((ax25_address *)n->ha, hbuffer);
                        else {
#endif
                        for (k=0,j=0;k<HBUFFERLEN-3 && j<dev->addr_len;j++) {
                                hbuffer[k++]=hexbuf[(n->ha[j]>>4)&15 ];
                                hbuffer[k++]=hexbuf[n->ha[j]&15     ];
                                hbuffer[k++]=':';
                        }
                        hbuffer[--k]=0;

#if defined(CONFIG_AX25) || defined(CONFIG_AX25_MODULE)
                }
#endif

                        {
                                char tbuf[16];
                                sprintf(tbuf, "%u.%u.%u.%u", NIPQUAD(*(u32*)n->primary_key));
                                size = sprintf(buffer+len, "%-16s 0x%-10x0x%-10x%s"
                                                        "     *        %s\n",
                                        tbuf,
                                        hatype,
                                        arp_state_to_flags(n), 
                                        hbuffer,
                                        dev->name);
                        }

                        read_unlock(&n->lock);

                        len += size;
                        pos += size;
                  
                        if (pos <= offset)
                                len=0;
                        if (pos >= offset+length) {
                                read_unlock_bh(&arp_tbl.lock);
                                goto done;
                        }
                }
                read_unlock_bh(&arp_tbl.lock);
        }

        for (i=0; i<=PNEIGH_HASHMASK; i++) {
                struct pneigh_entry *n;
                for (n=arp_tbl.phash_buckets[i]; n; n=n->next) {
                        struct net_device *dev = n->dev;
                        int hatype = dev ? dev->type : 0;

                        {
                                char tbuf[16];
                                sprintf(tbuf, "%u.%u.%u.%u", NIPQUAD(*(u32*)n->key));
                                size = sprintf(buffer+len, "%-16s 0x%-10x0x%-10x%s"
                                                        "     *        %s\n",
                                        tbuf,
                                        hatype,
                                        ATF_PUBL|ATF_PERM,
                                        "00:00:00:00:00:00",
                                        dev ? dev->name : "*");
                        }

                        len += size;
                        pos += size;
                  
                        if (pos <= offset)
                                len=0;
                        if (pos >= offset+length)
                                goto done;
                }
        }

done:
  
        *start = buffer+len-(pos-offset);       /* Start of wanted data */
        len = pos-offset;                       /* Start slop */
        if (len>length)
                len = length;                   /* Ending slop */
        if (len<0)
                len = 0;
        return len;
}
#endif

static int arp_netdev_event(struct notifier_block *this, unsigned long event, void *ptr)
{
        struct net_device *dev = ptr;

        switch (event) {
        case NETDEV_CHANGEADDR:
                neigh_changeaddr(&arp_tbl, dev);
                rt_cache_flush(0);
                break;
        default:
                break;
        }

        return NOTIFY_DONE;
}

struct notifier_block arp_netdev_notifier = {
        .notifier_call = arp_netdev_event,
};

/* Note, that it is not on notifier chain.
   It is necessary, that this routine was called after route cache will be
   flushed.
 */
void arp_ifdown(struct net_device *dev)
{
        neigh_ifdown(&arp_tbl, dev);
}


/*
 *      Called once on startup.
 */

static struct packet_type arp_packet_type = {
        type:   __constant_htons(ETH_P_ARP),
        func:   arp_rcv,
        data:   (void*) 1, /* understand shared skbs */
};

void __init arp_init (void)
{
        neigh_table_init(&arp_tbl);

        dev_add_pack(&arp_packet_type);

        proc_net_create ("arp", 0, arp_get_info);

#ifdef CONFIG_SYSCTL
        neigh_sysctl_register(NULL, &arp_tbl.parms, NET_IPV4, NET_IPV4_NEIGH, "ipv4");
#endif
        register_netdevice_notifier(&arp_netdev_notifier);
}


#ifdef CONFIG_PROC_FS
#if defined(CONFIG_AX25) || defined(CONFIG_AX25_MODULE)

/*
 *      ax25 -> ASCII conversion
 */
char *ax2asc2(ax25_address *a, char *buf)
{
        char c, *s;
        int n;

        for (n = 0, s = buf; n < 6; n++) {
                c = (a->ax25_call[n] >> 1) & 0x7F;

                if (c != ' ') *s++ = c;
        }
        
        *s++ = '-';

        if ((n = ((a->ax25_call[6] >> 1) & 0x0F)) > 9) {
                *s++ = '1';
                n -= 10;
        }
        
        *s++ = n + '0';
        *s++ = '\0';

        if (*buf == '\0' || *buf == '-')
           return "*";

        return buf;

}

#endif
#endif

---