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. */
//判斷skb是否含有足夠的數據
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;
//netfiter處理後，轉至arp_process中處理
return NF_HOOK(NF_ARP, NF_ARP_IN, skb, dev, NULL, arp_process);
freeskb:
kfree_skb(skb);
out_of_mem:
return 0;
}
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 and verifies the device
* is ARP'able.
*/
//接口上沒有IP
if (in_dev == NULL)
goto out;
//取得arp 頭部
arp = skb->nh.arph;
switch (dev_type) {
default:
//arp 不為IP類型,或者且不與接口相同
if (arp->ar_pro != htons(ETH_P_IP) ||
htons(dev_type) != arp->ar_hrd)
goto out;
break;
#ifdef CONFIG_NET_ETHERNET
case ARPHRD_ETHER:
#endif
#ifdef CONFIG_TR
case ARPHRD_IEEE802_TR:
#endif
#ifdef CONFIG_FDDI
case ARPHRD_FDDI:
#endif
#ifdef CONFIG_NET_FC
case ARPHRD_IEEE802:
#endif
#if defined(CONFIG_NET_ETHERNET) || defined(CONFIG_TR) || \
defined(CONFIG_FDDI) || defined(CONFIG_NET_FC)
/*
* 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;
#endif
#if defined(CONFIG_AX25) || defined(CONFIG_AX25_MODULE)
case ARPHRD_AX25:
if (arp->ar_pro != htons(AX25_P_IP) ||
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) ||
arp->ar_hrd != htons(ARPHRD_NETROM))
goto out;
break;
#endif
#endif
}
/* Understand only these message types */
//不為請求或者應答
if (arp->ar_op != htons(ARPOP_REPLY) &&
arp->ar_op != htons(ARPOP_REQUEST))
goto out;
/*
* Extract fields
*/
arp_ptr= (unsigned char *)(arp+1);
//發送端以太網地址首地址
sha = arp_ptr;
arp_ptr += dev->addr_len;
//sip 發送端IP地址
memcpy(&sip, arp_ptr, 4);
arp_ptr += 4;
tha = arp_ptr;
arp_ptr += dev->addr_len;
//tip 目的IP地址
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.
*/
//回環或者多播地址
if (LOOPBACK(tip) || MULTICAST(tip))
