linux原始套接字(1)-arp请求与接收

一.概述                                                  

以太网的arp数据包结构：

arp结构op操作参数：1为请求，2为应答。

常用的数据结构如下：

1.物理地址结构位于netpacket/packet.h

 1 struct sockaddr_ll 2 { 3     unsigned short int sll_family; 4     unsigned short int sll_protocol; 5     int sll_ifindex; 6     unsigned short int sll_hatype; 7     unsigned char sll_pkttype; 8     unsigned char sll_halen; 9     unsigned char sll_addr[8];10 };

sll_ifindex是网络(网卡)接口索引，代表从这个接口收发数据包

2.网络(网卡)接口数据结构位于net/if.h

 1 struct ifreq 2 { 3 # define IFHWADDRLEN    6 4 # define IFNAMSIZ    IF_NAMESIZE 5     union 6       { 7     char ifrn_name[IFNAMSIZ];    /* Interface name, e.g. "en0".  */ 8       } ifr_ifrn; 9 10     union11       {12     struct sockaddr ifru_addr;13     struct sockaddr ifru_dstaddr;14     struct sockaddr ifru_broadaddr;15     struct sockaddr ifru_netmask;16     struct sockaddr ifru_hwaddr;17     short int ifru_flags;18     int ifru_ivalue;19     int ifru_mtu;20     struct ifmap ifru_map;21     char ifru_slave[IFNAMSIZ];    /* Just fits the size */22     char ifru_newname[IFNAMSIZ];23     __caddr_t ifru_data;24       } ifr_ifru;25 };

该结构里面包含2个union，第一个是接口名，如：eth0，wlan0等。可以通过ioctl()函数来获取对应的接口信息，ip地址，mac地址，接口索引等。

3.以太网首部结构位于net/ethernet.h

1 struct ether_header2 {3   u_int8_t  ether_dhost[ETH_ALEN];    /* destination eth addr    */4   u_int8_t  ether_shost[ETH_ALEN];    /* source ether addr    */5   u_int16_t ether_type;                /* packet type ID field    */6 } __attribute__ ((__packed__));

ether_type帧类型：常见的有IP，ARP，RARP，都有对应的宏定义。

4.arp包结构位于netinet/if_ether.h

 1 struct    ether_arp { 2     struct    arphdr ea_hdr;        /* fixed-size header */ 3     u_int8_t arp_sha[ETH_ALEN];    /* sender hardware address */ 4     u_int8_t arp_spa[4];        /* sender protocol address */ 5     u_int8_t arp_tha[ETH_ALEN];    /* target hardware address */ 6     u_int8_t arp_tpa[4];        /* target protocol address */ 7 }; 8 #define    arp_hrd    ea_hdr.ar_hrd 9 #define    arp_pro    ea_hdr.ar_pro10 #define    arp_hln    ea_hdr.ar_hln11 #define    arp_pln    ea_hdr.ar_pln12 #define    arp_op    ea_hdr.ar_op

上面的ether_arp结构还包含一个arp首部，位于net/if_arp.h

1 struct arphdr2 {3     unsigned short int ar_hrd;        /* Format of hardware address.  */4     unsigned short int ar_pro;        /* Format of protocol address.  */5     unsigned char ar_hln;        /* Length of hardware address.  */6     unsigned char ar_pln;        /* Length of protocol address.  */7     unsigned short int ar_op;        /* ARP opcode (command).  */8 }

二.arp请求代码                                      

  1 /**  2  * @file arp_request.c  3  */  4   5 #include <stdio.h>  6 #include <stdlib.h>  7 #include <string.h>  8 #include <unistd.h>  9 #include <sys/ioctl.h> 10 #include <sys/socket.h> 11 #include <arpa/inet.h> 12 #include <netinet/in.h> 13 #include <netinet/if_ether.h> 14 #include <net/ethernet.h> 15 #include <net/if_arp.h> 16 #include <net/if.h> 17 #include <netpacket/packet.h> 18  19 /* 以太网帧首部长度 */ 20 #define ETHER_HEADER_LEN sizeof(struct ether_header) 21 /* 整个arp结构长度 */ 22 #define ETHER_ARP_LEN sizeof(struct ether_arp) 23 /* 以太网 + 整个arp结构长度 */ 24 #define ETHER_ARP_PACKET_LEN ETHER_HEADER_LEN + ETHER_ARP_LEN 25 /* IP地址长度 */ 26 #define IP_ADDR_LEN 4 27 /* 广播地址 */ 28 #define BROADCAST_ADDR {0xff, 0xff, 0xff, 0xff, 0xff, 0xff} 29  30 void err_exit(const char *err_msg) 31 { 32     perror(err_msg); 33     exit(1); 34 } 35  36 /* 填充arp包 */ 37 struct ether_arp *fill_arp_packet(const unsigned char *src_mac_addr, const char *src_ip, const char *dst_ip) 38 { 39     struct ether_arp *arp_packet; 40     struct in_addr src_in_addr, dst_in_addr; 41     unsigned char dst_mac_addr[ETH_ALEN] = BROADCAST_ADDR; 42  43     /* IP地址转换 */ 44     inet_pton(AF_INET, src_ip, &src_in_addr); 45     inet_pton(AF_INET, dst_ip, &dst_in_addr); 46  47     /* 整个arp包 */ 48     arp_packet = (struct ether_arp *)malloc(ETHER_ARP_LEN); 49     arp_packet->arp_hrd = htons(ARPHRD_ETHER); 50     arp_packet->arp_pro = htons(ETHERTYPE_IP); 51     arp_packet->arp_hln = ETH_ALEN; 52     arp_packet->arp_pln = IP_ADDR_LEN; 53     arp_packet->arp_op = htons(ARPOP_REQUEST); 54     memcpy(arp_packet->arp_sha, src_mac_addr, ETH_ALEN); 55     memcpy(arp_packet->arp_tha, dst_mac_addr, ETH_ALEN); 56     memcpy(arp_packet->arp_spa, &src_in_addr, IP_ADDR_LEN); 57     memcpy(arp_packet->arp_tpa, &dst_in_addr, IP_ADDR_LEN); 58  59     return arp_packet; 60 } 61  62 /* arp请求 */ 63 void arp_request(const char *if_name, const char *dst_ip) 64 { 65     struct sockaddr_ll saddr_ll; 66     struct ether_header *eth_header; 67     struct ether_arp *arp_packet; 68     struct ifreq ifr; 69     char buf[ETHER_ARP_PACKET_LEN]; 70     unsigned char src_mac_addr[ETH_ALEN]; 71     unsigned char dst_mac_addr[ETH_ALEN] = BROADCAST_ADDR; 72     char *src_ip; 73     int sock_raw_fd, ret_len, i; 74  75     if ((sock_raw_fd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ARP))) == -1) 76         err_exit("socket()"); 77  78     bzero(&saddr_ll, sizeof(struct sockaddr_ll)); 79     bzero(&ifr, sizeof(struct ifreq)); 80     /* 网卡接口名 */ 81     memcpy(ifr.ifr_name, if_name, strlen(if_name)); 82  83     /* 获取网卡接口索引 */ 84     if (ioctl(sock_raw_fd, SIOCGIFINDEX, &ifr) == -1) 85         err_exit("ioctl() get ifindex"); 86     saddr_ll.sll_ifindex = ifr.ifr_ifindex; 87     saddr_ll.sll_family = PF_PACKET; 88  89     /* 获取网卡接口IP */ 90     if (ioctl(sock_raw_fd, SIOCGIFADDR, &ifr) == -1) 91         err_exit("ioctl() get ip"); 92     src_ip = inet_ntoa(((struct sockaddr_in *)&(ifr.ifr_addr))->sin_addr); 93     printf("local ip:%s\n", src_ip); 94  95     /* 获取网卡接口MAC地址 */ 96     if (ioctl(sock_raw_fd, SIOCGIFHWADDR, &ifr)) 97         err_exit("ioctl() get mac"); 98     memcpy(src_mac_addr, ifr.ifr_hwaddr.sa_data, ETH_ALEN); 99     printf("local mac");100     for (i = 0; i < ETH_ALEN; i++)101         printf(":%02x", src_mac_addr[i]);102     printf("\n");103 104     bzero(buf, ETHER_ARP_PACKET_LEN);105     /* 填充以太首部 */106     eth_header = (struct ether_header *)buf;107     memcpy(eth_header->ether_shost, src_mac_addr, ETH_ALEN);108     memcpy(eth_header->ether_dhost, dst_mac_addr, ETH_ALEN);109     eth_header->ether_type = htons(ETHERTYPE_ARP);110     /* arp包 */111     arp_packet = fill_arp_packet(src_mac_addr, src_ip, dst_ip);112     memcpy(buf + ETHER_HEADER_LEN, arp_packet, ETHER_ARP_LEN);113 114     /* 发送请求 */115     ret_len = sendto(sock_raw_fd, buf, ETHER_ARP_PACKET_LEN, 0, (struct sockaddr *)&saddr_ll, sizeof(struct sockaddr_ll));116     if ( ret_len > 0)117         printf("sendto() ok!!!\n");118 119     close(sock_raw_fd);120 }121 122 int main(int argc, const char *argv[])123 {124     if (argc != 3)125     {126         printf("usage:%s device_name dst_ip\n", argv[0]);127         exit(1);128     }129 130     arp_request(argv[1], argv[2]);131     132     return 0;133 }

流程：命令行接收网卡接口名和要请求的目标IP地址，传入arp_request()函数。用PF_PACKET选项创建ARP类型的原始套接字。用ioctl()函数通过网卡接口名来获取该接口对应的mac地址，ip地址，接口索引。接口索引填充到物理地址sockaddr_ll里面。然后填充以太首部，源地址对应刚刚的网卡接口mac地址，目标地址填广播地址(第28行定义的宏)。以太首部帧类型是ETHERTYPE_ARP，代表arp类型。接着填充arp数据包结构，同样要填充源/目标的ip地址和mac地址，arp包的操作选项填写ARPOP_REQUEST，代表请求操作。填充完成后发送到刚刚的物理地址sockaddr_ll。

三.接收arp数据包                                  

 1 /** 2  * @file arp_recv.c 3  */ 4  5 #include <stdio.h> 6 #include <stdlib.h> 7 #include <string.h> 8 #include <unistd.h> 9 #include <sys/socket.h>10 #include <arpa/inet.h>11 #include <netinet/in.h>12 #include <netinet/if_ether.h>13 #include <net/if_arp.h>14 #include <net/ethernet.h>15 16 /* 以太网帧首部长度 */17 #define ETHER_HEADER_LEN sizeof(struct ether_header)18 /* 整个arp结构长度 */19 #define ETHER_ARP_LEN sizeof(struct ether_arp)20 /* 以太网 + 整个arp结构长度 */21 #define ETHER_ARP_PACKET_LEN ETHER_HEADER_LEN + ETHER_ARP_LEN22 /* IP地址长度 */23 #define IP_ADDR_LEN 424 25 void err_exit(const char *err_msg)26 {27     perror(err_msg);28     exit(1);29 }30 31 int main(void)32 {33     struct ether_arp *arp_packet;34     char buf[ETHER_ARP_PACKET_LEN];35     int sock_raw_fd, ret_len, i;36 37     if ((sock_raw_fd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ARP))) == -1)38         err_exit("socket()");39 40     while (1)41     {42         bzero(buf, ETHER_ARP_PACKET_LEN);43         ret_len = recv(sock_raw_fd, buf, ETHER_ARP_PACKET_LEN, 0);44         if (ret_len > 0)45         {46             /* 剥去以太头部 */47             arp_packet = (struct ether_arp *)(buf + ETHER_HEADER_LEN);48             /* arp操作码为2代表arp应答 */49             if (ntohs(arp_packet->arp_op) == 2)50             {51                 printf("==========================arp replay======================\n");52                 printf("from ip:");53                 for (i = 0; i < IP_ADDR_LEN; i++)54                     printf(".%u", arp_packet->arp_spa[i]);55                 printf("\nfrom mac");56                 for (i = 0; i < ETH_ALEN; i++)57                     printf(":%02x", arp_packet->arp_sha[i]);58                 printf("\n");59             }60         }61     }62 63     close(sock_raw_fd);64     return 0;65 }

流程：创建ARP类型的原始套接字。直接调用接收函数，会收到网卡接收的arp数据包，判断收到的arp包操作是arp应答，操作码是2。然后剥去以太首部，取出源mac地址和ip地址！！！

四.实验                                                  

为了更直观，我们打开wireshark一起观察，我这里是wlan环境，监听wlan0。原始套接字要以root身份运行，先运行arp_recv，然后运行arp_request发送arp请求：

wireshark结果：

上面可以看到，第一条数据包询问谁是192.168.0.1，然后第二条数据包发送了一个回复，可以看到wireshark里面Opcode:reply(2)。源ip和mac地址跟我们自己的接收程序一样。