原始套接字

在计算机网络中, 原始套接字（raw socket）是一种网络套接字，允许直接发送/接收IP协议数据包而不需要任何传输层协议格式。 对于标准的套接字，通常数据按照选定的传输层协议(例如TCP、UDP)自动封装，socket用户并不知道在网络介质上广播的数据包含了这种协议包头。 从原始套接字读取数据包含了传输层协议包头。用原始套接字发送数据，是否自动增加传输层协议包头是可选的。 原始套接字用于安全相关的应用程序，如nmap。原始套接字一种可能的用例是在用户空间实现新的传输层协议。 原始套接字常在网络设备上用于路由协议，例如IGMPv4、开放式最短路径优先协议 (OSPF)、互联网控制消息协议 (ICMP)。Ping就是发送一个ICMP响应请求包然后接收ICMP响应回复. 大部分套接字API都支持原始套接字功能。Winsock自2001年起在Windows XP上支持原始套接字。但由于安全原因，2004年微软限制了Winsock的原始套接字功能。 下例在Linux上实现了Ping程序的主要功能： #include <stdio.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <unistd.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/socket.h> #include <netinet/in.h> #include <netinet/ip.h> #include <netinet/ip_icmp.h> #include <arpa/inet.h> #include <netdb.h> /* 校验和計算 */ u_int16_t checksum(unsigned short *buf, int size) { unsigned long sum = 0; while (size > 1) { sum += *buf; buf++; size -= 2; } if (size == 1) sum += *(unsigned char *)buf; sum = (sum & 0xffff) + (sum >> 16); sum = (sum & 0xffff) + (sum >> 16); return ~sum; } /* protocol指定的raw socket创建 */ int make_raw_socket(int protocol) { int s = socket(AF_INET, SOCK_RAW, protocol); if (s < 0) { perror("socket"); exit(EXIT_FAILURE); } return s; } /* ICMP头部的作成 */ void setup_icmphdr(u_int8_t type, u_int8_t code, u_int16_t id, u_int16_t seq, struct icmphdr *icmphdr) { memset(icmphdr, 0, sizeof(struct icmphdr)); icmphdr->type = type; icmphdr->code = code; icmphdr->checksum = 0; icmphdr->un.echo.id = id; icmphdr->un.echo.sequence = seq; icmphdr->checksum = checksum((unsigned short *)icmphdr, sizeof(struct icmphdr)); } int main(int argc, char **argv) { int n, soc; char buf[1500]; struct sockaddr_in addr; struct in_addr insaddr; struct icmphdr icmphdr; struct iphdr *recv_iphdr; struct icmphdr *recv_icmphdr; if (argc < 2) { printf("Usage : %s IP_ADDRESS\n", argv[0]); return 1; } addr.sin_family = AF_INET; addr.sin_addr.s_addr = inet_addr(argv[1]); soc = make_raw_socket(IPPROTO_ICMP); setup_icmphdr(ICMP_ECHO, 0, 0, 0, &icmphdr); /* ICMP包的送信 */ n = sendto(soc, (char *)&icmphdr, sizeof(icmphdr), 0, (struct sockaddr *)&addr, sizeof(addr)); if (n < 1) { perror("sendto"); return 1; } /* ICMP包的受信 */ n = recv(soc, buf, sizeof(buf), 0); if (n < 1) { perror("recv"); return 1; } recv_iphdr = (struct iphdr *)buf; /* 从IP包头获取IP包的长度，从而确定icmp包头的开始位置 */ recv_icmphdr = (struct icmphdr *)(buf + (recv_iphdr->ihl << 2)); insaddr.s_addr = recv_iphdr->saddr; /* 检查送信包的源地址匹配受信包的目的地址 */ if (!strcmp(argv[1], inet_ntoa(insaddr)) && recv_icmphdr->type == ICMP_ECHOREPLY) printf("icmp echo reply from %s\n", argv[1]); close(soc); return 0; } 下例是binding一个原始套接字并使用： #include<stdio.h> #include<stdlib.h> #include<sys/socket.h> #include<features.h> #include<linux/if_packet.h> #include<linux/if_ether.h> #include<errno.h> #include<sys/ioctl.h> #include<net/if.h> #define PACKET_LENGTH 1024 int CreateRawSocket(int protocol_to_sniff) { int rawsock; if((rawsock = socket(PF_PACKET, SOCK_RAW, htons(protocol_to_sniff)))== -1) { perror("Error creating raw socket: "); exit(-1); } return rawsock; } int BindRawSocketToInterface(char *device, int rawsock, int protocol) { struct sockaddr_ll sll; struct ifreq ifr; memset(&sll, 0, sizeof(sll)); memset(&ifr, 0, sizeof(ifr)); /* First Get the Interface Index */ strncpy((char *)ifr.ifr_name, device, IFNAMSIZ); if((ioctl(rawsock, SIOCGIFINDEX, &ifr)) == -1) { printf("Error getting Interface index !\n"); exit(-1); } /* Bind our raw socket to this interface */ sll.sll_family = AF_PACKET; sll.sll_ifindex = ifr.ifr_ifindex; sll.sll_protocol = htons(protocol); if((bind(rawsock, (struct sockaddr *)&sll, sizeof(sll)))== -1) { perror("Error binding raw socket to interface\n"); exit(-1); } return 1; } int SendRawPacket(int rawsock, unsigned char *pkt, int pkt_len) { int sent= 0; /* A simple write on the socket ..thats all it takes ! */ if((sent = write(rawsock, pkt, pkt_len)) != pkt_len) { return 0; } return 1; } /* argv[1] is the device e.g. eth0 argv[2] is the number of packets to send */ main(int argc, char **argv) { int raw; unsigned char packet[PACKET_LENGTH]; int num_of_pkts; /* Set the packet to all A's */ memset(packet, 'A', PACKET_LENGTH); /* Create the raw socket */ raw = CreateRawSocket(ETH_P_ALL); /* Bind raw socket to interface */ BindRawSocketToInterface(argv[1], raw, ETH_P_ALL); num_of_pkts = atoi(argv[2]); while((num_of_pkts--)>0) { if(!SendRawPacket(raw, packet, PACKET_LENGTH)) { perror("Error sending packet"); } else { printf("Packet sent successfully\n"); } } close(raw); return 0; } IPv4包格式 IPv6包格式 raw(7): IPv4 raw sockets - Linux man page. die.net. [2017-03-14]. （原始内容存档于2016-09-07）.  Raw IP Networking FAQ. faqs.org. [2017-03-14]. （原始内容存档于2012-01-19）.  Ian Griffiths for IanG on Tap. 12 August, 2004. Raw Sockets Gone in XP SP2 （页面存档备份，存于互联网档案馆） Net::RawIP; module for Perl applications. Created by Sergey Kolychev. Network Programming for Microsoft Windows (ISBN 0-7356-1579-9) A little more info on raw sockets and Windows XP SP2 - Michael Howard's Web Log an indication of what's actually allowed on Windows. SOCK_RAW Demystified: article describing inner workings of Raw Sockets （页面存档备份，存于互联网档案馆） C language examples of Linux raw sockets for IPv4 and IPv6 - David Buchan's C language examples of IPv4 and IPv6 raw sockets for Linux.