C语言实现Linux网络嗅探器

0x01 实验简介

网络嗅探器是拦截通过网络接口流入和流出的数据的程序。所以，如果你正在浏览的互联网，嗅探器以数据包的形式抓到它并且显示。在本实验中，我们用 C 语言实现了一个网络嗅探器。

0x02程序框架和功能描述

本程序使用c语言编程，实现linux环境下网络嗅探的功能，并实现对接收到的UDP数据报进行解析。

0x03程序代码

sniffer.h

#ifndef	__SNIFFER_H__
#define	__SNIFFER_H__


typedef struct	s_protocol
{
	int	tcp;
	int	udp;
	int	icmp;
	int	igmp;
	int	others;
	int	total;
} t_protocol;

typedef struct	s_sniffer
{
	FILE *logfile;
	t_protocol *prot;
} t_sniffer;

void ProcessPacket(unsigned char*, int, t_sniffer *);
void print_ip_header(unsigned char* , int, t_sniffer *);
void print_tcp_packet(unsigned char* , int, t_sniffer *);
void print_udp_packet(unsigned char * , int, t_sniffer *);
void print_icmp_packet(unsigned char* , int, t_sniffer *);
void PrintData (unsigned char* , int, t_sniffer *);
void display_time_and_date();
void getting_started();
void signal_white_now(int);

#endif

tools.h

#ifndef	__COLOR_H__
#define	__COLOR_H__

#include <stdio.h>

#define	CLEARSCREEN() printf("\033[H\033[2J")
#define	INITCOLOR(color) printf("\033[%sm", color)
#define	RED_COLOR "31"
#define	GREEN_COLOR	"32"
#define	YELLOW_COLOR "33"
#define	BLUE_COLOR "34"
#define	ZERO_COLOR "0"

#endif		

tools.c

#include	<signal.h>
#include	<stdio.h>

/* 信号处理函数 */
void signal_white_now(int signum)
{
	printf("Bye Bye !\n");
}

show_data.c

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/ip_icmp.h>
#include <netinet/udp.h>
#include <netinet/tcp.h>
#include <netinet/ip.h>
#include <sys/socket.h>
#include <arpa/inet.h>

#include "sniffer.h"
#include "tools.h"

/* 写 IP 头部到日志文件 */
void print_ip_header(unsigned char *buf, int size, t_sniffer *sniffer)
{
	unsigned short iphdrlen;
	struct iphdr *iph;
	struct sockaddr_in source;
	struct sockaddr_in dest;

	iph = (struct iphdr *)buf;
	iphdrlen = iph->ihl*4; 
	(void)iphdrlen;
	(void)size;
	memset(&source, 0, sizeof(source));
	source.sin_addr.s_addr = iph->saddr;
  
	memset(&dest, 0, sizeof(dest));
	dest.sin_addr.s_addr = iph->daddr;
  
	fprintf(sniffer->logfile,"\n");
	fprintf(sniffer->logfile,"IP Header\n");
	fprintf(sniffer->logfile,"   |-IP Version        : %d\n",(unsigned int)iph->version);
	fprintf(sniffer->logfile,"   |-IP Header Length  : %d DWORDS or %d Bytes\n",(unsigned int)iph->ihl,((unsigned int)(iph->ihl))*4);
	fprintf(sniffer->logfile,"   |-Type Of Service   : %d\n",(unsigned int)iph->tos);
	fprintf(sniffer->logfile,"   |-IP Total Length   : %d  Bytes(size of Packet)\n",ntohs(iph->tot_len));
	fprintf(sniffer->logfile,"   |-Identification    : %d\n",ntohs(iph->id));
	fprintf(sniffer->logfile,"   |-TTL      : %d\n",(unsigned int)iph->ttl);
	fprintf(sniffer->logfile,"   |-Protocol : %d\n",(unsigned int)iph->protocol);
	fprintf(sniffer->logfile,"   |-Checksum : %d\n",ntohs(iph->check));
	fprintf(sniffer->logfile,"   |-Source IP        : %s\n",inet_ntoa(source.sin_addr));
	fprintf(sniffer->logfile,"   |-Destination IP   : %s\n",inet_ntoa(dest.sin_addr));
}

/* 写 TCP 数据包到日志文件 */
void print_tcp_packet(unsigned char *buf, int size, t_sniffer *sniffer)
{
	unsigned short iphdrlen;
	struct iphdr *iph;
	struct tcphdr *tcph;
  
	iph = (struct iphdr *)buf;
	iphdrlen = iph->ihl * 4;  
	tcph = (struct tcphdr*)(buf + iphdrlen);
	print_ip_header(buf, size, sniffer);
    
	/* 把 tcp 头信息写入日志文件中 */
	fprintf(sniffer->logfile,"\n");
	fprintf(sniffer->logfile,"TCP Header\n");
	fprintf(sniffer->logfile,"   |-Source Port      : %u\n",ntohs(tcph->source));
	fprintf(sniffer->logfile,"   |-Destination Port : %u\n",ntohs(tcph->dest));
	fprintf(sniffer->logfile,"   |-Sequence Number    : %u\n",ntohl(tcph->seq));
	fprintf(sniffer->logfile,"   |-Acknowledge Number : %u\n",ntohl(tcph->ack_seq));
	fprintf(sniffer->logfile,"   |-Header Length      : %d DWORDS or %d BYTES\n" ,(unsigned int)tcph->doff,(unsigned int)tcph->doff*4);
	fprintf(sniffer->logfile,"   |-Urgent Flag          : %d\n",(unsigned int)tcph->urg);
	fprintf(sniffer->logfile,"   |-Acknowledgement Flag : %d\n",(unsigned int)tcph->ack);
	fprintf(sniffer->logfile,"   |-Push Flag            : %d\n",(unsigned int)tcph->psh);
	fprintf(sniffer->logfile,"   |-Reset Flag           : %d\n",(unsigned int)tcph->rst);
	fprintf(sniffer->logfile,"   |-Synchronise Flag     : %d\n",(unsigned int)tcph->syn);
	fprintf(sniffer->logfile,"   |-Finish Flag          : %d\n",(unsigned int)tcph->fin);
	fprintf(sniffer->logfile,"   |-Window         : %d\n",ntohs(tcph->window));
	fprintf(sniffer->logfile,"   |-Checksum       : %d\n",ntohs(tcph->check));
	fprintf(sniffer->logfile,"   |-Urgent Pointer : %d\n",tcph->urg_ptr);
	fprintf(sniffer->logfile,"\n");
	fprintf(sniffer->logfile,"                        DATA Dump                         ");
	fprintf(sniffer->logfile,"\n");
  
	fprintf(sniffer->logfile,"IP Header\n");
	PrintData(buf, iphdrlen, sniffer);
  
	fprintf(sniffer->logfile,"TCP Header\n");
	PrintData(buf+iphdrlen, tcph->doff*4, sniffer);
  
	fprintf(sniffer->logfile,"Data Payload\n");

	/* 把用户数据写入日志文件 */
	PrintData(buf + iphdrlen + tcph->doff*4,
		(size - tcph->doff*4-iph->ihl*4),
		sniffer );
  
	fprintf(sniffer->logfile,"\n###########################################################");
}

/* 写 UDP 数据包到日志文件 */
void print_udp_packet(unsigned char *buf , int size, t_sniffer *sniffer)
{
	unsigned short iphdrlen;

	struct iphdr *iph;
	struct udphdr *udph;

	iph = (struct iphdr *)buf;
	iphdrlen = iph->ihl*4;
	udph = (struct udphdr*)(buf + iphdrlen);
	fprintf(sniffer->logfile,"\n\n***********************UDP Packet*************************\n");
  
	print_ip_header(buf, size, sniffer);
    
	/* 把 udp 头信息写入日志文件中 */
	fprintf(sniffer->logfile,"\nUDP Header\n");
	fprintf(sniffer->logfile,"   |-Source Port      : %d\n" , ntohs(udph->source));
	fprintf(sniffer->logfile,"   |-Destination Port : %d\n" , ntohs(udph->dest));
	fprintf(sniffer->logfile,"   |-UDP Length       : %d\n" , ntohs(udph->len));
	fprintf(sniffer->logfile,"   |-UDP Checksum     : %d\n" , ntohs(udph->check));
  
	fprintf(sniffer->logfile,"\n");
	fprintf(sniffer->logfile,"IP Header\n");
	PrintData(buf , iphdrlen, sniffer);
  
	fprintf(sniffer->logfile,"UDP Header\n");
	PrintData(buf+iphdrlen, sizeof(udph), sniffer);
  
	fprintf(sniffer->logfile,"Data Payload\n");

	/* 把用户数据写入日志文件 */
	PrintData(buf + iphdrlen + sizeof udph,
		(size - sizeof udph - iph->ihl * 4),
		sniffer);
  
	fprintf(sniffer->logfile,"\n###########################################################");
}

/* 写 ICMP 数据包到日志文件 */
void print_icmp_packet(unsigned char *buf , int size, t_sniffer *sniffer)
{
	unsigned short iphdrlen;
	struct iphdr	*iph;
	struct icmphdr *icmph;
  
	iph = (struct iphdr *)buf;
	iphdrlen = iph->ihl * 4;
	icmph = (struct icmphdr *)(buf + iphdrlen);

	/* 把 icmp 头信息写入日志文件中 */
	fprintf(sniffer->logfile,"\n\n***********************ICMP Packet*************************\n");  
	print_ip_header(buf , size, sniffer);
	fprintf(sniffer->logfile,"\n");
	fprintf(sniffer->logfile,"ICMP Header\n");
	fprintf(sniffer->logfile,"   |-Type : %d",(unsigned int)(icmph->type));  
	if((unsigned int)(icmph->type) == 11) 
	fprintf(sniffer->logfile,"  (TTL Expired)\n");
	else if((unsigned int)(icmph->type) == ICMP_ECHOREPLY) 
	fprintf(sniffer->logfile,"  (ICMP Echo Reply)\n");
	fprintf(sniffer->logfile,"   |-Code : %d\n",(unsigned int)(icmph->code));
	fprintf(sniffer->logfile,"   |-Checksum : %d\n",ntohs(icmph->checksum));
	fprintf(sniffer->logfile,"\n");
	fprintf(sniffer->logfile,"IP Header\n");
	PrintData(buf, iphdrlen, sniffer);
	fprintf(sniffer->logfile,"UDP Header\n");
	PrintData(buf + iphdrlen , sizeof(icmph), sniffer);
  
	fprintf(sniffer->logfile,"Data Payload\n");  

	/* 最后将用户数据写入日志文件中 */
	PrintData(buf + iphdrlen + sizeof(icmph),
		(size - sizeof(icmph) - iph->ihl * 4),
		sniffer);
  
	fprintf(sniffer->logfile,"\n###########################################################");
}

/* 写用户数据到日志文件 */
void PrintData(unsigned char *buf, int size, t_sniffer *sniffer)
{
  int i;

  for(i = 0 ; i < size ; i++)
	{
		if(i % 16 == 0)
		fprintf(sniffer->logfile, "\n");
		fprintf(sniffer->logfile, " %02X",(unsigned int)buf[i]);
      
		if( i == size - 1)
			fprintf(sniffer->logfile, "\n");
	}
}

main.c

#include	<signal.h>
#include	<unistd.h>
#include	<stdio.h>
#include	<stdlib.h>
#include	<string.h>
#include	<netinet/ip.h>
#include	<sys/socket.h>
#include	<sys/select.h>
#include	<fcntl.h>
#include	<sys/types.h>
#include	<sys/time.h>
#include	<errno.h>

#include	"sniffer.h"
#include	"tools.h"

#define ETH_P_IP 0x0800

int	exec_cmd(char *buffer, int len)
{
	if (strncmp(buffer, "quit", 4) == 0)
		return (1);
	return (0);
}

int	command_interpreter(int sd)
{
	int	len;
	char buf[512];

	len = read(0, buf, 512);
	if (len > 0)
	{
		if (exec_cmd(buf, len) == 1)
			return (1);
	}
	return (0);
}

void display_time_and_date()
{
	INITCOLOR(RED_COLOR);
	printf("[%s]", __DATE__); /* 打印日期 */
	INITCOLOR(GREEN_COLOR);
	printf("[%s]  ", __TIME__); /* 打印时间 */
	INITCOLOR(ZERO_COLOR);
}

void getting_started()
{
	CLEARSCREEN(); /* 清空屏幕 */
	display_time_and_date();
	printf("Getting started of Network sniffer\n\n");  
}

/* 主函数入口 */
int	main()
{
	/* 声明部分 */
	int	sd;
	int	res;
	int	saddr_size;
	int	data_size;
	struct sockaddr saddr;
	unsigned char *buffer; /* 保存数据包的数据 */
	t_sniffer sniffer; /* 保存数据包的类型和日志文件等信息 */
	fd_set fd_read;

	buffer = malloc(sizeof(unsigned char *) * 65536); 

	/* 以可写的方式在当前文件夹中创建日志文件 */
	sniffer.logfile = fopen("log.txt", "w");
	fprintf(sniffer.logfile,"***LOGFILE(%s - %s)***\n", __DATE__, __TIME__);
	if (sniffer.logfile == NULL)
	{
		perror("fopen(): ");
		return (EXIT_FAILURE);
	}

	sniffer.prot = malloc(sizeof(t_protocol *));  

	/* 创建原始套接字，ETH_P_ALL 表示侦听负载为 IP 数据报的以太网帧 */
	sd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP)); 
	if (sd < 0)
	{
		perror("socket(): ");
		return (EXIT_FAILURE);
	}
	getting_started();
	signal(SIGINT, &signal_white_now);
	signal(SIGQUIT, &signal_white_now);

	/* 循环侦听以太网帧，并调用 ProcessPacket 函数解析 */
	while (1)
	{
		FD_ZERO(&fd_read);
		FD_SET(0, &fd_read);
		FD_SET(sd, &fd_read);

		/* 多路复用检测可读的套接字和标准输入 */
		res = select(sd + 1, &fd_read, NULL, NULL, NULL);
		if (res < 0)
			{
				close(sd);
				if (errno != EINTR)
				perror("select() ");
				return (EXIT_FAILURE);
			}
		else
			{
				/* 如果是标准输入可读，进入命令行处理程序 command_interpreter，暂时只支持 'quit' 命令 */
				if (FD_ISSET(0, &fd_read)) 
				{
					if (command_interpreter(sd) == 1)
					break;
				}

				/* 如果是套接字可读，则读取以太网数据帧的内容，并调用 ProcessPacket 函数解析出数据包的类型 */
				else if (FD_ISSET(sd, &fd_read))
					{
						/* 读取以太网数据帧的内容 */
						saddr_size = sizeof(saddr);
						data_size = recvfrom(sd, buffer, 65536, 0, &saddr,(socklen_t*)&saddr_size); /* 读取以太网数据帧的内容 */
						if (data_size <= 0)
							{
								close(sd);
								perror("recvfrom(): ");
								return (EXIT_FAILURE);
							}

						ProcessPacket(buffer, data_size, &sniffer); /* 调用 ProcessPacket 函数解析出数据包的类型 */
					}
			}
	}
	
	close(sd);
	return (EXIT_SUCCESS);
}

void ProcessPacket(unsigned char* buffer, int size, t_sniffer *sniffer)
{
	buffer = buffer + 6 + 6 + 2; /* 根据太网帧结构，前 6B 是目的 MAC 地址，接下来的是源 MAC 地址，接下来 2B 是帧长度，其余的是负载（上层的 IP 数据报） */
	struct iphdr *iph = (struct iphdr*)buffer;
	++sniffer->prot->total; /* 数据包总数加 1 */

	/* 根据 TCP/IP 协议规定的 IP 数据报头部的 protocol 字段的值，判断上层的数据包类型 */
	switch (iph->protocol)
		{
			/* 1 表示 icmp 协议 */
			case 1: 
				++sniffer->prot->icmp;
				print_icmp_packet(buffer, size, sniffer);
				break;
				
			/* 2 表示 igmp 协议 */
			case 2:
				++sniffer->prot->igmp;
				break;
				
			/* 6 表示 tcp 协议 */
			case 6:
				++sniffer->prot->tcp;
				print_tcp_packet(buffer , size, sniffer);
				break;
				
			/* 17 表示 udp 协议 */
			case 17:
				++sniffer->prot->udp;
				print_udp_packet(buffer , size, sniffer);
				break;
      
			default:
				++sniffer->prot->others;
				break;
		}

	display_time_and_date(); /* 显示时间 */

	/* 打印 sniffer 中的信息 */
	printf("TCP : %d   UDP : %d   ICMP : %d   IGMP : %d   Others : %d Total : %d\n",
	 sniffer->prot->tcp, sniffer->prot->udp,
	 sniffer->prot->icmp, sniffer->prot->igmp,
	 sniffer->prot->others, sniffer->prot->total);
}

0x04程序运行

本程序运行界面如下：

实现的功能之一就是解析UDP数据报，其扫描解析结果存放在log.txt中。这里从log.txt中以一个UDP数据包的解析为例

***LOGFILE(Dec 14 2017 - 21:41:38)***


***********************UDP Packet*************************

IP Header
   |-IP Version        : 4
   |-IP Header Length  : 5 DWORDS or 20 Bytes
   |-Type Of Service   : 0
   |-IP Total Length   : 213  Bytes(size of Packet)
   |-Identification    : 6639
   |-TTL      : 64
   |-Protocol : 17
   |-Checksum : 31927
   |-Source IP        : 172.16.69.82
   |-Destination IP   : 172.16.69.255

UDP Header
   |-Source Port      : 138
   |-Destination Port : 138
   |-UDP Length       : 193
   |-UDP Checksum     : 26258

IP Header

保护隐私，这部分我删除了
 AC 10 45 FF
UDP Header

保护隐私，这部分我删除了
Data Payload
保护隐私，这部分我删除了

###########################################################

0x05附

我认为本实验的亮点在于使用脚本控制，有必要好好学习下脚本编程
launcher.sh

#!/bin/sh

sigint()
{
    printf '\nQUIT !\n'
    exit 1
}

main()
{
    clear
    printf "\t\t\t\t\tWelcome to Sniffer Project r\n\n"

    while [ 1 ]; do
	printf "Select option: \n\n"
	printf "1 : Build Project\n"
	printf "2 : Launch Project\n"
	printf "3 : Remove Object files\n"
	printf "4 : Rebuild\n"
	printf "0 : Exit\n"

	printf "\nYou choose: "
	read option
	
	if [ $option = 0 ]
	then
	    exit
	fi
	if [ $option -ge 1 ] && [ $option -le 4 ]
	then
	    if [ $option = 1 ]
	    then
		make "network_sniffer"
	    fi
	    if [ $option = 2 ]
	    then
		"./network_sniffer"
	    fi
	    if [ $option = 3 ]
	    then
		make clean
	    fi
	    if [ $option = 4 ]
	    then
		make re
	    fi	    
	else
	    printf "This option does not exist\n"
	fi
    done
}

trap 'sigint' 2

main