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UNIX網絡編程:網絡數據包檢測

網絡數據包檢測

數據包捕獲(sniffer):是指在網絡上進行數據收集的行為,需要通過網卡來完成。

三種訪問方式:

BSD Packet Filter(BPF)

SVR4 Datalink Provider Interface(DLPI)

linux SOCK_PACKET interface

libpcap庫

安裝:

apt-get install libpcap-dev

常用API

捕獲數據包

查找缺省的用來捕獲數據網絡設備

char * pcap_lookupdev ( char * errbuf )//出錯時保存系統返回的錯誤信息。

返回值:

成功時返回指向設備名稱的指針,

失敗返回NULL

查找指定設備的網絡號和子網掩碼

int pcap_lookupnet( const char * device,//指向設備名稱的指針

bpf_u_int32 * netp,//指向獲取的網絡號的指針

bpf_u_int32 * maskp,//指向獲取的子網掩碼的指針

char * errbuf)//出錯時保存系統返回的錯誤信息

返回值:

成功返回0,

失敗返回-1,並保存錯誤信息到errbuf中。

打開一個網絡設備用於捕獲數據包

pcap_t * pcap_open_live( const char * device,//指向設備名稱的指針

int snaplen, //捕獲的數據包的長度

int promisc,//網絡接口工作模式

int to_ms,//讀取數據包時的超時

char * errbuf)//出錯時保存系統錯誤信息

返回值:

成功返回捕獲數據包的句柄

失敗返回NULL並保存錯誤信息到errbuf中

捕獲下一幀數據

const u_char * pcap_next ( pcap_t * p//pcap_open_live返回的句柄

struct pcap_pkthdr * h)保存捕獲的數據包屬性的結構體指針

返回值:

成功時返回捕獲的數據幀的指針,

失敗或無數據返回NULL。

循環捕獲多幀數據並處理

typedef void ( * pcap_handler )( u_char *user,

const struct pcap_pkthdr * h,const u_char *bytes);

int pcap_loop( pcap_t * p,//pcap_open_live返回的句柄

int cnt,//要捕獲的數據幀的個數

pcap_handler callback,//捕獲到一幀數據時執行的處理函數

u_char * user )//傳遞給callback的參數

查看本欄目更多精彩內容:http://www.bianceng.cn/OS/unix/

返回值:

成功返回0,

失敗返回-1,

被中斷返回-2.

過濾數據包

根據過濾器表達式生成過濾器

int * pcap_compile( pcap_t * p,//pcap_open_live返回的句柄

struct bpf_program * fp,//保存過濾器的結構體指針

const char * str,//要轉換的過濾器表達式

int optimize,//過濾程序是否優化

bpf_u_int32 netmask )//子網掩碼

返回值:

成功返回0,

失敗返回-1。

為指定的捕捉句柄安裝過濾器

int pcap_next ( pcap_t * p//pcap_open_live返回的句柄

struct bpf_program * fp);//指向要安裝的過濾器的指針

返回值:

成功返回0;

失敗返回-1.

捕獲數據包流程

示例程序:

//ping.c

#include <stdio.h>   
#include <stdlib.h>  
#include <string.h>   
#include <signal.h>   
#include <arpa/inet.h>   
#include <sys/types.h>   
#include <sys/socket.h>   
#include <unistd.h>   
#include <netinet/in.h>   
#include <netinet/ip.h>   
#include <netinet/ip_icmp.h>   
#include <netdb.h>   
#include <setjmp.h>   
#include <errno.h>   
      
#define PACKET_SIZE 4096   
#define MAX_WAIT_TIME 5   
#define MAX_NO_PACKETS 3   
      
char sendpacket[PACKET_SIZE];   
char recvpacket[PACKET_SIZE];   
int sockfd,datalen=56;   
int nsend=0,nreceived=0;   
struct sockaddr_in dest_addr;   
pid_t pid;   
struct sockaddr_in from;   
struct timeval tvrecv;   
      
void f(int signo) {}  
void statistics(int signo);   
unsigned short cal_chksum(unsigned short *addr,int len);   
int pack(int pack_no);   
void send_packet(void);   
void recv_packet(void);   
int unpack(char *buf,int len);   
void tv_sub(struct timeval *out,struct timeval *in);   
      
void statistics(int signo)   
{   
   printf("\n--------------------PING statistics-------------------\n");   
   printf("%d packets transmitted, %d received , %%%.2f lost\n",nsend,nreceived,(float)(nsend-nreceived)/nsend*100);   
   close(sockfd);   
   exit(1);   
}   
/*校驗和算法*/
unsigned short cal_chksum(unsigned short *addr,int len)   
{   
   int nleft=len;   
   int sum=0;   
   unsigned short *w=addr;   
   unsigned short answer=0;   
      
   /*把ICMP報頭二進制數據以2字節為單位累加起來*/
   while(nleft>1)   
   {   
     sum+=*w++;   
     nleft-=2;   
   }   
   /*若ICMP報頭為奇數個字節,會剩下最後一字節。把最後一個字節視為一個2字節數據的高字節,  
   這個2字節數據的低字節為0,繼續累加*/
   if( nleft==1)   
   {   
       *(unsigned char *)(&answer)=*(unsigned char *)w;   
       sum+=answer;   
   }   
   sum=(sum>>16)+(sum&0xffff);   
   sum+=(sum>>16);   
   answer=~sum;   
   return answer;   
}   
/*設置ICMP報頭*/
int pack(int pack_no)   
{   
    int i,packsize;   
    struct icmp *icmp;   
    struct timeval *tval;   
    icmp=(struct icmp*)sendpacket; //char sendpacket[4096];  
    icmp->icmp_type=ICMP_ECHO;   
    icmp->icmp_code=0;   
#if 1  
    icmp->icmp_seq=pack_no;   
    icmp->icmp_cksum = 0;  
#endif  
    icmp->icmp_id=pid;   
    packsize=8+datalen;   
    tval= (struct timeval *)icmp->icmp_data;   
    gettimeofday(tval,NULL); /*記錄發送時間*/
    icmp->icmp_cksum=cal_chksum( (unsigned short *)icmp,packsize); /*校驗算法*/
    return packsize;   
}   
      
/*發送三個ICMP報文*/
void send_packet()   
{   
    int packetsize;   
    //while(nsend)   
    //{   
      nsend++;   
      packetsize=pack(nsend); /*設置ICMP報頭*/
      if(sendto(sockfd,sendpacket,packetsize,0,(struct sockaddr *)&dest_addr,sizeof(dest_addr))<0 )   
      {   
        perror("sendto error");   
        return;  
      }   
     // sleep(1); /*每隔一秒發送一個ICMP報文*/   
//    }   
}   
      
/*接收所有ICMP報文*/
void recv_packet()   
{   
     int n,fromlen;   
     extern int errno;   
          
     struct sigaction act;  
     sigaction(SIGALRM, NULL, &act);  
     act.sa_handler = f;  
     sigaction(SIGALRM, &act, NULL);  
      
     fromlen=sizeof(from);   
     while(1)   
     {   
       alarm(5);   
       if( (n=recvfrom(sockfd,recvpacket,sizeof(recvpacket),0,(struct sockaddr *)&from,&fromlen)) <0)   
       {   
           if (errno == EINTR)  
           {  
               printf("errno=%d\n", errno);  
               break;  
           }  
           else
               exit(-1);  
       }   
       gettimeofday(&tvrecv,NULL); /*記錄接收時間*/
      
       if(unpack(recvpacket,n)==-1)   
       {  
           continue;   
       }  
       else
       {  
           nreceived++;   
           break;  
       }  
   }   
}   
/*剝去ICMP報頭*/
int unpack(char *buf,int len)   
{   
    int i,iphdrlen;   
    struct ip *ip;   
    struct icmp *icmp;   
    struct timeval *tvsend;   
    double rtt;   
    ip=(struct ip *)buf;   
    iphdrlen=ip->ip_hl<<2; /*求ip報頭長度,即ip報頭的長度標志乘4*/
    icmp=(struct icmp *)(buf+iphdrlen); /*越過ip報頭,指向ICMP報頭*/
    len-=iphdrlen; /*ICMP報頭及ICMP數據報的總長度*/
    if(len<8) /*小於ICMP報頭長度則不合理*/
    {   
      printf("ICMP packets\'s length is less than 8\n");   
      return -1;   
    }   
    /*確保所接收的是我所發的的ICMP的回應*/
    if( (icmp->icmp_type==ICMP_ECHOREPLY) && (icmp->icmp_id==pid) )   
    {   
        tvsend=(struct timeval *)icmp->icmp_data;   
        tv_sub(&tvrecv,tvsend); /*接收和發送的時間差*/
        rtt=tvrecv.tv_sec*1000+(float)tvrecv.tv_usec/1000; /*以毫秒為單位計算rtt*/
        /*顯示相關信息*/
        printf("%d byte from %s: icmp_seq=%u ttl=%d rtt=%.3f ms\n",   
        len,inet_ntoa(from.sin_addr),icmp->icmp_seq,ip->ip_ttl,rtt);   
    }   
    else return -1;   
}   
      
int main(int argc,char *argv[])   
{   
    struct hostent *host;   
    struct protoent *protocol;   
    unsigned long inaddr=0l;   
    int waittime=MAX_WAIT_TIME;   
    int size=50*1024;   
      
    if(argc<2)   
    {   
       printf("usage:%s hostname/IP address\n",argv[0]);   
       exit(1);   
    }   
      
    if( (protocol=getprotobyname("icmp") )==NULL)   
    {   
        perror("getprotobyname");   
        exit(1);   
    }   
    /*生成使用ICMP的原始套接字,這種套接字只有root才能生成*/
    if( (sockfd=socket(AF_INET,SOCK_RAW,protocol->p_proto) )<0)   
    {   
        perror("socket error");   
        exit(1);   
    }   
    /* 回收root權限,設置當前用戶權限*/
    setuid(getuid());   
    /*擴大套接字接收緩沖區到50K這樣做主要為了減小接收緩沖區溢出的  
    的可能性,若無意中ping一個廣播地址或多播地址,將會引來大量應答*/
    setsockopt(sockfd,SOL_SOCKET,SO_RCVBUF,&size,sizeof(size) );   
    bzero(&dest_addr,sizeof(dest_addr));   
    dest_addr.sin_family=AF_INET;   
      
    /*判斷是主機名還是ip地址*/
    if( (inaddr=inet_addr(argv[1]))==INADDR_NONE)   
    {   
        if((host=gethostbyname(argv[1]) )==NULL) /*是主機名*/
        {   
           perror("gethostbyname error");   
           exit(1);   
        }   
        memcpy( (char *)&dest_addr.sin_addr,host->h_addr,host->h_length);   
    }   
    else /*是ip地址*/
        dest_addr.sin_addr.s_addr = inaddr;  
    //memcpy( (char *)&dest_addr,(char *)&inaddr,host->h_length);   
    /*獲取main的進程id,用於設置ICMP的標志符*/
    pid=getpid();   
    printf("PING %s(%s): %d bytes data in ICMP packets.\n",argv[1],   
    inet_ntoa(dest_addr.sin_addr),datalen);   
      
    int i = 0;  
    bzero(sendpacket, PACKET_SIZE);   
    bzero(recvpacket, PACKET_SIZE);   
      
    while (i < 3)  
    {  
        send_packet(); /*發送所有ICMP報文*/
        recv_packet(); /*接收所有ICMP報文*/
        sleep(1);  
        i++;  
    }  
      
    statistics(SIGALRM); /*進行統計*/
      
    return 0;   
      
}   
/*兩個timeval結構相減*/
void tv_sub(struct timeval *out,struct timeval *in)   
{   
     if( (out->tv_usec-=in->tv_usec)<0)   
     {   
         --out->tv_sec;   
         out->tv_usec+=1000000;   
     }   
     out->tv_sec-=in->tv_sec;   
}   
      
/*------------- The End -----------*/

查看本欄目更多精彩內容:http://www.bianceng.cn/OS/unix/

//cap.c

#include <stdio.h>  
#include <stdlib.h>  
#include <string.h>  
#include <pcap.h>  
      
#define MAXBYTES2CAPTURE 2048  
      
void process_packet(u_char *arg, const struct pcap_pkthdr *pkthdr,   
        const u_char *packet)  
{  
    int i = 0, *counter = (int *)arg;  
      
    printf("packet count:%d\n", ++(*counter));  
    printf("received packet size %d\n", pkthdr->len);  
      
    printf("payload\n");  
    for (i = 0; i < pkthdr->len; i++)  
    {  
        printf("%02x ", (unsigned int)packet[i]);  
      
        if ((i % 16 == 15 && i != 0) || (i == pkthdr->len-1))  
            printf("\n");  
    }  
    printf("\n\n**************\n");  
    return;              
}  
      
int main(int argc, char *argv[])  
{  
    int i = 0, count = 0;  
    pcap_t *descr = NULL;  
    char errbuf[PCAP_ERRBUF_SIZE], *device = NULL;  
    bpf_u_int32 netaddr = 0, mask = 0;  
    struct bpf_program filter;  
      
    memset(errbuf, 0, sizeof(errbuf));  
      
    if (argc != 2)  
        device = pcap_lookupdev(errbuf);  
    else
        device = argv[1];  
      
    printf("Try to open device %s\n", device);  
      
          
    if ((descr = pcap_open_live(device, MAXBYTES2CAPTURE, 1, 0, errbuf)) == NULL )  
    {  
        printf("error:%s\n", errbuf);  
        exit(-1);  
    }  
    printf("pcap_open\n");  
      
    pcap_lookupnet(device, &netaddr, &mask, errbuf);  
    printf("pcap_look\n");  
      
    //if (pcap_compile(descr, &filter, "arp and ether host 00:0c:29:b7:f6:33", 0, mask) < 0)  
    if (pcap_compile(descr, &filter, "arp and ether host 00:0c:29:cd:d6:dd", 0, mask) < 0)  
    {  
        printf("pcap_compile error\n");  
        exit(-1);  
    }  
    printf("compile\n");  
    pcap_setfilter(descr, &filter);  
    printf("setfilter\n");  
      
    pcap_loop(descr, 1, process_packet, (u_char *)&count);  
      
    return 0;  
}

作者:csdn博客 ctthuangcheng

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