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嗅探時錯誤解析 udp 有效負載數據包

[英]Wrong parse udp payload packet while sniffing

 原文  2020-02-11 17:26:18  7   1    c/ udp/ wireshark/ packet-sniffers

問題描述

我有這個代碼來自https://www.binarytides.com/packet-sniffer-code-in-c-using-linux-sockets-bsd-part-2/

#include<netinet/in.h>
#include<errno.h>
#include<netdb.h>
#include<stdio.h>   //For standard things
#include<stdlib.h>  //malloc
#include<string.h>  //strlen

#include<netinet/ip_icmp.h> //Provides declarations for icmp header
#include<netinet/udp.h> //Provides declarations for udp header
#include<netinet/tcp.h> //Provides declarations for tcp header
#include<netinet/ip.h>  //Provides declarations for ip header
#include<netinet/if_ether.h>    //For ETH_P_ALL
#include<net/ethernet.h>    //For ether_header
#include<sys/socket.h>
#include<arpa/inet.h>
#include<sys/ioctl.h>
#include<sys/time.h>
#include<sys/types.h>
#include<unistd.h>

void ProcessPacket(unsigned char* , int);
void print_ip_header(unsigned char* , int);
void print_tcp_packet(unsigned char * , int );
void print_udp_packet(unsigned char * , int );
void print_icmp_packet(unsigned char* , int );
void PrintData (unsigned char* , int);

FILE *logfile;
struct sockaddr_in source,dest;
int tcp=0,udp=0,icmp=0,others=0,igmp=0,total=0,i,j; 

int main()
{
    int saddr_size , data_size;
    struct sockaddr saddr;

    unsigned char *buffer = (unsigned char *) malloc(65536); //Its Big!

    logfile=fopen("log.txt","w");
    if(logfile==NULL) 
    {
        printf("Unable to create log.txt file.");
    }
    printf("Starting...\n");

    int sock_raw = socket( AF_PACKET , SOCK_RAW , htons(ETH_P_ALL)) ;
    //setsockopt(sock_raw , SOL_SOCKET , SO_BINDTODEVICE , "eth0" , strlen("eth0")+ 1 );

    if(sock_raw < 0)
    {
        //Print the error with proper message
        perror("Socket Error");
        return 1;
    }
    while(1)
    {
        saddr_size = sizeof saddr;
        //Receive a packet
        data_size = recvfrom(sock_raw , buffer , 65536 , 0 , &saddr , (socklen_t*)&saddr_size);
        if(data_size <0 )
        {
            printf("Recvfrom error , failed to get packets\n");
            return 1;
        }
        //Now process the packet
        ProcessPacket(buffer , data_size);
    }
    close(sock_raw);
    printf("Finished");
    return 0;
}

void ProcessPacket(unsigned char* buffer, int size)
{
    //Get the IP Header part of this packet , excluding the ethernet header
    struct iphdr *iph = (struct iphdr*)(buffer + sizeof(struct ethhdr));
    ++total;
    switch (iph->protocol) //Check the Protocol and do accordingly...
    {
        case 1:  //ICMP Protocol
            ++icmp;
            //print_icmp_packet( buffer , size);
            break;

        case 2:  //IGMP Protocol
            ++igmp;
            break;

        case 6:  //TCP Protocol
            ++tcp;
            //print_tcp_packet(buffer , size);
            break;

        case 17: //UDP Protocol
            ++udp;
            print_udp_packet(buffer , size);
            break;

        default: //Some Other Protocol like ARP etc.
            ++others;
            break;
    }
    printf("TCP : %d   UDP : %d   ICMP : %d   IGMP : %d   Others : %d   Total : %d\r", tcp , udp , icmp , igmp , others , total);
}

void print_ethernet_header(unsigned char* Buffer, int Size)
{
    struct ethhdr *eth = (struct ethhdr *)Buffer;

    fprintf(logfile , "\n");
    fprintf(logfile , "Ethernet Header\n");
    fprintf(logfile , "   |-Destination Address : %.2X-%.2X-%.2X-%.2X-%.2X-%.2X \n", eth->h_dest[0] , eth->h_dest[1] , eth->h_dest[2] , eth->h_dest[3] , eth->h_dest[4] , eth->h_dest[5] );
    fprintf(logfile , "   |-Source Address      : %.2X-%.2X-%.2X-%.2X-%.2X-%.2X \n", eth->h_source[0] , eth->h_source[1] , eth->h_source[2] , eth->h_source[3] , eth->h_source[4] , eth->h_source[5] );
    fprintf(logfile , "   |-Protocol            : %u \n",(unsigned short)eth->h_proto);
}

void print_ip_header(unsigned char* Buffer, int Size)
{
    print_ethernet_header(Buffer , Size);

    unsigned short iphdrlen;

    struct iphdr *iph = (struct iphdr *)(Buffer  + sizeof(struct ethhdr) );
    iphdrlen =iph->ihl*4;

    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(logfile , "\n");
    fprintf(logfile , "IP Header\n");
    fprintf(logfile , "   |-IP Version        : %d\n",(unsigned int)iph->version);
    fprintf(logfile , "   |-IP Header Length  : %d DWORDS or %d Bytes\n",(unsigned int)iph->ihl,((unsigned int)(iph->ihl))*4);
    fprintf(logfile , "   |-Type Of Service   : %d\n",(unsigned int)iph->tos);
    fprintf(logfile , "   |-IP Total Length   : %d  Bytes(Size of Packet)\n",ntohs(iph->tot_len));
    fprintf(logfile , "   |-Identification    : %d\n",ntohs(iph->id));
    //fprintf(logfile , "   |-Reserved ZERO Field   : %d\n",(unsigned int)iphdr->ip_reserved_zero);
    //fprintf(logfile , "   |-Dont Fragment Field   : %d\n",(unsigned int)iphdr->ip_dont_fragment);
    //fprintf(logfile , "   |-More Fragment Field   : %d\n",(unsigned int)iphdr->ip_more_fragment);
    fprintf(logfile , "   |-TTL      : %d\n",(unsigned int)iph->ttl);
    fprintf(logfile , "   |-Protocol : %d\n",(unsigned int)iph->protocol);
    fprintf(logfile , "   |-Checksum : %d\n",ntohs(iph->check));
    fprintf(logfile , "   |-Source IP        : %s\n",inet_ntoa(source.sin_addr));
    fprintf(logfile , "   |-Destination IP   : %s\n",inet_ntoa(dest.sin_addr));
}

void print_tcp_packet(unsigned char* Buffer, int Size)
{
    unsigned short iphdrlen;

    struct iphdr *iph = (struct iphdr *)( Buffer  + sizeof(struct ethhdr) );
    iphdrlen = iph->ihl*4;

    struct tcphdr *tcph=(struct tcphdr*)(Buffer + iphdrlen + sizeof(struct ethhdr));

    int header_size =  sizeof(struct ethhdr) + iphdrlen + tcph->doff*4;

    fprintf(logfile , "\n\n***********************TCP Packet*************************\n");  

    print_ip_header(Buffer,Size);

    fprintf(logfile , "\n");
    fprintf(logfile , "TCP Header\n");
    fprintf(logfile , "   |-Source Port      : %u\n",ntohs(tcph->source));
    fprintf(logfile , "   |-Destination Port : %u\n",ntohs(tcph->dest));
    fprintf(logfile , "   |-Sequence Number    : %u\n",ntohl(tcph->seq));
    fprintf(logfile , "   |-Acknowledge Number : %u\n",ntohl(tcph->ack_seq));
    fprintf(logfile , "   |-Header Length      : %d DWORDS or %d BYTES\n" ,(unsigned int)tcph->doff,(unsigned int)tcph->doff*4);
    //fprintf(logfile , "   |-CWR Flag : %d\n",(unsigned int)tcph->cwr);
    //fprintf(logfile , "   |-ECN Flag : %d\n",(unsigned int)tcph->ece);
    fprintf(logfile , "   |-Urgent Flag          : %d\n",(unsigned int)tcph->urg);
    fprintf(logfile , "   |-Acknowledgement Flag : %d\n",(unsigned int)tcph->ack);
    fprintf(logfile , "   |-Push Flag            : %d\n",(unsigned int)tcph->psh);
    fprintf(logfile , "   |-Reset Flag           : %d\n",(unsigned int)tcph->rst);
    fprintf(logfile , "   |-Synchronise Flag     : %d\n",(unsigned int)tcph->syn);
    fprintf(logfile , "   |-Finish Flag          : %d\n",(unsigned int)tcph->fin);
    fprintf(logfile , "   |-Window         : %d\n",ntohs(tcph->window));
    fprintf(logfile , "   |-Checksum       : %d\n",ntohs(tcph->check));
    fprintf(logfile , "   |-Urgent Pointer : %d\n",tcph->urg_ptr);
    fprintf(logfile , "\n");
    fprintf(logfile , "                        DATA Dump                         ");
    fprintf(logfile , "\n");

    fprintf(logfile , "IP Header\n");
    PrintData(Buffer,iphdrlen);

    fprintf(logfile , "TCP Header\n");
    PrintData(Buffer+iphdrlen,tcph->doff*4);

    fprintf(logfile , "Data Payload\n");    
    PrintData(Buffer + header_size , Size - header_size );

    fprintf(logfile , "\n###########################################################");
}

void print_udp_packet(unsigned char *Buffer , int Size)
{

    unsigned short iphdrlen;

    struct iphdr *iph = (struct iphdr *)(Buffer +  sizeof(struct ethhdr));
    iphdrlen = iph->ihl*4;

    struct udphdr *udph = (struct udphdr*)(Buffer + iphdrlen  + sizeof(struct ethhdr));

    int header_size =  sizeof(struct ethhdr) + iphdrlen + sizeof udph;

    fprintf(logfile , "\n\n***********************UDP Packet*************************\n");

    print_ip_header(Buffer,Size);           

    fprintf(logfile , "\nUDP Header\n");
    fprintf(logfile , "   |-Source Port      : %d\n" , ntohs(udph->source));
    fprintf(logfile , "   |-Destination Port : %d\n" , ntohs(udph->dest));
    fprintf(logfile , "   |-UDP Length       : %d\n" , ntohs(udph->len));
    fprintf(logfile , "   |-UDP Checksum     : %d\n" , ntohs(udph->check));

    fprintf(logfile , "\n");
    fprintf(logfile , "IP Header\n");
    PrintData(Buffer , iphdrlen);

    fprintf(logfile , "UDP Header\n");
    PrintData(Buffer+iphdrlen , sizeof udph);

    fprintf(logfile , "Data Payload\n");    

    //Move the pointer ahead and reduce the size of string
    PrintData(Buffer + header_size , Size - header_size);

    fprintf(logfile , "\n###########################################################");
}

void print_icmp_packet(unsigned char* Buffer , int Size)
{
    unsigned short iphdrlen;

    struct iphdr *iph = (struct iphdr *)(Buffer  + sizeof(struct ethhdr));
    iphdrlen = iph->ihl * 4;

    struct icmphdr *icmph = (struct icmphdr *)(Buffer + iphdrlen  + sizeof(struct ethhdr));

    int header_size =  sizeof(struct ethhdr) + iphdrlen + sizeof icmph;

    fprintf(logfile , "\n\n***********************ICMP Packet*************************\n"); 

    print_ip_header(Buffer , Size);

    fprintf(logfile , "\n");

    fprintf(logfile , "ICMP Header\n");
    fprintf(logfile , "   |-Type : %d",(unsigned int)(icmph->type));

    if((unsigned int)(icmph->type) == 11)
    {
        fprintf(logfile , "  (TTL Expired)\n");
    }
    else if((unsigned int)(icmph->type) == ICMP_ECHOREPLY)
    {
        fprintf(logfile , "  (ICMP Echo Reply)\n");
    }

    fprintf(logfile , "   |-Code : %d\n",(unsigned int)(icmph->code));
    fprintf(logfile , "   |-Checksum : %d\n",ntohs(icmph->checksum));
    //fprintf(logfile , "   |-ID       : %d\n",ntohs(icmph->id));
    //fprintf(logfile , "   |-Sequence : %d\n",ntohs(icmph->sequence));
    fprintf(logfile , "\n");

    fprintf(logfile , "IP Header\n");
    PrintData(Buffer,iphdrlen);

    fprintf(logfile , "UDP Header\n");
    PrintData(Buffer + iphdrlen , sizeof icmph);

    fprintf(logfile , "Data Payload\n");    

    //Move the pointer ahead and reduce the size of string
    PrintData(Buffer + header_size , (Size - header_size) );

    fprintf(logfile , "\n###########################################################");
}

void PrintData (unsigned char* data , int Size)
{
    int i , j;
    for(i=0 ; i < Size ; i++)
    {
        if( i!=0 && i%16==0)   //if one line of hex printing is complete...
        {
            fprintf(logfile , "         ");
            for(j=i-16 ; j<i ; j++)
            {
                if(data[j]>=32 && data[j]<=128)
                    fprintf(logfile , "%c",(unsigned char)data[j]); //if its a number or alphabet

                else fprintf(logfile , "."); //otherwise print a dot
            }
            fprintf(logfile , "\n");
        } 

        if(i%16==0) fprintf(logfile , "   ");
            fprintf(logfile , " %02X",(unsigned int)data[i]);

        if( i==Size-1)  //print the last spaces
        {
            for(j=0;j<15-i%16;j++) 
            {
              fprintf(logfile , "   "); //extra spaces
            }

            fprintf(logfile , "         ");

            for(j=i-i%16 ; j<=i ; j++)
            {
                if(data[j]>=32 && data[j]<=128) 
                {
                  fprintf(logfile , "%c",(unsigned char)data[j]);
                }
                else 
                {
                  fprintf(logfile , ".");
                }
            }

            fprintf(logfile ,  "\n" );
        }
    }
}

我使用wireshark記錄確實驗證了代碼解析良好，並且我發現udp數據包沒有很好地解析。

這是UDP數據包

0000   xx xx xx xx xx xx xx xx xx xx xx xx 08 00 45 00
0010   00 30 4b 94 00 00 01 11 bc 8d c0 a8 01 04 ef ff
0020   ff ef 19 9b 19 9b 00 1c 58 36 01 00 00 00 00 00
0030   00 00 01 00 00 00 c0 a8 01 04 ff ff ff 00

此代碼解析數據包：

Ethernet Header
   |-Destination Address : xx-xx-xx-Xx-xx-xx 
   |-Source Address      : xx-xx-xx-xx-xx-xx 
   |-Protocol            : 8 

IP Header
   |-IP Version        : 4
   |-IP Header Length  : 5 DWORDS or 20 Bytes
   |-Type Of Service   : 0
   |-IP Total Length   : 48  Bytes(Size of Packet)
   |-Identification    : 19348
   |-TTL      : 1
   |-Protocol : 17
   |-Checksum : 48269
   |-Source IP        : 192.168.1.4
   |-Destination IP   : 239.255.255.239

UDP Header
   |-Source Port      : 6555
   |-Destination Port : 6555
   |-UDP Length       : 28
   |-UDP Checksum     : 22582

IP Header
    XX XX XX XX XX XX xx xx xx xx xx xx 08 00 45 00         ..^.......c..E.
    00 30 4B 94                                             .0K.
UDP Header
    00 00 01 11                                             ....
Data Payload
    00 1C 58 36 01 00 00 00 00 00 00 00 01 00 00 00         ..X6............
    C0 A8 01 04 FF FF FF 00                                 ........

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

如您所見，c 代碼解析數據有效負載不正確，因為有效負載（如 Wireshark 所說）以01 00 00 00開頭，但解析器說它從00 1C 58 36 （之前的 4 個字節）開始，即長度和校驗和udp ，那不是有效載荷。

進行解析的函數是print_udp_packet 。

有效載荷偏移量是sizeof(struct ethhdr) + iphdrlen + sizeof udph; 這看起來不錯

如何修復代碼？

1 個解決方案

解決方案1
 1  2020-02-11 23:03:56

問題是，變量 udph，聲明為

struct udphdr *udph;

是一個指針。 所以在這里

int header_size =  sizeof(struct ethhdr) + iphdrlen + sizeof udph;

和這里

fprintf(logfile , "UDP Header\n");
PrintData(Buffer+iphdrlen , sizeof udph);

你取的是指針的大小，而不是結構的大小。 在這兩種情況下，您都需要使用sizeof *udph ！

我假設您在 32 位系統上工作，因此指針的大小僅為4 ，而結構的大小為8 。

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