Обнюхивать фрагменты tcp пакетов с c

Question

У меня есть этот код из 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" );
        }
    }
}

Когда прибыл пакет Udp, код хорошо его проанализировал.

Проблема в том, что пакет tcp иногда фрагментируется поэтому я вижу с print_tcp_packet только разделенные данные.

Wireshark знает, как объединить 2 фрагмента пакетов в 1.

Как я могу сделать это с этим кодом?

Может быть использование recv вместо recvfrom будет ли что ли? Как я могу использовать recv ели нюхают?

Answer 1

RF C 791 описывает правила фрагментации для IP-пакетов.

Если будет еще несколько фрагментов, пакет будет иметь установленный флажок More Fragments (MF), и каждый фрагмент будет иметь смещение в поле Fragment Offset. Если вы получаете пакет с установленным флагом MF, вам следует отложить обработку до тех пор, пока не будут получены все фрагменты с одинаковым значением идентификации, а затем объединить их в один пакет.

Помимо этого, пакеты TCP являются объектом TCP сегментация. Один буфер, отправленный операцией send, может быть разделен на несколько сетевых пакетов в соответствии с согласованным значением MSS. Аналогично, несколько коротких буферов могут оказаться в одном сетевом пакете. В конце концов, TCP является потоковым протоколом.