Coders Packet

code packet sniffer in C with Sockets on Linux

By Kollu saisumanth

Packet sniffers are programs that intercept the network traffic flowing in and out of a system through network interfaces.

#include //For standard things
#include //malloc
#include //memset
#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<sys/socket.h>
#include<arpa/inet.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);

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

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

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

logfile=fopen("log.txt","w");
if(logfile==NULL) printf("Unable to create file.");
printf("Starting...\n");
//Create a raw socket that shall sniff
sock_raw = socket(AF_INET , SOCK_RAW , IPPROTO_TCP);
if(sock_raw < 0)
{
printf("Socket Error\n");
return 1;
}
while(1)
{
saddr_size = sizeof saddr;
//Receive a packet
data_size = recvfrom(sock_raw , buffer , 65536 , 0 , &saddr , &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
struct iphdr iph = (struct iphdr)buffer;
++total;
switch (iph->protocol) //Check the Protocol and do accordingly...
{
case 1: //ICMP Protocol
++icmp;
//PrintIcmpPacket(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_ip_header(unsigned char* Buffer, int Size)
{
unsigned short iphdrlen;

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

struct tcphdr tcph=(struct tcphdr)(Buffer + iphdrlen);

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 + iphdrlen + tcph->doff*4 , (Size - tcph->doff*4-iph->ihl*4) );

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

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

unsigned short iphdrlen;

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

struct udphdr udph = (struct udphdr)(Buffer + iphdrlen);

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");
PrintData(Buffer + iphdrlen + sizeof udph ,( Size - sizeof udph - iph->ihl * 4 ));

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

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

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

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

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");
PrintData(Buffer + iphdrlen + sizeof icmph , (Size - sizeof icmph - iph->ihl * 4));

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

void PrintData (unsigned char* data , int Size)
{

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{
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");
}
}
}

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