arp.c

#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/time.h>

#include <asm/types.h>

#include <math.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <arpa/inet.h>

#include <linux/if_packet.h>
#include <linux/if_ether.h>
#include <linux/if_arp.h>

#define BUF_SIZE 42
#define DEVICE "eth1"
#define ETH_P_NULL 0x0
#define ETH_MAC_LEN ETH_ALEN
#define ETH_ARP 0x0806

int s = -1; /*Socketdescriptor*/
void* buffer = NULL;
long total_packets = 0;
long answered_packets = 0;

void sigint(int signum);

struct __attribute__((packed)) arp_header
{
    unsigned short arp_hd;
    unsigned short arp_pr;
    unsigned char arp_hdl;
    unsigned char arp_prl;
    unsigned short arp_op;
    unsigned char arp_sha[6];
    unsigned char arp_spa[4];
    unsigned char arp_dha[6];
    unsigned char arp_dpa[4];
};
int main(void) {
    buffer = (void*)malloc(BUF_SIZE); /*Buffer for Ethernet Frame*/
    unsigned char* etherhead = buffer;  /*Pointer to Ethenet Header*/
    struct ethhdr *eh = (struct ethhdr *)etherhead; /*Another pointer to
                                                      ethernet header*/
    unsigned char* arphead = buffer + 14;
    struct arp_header *ah;
    unsigned char src_mac[6];    /*our MAC address*/

    struct ifreq ifr;
    struct sockaddr_ll socket_address;
    int ifindex = 0;     /*Ethernet Interface index*/
    int i;
    int length;  /*length of received packet*/
    int sent;

    printf("Server started, entering initialiation phase...\n");

    /*open socket*/
    s = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
    if (s == -1) {
        perror("socket():");
        exit(1);
    }
    printf("Successfully opened socket: %i\n", s);

    /*retrieve ethernet interface index*/
    strncpy(ifr.ifr_name, DEVICE, IFNAMSIZ);
    if (ioctl(s, SIOCGIFINDEX, &ifr) == -1) {
        perror("SIOCGIFINDEX");
        exit(1);
    }
    ifindex = ifr.ifr_ifindex;
    printf("Successfully got interface index: %i\n", ifindex);

    /*retrieve corresponding MAC*/
    if (ioctl(s, SIOCGIFHWADDR, &ifr) == -1) {
        perror("SIOCGIFINDEX");
        exit(1);
    }
    for (i = 0; i < 6; i++) {
        src_mac[i] = ifr.ifr_hwaddr.sa_data[i];
    }
    printf("Successfully got our MAC address: %02X:%02X:%02X:%02X:%02X:%02X\n",
            src_mac[0],src_mac[1],src_mac[2],src_mac[3],src_mac[4],src_mac[5]);

    /*prepare sockaddr_ll*/
    socket_address.sll_family = PF_PACKET;
    socket_address.sll_protocol = htons(ETH_P_ARP);
    socket_address.sll_ifindex = ifindex;
    socket_address.sll_hatype = ARPHRD_ETHER;
    socket_address.sll_pkttype = 0; //PACKET_OTHERHOST;
    socket_address.sll_halen = 0;
    socket_address.sll_addr[6] = 0x00;
    socket_address.sll_addr[7] = 0x00;
    /*establish signal handler*/
    signal(SIGINT, sigint);
    printf("Successfully established signal handler for SIGINT\n");
    printf("We are in production state, waiting for incoming packets....\n");

    while (1) {
        /*Wait for incoming packet...*/
        length = recvfrom(s, buffer, BUF_SIZE, 0, NULL, NULL);
        if (length == -1)
        {
            perror("recvfrom():");
            exit(1);
        }
        if(ntohs(eh->h_proto) == ETH_P_ARP)
        {
            //unsigned char buf_arp_dha[6];
            unsigned char buf_arp_dpa[4];

            ah = (struct arp_header *)arphead;
            if(ntohs(ah->arp_op) != ARPOP_REQUEST) continue;

            printf("buffer is---------------- %s \n",(char*)ah);
            printf("H/D TYPE : %x PROTO TYPE : %x \n",ah->arp_hd,ah->arp_pr);
            printf("H/D leng : %x PROTO leng : %x \n",ah->arp_hdl,ah->arp_prl);
            printf("OPERATION : %x \n", ah->arp_op);
            printf("SENDER MAC address: %02X:%02X:%02X:%02X:%02X:%02X\n",
                    ah->arp_sha[0],
                    ah->arp_sha[1],
                    ah->arp_sha[2],
                    ah->arp_sha[3],
                    ah->arp_sha[4],
                    ah->arp_sha[5]
                  );
            printf("SENDER IP address: %02d:%02d:%02d:%02d\n",
                    ah->arp_spa[0],
                    ah->arp_spa[1],
                    ah->arp_spa[2],
                    ah->arp_spa[3]
                  );
#if 0
            if(ah->arp_spa[0]==10&&ah->arp_spa[1]==00&&ah->arp_spa[2]==00&&ah->arp_spa[3]==01)
            {
                printf("Sender ip is .............bam bam..........................................\n");
                system("sudo arp -s 10.0.0.1  00:1e:73:91:04:0d");
            }
#endif
            printf("TARGET MAC address: %02X:%02X:%02X:%02X:%02X:%02X\n",
                    ah->arp_dha[0],
                    ah->arp_dha[1],
                    ah->arp_dha[2],
                    ah->arp_dha[3],
                    ah->arp_dha[4],
                    ah->arp_dha[5]
                  );
            printf("TARGET IP address: %02d:%02d:%02d:%02d\n",
                    ah->arp_dpa[0],
                    ah->arp_dpa[1],
                    ah->arp_dpa[2],
                    ah->arp_dpa[3]
                  );

            printf("+++++++++++++++++++++++++++++++++++++++\n" );
            printf("ETHER DST MAC address: %02X:%02X:%02X:%02X:%02X:%02X\n",
                    eh->h_dest[0],
                    eh->h_dest[1],
                    eh->h_dest[2],
                    eh->h_dest[3],
                    eh->h_dest[4],
                    eh->h_dest[5]
                  );
            printf("ETHER SRC MAC address: %02X:%02X:%02X:%02X:%02X:%02X\n",
                    eh->h_source[0],
                    eh->h_source[1],
                    eh->h_source[2],
                    eh->h_source[3],
                    eh->h_source[4],
                    eh->h_source[5]
                  );
            memcpy( (void*)etherhead, (const void*)(etherhead+ETH_MAC_LEN),
                    ETH_MAC_LEN);
            memcpy( (void*)(etherhead+ETH_MAC_LEN), (const void*)src_mac,
                    ETH_MAC_LEN);
            eh->h_proto = htons(ETH_P_ARP);
            printf("&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& \n");
            printf("ETHER DST MAC address: %02X:%02X:%02X:%02X:%02X:%02X\n",
                    eh->h_dest[0],
                    eh->h_dest[1],
                    eh->h_dest[2],
                    eh->h_dest[3],
                    eh->h_dest[4],
                    eh->h_dest[5]
                  );
            printf("ETHER SRC MAC address: %02X:%02X:%02X:%02X:%02X:%02X\n",
                    eh->h_source[0],
                    eh->h_source[1],
                    eh->h_source[2],
                    eh->h_source[3],
                    eh->h_source[4],
                    eh->h_source[5]
                  );
            //ah->arp_hd = ntohs(ah->arp_hd);
            //ah->arp_pr = ntohs(ah->arp_pr);

            ah->arp_op = htons(ARPOP_REPLY);

            buf_arp_dpa[0] = ah->arp_dpa[0];
            buf_arp_dpa[1] = ah->arp_dpa[1];
            buf_arp_dpa[2] = ah->arp_dpa[2];
            buf_arp_dpa[3] = ah->arp_dpa[3];

            ah->arp_dha[0] = ah->arp_sha[0];
            ah->arp_dha[1] = ah->arp_sha[1];
            ah->arp_dha[2] = ah->arp_sha[2];
            ah->arp_dha[3] = ah->arp_sha[3];
            ah->arp_dha[4] = ah->arp_sha[4];
            ah->arp_dha[5] = ah->arp_sha[5];

            ah->arp_dpa[0] = ah->arp_spa[0];
            ah->arp_dpa[1] = ah->arp_spa[1];
            ah->arp_dpa[2] = ah->arp_spa[2];
            ah->arp_dpa[3] = ah->arp_spa[3];

            ah->arp_spa[0] = buf_arp_dpa[0];
            ah->arp_spa[1] = buf_arp_dpa[1];
            ah->arp_spa[2] = buf_arp_dpa[2];
            ah->arp_spa[3] = buf_arp_dpa[3];
            //change the sender mac address
            ah->arp_sha[0] = 0x00;
            ah->arp_sha[1] = 0x1e;
            ah->arp_sha[2] = 0x73;
            ah->arp_sha[3] = 0x78;
            ah->arp_sha[4] = 0x9a;
            ah->arp_sha[5] = 0x0d;

            socket_address.sll_addr[0] = eh->h_dest[0];
            socket_address.sll_addr[1] = eh->h_dest[1];
            socket_address.sll_addr[2] = eh->h_dest[2];
            socket_address.sll_addr[3] = eh->h_dest[3];
            socket_address.sll_addr[4] = eh->h_dest[4];
            socket_address.sll_addr[5] = eh->h_dest[5];
            printf("=======================================\n" );
            printf("SENDER MAC address: %02X:%02X:%02X:%02X:%02X:%02X\n",
                    ah->arp_sha[0],
                    ah->arp_sha[1],
                    ah->arp_sha[2],
                    ah->arp_sha[3],
                    ah->arp_sha[4],
                    ah->arp_sha[5]
                  );
            printf("SENDER IP address: %02d:%02d:%02d:%02d\n",
                    ah->arp_spa[0],
                    ah->arp_spa[1],
                    ah->arp_spa[2],
                    ah->arp_spa[3]
                  );
            if((ah->arp_spa[0]==10 && ah->arp_spa[1]==0 && ah->arp_spa[2]==0 && ah->arp_spa[3]==1))
                printf("------------------------------------------10.0.0.1-----------------------------------------\n");
            printf("TARGET MAC address: %02X:%02X:%02X:%02X:%02X:%02X\n",
                    ah->arp_dha[0],
                    ah->arp_dha[1],
                    ah->arp_dha[2],
                    ah->arp_dha[3],
                    ah->arp_dha[4],
                    ah->arp_dha[5]
                  );
            printf("TARGET IP address: %02d:%02d:%02d:%02d\n",
                    ah->arp_dpa[0],
                    ah->arp_dpa[1],
                    ah->arp_dpa[2],
                    ah->arp_dpa[3]
                  );
            printf("H/D TYPE : %x PROTO TYPE : %x \n",ah->arp_hd,ah->arp_pr);
            printf("H/D leng : %x PROTO leng : %x \n",ah->arp_hdl,ah->arp_prl);
            printf("OPERATION : %x \n", ah->arp_op);

            sent = sendto
                (s, buffer, BUF_SIZE, 0, (struct sockaddr*)&socket_address,
                 sizeof(socket_address)
                );
            if (sent == -1) {
                perror("sendto():");
                exit(1);
            }
            answered_packets++;
        }
        total_packets++;
    }
}
void sigint(int signum) {
    /*Clean up.......*/
    struct ifreq ifr;

    if (s == -1) return;

    strncpy(ifr.ifr_name, DEVICE, IFNAMSIZ);
    ioctl(s, SIOCGIFFLAGS, &ifr);
    ifr.ifr_flags &= ~IFF_PROMISC;
    ioctl(s, SIOCSIFFLAGS, &ifr);
    close(s);

    free(buffer);

    printf("Server terminating....\n");

    printf("Totally received: %ld packets\n", total_packets);
    printf("Answered %ld packets\n", answered_packets);
    exit(0);
}