scanner.cpp

//
// Created by juraj on 08/04/19.
//

#include "scanner.h"
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <netinet/ip.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <unistd.h>
#include <iostream>
#include <pcap.h>


unsigned short Scanner::csum(unsigned short *buffer,int size)
{
    long sum = 0;
    unsigned short oddbyte;

    while (size > 1)
    {
        sum += *buffer++;
        size -= 2;
    }

    if (size == 1)
    {
        oddbyte=0;
        *((u_char*)&oddbyte)=*(u_char*)buffer;
        sum += oddbyte;
    }

    sum = (sum >> 16) + (sum & 0xffff);
    sum += (sum >> 16);

    return ~sum;
}

void Scanner::create_ip_hdr(int transport_layer)
{
    if (transport_layer == IPPROTO_TCP)
    {
        iphdr->tot_len = sizeof(struct iphdr) + sizeof(struct tcphdr);
        iphdr->protocol = IPPROTO_TCP;
    }
    else if (transport_layer == IPPROTO_UDP)
    {
        iphdr->tot_len = sizeof(struct iphdr) + sizeof(struct udphdr);
        iphdr->protocol = IPPROTO_UDP;
    }

    iphdr->ihl = 5;
    iphdr->version = 4;
    iphdr->tos = 0;
    iphdr->id = htons(20290); // port of this packet -> from range 49152 – 65535:Dynamic and/or Private Ports
    iphdr->frag_off = 0;
    iphdr->ttl = 64; // 64 hops
    iphdr->check = 0;
    iphdr->saddr = inet_addr(get_local_ipaddr().c_str());
    iphdr->daddr = dest_address.sin_addr.s_addr;
    iphdr->check = csum((unsigned short*)buffer, iphdr->tot_len);

}

string Scanner::get_local_ipaddr()
{
    int sock;
    if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
    {
        perror("ERROR: socket");
        exit(EXIT_FAILURE);
    }
    int domain_name_server_port = 53;
    struct sockaddr_in addr;

    memset(&addr, 0, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = inet_addr("8.8.8.8"); // google public dns ip https://developers.google.com/speed/public-dns/docs/using
    addr.sin_port = htons(domain_name_server_port);

    if (connect(sock, (const struct sockaddr *) &addr, sizeof(addr)) != 0)
    {
        perror("ERROR: connect");
        exit(EXIT_FAILURE);
    }
    struct sockaddr_in name;
    socklen_t len = sizeof(name);

    if (getsockname(sock, (struct sockaddr*)&name, &len) != 0)
    {
        perror("ERROR: getsockname");
        exit(EXIT_FAILURE);
    }

    char buff[256];
    inet_ntop(AF_INET, &name.sin_addr, buff, 256);
    close(sock);

    return string(buff);
}

void Scanner::find_iface(string dst_addr)
{
    char err[PCAP_ERRBUF_SIZE];
    pcap_if_t *all_devs;
    if (pcap_findalldevs(&all_devs, err) != 0)
    {
        perror("pcap_findalldevs");
        exit(1);
    }

    for (pcap_if_t *i = all_devs; i != NULL; i = i->next)
    {
        char buff[INET6_ADDRSTRLEN];
        for (pcap_addr_t *j = i->addresses; j != NULL; j = j->next)
        {
            if (j->addr->sa_family == AF_INET and string(i->name) != "lo")
            {
                this->iface = i->name;
                this->ipv4_addr = inet_ntoa(((struct sockaddr_in*)j->addr)->sin_addr);
            }
            if (j->addr->sa_family == AF_INET and string(i->name) == "lo")
                this->lo_addr = inet_ntoa(((struct sockaddr_in*)j->addr)->sin_addr);
            //else if (j->addr->sa_family == AF_INET6)
            //{
            //    inet_ntop(AF_INET6, (void*)&(((struct sockaddr_in6*)j->addr)->sin6_addr), buff, sizeof(buff));
            //    cout << i->name << " " << buff << "\n";
            //}
        }
    }
    
    if (this->lo_addr == dst_addr)
        this->iface = "any";

    if (this->iface.empty())
    {
        fprintf(stderr, "No interface found!\n");
        exit(1);
    }
}