Testing sending outbound packets inside network namespace via AF_PACKET sockets

test_veth.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/ip.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <linux/if.h>
#include <linux/if_packet.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/icmp.h>
#include <net/ethernet.h>
#include <string.h>
#include <error.h>
#include <errno.h>
#include <inttypes.h>
#include <pthread.h>
#include <sys/sysinfo.h>
#include <sys/ioctl.h>
#include <signal.h>
#include <ctype.h>

#define REDIRECT_HEADER

#include "csum.h"

#define MAX_PCKT_LENGTH 65535

static int cont = 1;
static unsigned char sMAC[ETH_ALEN];
static unsigned char dMAC[ETH_ALEN];

void signHdl(int tmp)
{
    cont = 0;
}

void GetGatewayMAC()
{
    char cmd[] = "ip neigh | grep \"$(ip -4 route list 0/0|cut -d' ' -f3) \"|cut -d' ' -f5|tr '[a-f]' '[A-F]'";

    FILE *fp =  popen(cmd, "r");

    if (fp != NULL)
    {
        char line[18];

        if (fgets(line, sizeof(line), fp) != NULL)
        {
            sscanf(line, "%hhx:%hhx:%hhx:%hhx:%hhx:%hhx", &dMAC[0], &dMAC[1], &dMAC[2], &dMAC[3], &dMAC[4], &dMAC[5]);
        }

        pclose(fp);
    }
}

int main(int argc, char *argv[])
{
    if (argc < 4)
    {
        perror("main");

        exit(1);
    }

    int sockfd;
    struct sockaddr_ll a;

    a.sll_family = PF_PACKET;
    a.sll_ifindex = if_nametoindex(argv[1]);
    a.sll_protocol = htons(ETH_P_IP);
    a.sll_halen = ETH_ALEN;

    sockfd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_IP));

    if (sockfd < 0)
    {
        perror("socket");

        exit(1);
    }

    struct ifreq ifr;
    memset(&ifr, 0, sizeof(ifr));
    strcpy(ifr.ifr_name, argv[1]);

    if (ioctl(sockfd, SIOCGIFHWADDR, &ifr) != 0)
    {
        perror("ioctl");

        exit(1);
    }

    memcpy(a.sll_addr, ifr.ifr_addr.sa_data, ETH_ALEN);
    memcpy(sMAC, a.sll_addr, ETH_ALEN);
    GetGatewayMAC();

    if (bind(sockfd, (struct sockaddr *)&a, sizeof(a)) < 0)
    {
        perror("bind");

        exit(1);
    }

    printf("Source MAC => ");

    for(uint8_t i = 0; i < ETH_ALEN; i++)
    {
        printf("%02x", sMAC[i]);

        if (i != 5)
        {
            printf(":");
        }
    }

    printf("\n");

    printf("Destination MAC => ");

    for(uint8_t i = 0; i < ETH_ALEN; i++)
    {
        printf("%02x", dMAC[i]);

        if (i != 5)
        {
            printf(":");
        }
    }

    printf("\n\n");

    signal(SIGINT, signHdl);

    while (cont)
    {
        char buffer[MAX_PCKT_LENGTH];

        struct ethhdr *ethhdr = (struct ethhdr *) (buffer);
        struct iphdr *iphdr = (struct iphdr *) (buffer + sizeof(struct ethhdr));
        struct udphdr *udphdr = (struct udphdr *) (buffer + sizeof(struct ethhdr) + sizeof(struct iphdr));

        // Eth
        memcpy(ethhdr->h_source, sMAC, ETH_ALEN);
        memcpy(ethhdr->h_dest, dMAC, ETH_ALEN);
        ethhdr->h_proto = htons(ETH_P_IP);

        // IP
        iphdr->ihl = 5;
        iphdr->version = 4;
        iphdr->id = rand();
        iphdr->protocol = IPPROTO_UDP;
        iphdr->frag_off = 0;
        iphdr->tos = 0x0;
        iphdr->ttl = 64;
        iphdr->saddr = inet_addr(argv[2]);
        iphdr->daddr = inet_addr(argv[3]);
        iphdr->tot_len = htons(sizeof(struct iphdr) + sizeof(struct udphdr));
        iphdr->check = 0;
        iphdr->check = ip_fast_csum(iphdr, iphdr->ihl);

        // UDP
        udphdr->source = htons(15000);
        udphdr->dest = htons(25000);
        udphdr->len = htons(sizeof(struct udphdr));
        udphdr->check = 0;
        udphdr->check = csum_tcpudp_magic(iphdr->saddr, iphdr->daddr, sizeof(struct udphdr), IPPROTO_UDP, csum_partial(udphdr, sizeof(struct udphdr), 0));

        uint16_t sent;

        if ((sent = write(sockfd, buffer, ntohs(iphdr->tot_len) + sizeof(struct ethhdr))) < 0)
        {
            perror("write");
        }

        printf("Sent %d (%lu)\n", sent, ntohs(iphdr->tot_len) + sizeof(struct ethhdr));

        sleep(1);
    }


    close(sockfd);

    exit(0);
}