Resend all incoming packets

Question

I am writing an educational Man in the Middle application (Linux sockets). What I am struggling with is how to resend TCP/UDP and ICMP packets coming from victim1 to victim2? My approach below seems not to be working:

unsigned char buffer[BUF_SZ];
struct ethhdr *eth_head = (struct ethhdr *)(buffer);

struct sockaddr_ll sock_adr_resnd = {0};
sock_adr_resnd.sll_family = AF_PACKET;
sock_adr_resnd.sll_ifindex = interface_i;
sock_adr_resnd.sll_protocol = htons(ETH_P_ALL);
sock_adr_resnd.sll_halen = MAC_LEN;
memcpy(sock_adr_resnd.sll_addr, source_mac, MAC_LEN); // my MAC

if ((sct = socket(AF_PACKET, SOCK_DGRAM, 0)) < 0) { //recieve all
    perror("Socket open error ");
    exit (EXIT_FAILURE);
}
if (bind(sct, (struct sockaddr *) &sock_adr_resnd, sizeof(sock_adr_resnd)) < 0) {
    printf("Failed to bind socket \n");
}
int res_len = sizeof(sock_adr_resnd);
if (recvfrom(sct, buffer, BUF_SZ, 0, (struct sockaddr*)&sock_adr_resnd, (socklen_t *)&res_len) < 0)
{
    process = 0; // nothing accepted
}
// change mac address to actual destination
memcpy(sock_adr.sll_addr, vic_mac1, MAC_LEN);
memcpy(eth_head->h_source, vic_mac1, MAC_LEN);

if (process) {
    if (sendto(sct, buffer, BUF_SZ, 0, (struct sockaddr *)&sock_adr_resnd, sizeof(sock_adr_resnd)) < 0)
    {
        close(sct);
        perror("sendto: ");
        exit (EXIT_FAILURE);
    }
}

What I am confused about is how the socket should be set. Shouldn't it be SOCK_RAW ? Does the packet have to be proccessed differently based on type - UDP, TCP, ICMP?

Answer 1

The issue was that it is better to use RAW packets - so u can get the dest/source IP and also when recieving, there is no need to post anything about the source recieveng from, so in the end the changes are like so:

1. Change SOCK_DGRAM to SOCK_RAW
2. Pass just buffer to recvfrom() function
3. State the type of socket when creating it

4. You don't have to bind

    if ((sct = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL))) < 0) { perror("Socket open error "); exit (EXIT_FAILURE); } if (recvfrom(sct, buffer, BUF_SZ, 0, NULL, NULL) < 0) { process = 0; // nothing accepted }