如何同时使用2个套接字PF_INET和PF_PACKET？

Question

I have the following 2 functions

int listen_socket(unsigned int ip, int port, char *inf)
{
    struct ifreq interface;
    int fd;
    struct sockaddr_in addr;
    int n = 1;

    DEBUG(LOG_INFO, "Opening listen socket on 0x%08x:%d %s\n", ip, port, inf);
    if ((fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0) {
        DEBUG(LOG_ERR, "socket call failed: %s", strerror(errno));
        return -1;
    }

    fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);

    memset(&addr, 0, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port = htons(port);
    addr.sin_addr.s_addr = ip;

    if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, (char *) &n, sizeof(n)) == -1) {
        close(fd);
        return -1;
    }
    if (setsockopt(fd, SOL_SOCKET, SO_BROADCAST, (char *) &n, sizeof(n)) == -1) {
        close(fd);
        return -1;
    }

    strncpy(interface.ifr_ifrn.ifrn_name, inf, IFNAMSIZ);
    if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE,(char *)&interface, sizeof(interface)) < 0) {
        close(fd);
        return -1;
    }

    if (bind(fd, (struct sockaddr *)&addr, sizeof(struct sockaddr)) == -1) {
        close(fd);
        return -1;
    }

    return fd;
}


int raw_socket(int ifindex)
{
    int fd;
    struct sockaddr_ll sock;

    DEBUG(LOG_INFO, "Opening raw socket on ifindex %d\n", ifindex);
    if ((fd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP))) < 0) {
        DEBUG(LOG_ERR, "socket call failed: %s", strerror(errno));
        return -1;
    }

    fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);

    sock.sll_family = AF_PACKET;
    sock.sll_protocol = htons(ETH_P_IP);
    sock.sll_ifindex = ifindex;
    if (bind(fd, (struct sockaddr *) &sock, sizeof(sock)) < 0) {
        DEBUG(LOG_ERR, "bind call failed: %s", strerror(errno));
        close(fd);
        return -1;
    }

    return fd;
}

Both are socket listener functions.

I used these functions in my application in this way

fd = listen_socket(INADDR_ANY, 67, client_config.interface);
fd2 = raw_socket(client_config.ifindex);

Now if I send packet to my application (with destination = ip of the interface and port=67). What socket should catch my packet? is it fd2 or fd or both?

And if I send a packet to my application (with destination = broacast:255.255.255.0 and port=67). What socket should catch my packet? is it fd2 or fd or both?

Answer 1

Both sockets will receive that packet. As each packet arrives from the network driver to the kernel, it is duplicated and sent to all PF_PACKET (layer 2) sockets. The packet is also sent to the layer 3 (IP/TCP) kernel code and from there, to the addressed socket.

If this didn't happen, running a separate program doing raw packet captures (eg wireshark) would prevent any other communications over the network.