/* Example 2: disabling checksums of packets with src ip of any local interface */
static int get_all_ifaces(struct ifreq **, int *);
static unsigned int get_addr_from_ifreq(struct ifreq *);

int all_local_ipaddrs_chksum_disable()
{
    struct ifreq *ifaces;
    int ifaces_count;
    int i, ind = 0;
    struct nids_chksum_ctl *ctlp;
    unsigned int tmp;

    if (!get_all_ifaces(&ifaces, &ifaces_count))
        return -1;
    ctlp =
        (struct nids_chksum_ctl *) malloc(ifaces_count *
                          sizeof(struct
                             nids_chksum_ctl));
    if (!ctlp)
        return -1;
    for (i = 0; i < ifaces_count; i++) {
        tmp = get_addr_from_ifreq(ifaces + i);
        if (tmp) {
            ctlp[ind].netaddr = tmp;
            ctlp[ind].mask = inet_addr("255.255.255.255");
            ctlp[ind].action = NIDS_DONT_CHKSUM;
            ind++;
        }
    }
    free(ifaces);
    nids_register_chksum_ctl(ctlp, ind);
}

/* helper functions for Example 2 */
unsigned int get_addr_from_ifreq(struct ifreq *iface)
{
    if (iface->ifr_addr.sa_family == AF_INET)
        return ((struct sockaddr_in *) &(iface->ifr_addr))->
            sin_addr.s_addr;
    return 0;
}

static int get_all_ifaces(struct ifreq **ifaces, int *count)
{
    int ifaces_size = 8 * sizeof(struct ifreq);
    struct ifconf param;
    int sock;
    unsigned int i;

    *ifaces = malloc(ifaces_size);
    sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP);
    if (sock <= 0)
        return 0;
    for (;;) {
        param.ifc_len = ifaces_size;
        param.ifc_req = *ifaces;
        if (ioctl(sock, SIOCGIFCONF, &param))
            goto err;
        if (param.ifc_len < ifaces_size)
            break;
        free(*ifaces);
        ifaces_size *= 2;
        ifaces = malloc(ifaces_size);
    }
    *count = param.ifc_len / sizeof(struct ifreq);
    close(sock);
    return 1;
      err:
    close(sock);
    return 0;
}