/*
                                  NETWOX
                             Network toolbox
                Copyright(c) 1999-2005 Laurent Constantin
                                  -----

  Main server    : http://www.laurentconstantin.com/
  Backup servers : http://go.to/laurentconstantin/
                   http://laurentconstantin.est-la.com/
                   http://laurentconstantin.free.fr/
                   http://membres.lycos.fr/lauconstantin/
  [my current email address is on the web servers]

                                  -----
  This file is part of Netwox.

  Netwox is free software; you can redistribute it and/or
  modify it under the terms of the GNU General Public License
  version 2 as published by the Free Software Foundation.

  Netwox is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  General Public License for more details (http://www.gnu.org/).

------------------------------------------------------------------------
*/

/*-------------------------------------------------------------*/
#include "../netwox.h"

/*-------------------------------------------------------------*/
netwib_conststring t000079_description[] = {
  "This tool acknowledges every TCP-SYN. It is used to protect against",
  "scanning tools.",
  "For example, host 192.168.0.1 has a webserver on port 80. A scan will",
  "quickly find this open port. Dropping packets on other ports will slow",
  "the scan, but it will finally find port 80 open.",
  "This tool answers to TCP SYN (except for port 80), so from scanner",
  "viewpoint, all ports will be open. In this case, use netwox like this:",
  "  netwox 79 --ips 192.168.0.1 --ports 1-79,81-65535",
  "Don't forget to DROP packets in kernel firewall, otherwise, scanner",
  "will see a SYN-ACK and a RST.",
  NETWOX_DESC_sniff_devfilter,
  NETWOX_DESC_spoofip,
  NETWOX_DESC_toolpriv_snsp,
  NULL
};
netwox_toolarg t000079_args[] = {
  NETWOX_TOOLARG_REQ_IPS_SU('i', NULL, "only answer to these IP", NULL),
  NETWOX_TOOLARG_REQ_PORTS_SU('p', NULL, "only answer to these ports", NULL),
  NETWOX_TOOLARG_OPT_BUF_DEVICE('d', NULL, NULL, NULL),
  NETWOX_TOOLARG_OPT_BUF_FILTER('f', NULL, NULL, NULL),
  NETWOX_TOOLARG_OPT_SPOOFIP('s', NULL, NULL, "linkbraw"),
  NETWOX_TOOLARG_END
};
netwox_tooltreenodetype t000079_nodes[] = {
  NETWOX_TOOLTREENODETYPE_NETAUDIT_TCP,
  NETWOX_TOOLTREENODETYPE_END
};
netwox_tool_info t000079_info = {
  "Acknowledge every TCP SYN",
  t000079_description,
  "firewall",
  t000079_args,
  t000079_nodes,
};

/*-------------------------------------------------------------*/
netwib_err t000079_core(int argc, char *argv[])
{
  netwox_arg *parg;
  netwib_io *psniffio, *pspoofio;
  netwib_spoof_ip_inittype inittype;
  netwib_buf pkt, filter, device;
  netwib_iphdr ipheader, ipheader2;
  netwib_tcphdr tcpheader, tcpheader2;
  netwib_ips *pips;
  netwib_ports *pports;
  netwib_bool contains;
  netwib_err ret;

  /* obtain parameters */
  netwib_er(netwox_arg_init(argc, argv, &t000079_info, &parg));
  netwib_er(netwox_arg_ips(parg, 'i', &pips));
  netwib_er(netwox_arg_ports(parg, 'p', &pports));
  netwib_er(netwox_arg_buf(parg, 'd', &device));
  netwib_er(netwox_arg_buf(parg, 'f', &filter));
  netwib_er(netwox_arg_spoofip(parg, 's', &inittype));

  /* initialize io */
  netwib_er(netwib_io_init_spoof_ip(inittype, &pspoofio));
  netwib_er(netwib_io_init_sniff_ip(&device, &filter, NETWIB_FALSE,
                                    NETWIB_FALSE, &psniffio));

  /* main loop */
  netwib_er(netwib_buf_init_mallocdefault(&pkt));
  while (NETWIB_TRUE) {
    /* sniff */
    netwib__buf_reinit(&pkt);
    ret = netwib_io_read(psniffio, &pkt);
    if (ret == NETWIB_ERR_DATANOTAVAIL) continue;
    netwib_er(ret);
    /* check if it's TCP */
    ret = netwib_pkt_decode_iptcpdata(&pkt, &ipheader, &tcpheader, NULL);
    if (ret != NETWIB_ERR_OK) continue;
    if (!tcpheader.syn) continue;
    if (tcpheader.ack || tcpheader.fin || tcpheader.rst) continue;
    /* check we can answer to it */
    netwib_er(netwib_ips_contains_ip(pips, &ipheader.dst, &contains));
    if (!contains) continue;
    netwib_er(netwib_ports_contains_port(pports, tcpheader.dst, &contains));
    if (!contains) continue;
    /* answer */
    netwib_er(netwib_iphdr_initdefault(ipheader.src.iptype, &ipheader2));
    ipheader2.src = ipheader.dst;
    ipheader2.dst = ipheader.src;
    netwib_er(netwib_tcphdr_initdefault(&tcpheader2));
    tcpheader2.syn = NETWIB_TRUE;
    tcpheader2.ack = NETWIB_TRUE;
    tcpheader2.src = tcpheader.dst;
    tcpheader2.dst = tcpheader.src;
    tcpheader2.acknum = tcpheader.seqnum + 1;
    netwib__buf_reinit(&pkt);
    netwib_er(netwib_pkt_append_iptcpdata(&ipheader2, &tcpheader2, NULL,
                                          &pkt));
    netwib_er(netwib_io_write(pspoofio, &pkt));
  }
  netwib_er(netwib_buf_close(&pkt));

  /* close */
  netwib_er(netwib_io_close(&psniffio));
  netwib_er(netwib_io_close(&pspoofio));
  netwib_er(netwox_arg_close(&parg));

  return(NETWIB_ERR_OK);
}
