gnunet-dns-redirector.c

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/*
     This file is part of GNUnet.
     Copyright (C) 2011 GNUnet e.V.

     GNUnet is free software: you can redistribute it and/or modify it
     under the terms of the GNU Affero General Public License as published
     by the Free Software Foundation, either version 3 of the License,
     or (at your option) any later version.

     GNUnet 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
     Affero General Public License for more details.

     You should have received a copy of the GNU Affero General Public License
     along with this program.  If not, see <http://www.gnu.org/licenses/>.

     SPDX-License-Identifier: AGPL3.0-or-later
 */

#include "platform.h"
#include "gnunet_util_lib.h"
#include "gnunet_dns_service.h"
#include "gnunet_dnsparser_lib.h"

static struct GNUNET_DNS_Handle *handle;

static char *n4;

static char *n6;

static int ret;

static unsigned int verbosity;


static void
modify_record(const struct GNUNET_DNSPARSER_Record *record)
{
  char buf[INET6_ADDRSTRLEN];

  switch (record->type)
    {
    case GNUNET_DNSPARSER_TYPE_A:
      if (record->data.raw.data_len != sizeof(struct in_addr))
        return;
      if (NULL != n4)
        {
          if (verbosity > 1)
            fprintf(stderr,
                    "Changing A record from `%s' to `%s'\n",
                    inet_ntop(AF_INET, record->data.raw.data, buf, sizeof(buf)),
                    n4);
          GNUNET_assert(1 == inet_pton(AF_INET, n4, record->data.raw.data));
        }
      break;

    case GNUNET_DNSPARSER_TYPE_AAAA:
      if (record->data.raw.data_len != sizeof(struct in6_addr))
        return;
      if (NULL != n6)
        {
          if (verbosity > 1)
            fprintf(stderr,
                    "Changing AAAA record from `%s' to `%s'\n",
                    inet_ntop(AF_INET6, record->data.raw.data, buf, sizeof(buf)),
                    n6);
          GNUNET_assert(1 == inet_pton(AF_INET6, n6, record->data.raw.data));
        }
      break;

    case GNUNET_DNSPARSER_TYPE_NS:
    case GNUNET_DNSPARSER_TYPE_CNAME:
    case GNUNET_DNSPARSER_TYPE_PTR:
    case GNUNET_DNSPARSER_TYPE_SOA:
    case GNUNET_DNSPARSER_TYPE_MX:
    case GNUNET_DNSPARSER_TYPE_TXT:
      break;

    default:
      break;
    }
}


static void
modify_request(void *cls,
               struct GNUNET_DNS_RequestHandle *rh,
               size_t request_length,
               const char *request)
{
  struct GNUNET_DNSPARSER_Packet *p;
  unsigned int i;
  char *buf;
  size_t len;
  int ret;

  p = GNUNET_DNSPARSER_parse(request, request_length);
  if (NULL == p)
    {
      fprintf(stderr, "Received malformed DNS packet, leaving it untouched\n");
      GNUNET_DNS_request_forward(rh);
      return;
    }
  for (i = 0; i < p->num_answers; i++)
    modify_record(&p->answers[i]);
  buf = NULL;
  ret = GNUNET_DNSPARSER_pack(p, 1024, &buf, &len);
  GNUNET_DNSPARSER_free_packet(p);
  if (GNUNET_OK != ret)
    {
      if (GNUNET_NO == ret)
        fprintf(stderr,
                "Modified DNS response did not fit, keeping old response\n");
      else
        GNUNET_break(0); /* our modifications should have been sane! */
      GNUNET_DNS_request_forward(rh);
    }
  else
    {
      if (verbosity > 0)
        fprintf(stdout,
                "Injecting modified DNS response\n");
      GNUNET_DNS_request_answer(rh, len, buf);
    }
  GNUNET_free_non_null(buf);
}


static void
do_disconnect(void *cls)
{
  if (NULL != handle)
    {
      GNUNET_DNS_disconnect(handle);
      handle = NULL;
    }
}


static void
run(void *cls, char *const *args, const char *cfgfile,
    const struct GNUNET_CONFIGURATION_Handle *cfg)
{
  struct in_addr i4;
  struct in6_addr i6;

  if ((n4 != NULL) &&
      (1 != inet_pton(AF_INET, n4, &i4)))
    {
      fprintf(stderr,
              "`%s' is nto a valid IPv4 address!\n",
              n4);
      return;
    }
  if ((n6 != NULL) &&
      (1 != inet_pton(AF_INET6, n6, &i6)))
    {
      fprintf(stderr,
              "`%s' is nto a valid IPv6 address!\n",
              n6);
      return;
    }

  handle =
    GNUNET_DNS_connect(cfg,
                       GNUNET_DNS_FLAG_POST_RESOLUTION,
                       &modify_request,
                       NULL);
  GNUNET_SCHEDULER_add_shutdown(&do_disconnect, NULL);
}


int
main(int argc, char *const *argv)
{
  struct GNUNET_GETOPT_CommandLineOption options[] = {
    GNUNET_GETOPT_option_string('4',
                                "ipv4",
                                "IPV4",
                                gettext_noop("set A records"),
                                &n4),

    GNUNET_GETOPT_option_string('6',
                                "ipv4",
                                "IPV6",
                                gettext_noop("set AAAA records"),
                                &n6),

    GNUNET_GETOPT_option_verbose(&verbosity),
    GNUNET_GETOPT_OPTION_END
  };

  if (GNUNET_OK != GNUNET_STRINGS_get_utf8_args(argc, argv, &argc, &argv))
    return 2;

  ret = (GNUNET_OK ==
         GNUNET_PROGRAM_run(argc, argv, "gnunet-dns-redirector",
                            gettext_noop
                              ("Change DNS replies to point elsewhere."), options,
                            &run, NULL)) ? ret : 1;
  GNUNET_free((void*)argv);
  return ret;
}


/* end of gnunet-dns-redirector.c */