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 */