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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
- */
- /**
- * @file src/dns/gnunet-dns-redirector.c
- * @brief Tool to change DNS replies (for testing)
- * @author Christian Grothoff
- */
- #include "platform.h"
- #include "gnunet_util_lib.h"
- #include "gnunet_dns_service.h"
- #include "gnunet_dnsparser_lib.h"
- /**
- * Handle to DNS service.
- */
- static struct GNUNET_DNS_Handle *handle;
- /**
- * New target for A records.
- */
- static char *n4;
- /**
- * New target for AAAA records.
- */
- static char *n6;
- /**
- * Global return value (0 success).
- */
- static int ret;
- /**
- * Selected level of verbosity.
- */
- static unsigned int verbosity;
- /**
- * Modify the given DNS record.
- *
- * @param record record to modify
- */
- 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;
- }
- }
- /**
- * Signature of a function that is called whenever the DNS service
- * encounters a DNS request and needs to do something with it. The
- * function has then the chance to generate or modify the response by
- * calling one of the three "GNUNET_DNS_request_*" continuations.
- *
- * When a request is intercepted, this function is called first to
- * give the client a chance to do the complete address resolution;
- * "rdata" will be NULL for this first call for a DNS request, unless
- * some other client has already filled in a response.
- *
- * If multiple clients exist, all of them are called before the global
- * DNS. The global DNS is only called if all of the clients'
- * functions call GNUNET_DNS_request_forward. Functions that call
- * GNUNET_DNS_request_forward will be called again before a final
- * response is returned to the application. If any of the clients'
- * functions call GNUNET_DNS_request_drop, the response is dropped.
- *
- * @param cls closure
- * @param rh request handle to user for reply
- * @param request_length number of bytes in request
- * @param request udp payload of the DNS request
- */
- 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);
- }
- /**
- * Shutdown.
- */
- static void
- do_disconnect (void *cls)
- {
- if (NULL != handle)
- {
- GNUNET_DNS_disconnect (handle);
- handle = NULL;
- }
- }
- /**
- * Main function that will be run by the scheduler.
- *
- * @param cls closure
- * @param args remaining command-line arguments
- * @param cfgfile name of the configuration file used (for saving, can be NULL!)
- * @param cfg configuration
- */
- 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 */
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