/*
This file is part of GNUnet.
(C) 2011 Christian Grothoff (and other contributing authors)
GNUnet is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published
by the Free Software Foundation; either version 3, 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
General Public License for more details.
You should have received a copy of the GNU General Public License
along with GNUnet; see the file COPYING. If not, write to the
Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.
*/
/**
* @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 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, const struct GNUNET_SCHEDULER_TaskContext *tc)
{
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_delayed (GNUNET_TIME_UNIT_FOREVER_REL,
&do_disconnect, NULL);
}
int
main (int argc, char *const *argv)
{
static const struct GNUNET_GETOPT_CommandLineOption options[] = {
{'4', "ipv4", "IPV4",
gettext_noop ("set A records"),
1, &GNUNET_GETOPT_set_string, &n4},
{'6', "ipv4", "IPV6",
gettext_noop ("set AAAA records"),
1, &GNUNET_GETOPT_set_string, &n6},
GNUNET_GETOPT_OPTION_VERBOSE (&verbosity),
GNUNET_GETOPT_OPTION_END
};
return (GNUNET_OK ==
GNUNET_PROGRAM_run (argc, argv, "gnunet-dns-redirector",
gettext_noop
("Change DNS replies to point elsewhere."), options,
&run, NULL)) ? ret : 1;
}
/* end of gnunet-dns-redirector.c */