Tool to change DNS replies (for testing) More...

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

Include dependency graph for gnunet-dns-redirector.c:

Functions
static void	modify_record (const struct GNUNET_DNSPARSER_Record *record)
	Modify the given DNS record. More...

static void	modify_request (void cls, struct GNUNET_DNS_RequestHandle rh, size_t request_length, const char *request)
	Signature of a function that is called whenever the DNS service encounters a DNS request and needs to do something with it. More...

static void	do_disconnect (void *cls)
	Shutdown. More...

static void	run (void cls, char const args, const char cfgfile, const struct GNUNET_CONFIGURATION_Handle *cfg)
	Main function that will be run by the scheduler. More...

int	main (int argc, char const argv)

Variables
static struct GNUNET_DNS_Handle *	handle
	Handle to DNS service. More...

static char *	n4
	New target for A records. More...

static char *	n6
	New target for AAAA records. More...

static int	ret
	Global return value (0 success). More...

static unsigned int	verbosity
	Selected level of verbosity. More...

Detailed Description

Tool to change DNS replies (for testing)

Author: Christian Grothoff

Definition in file gnunet-dns-redirector.c.

Function Documentation

◆ modify_record()

static void modify_record ( const struct GNUNET_DNSPARSER_Record * record )

static

Modify the given DNS record.

Parameters

record record to modify

Definition at line 63 of file gnunet-dns-redirector.c.

 {
   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;
   }
 }

References buf, GNUNET_assert, GNUNET_DNSPARSER_TYPE_A, GNUNET_DNSPARSER_TYPE_AAAA, GNUNET_DNSPARSER_TYPE_CNAME, GNUNET_DNSPARSER_TYPE_MX, GNUNET_DNSPARSER_TYPE_NS, GNUNET_DNSPARSER_TYPE_PTR, GNUNET_DNSPARSER_TYPE_SOA, GNUNET_DNSPARSER_TYPE_TXT, n4, n6, record(), and verbosity.

Referenced by modify_request().

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◆ modify_request()

static void modify_request	(	void *	cls,
		struct GNUNET_DNS_RequestHandle *	rh,
		size_t	request_length,
		const char *	request
	)

static

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.

Parameters

cls	closure
rh	request handle to user for reply
request_length	number of bytes in request
request	udp payload of the DNS request

Definition at line 135 of file gnunet-dns-redirector.c.

 {
   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 (buf);
 }

References buf, GNUNET_break, GNUNET_DNS_request_answer(), GNUNET_DNS_request_forward(), GNUNET_DNSPARSER_free_packet(), GNUNET_DNSPARSER_pack(), GNUNET_DNSPARSER_parse(), GNUNET_free, GNUNET_NO, GNUNET_OK, len, modify_record(), p, request, ret, and verbosity.

Referenced by run().

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◆ do_disconnect()

static void do_disconnect ( void * cls )

static

Shutdown.

Definition at line 182 of file gnunet-dns-redirector.c.

 {
   if (NULL != handle)
   {
     GNUNET_DNS_disconnect (handle);
     handle = NULL;
   }
 }

References GNUNET_DNS_disconnect(), and handle.

Referenced by run().

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◆ run()

static void run	(	void *	cls,
		char const	args,
		const char *	cfgfile,
		const struct GNUNET_CONFIGURATION_Handle *	cfg
	)

static

Main function that will be run by the scheduler.

Parameters

cls	closure
args	remaining command-line arguments
cfgfile	name of the configuration file used (for saving, can be NULL!)
cfg	configuration

Definition at line 201 of file gnunet-dns-redirector.c.

 {
   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);
 }

References cfg, do_disconnect(), GNUNET_DNS_connect(), GNUNET_DNS_FLAG_POST_RESOLUTION, GNUNET_SCHEDULER_add_shutdown(), handle, modify_request(), n4, and n6.

Referenced by main().

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◆ main()

int main	(	int	argc,
		char const	argv
	)

Definition at line 234 of file gnunet-dns-redirector.c.

 {
   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_nz ((void *) argv);
   return ret;
 }