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Diffstat (limited to 'src/dns/gnunet-dns-redirector.c')
| -rw-r--r-- | src/dns/gnunet-dns-redirector.c | 252 |
1 files changed, 252 insertions, 0 deletions
diff --git a/src/dns/gnunet-dns-redirector.c b/src/dns/gnunet-dns-redirector.c new file mode 100644 index 0000000..a45b896 --- /dev/null +++ b/src/dns/gnunet-dns-redirector.c @@ -0,0 +1,252 @@ +/* + 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 */ |