src/or/dnsserv.c

   1 /* Copyright (c) 2007-2013, The Tor Project, Inc. */
   2 /* See LICENSE for licensing information */
   3
   4 /**
   5  * \file dnsserv.c \brief Implements client-side DNS proxy server code.  Note:
   6  * this is the DNS Server code, not the Server DNS code.  Confused?  This code
   7  * runs on client-side, and acts as a DNS server.  The code in dns.c, on the
   8  * other hand, runs on Tor servers, and acts as a DNS client.
   9  **/
  10
  11 #include "or.h"
  12 #include "dnsserv.h"
  13 #include "config.h"
  14 #include "connection.h"
  15 #include "connection_edge.h"
  16 #include "control.h"
  17 #include "main.h"
  18 #include "policies.h"
  19 #ifdef HAVE_EVENT2_DNS_H
  20 #include <event2/dns.h>
  21 #include <event2/dns_compat.h>
  22 /* XXXX this implies we want an improved evdns  */
  23 #include <event2/dns_struct.h>
  24 #else
  25 #include "eventdns.h"
  26 #endif
  27
  28 /** Helper function: called by evdns whenever the client sends a request to our
  29  * DNSPort.  We need to eventually answer the request <b>req</b>.
  30  */
  31 static void
  32 evdns_server_callback(struct evdns_server_request *req, void *data_)
  33 {
  34   const listener_connection_t *listener = data_;
  35   entry_connection_t *entry_conn;
  36   edge_connection_t *conn;
  37   int i = 0;
  38   struct evdns_server_question *q = NULL, *supported_q = NULL;
  39   struct sockaddr_storage addr;
  40   struct sockaddr *sa;
  41   int addrlen;
  42   tor_addr_t tor_addr;
  43   uint16_t port;
  44   int err = DNS_ERR_NONE;
  45   char *q_name;
  46
  47   tor_assert(req);
  48
  49   log_info(LD_APP, "Got a new DNS request!");
  50
  51   req->flags |= 0x80; /* set RA */
  52
  53   /* First, check whether the requesting address matches our SOCKSPolicy. */
  54   if ((addrlen = evdns_server_request_get_requesting_addr(req,
  55                       (struct sockaddr*)&addr, (socklen_t)sizeof(addr))) < 0) {
  56     log_warn(LD_APP, "Couldn't get requesting address.");
  57     evdns_server_request_respond(req, DNS_ERR_SERVERFAILED);
  58     return;
  59   }
  60   (void) addrlen;
  61   sa = (struct sockaddr*) &addr;
  62   if (tor_addr_from_sockaddr(&tor_addr, sa, &port)<0) {
  63     log_warn(LD_APP, "Requesting address wasn't recognized.");
  64     evdns_server_request_respond(req, DNS_ERR_SERVERFAILED);
  65     return;
  66   }
  67
  68   if (!socks_policy_permits_address(&tor_addr)) {
  69     log_warn(LD_APP, "Rejecting DNS request from disallowed IP.");
  70     evdns_server_request_respond(req, DNS_ERR_REFUSED);
  71     return;
  72   }
  73
  74   /* Now, let's find the first actual question of a type we can answer in this
  75    * DNS request.  It makes us a little noncompliant to act like this; we
  76    * should fix that eventually if it turns out to make a difference for
  77    * anybody. */
  78   if (req->nquestions == 0) {
  79     log_info(LD_APP, "No questions in DNS request; sending back nil reply.");
  80     evdns_server_request_respond(req, 0);
  81     return;
  82   }
  83   if (req->nquestions > 1) {
  84     log_info(LD_APP, "Got a DNS request with more than one question; I only "
  85              "handle one question at a time for now.  Skipping the extras.");
  86   }
  87   for (i = 0; i < req->nquestions; ++i) {
  88     if (req->questions[i]->dns_question_class != EVDNS_CLASS_INET)
  89       continue;
  90     if (! q)
  91       q = req->questions[i];
  92     switch (req->questions[i]->type) {
  93       case EVDNS_TYPE_A:
  94       case EVDNS_TYPE_AAAA:
  95       case EVDNS_TYPE_PTR:
  96         /* We always pick the first one of these questions, if there is
  97            one. */
  98         if (! supported_q)
  99           supported_q = q;
 100         break;
 101       default:
 102         break;
 103       }
 104   }
 105   if (supported_q)
 106     q = supported_q;
 107   if (!q) {
 108     log_info(LD_APP, "None of the questions we got were ones we're willing "
 109              "to support. Sending NOTIMPL.");
 110     evdns_server_request_respond(req, DNS_ERR_NOTIMPL);
 111     return;
 112   }
 113
 114   /* Make sure the name isn't too long: This should be impossible, I think. */
 115   if (err == DNS_ERR_NONE && strlen(q->name) > MAX_SOCKS_ADDR_LEN-1)
 116     err = DNS_ERR_FORMAT;
 117
 118   if (err != DNS_ERR_NONE || !supported_q) {
 119     /* We got an error?  There's no question we're willing to answer? Then
 120      * send back an answer immediately; we're done. */
 121     evdns_server_request_respond(req, err);
 122     return;
 123   }
 124
 125   /* Make a new dummy AP connection, and attach the request to it. */
 126   entry_conn = entry_connection_new(CONN_TYPE_AP, AF_INET);
 127   conn = ENTRY_TO_EDGE_CONN(entry_conn);
 128   TO_CONN(conn)->state = AP_CONN_STATE_RESOLVE_WAIT;
 129   conn->is_dns_request = 1;
 130
 131   tor_addr_copy(&TO_CONN(conn)->addr, &tor_addr);
 132   TO_CONN(conn)->port = port;
 133   TO_CONN(conn)->address = tor_dup_addr(&tor_addr);
 134
 135   if (q->type == EVDNS_TYPE_A || q->type == EVDNS_TYPE_AAAA ||
 136       q->type == EVDNS_QTYPE_ALL) {
 137     entry_conn->socks_request->command = SOCKS_COMMAND_RESOLVE;
 138   } else {
 139     tor_assert(q->type == EVDNS_TYPE_PTR);
 140     entry_conn->socks_request->command = SOCKS_COMMAND_RESOLVE_PTR;
 141   }
 142
 143   if (q->type == EVDNS_TYPE_A || q->type == EVDNS_QTYPE_ALL) {
 144     entry_conn->ipv4_traffic_ok = 1;
 145     entry_conn->ipv6_traffic_ok = 0;
 146     entry_conn->prefer_ipv6_traffic = 0;
 147   } else if (q->type == EVDNS_TYPE_AAAA) {
 148     entry_conn->ipv4_traffic_ok = 0;
 149     entry_conn->ipv6_traffic_ok = 1;
 150     entry_conn->prefer_ipv6_traffic = 1;
 151   }
 152
 153   strlcpy(entry_conn->socks_request->address, q->name,
 154           sizeof(entry_conn->socks_request->address));
 155
 156   entry_conn->socks_request->listener_type = listener->base_.type;
 157   entry_conn->dns_server_request = req;
 158   entry_conn->isolation_flags = listener->isolation_flags;
 159   entry_conn->session_group = listener->session_group;
 160   entry_conn->nym_epoch = get_signewnym_epoch();
 161
 162   if (connection_add(ENTRY_TO_CONN(entry_conn)) < 0) {
 163     log_warn(LD_APP, "Couldn't register dummy connection for DNS request");
 164     evdns_server_request_respond(req, DNS_ERR_SERVERFAILED);
 165     connection_free(ENTRY_TO_CONN(entry_conn));
 166     return;
 167   }
 168
 169   control_event_stream_status(entry_conn, STREAM_EVENT_NEW_RESOLVE, 0);
 170
 171   /* Now, unless a controller asked us to leave streams unattached,
 172   * throw the connection over to get rewritten (which will
 173   * answer it immediately if it's in the cache, or completely bogus, or
 174   * automapped), and then attached to a circuit. */
 175   log_info(LD_APP, "Passing request for %s to rewrite_and_attach.",
 176            escaped_safe_str_client(q->name));
 177   q_name = tor_strdup(q->name); /* q could be freed in rewrite_and_attach */
 178   connection_ap_rewrite_and_attach_if_allowed(entry_conn, NULL, NULL);
 179   /* Now, the connection is marked if it was bad. */
 180
 181   log_info(LD_APP, "Passed request for %s to rewrite_and_attach_if_allowed.",
 182            escaped_safe_str_client(q_name));
 183   tor_free(q_name);
 184 }
 185
 186 /** Helper function: called whenever the client sends a resolve request to our
 187  * controller.  We need to eventually answer the request <b>req</b>.
 188  * Returns 0 if the controller will be getting (or has gotten) an event in
 189  * response; -1 if we couldn't launch the request.
 190  */
 191 int
 192 dnsserv_launch_request(const char *name, int reverse,
 193                        control_connection_t *control_conn)
 194 {
 195   entry_connection_t *entry_conn;
 196   edge_connection_t *conn;
 197   char *q_name;
 198
 199   /* Make a new dummy AP connection, and attach the request to it. */
 200   entry_conn = entry_connection_new(CONN_TYPE_AP, AF_INET);
 201   conn = ENTRY_TO_EDGE_CONN(entry_conn);
 202   conn->base_.state = AP_CONN_STATE_RESOLVE_WAIT;
 203
 204   tor_addr_copy(&TO_CONN(conn)->addr, &control_conn->base_.addr);
 205 #ifdef AF_UNIX
 206   /*
 207    * The control connection can be AF_UNIX and if so tor_dup_addr will
 208    * unhelpfully say "<unknown address type>"; say "(Tor_internal)"
 209    * instead.
 210    */
 211   if (control_conn->base_.socket_family == AF_UNIX) {
 212     TO_CONN(conn)->port = 0;
 213     TO_CONN(conn)->address = tor_strdup("(Tor_internal)");
 214   } else {
 215     TO_CONN(conn)->port = control_conn->base_.port;
 216     TO_CONN(conn)->address = tor_dup_addr(&control_conn->base_.addr);
 217   }
 218 #else
 219   TO_CONN(conn)->port = control_conn->base_.port;
 220   TO_CONN(conn)->address = tor_dup_addr(&control_conn->base_.addr);
 221 #endif
 222
 223   if (reverse)
 224     entry_conn->socks_request->command = SOCKS_COMMAND_RESOLVE_PTR;
 225   else
 226     entry_conn->socks_request->command = SOCKS_COMMAND_RESOLVE;
 227
 228   conn->is_dns_request = 1;
 229
 230   strlcpy(entry_conn->socks_request->address, name,
 231           sizeof(entry_conn->socks_request->address));
 232
 233   entry_conn->socks_request->listener_type = CONN_TYPE_CONTROL_LISTENER;
 234   entry_conn->original_dest_address = tor_strdup(name);
 235   entry_conn->session_group = SESSION_GROUP_CONTROL_RESOLVE;
 236   entry_conn->nym_epoch = get_signewnym_epoch();
 237   entry_conn->isolation_flags = ISO_DEFAULT;
 238
 239   if (connection_add(TO_CONN(conn))<0) {
 240     log_warn(LD_APP, "Couldn't register dummy connection for RESOLVE request");
 241     connection_free(TO_CONN(conn));
 242     return -1;
 243   }
 244
 245   control_event_stream_status(entry_conn, STREAM_EVENT_NEW_RESOLVE, 0);
 246
 247   /* Now, unless a controller asked us to leave streams unattached,
 248   * throw the connection over to get rewritten (which will
 249   * answer it immediately if it's in the cache, or completely bogus, or
 250   * automapped), and then attached to a circuit. */
 251   log_info(LD_APP, "Passing request for %s to rewrite_and_attach.",
 252            escaped_safe_str_client(name));
 253   q_name = tor_strdup(name); /* q could be freed in rewrite_and_attach */
 254   connection_ap_rewrite_and_attach_if_allowed(entry_conn, NULL, NULL);
 255   /* Now, the connection is marked if it was bad. */
 256
 257   log_info(LD_APP, "Passed request for %s to rewrite_and_attach_if_allowed.",
 258            escaped_safe_str_client(q_name));
 259   tor_free(q_name);
 260   return 0;
 261 }
 262
 263 /** If there is a pending request on <b>conn</b> that's waiting for an answer,
 264  * send back an error and free the request. */
 265 void
 266 dnsserv_reject_request(entry_connection_t *conn)
 267 {
 268   if (conn->dns_server_request) {
 269     evdns_server_request_respond(conn->dns_server_request,
 270                                  DNS_ERR_SERVERFAILED);
 271     conn->dns_server_request = NULL;
 272   }
 273 }
 274
 275 /** Look up the original name that corresponds to 'addr' in req.  We use this
 276  * to preserve case in order to facilitate people using 0x20-hacks to avoid
 277  * DNS poisoning. */
 278 static const char *
 279 evdns_get_orig_address(const struct evdns_server_request *req,
 280                        int rtype, const char *addr)
 281 {
 282   int i, type;
 283
 284   switch (rtype) {
 285   case RESOLVED_TYPE_IPV4:
 286     type = EVDNS_TYPE_A;
 287     break;
 288   case RESOLVED_TYPE_HOSTNAME:
 289     type = EVDNS_TYPE_PTR;
 290     break;
 291   case RESOLVED_TYPE_IPV6:
 292     type = EVDNS_TYPE_AAAA;
 293     break;
 294   default:
 295     tor_fragile_assert();
 296     return addr;
 297   }
 298
 299   for (i = 0; i < req->nquestions; ++i) {
 300     const struct evdns_server_question *q = req->questions[i];
 301     if (q->type == type && !strcasecmp(q->name, addr))
 302       return q->name;
 303   }
 304   return addr;
 305 }
 306
 307 /** Tell the dns request waiting for an answer on <b>conn</b> that we have an
 308  * answer of type <b>answer_type</b> (RESOLVE_TYPE_IPV4/IPV6/ERR), of length
 309  * <b>answer_len</b>, in <b>answer</b>, with TTL <b>ttl</b>.  Doesn't do
 310  * any caching; that's handled elsewhere. */
 311 void
 312 dnsserv_resolved(entry_connection_t *conn,
 313                  int answer_type,
 314                  size_t answer_len,
 315                  const char *answer,
 316                  int ttl)
 317 {
 318   struct evdns_server_request *req = conn->dns_server_request;
 319   const char *name;
 320   int err = DNS_ERR_NONE;
 321   if (!req)
 322     return;
 323   name = evdns_get_orig_address(req, answer_type,
 324                                 conn->socks_request->address);
 325
 326   /* XXXX Re-do; this is dumb. */
 327   if (ttl < 60)
 328     ttl = 60;
 329
 330   /* The evdns interface is: add a bunch of reply items (corresponding to one
 331    * or more of the questions in the request); then, call
 332    * evdns_server_request_respond. */
 333   if (answer_type == RESOLVED_TYPE_IPV6) {
 334     evdns_server_request_add_aaaa_reply(req,
 335                                         name,
 336                                         1, answer, ttl);
 337   } else if (answer_type == RESOLVED_TYPE_IPV4 && answer_len == 4 &&
 338              conn->socks_request->command == SOCKS_COMMAND_RESOLVE) {
 339     evdns_server_request_add_a_reply(req,
 340                                      name,
 341                                      1, answer, ttl);
 342   } else if (answer_type == RESOLVED_TYPE_HOSTNAME &&
 343              answer_len < 256 &&
 344              conn->socks_request->command == SOCKS_COMMAND_RESOLVE_PTR) {
 345     char *ans = tor_strndup(answer, answer_len);
 346     evdns_server_request_add_ptr_reply(req, NULL,
 347                                        name,
 348                                        ans, ttl);
 349     tor_free(ans);
 350   } else if (answer_type == RESOLVED_TYPE_ERROR) {
 351     err = DNS_ERR_NOTEXIST;
 352   } else { /* answer_type == RESOLVED_TYPE_ERROR_TRANSIENT */
 353     err = DNS_ERR_SERVERFAILED;
 354   }
 355
 356   evdns_server_request_respond(req, err);
 357
 358   conn->dns_server_request = NULL;
 359 }
 360
 361 /** Set up the evdns server port for the UDP socket on <b>conn</b>, which
 362  * must be an AP_DNS_LISTENER */
 363 void
 364 dnsserv_configure_listener(connection_t *conn)
 365 {
 366   listener_connection_t *listener_conn;
 367   tor_assert(conn);
 368   tor_assert(SOCKET_OK(conn->s));
 369   tor_assert(conn->type == CONN_TYPE_AP_DNS_LISTENER);
 370
 371   listener_conn = TO_LISTENER_CONN(conn);
 372   listener_conn->dns_server_port =
 373     tor_evdns_add_server_port(conn->s, 0, evdns_server_callback,
 374                               listener_conn);
 375 }
 376
 377 /** Free the evdns server port for <b>conn</b>, which must be an
 378  * AP_DNS_LISTENER. */
 379 void
 380 dnsserv_close_listener(connection_t *conn)
 381 {
 382   listener_connection_t *listener_conn;
 383   tor_assert(conn);
 384   tor_assert(conn->type == CONN_TYPE_AP_DNS_LISTENER);
 385
 386   listener_conn = TO_LISTENER_CONN(conn);
 387
 388   if (listener_conn->dns_server_port) {
 389     evdns_close_server_port(listener_conn->dns_server_port);
 390     listener_conn->dns_server_port = NULL;
 391   }
 392 }
 393