src/or/dnsserv.c

   1 /* Copyright (c) 2007-2017, The Tor Project, Inc. */
   2 /* See LICENSE for licensing information */
   3
   4 /**
   5  * \file dnsserv.c
   6  * \brief Implements client-side DNS proxy server code.
   7  *
   8  * When a user enables the DNSPort configuration option to have their local
   9  * Tor client handle DNS requests, this module handles it.  It functions as a
  10  * "DNS Server" on the client side, which client applications use.
  11  *
  12  * Inbound DNS requests are represented as entry_connection_t here (since
  13  * that's how Tor represents client-side streams), which are kept associated
  14  * with an evdns_server_request structure as exposed by Libevent's
  15  * evdns code.
  16  *
  17  * Upon receiving a DNS request, libevent calls our evdns_server_callback()
  18  * function here, which causes this module to create an entry_connection_t
  19  * request as appropriate.  Later, when that request is answered,
  20  * connection_edge.c calls dnsserv_resolved() so we can finish up and tell the
  21  * DNS client.
  22  **/
  23
  24 #include "or.h"
  25 #include "dnsserv.h"
  26 #include "config.h"
  27 #include "connection.h"
  28 #include "connection_edge.h"
  29 #include "control.h"
  30 #include "main.h"
  31 #include "policies.h"
  32 #include <event2/dns.h>
  33 #include <event2/dns_compat.h>
  34 /* XXXX this implies we want an improved evdns  */
  35 #include <event2/dns_struct.h>
  36
  37 /** Helper function: called by evdns whenever the client sends a request to our
  38  * DNSPort.  We need to eventually answer the request <b>req</b>.
  39  */
  40 static void
  41 evdns_server_callback(struct evdns_server_request *req, void *data_)
  42 {
  43   const listener_connection_t *listener = data_;
  44   entry_connection_t *entry_conn;
  45   edge_connection_t *conn;
  46   int i = 0;
  47   struct evdns_server_question *q = NULL, *supported_q = NULL;
  48   struct sockaddr_storage addr;
  49   struct sockaddr *sa;
  50   int addrlen;
  51   tor_addr_t tor_addr;
  52   uint16_t port;
  53   int err = DNS_ERR_NONE;
  54   char *q_name;
  55
  56   tor_assert(req);
  57
  58   log_info(LD_APP, "Got a new DNS request!");
  59
  60   req->flags |= 0x80; /* set RA */
  61
  62   /* First, check whether the requesting address matches our SOCKSPolicy. */
  63   if ((addrlen = evdns_server_request_get_requesting_addr(req,
  64                       (struct sockaddr*)&addr, (socklen_t)sizeof(addr))) < 0) {
  65     log_warn(LD_APP, "Couldn't get requesting address.");
  66     evdns_server_request_respond(req, DNS_ERR_SERVERFAILED);
  67     return;
  68   }
  69   (void) addrlen;
  70   sa = (struct sockaddr*) &addr;
  71   if (tor_addr_from_sockaddr(&tor_addr, sa, &port)<0) {
  72     log_warn(LD_APP, "Requesting address wasn't recognized.");
  73     evdns_server_request_respond(req, DNS_ERR_SERVERFAILED);
  74     return;
  75   }
  76
  77   if (!socks_policy_permits_address(&tor_addr)) {
  78     log_warn(LD_APP, "Rejecting DNS request from disallowed IP.");
  79     evdns_server_request_respond(req, DNS_ERR_REFUSED);
  80     return;
  81   }
  82
  83   /* Now, let's find the first actual question of a type we can answer in this
  84    * DNS request.  It makes us a little noncompliant to act like this; we
  85    * should fix that eventually if it turns out to make a difference for
  86    * anybody. */
  87   if (req->nquestions == 0) {
  88     log_info(LD_APP, "No questions in DNS request; sending back nil reply.");
  89     evdns_server_request_respond(req, 0);
  90     return;
  91   }
  92   if (req->nquestions > 1) {
  93     log_info(LD_APP, "Got a DNS request with more than one question; I only "
  94              "handle one question at a time for now.  Skipping the extras.");
  95   }
  96   for (i = 0; i < req->nquestions; ++i) {
  97     if (req->questions[i]->dns_question_class != EVDNS_CLASS_INET)
  98       continue;
  99     switch (req->questions[i]->type) {
 100       case EVDNS_TYPE_A:
 101       case EVDNS_TYPE_AAAA:
 102       case EVDNS_TYPE_PTR:
 103         /* We always pick the first one of these questions, if there is
 104            one. */
 105         if (! supported_q)
 106           supported_q = req->questions[i];
 107         break;
 108       default:
 109         break;
 110       }
 111   }
 112   if (supported_q)
 113     q = supported_q;
 114   if (!q) {
 115     log_info(LD_APP, "None of the questions we got were ones we're willing "
 116              "to support. Sending NOTIMPL.");
 117     evdns_server_request_respond(req, DNS_ERR_NOTIMPL);
 118     return;
 119   }
 120
 121   /* Make sure the name isn't too long: This should be impossible, I think. */
 122   if (err == DNS_ERR_NONE && strlen(q->name) > MAX_SOCKS_ADDR_LEN-1)
 123     err = DNS_ERR_FORMAT;
 124
 125   if (err != DNS_ERR_NONE || !supported_q) {
 126     /* We got an error?  There's no question we're willing to answer? Then
 127      * send back an answer immediately; we're done. */
 128     evdns_server_request_respond(req, err);
 129     return;
 130   }
 131
 132   /* Make a new dummy AP connection, and attach the request to it. */
 133   entry_conn = entry_connection_new(CONN_TYPE_AP, AF_INET);
 134   conn = ENTRY_TO_EDGE_CONN(entry_conn);
 135   CONNECTION_AP_EXPECT_NONPENDING(entry_conn);
 136   TO_CONN(conn)->state = AP_CONN_STATE_RESOLVE_WAIT;
 137   conn->is_dns_request = 1;
 138
 139   tor_addr_copy(&TO_CONN(conn)->addr, &tor_addr);
 140   TO_CONN(conn)->port = port;
 141   TO_CONN(conn)->address = tor_addr_to_str_dup(&tor_addr);
 142
 143   if (q->type == EVDNS_TYPE_A || q->type == EVDNS_TYPE_AAAA ||
 144       q->type == EVDNS_QTYPE_ALL) {
 145     entry_conn->socks_request->command = SOCKS_COMMAND_RESOLVE;
 146   } else {
 147     tor_assert(q->type == EVDNS_TYPE_PTR);
 148     entry_conn->socks_request->command = SOCKS_COMMAND_RESOLVE_PTR;
 149   }
 150
 151   /* This serves our DNS port so enable DNS request by default. */
 152   entry_conn->entry_cfg.dns_request = 1;
 153   if (q->type == EVDNS_TYPE_A || q->type == EVDNS_QTYPE_ALL) {
 154     entry_conn->entry_cfg.ipv4_traffic = 1;
 155     entry_conn->entry_cfg.ipv6_traffic = 0;
 156     entry_conn->entry_cfg.prefer_ipv6 = 0;
 157   } else if (q->type == EVDNS_TYPE_AAAA) {
 158     entry_conn->entry_cfg.ipv4_traffic = 0;
 159     entry_conn->entry_cfg.ipv6_traffic = 1;
 160     entry_conn->entry_cfg.prefer_ipv6 = 1;
 161   }
 162
 163   strlcpy(entry_conn->socks_request->address, q->name,
 164           sizeof(entry_conn->socks_request->address));
 165
 166   entry_conn->socks_request->listener_type = listener->base_.type;
 167   entry_conn->dns_server_request = req;
 168   entry_conn->entry_cfg.isolation_flags = listener->entry_cfg.isolation_flags;
 169   entry_conn->entry_cfg.session_group = listener->entry_cfg.session_group;
 170   entry_conn->nym_epoch = get_signewnym_epoch();
 171
 172   if (connection_add(ENTRY_TO_CONN(entry_conn)) < 0) {
 173     log_warn(LD_APP, "Couldn't register dummy connection for DNS request");
 174     evdns_server_request_respond(req, DNS_ERR_SERVERFAILED);
 175     connection_free_(ENTRY_TO_CONN(entry_conn));
 176     return;
 177   }
 178
 179   control_event_stream_status(entry_conn, STREAM_EVENT_NEW_RESOLVE, 0);
 180
 181   /* Now, unless a controller asked us to leave streams unattached,
 182   * throw the connection over to get rewritten (which will
 183   * answer it immediately if it's in the cache, or completely bogus, or
 184   * automapped), and then attached to a circuit. */
 185   log_info(LD_APP, "Passing request for %s to rewrite_and_attach.",
 186            escaped_safe_str_client(q->name));
 187   q_name = tor_strdup(q->name); /* q could be freed in rewrite_and_attach */
 188   connection_ap_rewrite_and_attach_if_allowed(entry_conn, NULL, NULL);
 189   /* Now, the connection is marked if it was bad. */
 190
 191   log_info(LD_APP, "Passed request for %s to rewrite_and_attach_if_allowed.",
 192            escaped_safe_str_client(q_name));
 193   tor_free(q_name);
 194 }
 195
 196 /** Helper function: called whenever the client sends a resolve request to our
 197  * controller.  We need to eventually answer the request <b>req</b>.
 198  * Returns 0 if the controller will be getting (or has gotten) an event in
 199  * response; -1 if we couldn't launch the request.
 200  */
 201 int
 202 dnsserv_launch_request(const char *name, int reverse,
 203                        control_connection_t *control_conn)
 204 {
 205   entry_connection_t *entry_conn;
 206   edge_connection_t *conn;
 207   char *q_name;
 208
 209   /* Make a new dummy AP connection, and attach the request to it. */
 210   entry_conn = entry_connection_new(CONN_TYPE_AP, AF_INET);
 211   entry_conn->entry_cfg.dns_request = 1;
 212   conn = ENTRY_TO_EDGE_CONN(entry_conn);
 213   CONNECTION_AP_EXPECT_NONPENDING(entry_conn);
 214   conn->base_.state = AP_CONN_STATE_RESOLVE_WAIT;
 215
 216   tor_addr_copy(&TO_CONN(conn)->addr, &control_conn->base_.addr);
 217 #ifdef AF_UNIX
 218   /*
 219    * The control connection can be AF_UNIX and if so tor_addr_to_str_dup will
 220    * unhelpfully say "<unknown address type>"; say "(Tor_internal)"
 221    * instead.
 222    */
 223   if (control_conn->base_.socket_family == AF_UNIX) {
 224     TO_CONN(conn)->port = 0;
 225     TO_CONN(conn)->address = tor_strdup("(Tor_internal)");
 226   } else {
 227     TO_CONN(conn)->port = control_conn->base_.port;
 228     TO_CONN(conn)->address = tor_addr_to_str_dup(&control_conn->base_.addr);
 229   }
 230 #else /* !(defined(AF_UNIX)) */
 231   TO_CONN(conn)->port = control_conn->base_.port;
 232   TO_CONN(conn)->address = tor_addr_to_str_dup(&control_conn->base_.addr);
 233 #endif /* defined(AF_UNIX) */
 234
 235   if (reverse)
 236     entry_conn->socks_request->command = SOCKS_COMMAND_RESOLVE_PTR;
 237   else
 238     entry_conn->socks_request->command = SOCKS_COMMAND_RESOLVE;
 239
 240   conn->is_dns_request = 1;
 241
 242   strlcpy(entry_conn->socks_request->address, name,
 243           sizeof(entry_conn->socks_request->address));
 244
 245   entry_conn->socks_request->listener_type = CONN_TYPE_CONTROL_LISTENER;
 246   entry_conn->original_dest_address = tor_strdup(name);
 247   entry_conn->entry_cfg.session_group = SESSION_GROUP_CONTROL_RESOLVE;
 248   entry_conn->nym_epoch = get_signewnym_epoch();
 249   entry_conn->entry_cfg.isolation_flags = ISO_DEFAULT;
 250
 251   if (connection_add(TO_CONN(conn))<0) {
 252     log_warn(LD_APP, "Couldn't register dummy connection for RESOLVE request");
 253     connection_free_(TO_CONN(conn));
 254     return -1;
 255   }
 256
 257   control_event_stream_status(entry_conn, STREAM_EVENT_NEW_RESOLVE, 0);
 258
 259   /* Now, unless a controller asked us to leave streams unattached,
 260   * throw the connection over to get rewritten (which will
 261   * answer it immediately if it's in the cache, or completely bogus, or
 262   * automapped), and then attached to a circuit. */
 263   log_info(LD_APP, "Passing request for %s to rewrite_and_attach.",
 264            escaped_safe_str_client(name));
 265   q_name = tor_strdup(name); /* q could be freed in rewrite_and_attach */
 266   connection_ap_rewrite_and_attach_if_allowed(entry_conn, NULL, NULL);
 267   /* Now, the connection is marked if it was bad. */
 268
 269   log_info(LD_APP, "Passed request for %s to rewrite_and_attach_if_allowed.",
 270            escaped_safe_str_client(q_name));
 271   tor_free(q_name);
 272   return 0;
 273 }
 274
 275 /** If there is a pending request on <b>conn</b> that's waiting for an answer,
 276  * send back an error and free the request. */
 277 void
 278 dnsserv_reject_request(entry_connection_t *conn)
 279 {
 280   if (conn->dns_server_request) {
 281     evdns_server_request_respond(conn->dns_server_request,
 282                                  DNS_ERR_SERVERFAILED);
 283     conn->dns_server_request = NULL;
 284   }
 285 }
 286
 287 /** Look up the original name that corresponds to 'addr' in req.  We use this
 288  * to preserve case in order to facilitate clients using 0x20-hacks to avoid
 289  * DNS poisoning. */
 290 static const char *
 291 evdns_get_orig_address(const struct evdns_server_request *req,
 292                        int rtype, const char *addr)
 293 {
 294   int i, type;
 295
 296   switch (rtype) {
 297   case RESOLVED_TYPE_IPV4:
 298     type = EVDNS_TYPE_A;
 299     break;
 300   case RESOLVED_TYPE_HOSTNAME:
 301     type = EVDNS_TYPE_PTR;
 302     break;
 303   case RESOLVED_TYPE_IPV6:
 304     type = EVDNS_TYPE_AAAA;
 305     break;
 306   case RESOLVED_TYPE_ERROR:
 307   case RESOLVED_TYPE_ERROR_TRANSIENT:
 308      /* Addr doesn't matter, since we're not sending it back in the reply.*/
 309     return addr;
 310   default:
 311     tor_fragile_assert();
 312     return addr;
 313   }
 314
 315   for (i = 0; i < req->nquestions; ++i) {
 316     const struct evdns_server_question *q = req->questions[i];
 317     if (q->type == type && !strcasecmp(q->name, addr))
 318       return q->name;
 319   }
 320   return addr;
 321 }
 322
 323 /** Tell the dns request waiting for an answer on <b>conn</b> that we have an
 324  * answer of type <b>answer_type</b> (RESOLVE_TYPE_IPV4/IPV6/ERR), of length
 325  * <b>answer_len</b>, in <b>answer</b>, with TTL <b>ttl</b>.  Doesn't do
 326  * any caching; that's handled elsewhere. */
 327 void
 328 dnsserv_resolved(entry_connection_t *conn,
 329                  int answer_type,
 330                  size_t answer_len,
 331                  const char *answer,
 332                  int ttl)
 333 {
 334   struct evdns_server_request *req = conn->dns_server_request;
 335   const char *name;
 336   int err = DNS_ERR_NONE;
 337   if (!req)
 338     return;
 339   name = evdns_get_orig_address(req, answer_type,
 340                                 conn->socks_request->address);
 341
 342   /* XXXX Re-do; this is dumb. */
 343   if (ttl < 60)
 344     ttl = 60;
 345
 346   /* The evdns interface is: add a bunch of reply items (corresponding to one
 347    * or more of the questions in the request); then, call
 348    * evdns_server_request_respond. */
 349   if (answer_type == RESOLVED_TYPE_IPV6) {
 350     evdns_server_request_add_aaaa_reply(req,
 351                                         name,
 352                                         1, answer, ttl);
 353   } else if (answer_type == RESOLVED_TYPE_IPV4 && answer_len == 4 &&
 354              conn->socks_request->command == SOCKS_COMMAND_RESOLVE) {
 355     evdns_server_request_add_a_reply(req,
 356                                      name,
 357                                      1, answer, ttl);
 358   } else if (answer_type == RESOLVED_TYPE_HOSTNAME &&
 359              answer_len < 256 &&
 360              conn->socks_request->command == SOCKS_COMMAND_RESOLVE_PTR) {
 361     char *ans = tor_strndup(answer, answer_len);
 362     evdns_server_request_add_ptr_reply(req, NULL,
 363                                        name,
 364                                        ans, ttl);
 365     tor_free(ans);
 366   } else if (answer_type == RESOLVED_TYPE_ERROR) {
 367     err = DNS_ERR_NOTEXIST;
 368   } else { /* answer_type == RESOLVED_TYPE_ERROR_TRANSIENT */
 369     err = DNS_ERR_SERVERFAILED;
 370   }
 371
 372   evdns_server_request_respond(req, err);
 373
 374   conn->dns_server_request = NULL;
 375 }
 376
 377 /** Set up the evdns server port for the UDP socket on <b>conn</b>, which
 378  * must be an AP_DNS_LISTENER */
 379 void
 380 dnsserv_configure_listener(connection_t *conn)
 381 {
 382   listener_connection_t *listener_conn;
 383   tor_assert(conn);
 384   tor_assert(SOCKET_OK(conn->s));
 385   tor_assert(conn->type == CONN_TYPE_AP_DNS_LISTENER);
 386
 387   listener_conn = TO_LISTENER_CONN(conn);
 388   listener_conn->dns_server_port =
 389     tor_evdns_add_server_port(conn->s, 0, evdns_server_callback,
 390                               listener_conn);
 391 }
 392
 393 /** Free the evdns server port for <b>conn</b>, which must be an
 394  * AP_DNS_LISTENER. */
 395 void
 396 dnsserv_close_listener(connection_t *conn)
 397 {
 398   listener_connection_t *listener_conn;
 399   tor_assert(conn);
 400   tor_assert(conn->type == CONN_TYPE_AP_DNS_LISTENER);
 401
 402   listener_conn = TO_LISTENER_CONN(conn);
 403
 404   if (listener_conn->dns_server_port) {
 405     evdns_close_server_port(listener_conn->dns_server_port);
 406     listener_conn->dns_server_port = NULL;
 407   }
 408 }
 409