dns.c 74.4 KB
Newer Older
1
2
/* Copyright (c) 2003-2004, Roger Dingledine.
 * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
Nick Mathewson's avatar
Nick Mathewson committed
3
 * Copyright (c) 2007-2019, The Tor Project, Inc. */
4
5
/* See LICENSE for licensing information */

Roger Dingledine's avatar
Roger Dingledine committed
6
7
/**
 * \file dns.c
8
 * \brief Implements a local cache for DNS results for Tor servers.
Roger Dingledine's avatar
Roger Dingledine committed
9
 * This is implemented as a wrapper around Adam Langley's eventdns.c code.
10
11
 * (We can't just use gethostbyname() and friends because we really need to
 * be nonblocking.)
12
13
14
15
16
17
18
19
20
21
 *
 * There are three main cases when a Tor relay uses dns.c to launch a DNS
 * request:
 *   <ol>
 *    <li>To check whether the DNS server is working more or less correctly.
 *      This happens via dns_launch_correctness_checks().  The answer is
 *      reported in the return value from later calls to
 *      dns_seems_to_be_broken().
 *    <li>When a client has asked the relay, in a RELAY_BEGIN cell, to connect
 *      to a given server by hostname.  This happens via dns_resolve().
22
 *    <li>When a client has asked the relay, in a RELAY_RESOLVE cell, to look
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
 *      up a given server's IP address(es) by hostname. This also happens via
 *      dns_resolve().
 *   </ol>
 *
 * Each of these gets handled a little differently.
 *
 * To check for correctness, we look up some hostname we expect to exist and
 * have real entries, some hostnames which we expect to definitely not exist,
 * and some hostnames that we expect to probably not exist.  If too many of
 * the hostnames that shouldn't exist do exist, that's a DNS hijacking
 * attempt.  If too many of the hostnames that should exist have the same
 * addresses as the ones that shouldn't exist, that's a very bad DNS hijacking
 * attempt, or a very naughty captive portal.  And if the hostnames that
 * should exist simply don't exist, we probably have a broken nameserver.
 *
 * To handle client requests, we first check our cache for answers. If there
 * isn't something up-to-date, we've got to launch A or AAAA requests as
 * appropriate.  How we handle responses to those in particular is a bit
 * complex; see dns_lookup() and set_exitconn_info_from_resolve().
 *
 * When a lookup is finally complete, the inform_pending_connections()
 * function will tell all of the streams that have been waiting for the
 * resolve, by calling connection_exit_connect() if the client sent a
 * RELAY_BEGIN cell, and by calling send_resolved_cell() or
 * send_hostname_cell() if the client sent a RELAY_RESOLVE cell.
Roger Dingledine's avatar
Roger Dingledine committed
48
 **/
49

50
51
#define DNS_PRIVATE

52
53
54
#include "core/or/or.h"
#include "app/config/config.h"
#include "core/mainloop/connection.h"
55
#include "core/mainloop/mainloop.h"
56
57
58
59
#include "core/mainloop/netstatus.h"
#include "core/or/circuitlist.h"
#include "core/or/circuituse.h"
#include "core/or/connection_edge.h"
60
61
#include "core/or/policies.h"
#include "core/or/relay.h"
62
63
#include "feature/control/control.h"
#include "feature/relay/dns.h"
64
#include "feature/relay/router.h"
65
#include "feature/relay/routermode.h"
66
#include "lib/crypt_ops/crypto_rand.h"
67
#include "lib/evloop/compat_libevent.h"
68
#include "lib/sandbox/sandbox.h"
69

70
71
#include "core/or/edge_connection_st.h"
#include "core/or/or_circuit_st.h"
72

73
74
#include "ht.h"

75
76
77
78
#ifdef HAVE_SYS_STAT_H
#include <sys/stat.h>
#endif

79
#include <event2/event.h>
80
#include <event2/dns.h>
81

82
83
/** How long will we wait for an answer from the resolver before we decide
 * that the resolver is wedged? */
84
85
#define RESOLVE_MAX_TIMEOUT 300

86
87
88
/** Our evdns_base; this structure handles all our name lookups. */
static struct evdns_base *the_evdns_base = NULL;

89
90
/** Have we currently configured nameservers with eventdns? */
static int nameservers_configured = 0;
91
92
/** Did our most recent attempt to configure nameservers with eventdns fail? */
static int nameserver_config_failed = 0;
93
94
95
96
97
98
/** What was the resolv_conf fname we last used when configuring the
 * nameservers? Used to check whether we need to reconfigure. */
static char *resolv_conf_fname = NULL;
/** What was the mtime on the resolv.conf file we last used when configuring
 * the nameservers?  Used to check whether we need to reconfigure. */
static time_t resolv_conf_mtime = 0;
99

100
static void purge_expired_resolves(time_t now);
101
102
103
104
static void dns_found_answer(const char *address, uint8_t query_type,
                             int dns_answer,
                             const tor_addr_t *addr,
                             const char *hostname,
105
                             uint32_t ttl);
106
static void add_wildcarded_test_address(const char *address);
107
static int configure_nameservers(int force);
108
static int answer_is_wildcarded(const char *ip);
109
110
111
112
static int evdns_err_is_transient(int err);
static void inform_pending_connections(cached_resolve_t *resolve);
static void make_pending_resolve_cached(cached_resolve_t *cached);

113
#ifdef DEBUG_DNS_CACHE
114
115
static void assert_cache_ok_(void);
#define assert_cache_ok() assert_cache_ok_()
116
#else
117
#define assert_cache_ok() STMT_NIL
118
#endif /* defined(DEBUG_DNS_CACHE) */
119
static void assert_resolve_ok(cached_resolve_t *resolve);
120

121
122
/** Hash table of cached_resolve objects. */
static HT_HEAD(cache_map, cached_resolve_t) cache_root;
123

124
/** Global: how many IPv6 requests have we made in all? */
125
static uint64_t n_ipv6_requests_made = 0;
126
/** Global: how many IPv6 requests have timed out? */
127
static uint64_t n_ipv6_timeouts = 0;
128
/** Global: Do we think that IPv6 DNS is broken? */
129
130
static int dns_is_broken_for_ipv6 = 0;

Roger Dingledine's avatar
Roger Dingledine committed
131
/** Function to compare hashed resolves on their addresses; used to
132
 * implement hash tables. */
133
static inline int
134
cached_resolves_eq(cached_resolve_t *a, cached_resolve_t *b)
135
{
136
  /* make this smarter one day? */
137
  assert_resolve_ok(a); // Not b; b may be just a search.
138
139
140
  return !strncmp(a->address, b->address, MAX_ADDRESSLEN);
}

141
/** Hash function for cached_resolve objects */
142
static inline unsigned int
143
144
cached_resolve_hash(cached_resolve_t *a)
{
145
  return (unsigned) siphash24g((const uint8_t*)a->address, strlen(a->address));
146
147
}

148
HT_PROTOTYPE(cache_map, cached_resolve_t, node, cached_resolve_hash,
149
             cached_resolves_eq)
150
151
HT_GENERATE2(cache_map, cached_resolve_t, node, cached_resolve_hash,
             cached_resolves_eq, 0.6, tor_reallocarray_, tor_free_)
152

153
/** Initialize the DNS cache. */
154
static void
155
init_cache_map(void)
156
{
157
  HT_INIT(cache_map, &cache_root);
158
159
}

160
/** Helper: called by eventdns when eventdns wants to log something. */
161
static void
162
evdns_log_cb(int warn, const char *msg)
163
{
164
  const char *cp;
165
166
  static int all_down = 0;
  int severity = warn ? LOG_WARN : LOG_INFO;
167
168
  if (!strcmpstart(msg, "Resolve requested for") &&
      get_options()->SafeLogging) {
169
    log_info(LD_EXIT, "eventdns: Resolve requested.");
170
    return;
171
172
  } else if (!strcmpstart(msg, "Search: ")) {
    return;
173
  }
174
175
  if (!strcmpstart(msg, "Nameserver ") && (cp=strstr(msg, " has failed: "))) {
    char *ns = tor_strndup(msg+11, cp-(msg+11));
176
177
178
    const char *colon = strchr(cp, ':');
    tor_assert(colon);
    const char *err = colon+2;
179
180
181
    /* Don't warn about a single failed nameserver; we'll warn with 'all
     * nameservers have failed' if we're completely out of nameservers;
     * otherwise, the situation is tolerable. */
182
    severity = LOG_INFO;
183
    control_event_server_status(LOG_NOTICE,
184
185
186
187
188
189
                                "NAMESERVER_STATUS NS=%s STATUS=DOWN ERR=%s",
                                ns, escaped(err));
    tor_free(ns);
  } else if (!strcmpstart(msg, "Nameserver ") &&
             (cp=strstr(msg, " is back up"))) {
    char *ns = tor_strndup(msg+11, cp-(msg+11));
190
    severity = (all_down && warn) ? LOG_NOTICE : LOG_INFO;
191
    all_down = 0;
192
193
194
195
196
    control_event_server_status(LOG_NOTICE,
                                "NAMESERVER_STATUS NS=%s STATUS=UP", ns);
    tor_free(ns);
  } else if (!strcmp(msg, "All nameservers have failed")) {
    control_event_server_status(LOG_WARN, "NAMESERVER_ALL_DOWN");
197
    all_down = 1;
198
199
200
201
202
203
204
205
206
207
208
209
  } else if (!strcmpstart(msg, "Address mismatch on received DNS")) {
    static ratelim_t mismatch_limit = RATELIM_INIT(3600);
    const char *src = strstr(msg, " Apparent source");
    if (!src || get_options()->SafeLogging) {
      src = "";
    }
    log_fn_ratelim(&mismatch_limit, severity, LD_EXIT,
                   "eventdns: Received a DNS packet from "
                   "an IP address to which we did not send a request. This "
                   "could be a DNS spoofing attempt, or some kind of "
                   "misconfiguration.%s", src);
    return;
210
  }
211
  tor_log(severity, LD_EXIT, "eventdns: %s", msg);
212
213
}

214
215
/** Helper: passed to eventdns.c as a callback so it can generate random
 * numbers for transaction IDs and 0x20-hack coding. */
216
static void
217
dns_randfn_(char *b, size_t n)
218
{
219
  crypto_rand(b,n);
220
221
}

Roger Dingledine's avatar
Roger Dingledine committed
222
/** Initialize the DNS subsystem; called by the OR process. */
223
int
224
225
dns_init(void)
{
226
  init_cache_map();
227
  evdns_set_random_bytes_fn(dns_randfn_);
228
229
230
231
  if (server_mode(get_options())) {
    int r = configure_nameservers(1);
    return r;
  }
232
  return 0;
233
}
234

235
236
237
/** Called when DNS-related options change (or may have changed).  Returns -1
 * on failure, 0 on success. */
int
238
239
dns_reset(void)
{
240
  const or_options_t *options = get_options();
241
  if (! server_mode(options)) {
242
243
244
245
246
247
248
249

    if (!the_evdns_base) {
      if (!(the_evdns_base = evdns_base_new(tor_libevent_get_base(), 0))) {
        log_err(LD_BUG, "Couldn't create an evdns_base");
        return -1;
      }
    }

250
251
    evdns_base_clear_nameservers_and_suspend(the_evdns_base);
    evdns_base_search_clear(the_evdns_base);
252
253
254
255
    nameservers_configured = 0;
    tor_free(resolv_conf_fname);
    resolv_conf_mtime = 0;
  } else {
256
    if (configure_nameservers(0) < 0) {
257
      return -1;
258
    }
259
  }
260
  return 0;
261
262
}

Nick Mathewson's avatar
Nick Mathewson committed
263
264
/** Return true iff the most recent attempt to initialize the DNS subsystem
 * failed. */
265
266
267
268
269
270
int
has_dns_init_failed(void)
{
  return nameserver_config_failed;
}

271
/** Helper: Given a TTL from a DNS response, determine what TTL to give the
272
273
 * OP that asked us to resolve it, and how long to cache that record
 * ourselves. */
274
275
276
uint32_t
dns_clip_ttl(uint32_t ttl)
{
277
278
279
280
281
282
  /* This logic is a defense against "DefectTor" DNS-based traffic
   * confirmation attacks, as in https://nymity.ch/tor-dns/tor-dns.pdf .
   * We only give two values: a "low" value and a "high" value.
   */
  if (ttl < MIN_DNS_TTL_AT_EXIT)
    return MIN_DNS_TTL_AT_EXIT;
283
  else
284
    return MAX_DNS_TTL_AT_EXIT;
285
286
}

287
/** Helper: free storage held by an entry in the DNS cache. */
288
static void
289
free_cached_resolve_(cached_resolve_t *r)
290
{
291
292
  if (!r)
    return;
Nick Mathewson's avatar
Nick Mathewson committed
293
  while (r->pending_connections) {
294
    pending_connection_t *victim = r->pending_connections;
295
296
297
    r->pending_connections = victim->next;
    tor_free(victim);
  }
298
299
  if (r->res_status_hostname == RES_STATUS_DONE_OK)
    tor_free(r->result_ptr.hostname);
300
  r->magic = 0xFF00FF00;
301
302
303
  tor_free(r);
}

304
305
306
/** Compare two cached_resolve_t pointers by expiry time, and return
 * less-than-zero, zero, or greater-than-zero as appropriate. Used for
 * the priority queue implementation. */
307
static int
308
compare_cached_resolves_by_expiry_(const void *_a, const void *_b)
309
{
310
  const cached_resolve_t *a = _a, *b = _b;
311
312
313
314
315
316
  if (a->expire < b->expire)
    return -1;
  else if (a->expire == b->expire)
    return 0;
  else
    return 1;
317
318
}

319
320
/** Priority queue of cached_resolve_t objects to let us know when they
 * will expire. */
321
322
static smartlist_t *cached_resolve_pqueue = NULL;

323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
static void
cached_resolve_add_answer(cached_resolve_t *resolve,
                          int query_type,
                          int dns_result,
                          const tor_addr_t *answer_addr,
                          const char *answer_hostname,
                          uint32_t ttl)
{
  if (query_type == DNS_PTR) {
    if (resolve->res_status_hostname != RES_STATUS_INFLIGHT)
      return;

    if (dns_result == DNS_ERR_NONE && answer_hostname) {
      resolve->result_ptr.hostname = tor_strdup(answer_hostname);
      resolve->res_status_hostname = RES_STATUS_DONE_OK;
    } else {
      resolve->result_ptr.err_hostname = dns_result;
      resolve->res_status_hostname = RES_STATUS_DONE_ERR;
    }
    resolve->ttl_hostname = ttl;
  } else if (query_type == DNS_IPv4_A) {
    if (resolve->res_status_ipv4 != RES_STATUS_INFLIGHT)
      return;

347
348
    if (dns_result == DNS_ERR_NONE && answer_addr &&
        tor_addr_family(answer_addr) == AF_INET) {
349
350
351
352
353
354
      resolve->result_ipv4.addr_ipv4 = tor_addr_to_ipv4h(answer_addr);
      resolve->res_status_ipv4 = RES_STATUS_DONE_OK;
    } else {
      resolve->result_ipv4.err_ipv4 = dns_result;
      resolve->res_status_ipv4 = RES_STATUS_DONE_ERR;
    }
355
    resolve->ttl_ipv4 = ttl;
356
357
358
359
  } else if (query_type == DNS_IPv6_AAAA) {
    if (resolve->res_status_ipv6 != RES_STATUS_INFLIGHT)
      return;

360
361
    if (dns_result == DNS_ERR_NONE && answer_addr &&
        tor_addr_family(answer_addr) == AF_INET6) {
362
363
364
365
366
367
368
369
      memcpy(&resolve->result_ipv6.addr_ipv6,
             tor_addr_to_in6(answer_addr),
             sizeof(struct in6_addr));
      resolve->res_status_ipv6 = RES_STATUS_DONE_OK;
    } else {
      resolve->result_ipv6.err_ipv6 = dns_result;
      resolve->res_status_ipv6 = RES_STATUS_DONE_ERR;
    }
370
    resolve->ttl_ipv6 = ttl;
371
372
373
  }
}

374
/** Return true iff there are no in-flight requests for <b>resolve</b>. */
375
376
377
378
379
380
381
382
static int
cached_resolve_have_all_answers(const cached_resolve_t *resolve)
{
  return (resolve->res_status_ipv4 != RES_STATUS_INFLIGHT &&
          resolve->res_status_ipv6 != RES_STATUS_INFLIGHT &&
          resolve->res_status_hostname != RES_STATUS_INFLIGHT);
}

383
384
/** Set an expiry time for a cached_resolve_t, and add it to the expiry
 * priority queue */
385
386
387
388
static void
set_expiry(cached_resolve_t *resolve, time_t expires)
{
  tor_assert(resolve && resolve->expire == 0);
389
  if (!cached_resolve_pqueue)
390
    cached_resolve_pqueue = smartlist_new();
391
392
  resolve->expire = expires;
  smartlist_pqueue_add(cached_resolve_pqueue,
393
                       compare_cached_resolves_by_expiry_,
Neel Chauhan's avatar
Neel Chauhan committed
394
                       offsetof(cached_resolve_t, minheap_idx),
395
396
397
                       resolve);
}

398
/** Free all storage held in the DNS cache and related structures. */
399
400
401
void
dns_free_all(void)
{
402
  cached_resolve_t **ptr, **next, *item;
403
  assert_cache_ok();
404
405
406
  if (cached_resolve_pqueue) {
    SMARTLIST_FOREACH(cached_resolve_pqueue, cached_resolve_t *, res,
      {
407
        if (res->state == CACHE_STATE_DONE)
408
          free_cached_resolve_(res);
409
410
      });
  }
411
  for (ptr = HT_START(cache_map, &cache_root); ptr != NULL; ptr = next) {
412
    item = *ptr;
413
    next = HT_NEXT_RMV(cache_map, &cache_root, ptr);
414
    free_cached_resolve_(item);
415
  }
416
  HT_CLEAR(cache_map, &cache_root);
417
  smartlist_free(cached_resolve_pqueue);
418
  cached_resolve_pqueue = NULL;
419
  tor_free(resolv_conf_fname);
420
421
}

422
423
/** Remove every cached_resolve whose <b>expire</b> time is before or
 * equal to <b>now</b> from the cache. */
424
static void
425
purge_expired_resolves(time_t now)
426
{
Nick Mathewson's avatar
Nick Mathewson committed
427
  cached_resolve_t *resolve, *removed;
428
  pending_connection_t *pend;
429
  edge_connection_t *pendconn;
430

Nick Mathewson's avatar
Nick Mathewson committed
431
  assert_cache_ok();
432
433
434
435
436
437
438
439
  if (!cached_resolve_pqueue)
    return;

  while (smartlist_len(cached_resolve_pqueue)) {
    resolve = smartlist_get(cached_resolve_pqueue, 0);
    if (resolve->expire > now)
      break;
    smartlist_pqueue_pop(cached_resolve_pqueue,
440
                         compare_cached_resolves_by_expiry_,
Neel Chauhan's avatar
Neel Chauhan committed
441
                         offsetof(cached_resolve_t, minheap_idx));
442

443
    if (resolve->state == CACHE_STATE_PENDING) {
444
      log_debug(LD_EXIT,
445
446
                "Expiring a dns resolve %s that's still pending. Forgot to "
                "cull it? DNS resolve didn't tell us about the timeout?",
447
                escaped_safe_str(resolve->address));
448
    } else if (resolve->state == CACHE_STATE_CACHED) {
449
450
451
452
453
454
455
456
      log_debug(LD_EXIT,
                "Forgetting old cached resolve (address %s, expires %lu)",
                escaped_safe_str(resolve->address),
                (unsigned long)resolve->expire);
      tor_assert(!resolve->pending_connections);
    } else {
      tor_assert(resolve->state == CACHE_STATE_DONE);
      tor_assert(!resolve->pending_connections);
457
    }
458

459
    if (resolve->pending_connections) {
460
      log_debug(LD_EXIT,
461
                "Closing pending connections on timed-out DNS resolve!");
462
463
464
465
      while (resolve->pending_connections) {
        pend = resolve->pending_connections;
        resolve->pending_connections = pend->next;
        /* Connections should only be pending if they have no socket. */
466
        tor_assert(!SOCKET_OK(pend->conn->base_.s));
467
        pendconn = pend->conn;
468
469
        /* Prevent double-remove */
        pendconn->base_.state = EXIT_CONN_STATE_RESOLVEFAILED;
470
        if (!pendconn->base_.marked_for_close) {
471
472
          connection_edge_end(pendconn, END_STREAM_REASON_TIMEOUT);
          circuit_detach_stream(circuit_get_by_edge_conn(pendconn), pendconn);
473
          connection_free_(TO_CONN(pendconn));
474
        }
475
476
        tor_free(pend);
      }
477
    }
478

479
    if (resolve->state == CACHE_STATE_CACHED ||
480
481
482
483
484
        resolve->state == CACHE_STATE_PENDING) {
      removed = HT_REMOVE(cache_map, &cache_root, resolve);
      if (removed != resolve) {
        log_err(LD_BUG, "The expired resolve we purged didn't match any in"
                " the cache. Tried to purge %s (%p); instead got %s (%p).",
485
                resolve->address, (void*)resolve,
486
                removed ? removed->address : "NULL", (void*)removed);
487
488
489
      }
      tor_assert(removed == resolve);
    } else {
490
      /* This should be in state DONE. Make sure it's not in the cache. */
491
492
      cached_resolve_t *tmp = HT_FIND(cache_map, &cache_root, resolve);
      tor_assert(tmp != resolve);
493
    }
494
495
    if (resolve->res_status_hostname == RES_STATUS_DONE_OK)
      tor_free(resolve->result_ptr.hostname);
496
497
    resolve->magic = 0xF0BBF0BB;
    tor_free(resolve);
498
  }
499

Nick Mathewson's avatar
Nick Mathewson committed
500
  assert_cache_ok();
501
502
}

503
504
505
506
/* argument for send_resolved_cell only, meaning "let the answer type be ipv4
 * or ipv6 depending on the connection's address". */
#define RESOLVED_TYPE_AUTO 0xff

507
508
/** Send a response to the RESOLVE request of a connection.
 * <b>answer_type</b> must be one of
509
 * RESOLVED_TYPE_(AUTO|ERROR|ERROR_TRANSIENT|).
510
511
 *
 * If <b>circ</b> is provided, and we have a cached answer, send the
512
513
 * answer back along circ; otherwise, send the answer back along
 * <b>conn</b>'s attached circuit.
514
 */
515
516
517
MOCK_IMPL(STATIC void,
send_resolved_cell,(edge_connection_t *conn, uint8_t answer_type,
                    const cached_resolve_t *resolved))
518
{
519
520
  char buf[RELAY_PAYLOAD_SIZE], *cp = buf;
  size_t buflen = 0;
521
  uint32_t ttl;
522
523

  buf[0] = answer_type;
524
  ttl = dns_clip_ttl(conn->address_ttl);
525
526
527

  switch (answer_type)
    {
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
    case RESOLVED_TYPE_AUTO:
      if (resolved && resolved->res_status_ipv4 == RES_STATUS_DONE_OK) {
        cp[0] = RESOLVED_TYPE_IPV4;
        cp[1] = 4;
        set_uint32(cp+2, htonl(resolved->result_ipv4.addr_ipv4));
        set_uint32(cp+6, htonl(ttl));
        cp += 10;
      }
      if (resolved && resolved->res_status_ipv6 == RES_STATUS_DONE_OK) {
        const uint8_t *bytes = resolved->result_ipv6.addr_ipv6.s6_addr;
        cp[0] = RESOLVED_TYPE_IPV6;
        cp[1] = 16;
        memcpy(cp+2, bytes, 16);
        set_uint32(cp+18, htonl(ttl));
        cp += 22;
      }
      if (cp != buf) {
        buflen = cp - buf;
        break;
      } else {
        answer_type = RESOLVED_TYPE_ERROR;
        /* fall through. */
550
      }
551
      /* Falls through. */
552
553
    case RESOLVED_TYPE_ERROR_TRANSIENT:
    case RESOLVED_TYPE_ERROR:
554
555
      {
        const char *errmsg = "Error resolving hostname";
556
        size_t msglen = strlen(errmsg);
557

558
        buf[0] = answer_type;
559
560
        buf[1] = msglen;
        strlcpy(buf+2, errmsg, sizeof(buf)-2);
561
        set_uint32(buf+2+msglen, htonl(ttl));
562
563
564
        buflen = 6+msglen;
        break;
      }
565
566
    default:
      tor_assert(0);
567
      return;
568
    }
569
  // log_notice(LD_EXIT, "Sending a regular RESOLVED reply: ");
Roger Dingledine's avatar
Roger Dingledine committed
570

571
  connection_edge_send_command(conn, RELAY_COMMAND_RESOLVED, buf, buflen);
572
573
}

574
575
576
/** Send a response to the RESOLVE request of a connection for an in-addr.arpa
 * address on connection <b>conn</b> which yielded the result <b>hostname</b>.
 * The answer type will be RESOLVED_HOSTNAME.
577
578
579
 *
 * If <b>circ</b> is provided, and we have a cached answer, send the
 * answer back along circ; otherwise, send the answer back along
580
 * <b>conn</b>'s attached circuit.
581
 */
582
583
584
MOCK_IMPL(STATIC void,
send_resolved_hostname_cell,(edge_connection_t *conn,
                             const char *hostname))
585
586
587
588
{
  char buf[RELAY_PAYLOAD_SIZE];
  size_t buflen;
  uint32_t ttl;
589
590
591
592

  if (BUG(!hostname))
    return;

593
594
595
596
597
598
599
600
601
602
603
  size_t namelen = strlen(hostname);

  tor_assert(namelen < 256);
  ttl = dns_clip_ttl(conn->address_ttl);

  buf[0] = RESOLVED_TYPE_HOSTNAME;
  buf[1] = (uint8_t)namelen;
  memcpy(buf+2, hostname, namelen);
  set_uint32(buf+2+namelen, htonl(ttl));
  buflen = 2+namelen+4;

604
  // log_notice(LD_EXIT, "Sending a reply RESOLVED reply: %s", hostname);
605
  connection_edge_send_command(conn, RELAY_COMMAND_RESOLVED, buf, buflen);
606
  // log_notice(LD_EXIT, "Sent");
607
608
}

Roger Dingledine's avatar
Roger Dingledine committed
609
/** See if we have a cache entry for <b>exitconn</b>-\>address. If so,
Nick Mathewson's avatar
Nick Mathewson committed
610
 * if resolve valid, put it into <b>exitconn</b>-\>addr and return 1.
Roger Dingledine's avatar
Roger Dingledine committed
611
 * If resolve failed, free exitconn and return -1.
612
 *
613
614
615
616
617
 * (For EXIT_PURPOSE_RESOLVE connections, send back a RESOLVED error cell
 * on returning -1.  For EXIT_PURPOSE_CONNECT connections, there's no
 * need to send back an END cell, since connection_exit_begin_conn will
 * do that for us.)
 *
618
 * If we have a cached answer, send the answer back along <b>exitconn</b>'s
619
 * circuit.
620
 *
621
622
623
624
625
 * Else, if seen before and pending, add conn to the pending list,
 * and return 0.
 *
 * Else, if not seen before, add conn to pending list, hand to
 * dns farm, and return 0.
626
627
628
629
630
631
 *
 * Exitconn's on_circuit field must be set, but exitconn should not
 * yet be linked onto the n_streams/resolving_streams list of that circuit.
 * On success, link the connection to n_streams if it's an exit connection.
 * On "pending", link the connection to resolving streams.  Otherwise,
 * clear its on_circuit field.
632
 */
633
int
634
dns_resolve(edge_connection_t *exitconn)
635
636
637
{
  or_circuit_t *oncirc = TO_OR_CIRCUIT(exitconn->on_circuit);
  int is_resolve, r;
638
  int made_connection_pending = 0;
639
  char *hostname = NULL;
640
  cached_resolve_t *resolve = NULL;
641
  is_resolve = exitconn->base_.purpose == EXIT_PURPOSE_RESOLVE;
642

643
  r = dns_resolve_impl(exitconn, is_resolve, oncirc, &hostname,
644
                       &made_connection_pending, &resolve);
645

646
647
  switch (r) {
    case 1:
648
649
      /* We got an answer without a lookup -- either the answer was
       * cached, or it was obvious (like an IP address). */
650
      if (is_resolve) {
651
        /* Send the answer back right now, and detach. */
652
653
654
        if (hostname)
          send_resolved_hostname_cell(exitconn, hostname);
        else
655
          send_resolved_cell(exitconn, RESOLVED_TYPE_AUTO, resolve);
656
        exitconn->on_circuit = NULL;
657
      } else {
658
659
        /* Add to the n_streams list; the calling function will send back a
         * connected cell. */
660
661
662
663
664
        exitconn->next_stream = oncirc->n_streams;
        oncirc->n_streams = exitconn;
      }
      break;
    case 0:
665
666
      /* The request is pending: add the connection into the linked list of
       * resolving_streams on this circuit. */
667
      exitconn->base_.state = EXIT_CONN_STATE_RESOLVING;
668
669
670
671
672
      exitconn->next_stream = oncirc->resolving_streams;
      oncirc->resolving_streams = exitconn;
      break;
    case -2:
    case -1:
673
      /* The request failed before it could start: cancel this connection,
674
       * and stop everybody waiting for the same connection. */
675
676
      if (is_resolve) {
        send_resolved_cell(exitconn,
677
678
             (r == -1) ? RESOLVED_TYPE_ERROR : RESOLVED_TYPE_ERROR_TRANSIENT,
             NULL);
679
      }
680

681
      exitconn->on_circuit = NULL;
682

683
      dns_cancel_pending_resolve(exitconn->base_.address);
684

685
      if (!made_connection_pending && !exitconn->base_.marked_for_close) {
686
687
688
        /* If we made the connection pending, then we freed it already in
         * dns_cancel_pending_resolve().  If we marked it for close, it'll
         * get freed from the main loop.  Otherwise, can free it now. */
689
        connection_free_(TO_CONN(exitconn));
690
      }
691
692
693
694
695
696
697
698
699
700
701
702
703
704
      break;
    default:
      tor_assert(0);
  }

  tor_free(hostname);
  return r;
}

/** Helper function for dns_resolve: same functionality, but does not handle:
 *     - marking connections on error and clearing their on_circuit
 *     - linking connections to n_streams/resolving_streams,
 *     - sending resolved cells if we have an answer/error right away,
 *
Roger Dingledine's avatar
Roger Dingledine committed
705
706
707
 * Return -2 on a transient error. If it's a reverse resolve and it's
 * successful, sets *<b>hostname_out</b> to a newly allocated string
 * holding the cached reverse DNS value.
708
709
710
711
 *
 * Set *<b>made_connection_pending_out</b> to true if we have placed
 * <b>exitconn</b> on the list of pending connections for some resolve; set it
 * to false otherwise.
712
713
 *
 * Set *<b>resolve_out</b> to a cached resolve, if we found one.
714
 */
715
716
MOCK_IMPL(STATIC int,
dns_resolve_impl,(edge_connection_t *exitconn, int is_resolve,
717
                 or_circuit_t *oncirc, char **hostname_out,
718
                 int *made_connection_pending_out,
719
                 cached_resolve_t **resolve_out))
720
{
721
722
723
  cached_resolve_t *resolve;
  cached_resolve_t search;
  pending_connection_t *pending_connection;
724
  int is_reverse = 0;
725
  tor_addr_t addr;
726
  time_t now = time(NULL);
727
  int r;
728
  assert_connection_ok(TO_CONN(exitconn), 0);
729
  tor_assert(!SOCKET_OK(exitconn->base_.s));
730
  assert_cache_ok();
731
  tor_assert(oncirc);
732
  *made_connection_pending_out = 0;
733

734
  /* first check if exitconn->base_.address is an IP. If so, we already
735
   * know the answer. */
736
  if (tor_addr_parse(&addr, exitconn->base_.address) >= 0) {
737
738
    if (tor_addr_family(&addr) == AF_INET ||
        tor_addr_family(&addr) == AF_INET6) {
739
      tor_addr_copy(&exitconn->base_.addr, &addr);
740
741
742
      exitconn->address_ttl = DEFAULT_DNS_TTL;
      return 1;
    } else {
743
      /* XXXX unspec? Bogus? */
744
745
      return -1;
    }
746
  }
747

748
  /* If we're a non-exit, don't even do DNS lookups. */
749
  if (router_my_exit_policy_is_reject_star())
750
    return -1;
751

752
  if (address_is_invalid_destination(exitconn->base_.address, 0)) {
753
    tor_log(LOG_PROTOCOL_WARN, LD_EXIT,
754
        "Rejecting invalid destination address %s",
755
        escaped_safe_str(exitconn->base_.address));
756
757
    return -1;
  }
758
759

  /* then take this opportunity to see if there are any expired
760
   * resolves in the hash table. */
761
  purge_expired_resolves(now);
762

763
764
  /* lower-case exitconn->base_.address, so it's in canonical form */
  tor_strlower(exitconn->base_.address);
765

766
767
  /* Check whether this is a reverse lookup.  If it's malformed, or it's a
   * .in-addr.arpa address but this isn't a resolve request, kill the
768
   * connection.
769
   */
770
  if ((r = tor_addr_parse_PTR_name(&addr, exitconn->base_.address,
771
                                              AF_UNSPEC, 0)) != 0) {
772
    if (r == 1) {
773
      is_reverse = 1;
774
775
      if (tor_addr_is_internal(&addr, 0)) /* internal address? */
        return -1;
776
    }
777
778
779
780

    if (!is_reverse || !is_resolve) {
      if (!is_reverse)
        log_info(LD_EXIT, "Bad .in-addr.arpa address \"%s\"; sending error.",
781
                 escaped_safe_str(exitconn->base_.address));
782
783
784
785
      else if (!is_resolve)
        log_info(LD_EXIT,
                 "Attempt to connect to a .in-addr.arpa address \"%s\"; "
                 "sending error.",
786
                 escaped_safe_str(exitconn->base_.address));
787
788
789

      return -1;
    }
790
    //log_notice(LD_EXIT, "Looks like an address %s",
791
    //exitconn->base_.address);
792
  }
793
  exitconn->is_reverse_dns_lookup = is_reverse;
794

795
  /* now check the hash table to see if 'address' is already there. */
796
  strlcpy(search.address, exitconn->base_.address, sizeof(search.address));
797
  resolve = HT_FIND(cache_map, &cache_root, &search);
798
  if (resolve && resolve->expire > now) { /* already there */
799
    switch (resolve->state) {
800
801
      case CACHE_STATE_PENDING:
        /* add us to the pending list */
802
        pending_connection = tor_malloc_zero(
803
                                      sizeof(pending_connection_t));
804
        pending_connection->conn = exitconn;
Roger Dingledine's avatar
   
Roger Dingledine committed
805
806
        pending_connection->next = resolve->pending_connections;
        resolve->pending_connections = pending_connection;
807
        *made_connection_pending_out = 1;
808
809
        log_debug(LD_EXIT,"Connection (fd "TOR_SOCKET_T_FORMAT") waiting "
                  "for pending DNS resolve of %s", exitconn->base_.s,
810
                  escaped_safe_str(exitconn->base_.address));
Roger Dingledine's avatar
   
Roger Dingledine committed
811
        return 0;
812
      case CACHE_STATE_CACHED:
813
814
        log_debug(LD_EXIT,"Connection (fd "TOR_SOCKET_T_FORMAT") found "
                  "cached answer for %s",
815
                  exitconn->base_.s,
816
                  escaped_safe_str(resolve->address));
817

818
819
        *resolve_out = resolve;

820
        return set_exitconn_info_from_resolve(exitconn, resolve, hostname_out);
821
822
823
      case CACHE_STATE_DONE:
        log_err(LD_BUG, "Found a 'DONE' dns resolve still in the cache.");
        tor_fragile_assert();
824
    }
Roger Dingledine's avatar
Roger Dingledine committed
825
    tor_assert(0);
Roger Dingledine's avatar
Roger Dingledine committed
826
  }
827
  tor_assert(!resolve);
Roger Dingledine's avatar
Roger Dingledine committed
828
  /* not there, need to add it */
829
  resolve = tor_malloc_zero(sizeof(cached_resolve_t));
830
  resolve->magic = CACHED_RESOLVE_MAGIC;
Roger Dingledine's avatar
Roger Dingledine committed
831
  resolve->state = CACHE_STATE_PENDING;
832
  resolve->minheap_idx = -1;
833
  strlcpy(resolve->address, exitconn->base_.address, sizeof(resolve->address));
Roger Dingledine's avatar
Roger Dingledine committed
834

835
  /* add this connection to the pending list */
836
  pending_connection = tor_malloc_zero(sizeof(pending_connection_t));
Roger Dingledine's avatar
Roger Dingledine committed
837
838
  pending_connection->conn = exitconn;
  resolve->pending_connections = pending_connection;
839
  *made_connection_pending_out = 1;
Roger Dingledine's avatar
Roger Dingledine committed
840

841
  /* Add this resolve to the cache and priority queue. */
842
  HT_INSERT(cache_map, &cache_root, resolve);
843
  set_expiry(resolve, now + RESOLVE_MAX_TIMEOUT);
844

845
  log_debug(LD_EXIT,"Launching %s.",
846
            escaped_safe_str(exitconn->base_.address));
847
  assert_cache_ok();
848

849
850
851
  return launch_resolve(resolve);
}

852
/** Given an exit connection <b>exitconn</b>, and a cached_resolve_t
853
854
855
856
857
858
859
860
 * <b>resolve</b> whose DNS lookups have all either succeeded or failed,
 * update the appropriate fields (address_ttl and addr) of <b>exitconn</b>.
 *
 * The logic can be complicated here, since we might have launched both
 * an A lookup and an AAAA lookup, and since either of those might have
 * succeeded or failed, and since we want to answer a RESOLVE cell with
 * a full answer but answer a BEGIN cell with whatever answer the client
 * would accept <i>and</i> we could still connect to.
861
862
863
864
865
866
867
 *
 * If this is a reverse lookup, set *<b>hostname_out</b> to a newly allocated
 * copy of the name resulting hostname.
 *
 * Return -2 on a transient error, -1 on a permenent error, and 1 on
 * a successful lookup.
 */
rl1987's avatar
rl1987 committed
868
869
870
871
MOCK_IMPL(STATIC int,
set_exitconn_info_from_resolve,(edge_connection_t *exitconn,
                                const cached_resolve_t *resolve,
                                char **hostname_out))
872
873
{
  int ipv4_ok, ipv6_ok, answer_with_ipv4, r;
874
875
  uint32_t begincell_flags;
  const int is_resolve = exitconn->base_.purpose == EXIT_PURPOSE_RESOLVE;
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
  tor_assert(exitconn);
  tor_assert(resolve);

  if (exitconn->is_reverse_dns_lookup) {
    exitconn->address_ttl = resolve->ttl_hostname;
    if (resolve->res_status_hostname == RES_STATUS_DONE_OK) {
      *hostname_out = tor_strdup(resolve->result_ptr.hostname);
      return 1;
    } else {
      return -1;
    }
  }

  /* If we're here then the connection wants one or either of ipv4, ipv6, and
   * we can give it one or both. */
891
892
893
894
895
896
  if (is_resolve) {
    begincell_flags = BEGIN_FLAG_IPV6_OK;
  } else {
    begincell_flags = exitconn->begincell_flags;
  }

897
  ipv4_ok = (resolve->res_status_ipv4 == RES_STATUS_DONE_OK) &&
898
    ! (begincell_flags & BEGIN_FLAG_IPV4_NOT_OK);
899
  ipv6_ok = (resolve->res_status_ipv6 == RES_STATUS_DONE_OK) &&
900
    (begincell_flags & BEGIN_FLAG_IPV6_OK) &&
901
902
903
    get_options()->IPv6Exit;

  /* Now decide which one to actually give. */
904
905
906
  if (ipv4_ok && ipv6_ok && is_resolve) {
    answer_with_ipv4 = 1;
  } else if (ipv4_ok && ipv6_ok) {
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
    /* If we have both, see if our exit policy has an opinion. */
    const uint16_t port = exitconn->base_.port;
    int ipv4_allowed, ipv6_allowed;
    tor_addr_t a4, a6;
    tor_addr_from_ipv4h(&a4, resolve->result_ipv4.addr_ipv4);
    tor_addr_from_in6(&a6, &resolve->result_ipv6.addr_ipv6);
    ipv4_allowed = !router_compare_to_my_exit_policy(&a4, port);
    ipv6_allowed = !router_compare_to_my_exit_policy(&a6, port);
    if (ipv4_allowed && !ipv6_allowed) {
      answer_with_