dns.c 60 KB
Newer Older
1
2
/* Copyright (c) 2003-2004, Roger Dingledine.
 * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
Karsten Loesing's avatar
Karsten Loesing committed
3
 * Copyright (c) 2007-2009, 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.)
Roger Dingledine's avatar
Roger Dingledine committed
12
 **/
13

14
#include "or.h"
15
#include "ht.h"
16
#ifdef HAVE_EVENT2_DNS_H
17
#include <event2/event.h>
18
19
#include <event2/dns.h>
#else
20
#include <event.h>
21
#include "eventdns.h"
22
23
24
25
#ifndef HAVE_EVDNS_SET_DEFAULT_OUTGOING_BIND_ADDRESS
#define HAVE_EVDNS_SET_DEFAULT_OUTGOING_BIND_ADDRESS
#endif
#endif
26

27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
#ifndef HAVE_EVENT2_DNS_H
struct evdns_base;
struct evdns_request;
#define evdns_base_new(x,y) tor_malloc(1)
#define evdns_base_clear_nameservers_and_suspend(base) \
  evdns_clear_nameservers_and_suspend()
#define evdns_base_search_clear(base) evdns_search_clear()
#define evdns_base_set_default_outgoing_bind_address(base, a, len)  \
  evdns_set_default_outgoing_bind_address((a),(len))
#define evdns_base_resolv_conf_parse(base, options, fname) \
  evdns_resolv_conf_parse((options), (fname))
#define evdns_base_count_nameservers(base)      \
  evdns_count_nameservers()
#define evdns_base_resume(base)                 \
  evdns_resume()
#define evdns_base_config_windows_nameservers(base)     \
  evdns_config_windows_nameservers()
#define evdns_base_set_option(base, opt, val, flags) \
  evdns_set_option((opt),(val),(flags))
#define evdns_base_resolve_ipv4(base, addr, options, cb, ptr) \
  ((evdns_resolve_ipv4(addr, options, cb, ptr)<0) ? NULL : ((void*)1))
#define evdns_base_resolve_reverse(base, addr, options, cb, ptr) \
  ((evdns_resolve_reverse(addr, options, cb, ptr)<0) ? NULL : ((void*)1))
#define evdns_base_resolve_reverse_ipv6(base, addr, options, cb, ptr) \
  ((evdns_resolve_reverse_ipv6(addr, options, cb, ptr)<0) ? NULL : ((void*)1))
#endif

Roger Dingledine's avatar
Roger Dingledine committed
54
/** Longest hostname we're willing to resolve. */
55
56
#define MAX_ADDRESSLEN 256

57
58
/** How long will we wait for an answer from the resolver before we decide
 * that the resolver is wedged? */
59
60
#define RESOLVE_MAX_TIMEOUT 300

Roger Dingledine's avatar
Roger Dingledine committed
61
/** Possible outcomes from hostname lookup: permanent failure,
62
 * transient (retryable) failure, and success. */
63
64
65
66
#define DNS_RESOLVE_FAILED_TRANSIENT 1
#define DNS_RESOLVE_FAILED_PERMANENT 2
#define DNS_RESOLVE_SUCCEEDED 3

67
68
69
/** Our evdns_base; this structure handles all our name lookups. */
static struct evdns_base *the_evdns_base = NULL;

70
71
/** Have we currently configured nameservers with eventdns? */
static int nameservers_configured = 0;
72
73
/** Did our most recent attempt to configure nameservers with eventdns fail? */
static int nameserver_config_failed = 0;
74
75
76
77
78
79
/** 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;
80

Roger Dingledine's avatar
Roger Dingledine committed
81
/** Linked list of connections waiting for a DNS answer. */
82
typedef struct pending_connection_t {
83
  edge_connection_t *conn;
84
  struct pending_connection_t *next;
85
} pending_connection_t;
86

87
88
/** Value of 'magic' field for cached_resolve_t.  Used to try to catch bad
 * pointers and memory stomping. */
89
90
#define CACHED_RESOLVE_MAGIC 0x1234F00D

91
92
93
94
95
96
97
/* Possible states for a cached resolve_t */
/** We are waiting for the resolver system to tell us an answer here.
 * When we get one, or when we time out, the state of this cached_resolve_t
 * will become "DONE" and we'll possibly add a CACHED_VALID or a CACHED_FAILED
 * entry. This cached_resolve_t will be in the hash table so that we will
 * know not to launch more requests for this addr, but rather to add more
 * connections to the pending list for the addr. */
98
#define CACHE_STATE_PENDING 0
99
100
101
/** This used to be a pending cached_resolve_t, and we got an answer for it.
 * Now we're waiting for this cached_resolve_t to expire.  This should
 * have no pending connections, and should not appear in the hash table. */
102
#define CACHE_STATE_DONE 1
103
104
/** We are caching an answer for this address. This should have no pending
 * connections, and should appear in the hash table. */
105
#define CACHE_STATE_CACHED_VALID 2
106
107
/** We are caching a failure for this address. This should have no pending
 * connections, and should appear in the hash table */
108
109
#define CACHE_STATE_CACHED_FAILED 3

Roger Dingledine's avatar
Roger Dingledine committed
110
/** A DNS request: possibly completed, possibly pending; cached_resolve
111
 * structs are stored at the OR side in a hash table, and as a linked
112
113
 * list from oldest to newest.
 */
114
typedef struct cached_resolve_t {
115
  HT_ENTRY(cached_resolve_t) node;
116
  uint32_t magic;
117
  char address[MAX_ADDRESSLEN]; /**< The hostname to be resolved. */
118
  union {
119
120
121
122
    struct {
      struct in6_addr addr6; /**< IPv6 addr for <b>address</b>. */
      uint32_t addr;  /**< IPv4 addr for <b>address</b>. */
    } a;
123
124
    char *hostname; /**< Hostname for <b>address</b> (if a reverse lookup) */
  } result;
125
  uint8_t state; /**< Is this cached entry pending/done/valid/failed? */
126
  uint8_t is_reverse; /**< Is this a reverse (addr-to-hostname) lookup? */
127
  time_t expire; /**< Remove items from cache after this time. */
128
  uint32_t ttl; /**< What TTL did the nameserver tell us? */
129
  /** Connections that want to know when we get an answer for this resolve. */
130
  pending_connection_t *pending_connections;
131
132
  /** Position of this element in the heap*/
  int minheap_idx;
133
} cached_resolve_t;
134

135
static void purge_expired_resolves(time_t now);
136
static void dns_found_answer(const char *address, uint8_t is_reverse,
137
                             uint32_t addr, const char *hostname, char outcome,
138
                             uint32_t ttl);
139
140
static void send_resolved_cell(edge_connection_t *conn, uint8_t answer_type);
static int launch_resolve(edge_connection_t *exitconn);
141
static void add_wildcarded_test_address(const char *address);
142
static int configure_nameservers(int force);
143
static int answer_is_wildcarded(const char *ip);
144
145
static int dns_resolve_impl(edge_connection_t *exitconn, int is_resolve,
                            or_circuit_t *oncirc, char **resolved_to_hostname);
146
#ifdef DEBUG_DNS_CACHE
147
static void _assert_cache_ok(void);
148
149
#define assert_cache_ok() _assert_cache_ok()
#else
150
#define assert_cache_ok() STMT_NIL
151
#endif
152
static void assert_resolve_ok(cached_resolve_t *resolve);
153

154
155
/** Hash table of cached_resolve objects. */
static HT_HEAD(cache_map, cached_resolve_t) cache_root;
156

Roger Dingledine's avatar
Roger Dingledine committed
157
/** Function to compare hashed resolves on their addresses; used to
158
 * implement hash tables. */
159
160
static INLINE int
cached_resolves_eq(cached_resolve_t *a, cached_resolve_t *b)
161
{
162
  /* make this smarter one day? */
163
  assert_resolve_ok(a); // Not b; b may be just a search.
164
165
166
  return !strncmp(a->address, b->address, MAX_ADDRESSLEN);
}

167
/** Hash function for cached_resolve objects */
168
169
170
171
static INLINE unsigned int
cached_resolve_hash(cached_resolve_t *a)
{
  return ht_string_hash(a->address);
172
173
}

174
HT_PROTOTYPE(cache_map, cached_resolve_t, node, cached_resolve_hash,
175
             cached_resolves_eq)
176
HT_GENERATE(cache_map, cached_resolve_t, node, cached_resolve_hash,
177
            cached_resolves_eq, 0.6, malloc, realloc, free)
178

179
/** Initialize the DNS cache. */
180
static void
181
init_cache_map(void)
182
{
183
  HT_INIT(cache_map, &cache_root);
184
185
}

186
/** Helper: called by eventdns when eventdns wants to log something. */
187
static void
188
evdns_log_cb(int warn, const char *msg)
189
{
190
  const char *cp;
191
192
  static int all_down = 0;
  int severity = warn ? LOG_WARN : LOG_INFO;
193
194
195
196
  if (!strcmpstart(msg, "Resolve requested for") &&
      get_options()->SafeLogging) {
    log(LOG_INFO, LD_EXIT, "eventdns: Resolve requested.");
    return;
197
198
  } else if (!strcmpstart(msg, "Search: ")) {
    return;
199
  }
200
201
  if (!strcmpstart(msg, "Nameserver ") && (cp=strstr(msg, " has failed: "))) {
    char *ns = tor_strndup(msg+11, cp-(msg+11));
202
    const char *err = strchr(cp, ':')+2;
203
    tor_assert(err);
204
205
206
    /* 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. */
207
    severity = LOG_INFO;
208
    control_event_server_status(LOG_NOTICE,
209
210
211
212
213
214
                                "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));
215
    severity = (all_down && warn) ? LOG_NOTICE : LOG_INFO;
216
    all_down = 0;
217
218
219
220
221
    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");
222
    all_down = 1;
223
  }
224
  log(severity, LD_EXIT, "eventdns: %s", msg);
225
226
}

227
228
/** Helper: passed to eventdns.c as a callback so it can generate random
 * numbers for transaction IDs and 0x20-hack coding. */
229
static void
230
_dns_randfn(char *b, size_t n)
231
{
232
  crypto_rand(b,n);
233
234
}

Roger Dingledine's avatar
Roger Dingledine committed
235
/** Initialize the DNS subsystem; called by the OR process. */
236
int
237
238
dns_init(void)
{
239
  init_cache_map();
240
  evdns_set_random_bytes_fn(_dns_randfn);
241
242
243
244
  if (server_mode(get_options())) {
    int r = configure_nameservers(1);
    return r;
  }
245
  return 0;
246
}
247

248
249
250
/** Called when DNS-related options change (or may have changed).  Returns -1
 * on failure, 0 on success. */
int
251
252
253
254
dns_reset(void)
{
  or_options_t *options = get_options();
  if (! server_mode(options)) {
255
256
    evdns_base_clear_nameservers_and_suspend(the_evdns_base);
    evdns_base_search_clear(the_evdns_base);
257
258
259
260
    nameservers_configured = 0;
    tor_free(resolv_conf_fname);
    resolv_conf_mtime = 0;
  } else {
261
    if (configure_nameservers(0) < 0) {
262
      return -1;
263
    }
264
  }
265
  return 0;
266
267
}

Nick Mathewson's avatar
Nick Mathewson committed
268
269
/** Return true iff the most recent attempt to initialize the DNS subsystem
 * failed. */
270
271
272
273
274
275
int
has_dns_init_failed(void)
{
  return nameserver_config_failed;
}

276
277
/** Helper: Given a TTL from a DNS response, determine what TTL to give the
 * OP that asked us to resolve it. */
278
279
280
281
282
283
284
285
286
287
288
uint32_t
dns_clip_ttl(uint32_t ttl)
{
  if (ttl < MIN_DNS_TTL)
    return MIN_DNS_TTL;
  else if (ttl > MAX_DNS_TTL)
    return MAX_DNS_TTL;
  else
    return ttl;
}

289
290
/** Helper: Given a TTL from a DNS response, determine how long to hold it in
 * our cache. */
291
292
293
294
295
296
297
298
299
300
301
static uint32_t
dns_get_expiry_ttl(uint32_t ttl)
{
  if (ttl < MIN_DNS_TTL)
    return MIN_DNS_TTL;
  else if (ttl > MAX_DNS_ENTRY_AGE)
    return MAX_DNS_ENTRY_AGE;
  else
    return ttl;
}

302
/** Helper: free storage held by an entry in the DNS cache. */
303
static void
304
_free_cached_resolve(cached_resolve_t *r)
305
{
306
307
  if (!r)
    return;
Nick Mathewson's avatar
Nick Mathewson committed
308
  while (r->pending_connections) {
309
    pending_connection_t *victim = r->pending_connections;
310
311
312
    r->pending_connections = victim->next;
    tor_free(victim);
  }
313
314
  if (r->is_reverse)
    tor_free(r->result.hostname);
315
  r->magic = 0xFF00FF00;
316
317
318
  tor_free(r);
}

319
320
321
/** 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. */
322
static int
323
_compare_cached_resolves_by_expiry(const void *_a, const void *_b)
324
{
325
  const cached_resolve_t *a = _a, *b = _b;
326
327
328
329
330
331
  if (a->expire < b->expire)
    return -1;
  else if (a->expire == b->expire)
    return 0;
  else
    return 1;
332
333
}

334
335
/** Priority queue of cached_resolve_t objects to let us know when they
 * will expire. */
336
337
static smartlist_t *cached_resolve_pqueue = NULL;

338
339
/** Set an expiry time for a cached_resolve_t, and add it to the expiry
 * priority queue */
340
341
342
343
static void
set_expiry(cached_resolve_t *resolve, time_t expires)
{
  tor_assert(resolve && resolve->expire == 0);
344
345
  if (!cached_resolve_pqueue)
    cached_resolve_pqueue = smartlist_create();
346
347
348
  resolve->expire = expires;
  smartlist_pqueue_add(cached_resolve_pqueue,
                       _compare_cached_resolves_by_expiry,
349
                       STRUCT_OFFSET(cached_resolve_t, minheap_idx),
350
351
352
                       resolve);
}

353
/** Free all storage held in the DNS cache and related structures. */
354
355
356
void
dns_free_all(void)
{
357
  cached_resolve_t **ptr, **next, *item;
358
  assert_cache_ok();
359
360
361
  if (cached_resolve_pqueue) {
    SMARTLIST_FOREACH(cached_resolve_pqueue, cached_resolve_t *, res,
      {
362
        if (res->state == CACHE_STATE_DONE)
363
364
365
          _free_cached_resolve(res);
      });
  }
366
  for (ptr = HT_START(cache_map, &cache_root); ptr != NULL; ptr = next) {
367
    item = *ptr;
368
    next = HT_NEXT_RMV(cache_map, &cache_root, ptr);
369
    _free_cached_resolve(item);
370
  }
371
  HT_CLEAR(cache_map, &cache_root);
372
  smartlist_free(cached_resolve_pqueue);
373
  cached_resolve_pqueue = NULL;
374
  tor_free(resolv_conf_fname);
375
376
}

377
378
/** Remove every cached_resolve whose <b>expire</b> time is before or
 * equal to <b>now</b> from the cache. */
379
static void
380
purge_expired_resolves(time_t now)
381
{
Nick Mathewson's avatar
Nick Mathewson committed
382
  cached_resolve_t *resolve, *removed;
383
  pending_connection_t *pend;
384
  edge_connection_t *pendconn;
385

Nick Mathewson's avatar
Nick Mathewson committed
386
  assert_cache_ok();
387
388
389
390
391
392
393
394
  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,
395
396
                         _compare_cached_resolves_by_expiry,
                         STRUCT_OFFSET(cached_resolve_t, minheap_idx));
397

398
    if (resolve->state == CACHE_STATE_PENDING) {
399
      log_debug(LD_EXIT,
400
401
                "Expiring a dns resolve %s that's still pending. Forgot to "
                "cull it? DNS resolve didn't tell us about the timeout?",
402
403
404
405
406
407
408
409
410
411
412
                escaped_safe_str(resolve->address));
    } else if (resolve->state == CACHE_STATE_CACHED_VALID ||
               resolve->state == CACHE_STATE_CACHED_FAILED) {
      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);
413
    }
414

415
    if (resolve->pending_connections) {
416
      log_debug(LD_EXIT,
417
                "Closing pending connections on timed-out DNS resolve!");
418
      tor_fragile_assert();
419
420
421
422
      while (resolve->pending_connections) {
        pend = resolve->pending_connections;
        resolve->pending_connections = pend->next;
        /* Connections should only be pending if they have no socket. */
423
        tor_assert(pend->conn->_base.s == -1);
424
        pendconn = pend->conn;
425
        connection_edge_end(pendconn, END_STREAM_REASON_TIMEOUT);
426
        circuit_detach_stream(circuit_get_by_edge_conn(pendconn), pendconn);
427
        connection_free(TO_CONN(pendconn));
428
429
        tor_free(pend);
      }
430
    }
431

432
433
434
435
436
437
438
    if (resolve->state == CACHE_STATE_CACHED_VALID ||
        resolve->state == CACHE_STATE_CACHED_FAILED ||
        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).",
439
440
                resolve->address, (void*)resolve,
                removed ? removed->address : "NULL", (void*)remove);
441
442
443
      }
      tor_assert(removed == resolve);
    } else {
444
      /* This should be in state DONE. Make sure it's not in the cache. */
445
446
      cached_resolve_t *tmp = HT_FIND(cache_map, &cache_root, resolve);
      tor_assert(tmp != resolve);
447
    }
448
449
450
451
    if (resolve->is_reverse)
      tor_free(resolve->result.hostname);
    resolve->magic = 0xF0BBF0BB;
    tor_free(resolve);
452
  }
453

Nick Mathewson's avatar
Nick Mathewson committed
454
  assert_cache_ok();
455
456
}

457
458
459
/** Send a response to the RESOLVE request of a connection.
 * <b>answer_type</b> must be one of
 * RESOLVED_TYPE_(IPV4|ERROR|ERROR_TRANSIENT).
460
461
 *
 * If <b>circ</b> is provided, and we have a cached answer, send the
462
463
 * answer back along circ; otherwise, send the answer back along
 * <b>conn</b>'s attached circuit.
464
 */
465
static void
466
send_resolved_cell(edge_connection_t *conn, uint8_t answer_type)
467
468
{
  char buf[RELAY_PAYLOAD_SIZE];
469
  size_t buflen;
470
  uint32_t ttl;
471
472

  buf[0] = answer_type;
473
  ttl = dns_clip_ttl(conn->address_ttl);
474
475
476
477
478

  switch (answer_type)
    {
    case RESOLVED_TYPE_IPV4:
      buf[1] = 4;
479
      set_uint32(buf+2, tor_addr_to_ipv4n(&conn->_base.addr));
480
      set_uint32(buf+6, htonl(ttl));
481
      buflen = 10;
482
      break;
483
    /*XXXX IP6 need ipv6 implementation */
484
485
    case RESOLVED_TYPE_ERROR_TRANSIENT:
    case RESOLVED_TYPE_ERROR:
486
487
      {
        const char *errmsg = "Error resolving hostname";
488
        size_t msglen = strlen(errmsg);
489

490
491
        buf[1] = msglen;
        strlcpy(buf+2, errmsg, sizeof(buf)-2);
492
        set_uint32(buf+2+msglen, htonl(ttl));
493
494
495
        buflen = 6+msglen;
        break;
      }
496
497
    default:
      tor_assert(0);
498
      return;
499
    }
500
  // log_notice(LD_EXIT, "Sending a regular RESOLVED reply: ");
Roger Dingledine's avatar
Roger Dingledine committed
501

502
  connection_edge_send_command(conn, RELAY_COMMAND_RESOLVED, buf, buflen);
503
504
}

505
506
507
/** 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.
508
509
510
 *
 * If <b>circ</b> is provided, and we have a cached answer, send the
 * answer back along circ; otherwise, send the answer back along
511
 * <b>conn</b>'s attached circuit.
512
513
 */
static void
514
send_resolved_hostname_cell(edge_connection_t *conn, const char *hostname)
515
516
517
518
519
{
  char buf[RELAY_PAYLOAD_SIZE];
  size_t buflen;
  uint32_t ttl;
  size_t namelen = strlen(hostname);
520
  tor_assert(hostname);
521
522
523
524
525
526
527
528
529
530

  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;

531
  // log_notice(LD_EXIT, "Sending a reply RESOLVED reply: %s", hostname);
532
  connection_edge_send_command(conn, RELAY_COMMAND_RESOLVED, buf, buflen);
533
  // log_notice(LD_EXIT, "Sent");
534
535
}

Nick Mathewson's avatar
Nick Mathewson committed
536
537
/** See if we have a cache entry for <b>exitconn</b>-\>address. if so,
 * if resolve valid, put it into <b>exitconn</b>-\>addr and return 1.
Roger Dingledine's avatar
Roger Dingledine committed
538
 * If resolve failed, free exitconn and return -1.
539
 *
540
541
542
543
544
 * (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.)
 *
545
 * If we have a cached answer, send the answer back along <b>exitconn</b>'s
546
 * circuit.
547
 *
548
549
550
551
552
 * 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.
553
554
555
556
557
558
 *
 * 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.
559
 */
560
int
561
dns_resolve(edge_connection_t *exitconn)
562
563
564
565
566
567
{
  or_circuit_t *oncirc = TO_OR_CIRCUIT(exitconn->on_circuit);
  int is_resolve, r;
  char *hostname = NULL;
  is_resolve = exitconn->_base.purpose == EXIT_PURPOSE_RESOLVE;

568
569
  r = dns_resolve_impl(exitconn, is_resolve, oncirc, &hostname);

570
571
  switch (r) {
    case 1:
572
573
      /* We got an answer without a lookup -- either the answer was
       * cached, or it was obvious (like an IP address). */
574
      if (is_resolve) {
575
        /* Send the answer back right now, and detach. */
576
577
578
579
        if (hostname)
          send_resolved_hostname_cell(exitconn, hostname);
        else
          send_resolved_cell(exitconn, RESOLVED_TYPE_IPV4);
580
        exitconn->on_circuit = NULL;
581
      } else {
582
583
        /* Add to the n_streams list; the calling function will send back a
         * connected cell. */
584
585
586
587
588
        exitconn->next_stream = oncirc->n_streams;
        oncirc->n_streams = exitconn;
      }
      break;
    case 0:
589
590
      /* The request is pending: add the connection into the linked list of
       * resolving_streams on this circuit. */
591
592
593
594
595
596
      exitconn->_base.state = EXIT_CONN_STATE_RESOLVING;
      exitconn->next_stream = oncirc->resolving_streams;
      oncirc->resolving_streams = exitconn;
      break;
    case -2:
    case -1:
597
      /* The request failed before it could start: cancel this connection,
598
       * and stop everybody waiting for the same connection. */
599
600
601
602
      if (is_resolve) {
        send_resolved_cell(exitconn,
             (r == -1) ? RESOLVED_TYPE_ERROR : RESOLVED_TYPE_ERROR_TRANSIENT);
      }
603

604
      exitconn->on_circuit = NULL;
605
606
607

      dns_cancel_pending_resolve(exitconn->_base.address);

608
      if (!exitconn->_base.marked_for_close) {
609
        connection_free(TO_CONN(exitconn));
610
        // XXX ... and we just leak exitconn otherwise? -RD
611
612
613
        // If it's marked for close, it's on closeable_connection_lst in
        // main.c.  If it's on the closeable list, it will get freed from
        // main.c. -NM
614
        // "<armadev> If that's true, there are other bugs around, where we
615
        //  don't check if it's marked, and will end up double-freeing."
616
617
        // On the other hand, I don't know of any actual bugs here, so this
        // shouldn't be holding up the rc. -RD
618
      }
619
620
621
622
623
624
625
626
627
628
629
630
631
632
      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
633
634
635
 * 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.
636
637
638
639
 */
static int
dns_resolve_impl(edge_connection_t *exitconn, int is_resolve,
                 or_circuit_t *oncirc, char **hostname_out)
640
{
641
642
643
  cached_resolve_t *resolve;
  cached_resolve_t search;
  pending_connection_t *pending_connection;
644
  routerinfo_t *me;
645
  tor_addr_t addr;
646
  time_t now = time(NULL);
647
648
  uint8_t is_reverse = 0;
  int r;
649
650
  assert_connection_ok(TO_CONN(exitconn), 0);
  tor_assert(exitconn->_base.s == -1);
651
  assert_cache_ok();
652
  tor_assert(oncirc);
653

654
  /* first check if exitconn->_base.address is an IP. If so, we already
655
   * know the answer. */
656
  if (tor_addr_from_str(&addr, exitconn->_base.address) >= 0) {
657
    if (tor_addr_family(&addr) == AF_INET) {
658
      tor_addr_copy(&exitconn->_base.addr, &addr);
659
660
661
662
663
664
      exitconn->address_ttl = DEFAULT_DNS_TTL;
      return 1;
    } else {
      /* XXXX IPv6 */
      return -1;
    }
665
  }
666

667
668
669
670
671
  /* If we're a non-exit, don't even do DNS lookups. */
  if (!(me = router_get_my_routerinfo()) ||
      policy_is_reject_star(me->exit_policy)) {
    return -1;
  }
672
673
674
675
676
677
  if (address_is_invalid_destination(exitconn->_base.address, 0)) {
    log(LOG_PROTOCOL_WARN, LD_EXIT,
        "Rejecting invalid destination address %s",
        escaped_safe_str(exitconn->_base.address));
    return -1;
  }
678
679

  /* then take this opportunity to see if there are any expired
680
   * resolves in the hash table. */
681
  purge_expired_resolves(now);
682

683
684
  /* lower-case exitconn->_base.address, so it's in canonical form */
  tor_strlower(exitconn->_base.address);
685

686
687
  /* 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
688
   * connection.
689
   */
690
691
  if ((r = tor_addr_parse_reverse_lookup_name(&addr, exitconn->_base.address,
                                              AF_UNSPEC, 0)) != 0) {
692
    if (r == 1) {
693
      is_reverse = 1;
694
695
      if (tor_addr_is_internal(&addr, 0)) /* internal address? */
        return -1;
696
    }
697
698
699
700
701
702
703
704
705
706
707
708
709

    if (!is_reverse || !is_resolve) {
      if (!is_reverse)
        log_info(LD_EXIT, "Bad .in-addr.arpa address \"%s\"; sending error.",
                 escaped_safe_str(exitconn->_base.address));
      else if (!is_resolve)
        log_info(LD_EXIT,
                 "Attempt to connect to a .in-addr.arpa address \"%s\"; "
                 "sending error.",
                 escaped_safe_str(exitconn->_base.address));

      return -1;
    }
710
    //log_notice(LD_EXIT, "Looks like an address %s",
Roger Dingledine's avatar
Roger Dingledine committed
711
    //exitconn->_base.address);
712
713
  }

714
  /* now check the hash table to see if 'address' is already there. */
715
  strlcpy(search.address, exitconn->_base.address, sizeof(search.address));
716
  resolve = HT_FIND(cache_map, &cache_root, &search);
717
  if (resolve && resolve->expire > now) { /* already there */
718
    switch (resolve->state) {
719
720
      case CACHE_STATE_PENDING:
        /* add us to the pending list */
721
        pending_connection = tor_malloc_zero(
722
                                      sizeof(pending_connection_t));
723
        pending_connection->conn = exitconn;
Roger Dingledine's avatar
   
Roger Dingledine committed
724
725
        pending_connection->next = resolve->pending_connections;
        resolve->pending_connections = pending_connection;
726
        log_debug(LD_EXIT,"Connection (fd %d) waiting for pending DNS "
727
728
                  "resolve of %s", exitconn->_base.s,
                  escaped_safe_str(exitconn->_base.address));
Roger Dingledine's avatar
   
Roger Dingledine committed
729
        return 0;
730
      case CACHE_STATE_CACHED_VALID:
731
        log_debug(LD_EXIT,"Connection (fd %d) found cached answer for %s",
732
                  exitconn->_base.s,
733
734
735
736
                  escaped_safe_str(resolve->address));
        exitconn->address_ttl = resolve->ttl;
        if (resolve->is_reverse) {
          tor_assert(is_resolve);
737
          *hostname_out = tor_strdup(resolve->result.hostname);
738
        } else {
739
          tor_addr_from_ipv4h(&exitconn->_base.addr, resolve->result.a.addr);
740
        }
741
        return 1;
742
      case CACHE_STATE_CACHED_FAILED:
743
        log_debug(LD_EXIT,"Connection (fd %d) found cached error for %s",
744
745
                  exitconn->_base.s,
                  escaped_safe_str(exitconn->_base.address));
746
        return -1;
747
748
749
      case CACHE_STATE_DONE:
        log_err(LD_BUG, "Found a 'DONE' dns resolve still in the cache.");
        tor_fragile_assert();
750
    }
Roger Dingledine's avatar
Roger Dingledine committed
751
    tor_assert(0);
Roger Dingledine's avatar
Roger Dingledine committed
752
  }
753
  tor_assert(!resolve);
Roger Dingledine's avatar
Roger Dingledine committed
754
  /* not there, need to add it */
755
  resolve = tor_malloc_zero(sizeof(cached_resolve_t));
756
  resolve->magic = CACHED_RESOLVE_MAGIC;
Roger Dingledine's avatar
Roger Dingledine committed
757
  resolve->state = CACHE_STATE_PENDING;
758
  resolve->minheap_idx = -1;
759
  resolve->is_reverse = is_reverse;
760
  strlcpy(resolve->address, exitconn->_base.address, sizeof(resolve->address));
Roger Dingledine's avatar
Roger Dingledine committed
761

762
  /* add this connection to the pending list */
763
  pending_connection = tor_malloc_zero(sizeof(pending_connection_t));
Roger Dingledine's avatar
Roger Dingledine committed
764
765
766
  pending_connection->conn = exitconn;
  resolve->pending_connections = pending_connection;

767
  /* Add this resolve to the cache and priority queue. */
768
  HT_INSERT(cache_map, &cache_root, resolve);
769
  set_expiry(resolve, now + RESOLVE_MAX_TIMEOUT);
770

771
  log_debug(LD_EXIT,"Launching %s.",
772
            escaped_safe_str(exitconn->_base.address));
773
  assert_cache_ok();
774

775
  return launch_resolve(exitconn);
776
777
}

778
/** Log an error and abort if conn is waiting for a DNS resolve.
779
 */
780
void
781
assert_connection_edge_not_dns_pending(edge_connection_t *conn)
782
{
783
  pending_connection_t *pend;
784
  cached_resolve_t search;
785

786
787
788
789
790
791
792
793
794
795
796
#if 1
  cached_resolve_t *resolve;
  strlcpy(search.address, conn->_base.address, sizeof(search.address));
  resolve = HT_FIND(cache_map, &cache_root, &search);
  if (!resolve)
    return;
  for (pend = resolve->pending_connections; pend; pend = pend->next) {
    tor_assert(pend->conn != conn);
  }
#else
  cached_resolve_t **resolve;
797
  HT_FOREACH(resolve, cache_map, &cache_root) {
798
    for (pend = (*resolve)->pending_connections; pend; pend = pend->next) {
799
800
      tor_assert(pend->conn != conn);
    }
801
  }
802
#endif
803
}
804

805
806
807
808
809
810
811
/** Log an error and abort if any connection waiting for a DNS resolve is
 * corrupted. */
void
assert_all_pending_dns_resolves_ok(void)
{
  pending_connection_t *pend;
  cached_resolve_t **resolve;
812

813
814
815
816
  HT_FOREACH(resolve, cache_map, &cache_root) {
    for (pend = (*resolve)->pending_connections;
         pend;
         pend = pend->next) {
817
818
819
      assert_connection_ok(TO_CONN(pend->conn), 0);
      tor_assert(pend->conn->_base.s == -1);
      tor_assert(!connection_in_array(TO_CONN(pend->conn)));
820
    }
821
822
823
  }
}

Nick Mathewson's avatar
Nick Mathewson committed
824
/** Remove <b>conn</b> from the list of connections waiting for conn-\>address.
825
 */
826
void
827
connection_dns_remove(edge_connection_t *conn)
828
{
829
830
831
  pending_connection_t *pend, *victim;
  cached_resolve_t search;
  cached_resolve_t *resolve;
832

833
834
  tor_assert(conn->_base.type == CONN_TYPE_EXIT);
  tor_assert(conn->_base.state == EXIT_CONN_STATE_RESOLVING);
835

836
  strlcpy(search.address, conn->_base.address, sizeof(search.address));
837

838
  resolve = HT_FIND(cache_map, &cache_root, &search);
839
  if (!resolve) {
840
    log_notice(LD_BUG, "Address %s is not pending. Dropping.",
841
               escaped_safe_str(conn->_base.address));
842
843
844
    return;
  }

Roger Dingledine's avatar
Roger Dingledine committed
845
  tor_assert(resolve->pending_connections);
846
  assert_connection_ok(TO_CONN(conn),0);
847
848
849

  pend = resolve->pending_connections;

850
  if (pend->conn == conn) {
851
    resolve->pending_connections = pend->next;
852
    tor_free(pend);
853
    log_debug(LD_EXIT, "First connection (fd %d) no longer waiting "
854
              "for resolve of %s",
855
              conn->_base.s,
856
              escaped_safe_str(conn->_base.address));
857
858
    return;
  } else {
859
860
    for ( ; pend->next; pend = pend->next) {
      if (pend->next->conn == conn) {
861
862
        victim = pend->next;
        pend->next = victim->next;
863
        tor_free(victim);
864
        log_debug(LD_EXIT,
865
                  "Connection (fd %d) no longer waiting for resolve of %s",
866
                  conn->_base.s, escaped_safe_str(conn->_base.address));
867
868
869
        return; /* more are pending */
      }
    }
Roger Dingledine's avatar
Roger Dingledine committed
870
    tor_assert(0); /* not reachable unless onlyconn not in pending list */
871
872
873
  }
}

Nick Mathewson's avatar
Nick Mathewson committed
874
875
876
/** Mark all connections waiting for <b