dns.c 55 KB
Newer Older
1
2
/* Copyright (c) 2003-2004, Roger Dingledine.
 * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
3
 * Copyright (c) 2007-2008, The Tor Project, Inc. */
4
5
/* See LICENSE for licensing information */
/* $Id$ */
6
7
const char dns_c_id[] =
  "$Id$";
8

Roger Dingledine's avatar
Roger Dingledine committed
9
10
/**
 * \file dns.c
11
 * \brief Implements a local cache for DNS results for Tor servers.
Roger Dingledine's avatar
Roger Dingledine committed
12
 * This is implemented as a wrapper around Adam Langley's eventdns.c code.
13
14
 * (We can't just use gethostbyname() and friends because we really need to
 * be nonblocking.)
Roger Dingledine's avatar
Roger Dingledine committed
15
 **/
16

17
#include "or.h"
18
#include "ht.h"
19
#include "eventdns.h"
20

Roger Dingledine's avatar
Roger Dingledine committed
21
/** Longest hostname we're willing to resolve. */
22
23
#define MAX_ADDRESSLEN 256

24
25
/** How long will we wait for an answer from the resolver before we decide
 * that the resolver is wedged? */
26
27
#define RESOLVE_MAX_TIMEOUT 300

Roger Dingledine's avatar
Roger Dingledine committed
28
/** Possible outcomes from hostname lookup: permanent failure,
29
 * transient (retryable) failure, and success. */
30
31
32
33
#define DNS_RESOLVE_FAILED_TRANSIENT 1
#define DNS_RESOLVE_FAILED_PERMANENT 2
#define DNS_RESOLVE_SUCCEEDED 3

34
35
36
37
38
39
40
41
/** Have we currently configured nameservers with eventdns? */
static int nameservers_configured = 0;
/** 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;
42

Roger Dingledine's avatar
Roger Dingledine committed
43
/** Linked list of connections waiting for a DNS answer. */
44
typedef struct pending_connection_t {
45
  edge_connection_t *conn;
46
  struct pending_connection_t *next;
47
} pending_connection_t;
48

49
50
/** Value of 'magic' field for cached_resolve_t.  Used to try to catch bad
 * pointers and memory stomping. */
51
52
#define CACHED_RESOLVE_MAGIC 0x1234F00D

53
54
55
56
57
58
59
/* 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. */
60
#define CACHE_STATE_PENDING 0
61
62
63
/** 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. */
64
#define CACHE_STATE_DONE 1
65
66
/** We are caching an answer for this address. This should have no pending
 * connections, and should appear in the hash table. */
67
#define CACHE_STATE_CACHED_VALID 2
68
69
/** We are caching a failure for this address. This should have no pending
 * connections, and should appear in the hash table */
70
71
#define CACHE_STATE_CACHED_FAILED 3

Roger Dingledine's avatar
Roger Dingledine committed
72
/** A DNS request: possibly completed, possibly pending; cached_resolve
73
 * structs are stored at the OR side in a hash table, and as a linked
74
75
 * list from oldest to newest.
 */
76
typedef struct cached_resolve_t {
77
  HT_ENTRY(cached_resolve_t) node;
78
  uint32_t magic;
79
  char address[MAX_ADDRESSLEN]; /**< The hostname to be resolved. */
80
81
82
83
  union {
    uint32_t addr;  /**< IPv4 addr for <b>address</b>. */
    char *hostname; /**< Hostname for <b>address</b> (if a reverse lookup) */
  } result;
84
  uint8_t state; /**< Is this cached entry pending/done/valid/failed? */
85
  uint8_t is_reverse; /**< Is this a reverse (addr-to-hostname) lookup? */
86
  time_t expire; /**< Remove items from cache after this time. */
87
  uint32_t ttl; /**< What TTL did the nameserver tell us? */
88
  /** Connections that want to know when we get an answer for this resolve. */
89
90
  pending_connection_t *pending_connections;
} cached_resolve_t;
91

92
static void purge_expired_resolves(time_t now);
93
static void dns_found_answer(const char *address, uint8_t is_reverse,
94
                             uint32_t addr, const char *hostname, char outcome,
95
                             uint32_t ttl);
96
97
static void send_resolved_cell(edge_connection_t *conn, uint8_t answer_type);
static int launch_resolve(edge_connection_t *exitconn);
98
static void add_wildcarded_test_address(const char *address);
99
static int configure_nameservers(int force);
100
static int answer_is_wildcarded(const char *ip);
101
102
static int dns_resolve_impl(edge_connection_t *exitconn, int is_resolve,
                            or_circuit_t *oncirc, char **resolved_to_hostname);
103
#ifdef DEBUG_DNS_CACHE
104
static void _assert_cache_ok(void);
105
106
#define assert_cache_ok() _assert_cache_ok()
#else
107
#define assert_cache_ok() STMT_NIL
108
#endif
109
static void assert_resolve_ok(cached_resolve_t *resolve);
110

111
112
/** Hash table of cached_resolve objects. */
static HT_HEAD(cache_map, cached_resolve_t) cache_root;
113

Roger Dingledine's avatar
Roger Dingledine committed
114
/** Function to compare hashed resolves on their addresses; used to
115
 * implement hash tables. */
116
117
static INLINE int
cached_resolves_eq(cached_resolve_t *a, cached_resolve_t *b)
118
{
119
  /* make this smarter one day? */
120
  assert_resolve_ok(a); // Not b; b may be just a search.
121
122
123
  return !strncmp(a->address, b->address, MAX_ADDRESSLEN);
}

124
/** Hash function for cached_resolve objects */
125
126
127
128
static INLINE unsigned int
cached_resolve_hash(cached_resolve_t *a)
{
  return ht_string_hash(a->address);
129
130
}

131
HT_PROTOTYPE(cache_map, cached_resolve_t, node, cached_resolve_hash,
132
             cached_resolves_eq)
133
HT_GENERATE(cache_map, cached_resolve_t, node, cached_resolve_hash,
134
            cached_resolves_eq, 0.6, malloc, realloc, free)
135

136
/** Initialize the DNS cache. */
137
static void
138
init_cache_map(void)
139
{
140
  HT_INIT(cache_map, &cache_root);
141
142
}

143
/** Helper: called by eventdns when eventdns wants to log something. */
144
static void
145
evdns_log_cb(int warn, const char *msg)
146
{
147
  const char *cp;
148
149
  static int all_down = 0;
  int severity = warn ? LOG_WARN : LOG_INFO;
150
151
152
153
  if (!strcmpstart(msg, "Resolve requested for") &&
      get_options()->SafeLogging) {
    log(LOG_INFO, LD_EXIT, "eventdns: Resolve requested.");
    return;
154
155
  } else if (!strcmpstart(msg, "Search: ")) {
    return;
156
  }
157
158
159
  if (!strcmpstart(msg, "Nameserver ") && (cp=strstr(msg, " has failed: "))) {
    char *ns = tor_strndup(msg+11, cp-(msg+11));
    const char *err = strchr(cp, ':'+2);
160
    tor_assert(err);
161
162
163
    /* 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. */
164
    severity = LOG_INFO;
165
    control_event_server_status(LOG_NOTICE,
166
167
168
169
170
171
                                "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));
172
    severity = (all_down && warn) ? LOG_NOTICE : LOG_INFO;
173
    all_down = 0;
174
175
176
177
178
    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");
179
    all_down = 1;
180
  }
181
  log(severity, LD_EXIT, "eventdns: %s", msg);
182
183
}

184
185
186
187
188
189
190
191
192
/** Helper: generate a good random transaction ID. */
static uint16_t
dns_get_transaction_id(void)
{
  uint16_t result;
  crypto_rand((void*)&result, sizeof(result));
  return result;
}

Roger Dingledine's avatar
Roger Dingledine committed
193
/** Initialize the DNS subsystem; called by the OR process. */
194
int
195
196
dns_init(void)
{
197
  init_cache_map();
198
  evdns_set_transaction_id_fn(dns_get_transaction_id);
199
  if (server_mode(get_options()))
200
    return configure_nameservers(1);
201
  return 0;
202
}
203

204
205
206
/** Called when DNS-related options change (or may have changed).  Returns -1
 * on failure, 0 on success. */
int
207
208
209
210
dns_reset(void)
{
  or_options_t *options = get_options();
  if (! server_mode(options)) {
211
212
    evdns_clear_nameservers_and_suspend();
    evdns_search_clear();
213
214
215
216
217
    nameservers_configured = 0;
    tor_free(resolv_conf_fname);
    resolv_conf_mtime = 0;
  } else {
    if (configure_nameservers(0) < 0)
218
      return -1;
219
  }
220
  return 0;
221
222
}

223
224
/** Helper: Given a TTL from a DNS response, determine what TTL to give the
 * OP that asked us to resolve it. */
225
226
227
228
229
230
231
232
233
234
235
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;
}

236
237
/** Helper: Given a TTL from a DNS response, determine how long to hold it in
 * our cache. */
238
239
240
241
242
243
244
245
246
247
248
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;
}

249
/** Helper: free storage held by an entry in the DNS cache. */
250
static void
251
_free_cached_resolve(cached_resolve_t *r)
252
{
Nick Mathewson's avatar
Nick Mathewson committed
253
  while (r->pending_connections) {
254
    pending_connection_t *victim = r->pending_connections;
255
256
257
    r->pending_connections = victim->next;
    tor_free(victim);
  }
258
259
  if (r->is_reverse)
    tor_free(r->result.hostname);
260
  r->magic = 0xFF00FF00;
261
262
263
  tor_free(r);
}

264
265
266
/** 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. */
267
static int
268
_compare_cached_resolves_by_expiry(const void *_a, const void *_b)
269
{
270
  const cached_resolve_t *a = _a, *b = _b;
271
  return a->expire - b->expire;
272
273
}

274
275
/** Priority queue of cached_resolve_t objects to let us know when they
 * will expire. */
276
277
static smartlist_t *cached_resolve_pqueue = NULL;

278
279
/** Set an expiry time for a cached_resolve_t, and add it to the expiry
 * priority queue */
280
281
282
283
static void
set_expiry(cached_resolve_t *resolve, time_t expires)
{
  tor_assert(resolve && resolve->expire == 0);
284
285
  if (!cached_resolve_pqueue)
    cached_resolve_pqueue = smartlist_create();
286
287
288
289
290
291
  resolve->expire = expires;
  smartlist_pqueue_add(cached_resolve_pqueue,
                       _compare_cached_resolves_by_expiry,
                       resolve);
}

292
/** Free all storage held in the DNS cache and related structures. */
293
294
295
void
dns_free_all(void)
{
296
  cached_resolve_t **ptr, **next, *item;
297
  assert_cache_ok();
298
299
300
  if (cached_resolve_pqueue) {
    SMARTLIST_FOREACH(cached_resolve_pqueue, cached_resolve_t *, res,
      {
301
        if (res->state == CACHE_STATE_DONE)
302
303
304
          _free_cached_resolve(res);
      });
  }
305
  for (ptr = HT_START(cache_map, &cache_root); ptr != NULL; ptr = next) {
306
    item = *ptr;
307
    next = HT_NEXT_RMV(cache_map, &cache_root, ptr);
308
    _free_cached_resolve(item);
309
  }
310
  HT_CLEAR(cache_map, &cache_root);
311
312
  if (cached_resolve_pqueue)
    smartlist_free(cached_resolve_pqueue);
313
  cached_resolve_pqueue = NULL;
314
  tor_free(resolv_conf_fname);
315
316
}

317
318
/** Remove every cached_resolve whose <b>expire</b> time is before or
 * equal to <b>now</b> from the cache. */
319
static void
320
purge_expired_resolves(time_t now)
321
{
Nick Mathewson's avatar
Nick Mathewson committed
322
  cached_resolve_t *resolve, *removed;
323
  pending_connection_t *pend;
324
  edge_connection_t *pendconn;
325

Nick Mathewson's avatar
Nick Mathewson committed
326
  assert_cache_ok();
327
328
329
330
331
332
333
334
335
336
  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,
                         _compare_cached_resolves_by_expiry);

337
    if (resolve->state == CACHE_STATE_PENDING) {
338
      log_debug(LD_EXIT,
339
340
                "Expiring a dns resolve %s that's still pending. Forgot to "
                "cull it? DNS resolve didn't tell us about the timeout?",
341
342
343
344
345
346
347
348
349
350
351
                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);
352
    }
353

354
    if (resolve->pending_connections) {
355
      log_debug(LD_EXIT,
356
                "Closing pending connections on timed-out DNS resolve!");
357
      tor_fragile_assert();
358
359
360
361
      while (resolve->pending_connections) {
        pend = resolve->pending_connections;
        resolve->pending_connections = pend->next;
        /* Connections should only be pending if they have no socket. */
362
        tor_assert(pend->conn->_base.s == -1);
363
        pendconn = pend->conn;
364
        connection_edge_end(pendconn, END_STREAM_REASON_TIMEOUT);
365
        circuit_detach_stream(circuit_get_by_edge_conn(pendconn), pendconn);
366
        connection_free(TO_CONN(pendconn));
367
368
        tor_free(pend);
      }
369
    }
370

371
372
373
374
375
376
377
    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).",
378
379
                resolve->address, (void*)resolve,
                removed ? removed->address : "NULL", (void*)remove);
380
381
382
      }
      tor_assert(removed == resolve);
    } else {
383
      /* This should be in state DONE. Make sure it's not in the cache. */
384
385
      cached_resolve_t *tmp = HT_FIND(cache_map, &cache_root, resolve);
      tor_assert(tmp != resolve);
386
    }
387
388
389
390
    if (resolve->is_reverse)
      tor_free(resolve->result.hostname);
    resolve->magic = 0xF0BBF0BB;
    tor_free(resolve);
391
  }
392

Nick Mathewson's avatar
Nick Mathewson committed
393
  assert_cache_ok();
394
395
}

396
397
398
/** Send a response to the RESOLVE request of a connection.
 * <b>answer_type</b> must be one of
 * RESOLVED_TYPE_(IPV4|ERROR|ERROR_TRANSIENT).
399
400
 *
 * If <b>circ</b> is provided, and we have a cached answer, send the
401
402
 * answer back along circ; otherwise, send the answer back along
 * <b>conn</b>'s attached circuit.
403
 */
404
static void
405
send_resolved_cell(edge_connection_t *conn, uint8_t answer_type)
406
407
{
  char buf[RELAY_PAYLOAD_SIZE];
408
  size_t buflen;
409
  uint32_t ttl;
410
411

  buf[0] = answer_type;
412
  ttl = dns_clip_ttl(conn->address_ttl);
413
414
415
416
417

  switch (answer_type)
    {
    case RESOLVED_TYPE_IPV4:
      buf[1] = 4;
418
      set_uint32(buf+2, htonl(conn->_base.addr));
419
      set_uint32(buf+6, htonl(ttl));
420
      buflen = 10;
421
422
423
      break;
    case RESOLVED_TYPE_ERROR_TRANSIENT:
    case RESOLVED_TYPE_ERROR:
424
425
426
      {
        const char *errmsg = "Error resolving hostname";
        int msglen = strlen(errmsg);
427

428
429
        buf[1] = msglen;
        strlcpy(buf+2, errmsg, sizeof(buf)-2);
430
        set_uint32(buf+2+msglen, htonl(ttl));
431
432
433
        buflen = 6+msglen;
        break;
      }
434
435
    default:
      tor_assert(0);
436
      return;
437
    }
438
  // log_notice(LD_EXIT, "Sending a regular RESOLVED reply: ");
Roger Dingledine's avatar
Roger Dingledine committed
439

440
  connection_edge_send_command(conn, RELAY_COMMAND_RESOLVED, buf, buflen);
441
442
}

443
444
445
/** 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.
446
447
448
 *
 * If <b>circ</b> is provided, and we have a cached answer, send the
 * answer back along circ; otherwise, send the answer back along
449
 * <b>conn</b>'s attached circuit.
450
451
 */
static void
452
send_resolved_hostname_cell(edge_connection_t *conn, const char *hostname)
453
454
455
456
457
{
  char buf[RELAY_PAYLOAD_SIZE];
  size_t buflen;
  uint32_t ttl;
  size_t namelen = strlen(hostname);
458
  tor_assert(hostname);
459
460
461
462
463
464
465
466
467
468

  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;

469
  // log_notice(LD_EXIT, "Sending a reply RESOLVED reply: %s", hostname);
470
  connection_edge_send_command(conn, RELAY_COMMAND_RESOLVED, buf, buflen);
471
  // log_notice(LD_EXIT, "Sent");
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
}

/** Given a lower-case <b>address</b>, check to see whether it's a
 * 1.2.3.4.in-addr.arpa address used for reverse lookups.  If so,
 * parse it and place the address in <b>in</b> if present. Return 1 on success;
 * 0 if the address is not in in-addr.arpa format, and -1 if the address is
 * malformed. */
static int
parse_inaddr_arpa_address(const char *address, struct in_addr *in)
{
  char buf[INET_NTOA_BUF_LEN];
  char *cp;
  size_t len;
  struct in_addr inaddr;

  cp = strstr(address, ".in-addr.arpa");
  if (!cp || *(cp+strlen(".in-addr.arpa")))
    return 0; /* not an .in-addr.arpa address  */

  len = cp - address;

  if (len >= INET_NTOA_BUF_LEN)
    return -1; /* Too long. */

496
  memcpy(buf, address, len);
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
  buf[len] = '\0';
  if (tor_inet_aton(buf, &inaddr) == 0)
    return -1; /* malformed. */

  if (in) {
    uint32_t a;
    /* reverse the bytes */
    a = (  ((inaddr.s_addr & 0x000000fful) << 24)
          |((inaddr.s_addr & 0x0000ff00ul) << 8)
          |((inaddr.s_addr & 0x00ff0000ul) >> 8)
          |((inaddr.s_addr & 0xff000000ul) >> 24));
    inaddr.s_addr = a;

    memcpy(in, &inaddr, sizeof(inaddr));
  }

  return 1;
}

Nick Mathewson's avatar
Nick Mathewson committed
516
517
/** 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
518
 * If resolve failed, free exitconn and return -1.
519
 *
520
521
522
523
524
 * (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.)
 *
525
 * If we have a cached answer, send the answer back along <b>exitconn</b>'s
526
 * circuit.
527
 *
528
529
530
531
532
 * 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.
533
534
535
536
537
538
 *
 * 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.
539
 */
540
int
541
dns_resolve(edge_connection_t *exitconn)
542
543
544
545
546
547
548
549
550
{
  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;

  r = dns_resolve_impl(exitconn, is_resolve, oncirc, &hostname);
  switch (r) {
    case 1:
551
552
      /* We got an answer without a lookup -- either the answer was
       * cached, or it was obvious (like an IP address). */
553
      if (is_resolve) {
554
        /* Send the answer back right now, and detach. */
555
556
557
558
        if (hostname)
          send_resolved_hostname_cell(exitconn, hostname);
        else
          send_resolved_cell(exitconn, RESOLVED_TYPE_IPV4);
559
        exitconn->on_circuit = NULL;
560
      } else {
561
562
        /* Add to the n_streams list; the calling function will send back a
         * connected cell. */
563
564
565
566
567
        exitconn->next_stream = oncirc->n_streams;
        oncirc->n_streams = exitconn;
      }
      break;
    case 0:
568
569
      /* The request is pending: add the connection into the linked list of
       * resolving_streams on this circuit. */
570
571
572
573
574
575
      exitconn->_base.state = EXIT_CONN_STATE_RESOLVING;
      exitconn->next_stream = oncirc->resolving_streams;
      oncirc->resolving_streams = exitconn;
      break;
    case -2:
    case -1:
576
      /* The request failed before it could start: cancel this connection,
577
       * and stop everybody waiting for the same connection. */
578
579
580
581
      if (is_resolve) {
        send_resolved_cell(exitconn,
             (r == -1) ? RESOLVED_TYPE_ERROR : RESOLVED_TYPE_ERROR_TRANSIENT);
      }
582

583
      exitconn->on_circuit = NULL;
584
585
586

      dns_cancel_pending_resolve(exitconn->_base.address);

587
      if (!exitconn->_base.marked_for_close) {
588
        connection_free(TO_CONN(exitconn));
589
        //XXX020rc ... and we just leak exitconn otherwise? -RD
590
591
592
        // 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
593
        // "<armadev> If that's true, there are other bugs around, where we
594
        //  don't check if it's marked, and will end up double-freeing."
595
      }
596
597
598
599
600
601
602
603
604
605
606
607
608
609
      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
610
611
612
 * 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.
613
614
615
616
 */
static int
dns_resolve_impl(edge_connection_t *exitconn, int is_resolve,
                 or_circuit_t *oncirc, char **hostname_out)
617
{
618
619
620
  cached_resolve_t *resolve;
  cached_resolve_t search;
  pending_connection_t *pending_connection;
621
  struct in_addr in;
622
  time_t now = time(NULL);
623
624
  uint8_t is_reverse = 0;
  int r;
625
626
  assert_connection_ok(TO_CONN(exitconn), 0);
  tor_assert(exitconn->_base.s == -1);
627
  assert_cache_ok();
628
  tor_assert(oncirc);
629

630
  /* first check if exitconn->_base.address is an IP. If so, we already
631
   * know the answer. */
632
633
  if (tor_inet_aton(exitconn->_base.address, &in) != 0) {
    exitconn->_base.addr = ntohl(in.s_addr);
634
    exitconn->address_ttl = DEFAULT_DNS_TTL;
635
    return 1;
636
  }
637
638
639
640
641
642
  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;
  }
643
644

  /* then take this opportunity to see if there are any expired
645
   * resolves in the hash table. */
646
  purge_expired_resolves(now);
647

648
649
  /* lower-case exitconn->_base.address, so it's in canonical form */
  tor_strlower(exitconn->_base.address);
650

651
652
  /* 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
653
   * connection.
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
   */
  if ((r = parse_inaddr_arpa_address(exitconn->_base.address, NULL)) != 0) {
    if (r == 1)
      is_reverse = 1;

    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;
    }
671
    //log_notice(LD_EXIT, "Looks like an address %s",
Roger Dingledine's avatar
Roger Dingledine committed
672
    //exitconn->_base.address);
673
674
  }

675
  /* now check the hash table to see if 'address' is already there. */
676
  strlcpy(search.address, exitconn->_base.address, sizeof(search.address));
677
  resolve = HT_FIND(cache_map, &cache_root, &search);
678
  if (resolve && resolve->expire > now) { /* already there */
679
    switch (resolve->state) {
680
681
      case CACHE_STATE_PENDING:
        /* add us to the pending list */
682
        pending_connection = tor_malloc_zero(
683
                                      sizeof(pending_connection_t));
684
        pending_connection->conn = exitconn;
Roger Dingledine's avatar
   
Roger Dingledine committed
685
686
        pending_connection->next = resolve->pending_connections;
        resolve->pending_connections = pending_connection;
687
        log_debug(LD_EXIT,"Connection (fd %d) waiting for pending DNS "
688
689
                  "resolve of %s", exitconn->_base.s,
                  escaped_safe_str(exitconn->_base.address));
Roger Dingledine's avatar
   
Roger Dingledine committed
690
        return 0;
691
      case CACHE_STATE_CACHED_VALID:
692
        log_debug(LD_EXIT,"Connection (fd %d) found cached answer for %s",
693
                  exitconn->_base.s,
694
695
696
697
                  escaped_safe_str(resolve->address));
        exitconn->address_ttl = resolve->ttl;
        if (resolve->is_reverse) {
          tor_assert(is_resolve);
698
          *hostname_out = tor_strdup(resolve->result.hostname);
699
700
        } else {
          exitconn->_base.addr = resolve->result.addr;
701
        }
702
        return 1;
703
      case CACHE_STATE_CACHED_FAILED:
704
        log_debug(LD_EXIT,"Connection (fd %d) found cached error for %s",
705
706
                  exitconn->_base.s,
                  escaped_safe_str(exitconn->_base.address));
707
        return -1;
708
709
710
      case CACHE_STATE_DONE:
        log_err(LD_BUG, "Found a 'DONE' dns resolve still in the cache.");
        tor_fragile_assert();
711
    }
Roger Dingledine's avatar
Roger Dingledine committed
712
    tor_assert(0);
Roger Dingledine's avatar
Roger Dingledine committed
713
  }
714
  tor_assert(!resolve);
Roger Dingledine's avatar
Roger Dingledine committed
715
  /* not there, need to add it */
716
  resolve = tor_malloc_zero(sizeof(cached_resolve_t));
717
  resolve->magic = CACHED_RESOLVE_MAGIC;
Roger Dingledine's avatar
Roger Dingledine committed
718
  resolve->state = CACHE_STATE_PENDING;
719
  resolve->is_reverse = is_reverse;
720
  strlcpy(resolve->address, exitconn->_base.address, sizeof(resolve->address));
Roger Dingledine's avatar
Roger Dingledine committed
721

722
  /* add this connection to the pending list */
723
  pending_connection = tor_malloc_zero(sizeof(pending_connection_t));
Roger Dingledine's avatar
Roger Dingledine committed
724
725
726
  pending_connection->conn = exitconn;
  resolve->pending_connections = pending_connection;

727
  /* Add this resolve to the cache and priority queue. */
728
  HT_INSERT(cache_map, &cache_root, resolve);
729
  set_expiry(resolve, now + RESOLVE_MAX_TIMEOUT);
730

731
  log_debug(LD_EXIT,"Launching %s.",
732
            escaped_safe_str(exitconn->_base.address));
733
  assert_cache_ok();
734

735
  return launch_resolve(exitconn);
736
737
}

738
/** Log an error and abort if conn is waiting for a DNS resolve.
739
 */
740
void
741
assert_connection_edge_not_dns_pending(edge_connection_t *conn)
742
{
743
744
  pending_connection_t *pend;
  cached_resolve_t **resolve;
745

746
747
748
749
750
751
  HT_FOREACH(resolve, cache_map, &cache_root) {
    for (pend = (*resolve)->pending_connections;
         pend;
         pend = pend->next) {
      tor_assert(pend->conn != conn);
    }
752
  }
753
}
754

755
756
757
758
759
760
761
/** 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;
762

763
764
765
766
  HT_FOREACH(resolve, cache_map, &cache_root) {
    for (pend = (*resolve)->pending_connections;
         pend;
         pend = pend->next) {
767
768
769
      assert_connection_ok(TO_CONN(pend->conn), 0);
      tor_assert(pend->conn->_base.s == -1);
      tor_assert(!connection_in_array(TO_CONN(pend->conn)));
770
    }
771
772
773
  }
}

Nick Mathewson's avatar
Nick Mathewson committed
774
/** Remove <b>conn</b> from the list of connections waiting for conn-\>address.
775
 */
776
void
777
connection_dns_remove(edge_connection_t *conn)
778
{
779
780
781
  pending_connection_t *pend, *victim;
  cached_resolve_t search;
  cached_resolve_t *resolve;
782

783
784
  tor_assert(conn->_base.type == CONN_TYPE_EXIT);
  tor_assert(conn->_base.state == EXIT_CONN_STATE_RESOLVING);
785

786
  strlcpy(search.address, conn->_base.address, sizeof(search.address));
787

788
  resolve = HT_FIND(cache_map, &cache_root, &search);
789
  if (!resolve) {
790
    log_notice(LD_BUG, "Address %s is not pending. Dropping.",
791
               escaped_safe_str(conn->_base.address));
792
793
794
    return;
  }

Roger Dingledine's avatar
Roger Dingledine committed
795
  tor_assert(resolve->pending_connections);
796
  assert_connection_ok(TO_CONN(conn),0);
797
798
799

  pend = resolve->pending_connections;

800
  if (pend->conn == conn) {
801
    resolve->pending_connections = pend->next;
802
    tor_free(pend);
803
    log_debug(LD_EXIT, "First connection (fd %d) no longer waiting "
804
              "for resolve of %s",
805
              conn->_base.s, escaped_safe_str(conn->_base.address));
806
807
    return;
  } else {
808
809
    for ( ; pend->next; pend = pend->next) {
      if (pend->next->conn == conn) {
810
811
        victim = pend->next;
        pend->next = victim->next;
812
        tor_free(victim);
813
        log_debug(LD_EXIT,
814
                  "Connection (fd %d) no longer waiting for resolve of %s",
815
                  conn->_base.s, escaped_safe_str(conn->_base.address));
816
817
818
        return; /* more are pending */
      }
    }
Roger Dingledine's avatar
Roger Dingledine committed
819
    tor_assert(0); /* not reachable unless onlyconn not in pending list */
820
821
822
  }
}

Nick Mathewson's avatar
Nick Mathewson committed
823
824
825
/** Mark all connections waiting for <b>address</b> for close.  Then cancel
 * the resolve for <b>address</b> itself, and remove any cached results for
 * <b>address</b> from the cache.
826
 */
827
void
828
dns_cancel_pending_resolve(const char *address)
829
{
830
831
  pending_connection_t *pend;
  cached_resolve_t search;
832
  cached_resolve_t *resolve, *tmp;
833
  edge_connection_t *pendconn;
834
  circuit_t *circ;
835

Nick Mathewson's avatar
Nick Mathewson committed
836
  strlcpy(search.address, address, sizeof(search.address));
837

838
  resolve = HT_FIND(cache_map, &cache_root, &search);
839
840
841
  if (!resolve)
    return;

842
  if (resolve->state != CACHE_STATE_PENDING) {
843
844
845
846
847
848
849
850
851
    /* We can get into this state if we never actually created the pending
     * resolve, due to finding an earlier cached error or something.  Just
     * ignore it. */
    if (resolve->pending_connections) {
      log_warn(LD_BUG,
               "Address %s is not pending but has pending connections!",
               escaped_safe_str(address));
      tor_fragile_assert();
    }
852
853
854
    return;
  }

855
  if (!resolve->pending_connections) {
856
    log_warn(LD_BUG,
857
             "Address %s is pending but has no pending connections!",
858
             escaped_safe_str(address));
859
    tor_fragile_assert();
860
861
    return;
  }
Roger Dingledine's avatar
Roger Dingledine committed
862
  tor_assert(resolve->pending_connections);
863

864
  /* mark all pending connections to fail */
865
  log_debug(LD_EXIT,
866
867
             "Failing all connections waiting on DNS resolve of %s",
             escaped_safe_str(address));
868
  while (resolve->pending_connections) {
869
    pend = resolve->pending_connections;
870
    pend->conn->_base.state = EXIT_CONN_STATE_RESOLVEFAILED;
871
    pendconn = pend->conn;
872
873
874
    assert_connection_ok(TO_CONN(pendconn), 0);
    tor_assert(pendconn->_base.s == -1);
    if (!pendconn->_base.marked_for_close) {
875
      connection_edge_end(pendconn, END_STREAM_REASON_RESOLVEFAILED);
876
    }
877
    circ = circuit_get_by_edge_conn(pendconn);
878
879
    if (circ)
      circuit_detach_stream(circ, pendconn);
880
881
    if (!pendconn->_base.marked_for_close)
      connection_free(TO_CONN(pendconn));
882
883
    resolve->pending_connections = pend->next;
    tor_free(pend);
884
885
  }

Nick Mathewson's avatar
Nick Mathewson committed
886
  tmp = HT_REMOVE(cache_map, &cache_root, resolve);
887
888
889
  if (tmp != resolve) {
    log_err(LD_BUG, "The cancelled resolve we purged didn't match any in"
            " the cache. Tried to purge %s (%p); instead got %s (%p).",
890
891
            resolve->address, (void*)resolve,
            tmp ? tmp->address : "NULL", (void*)tmp);