dns.c 60.7 KB
Newer Older
1
2
/* Copyright (c) 2003-2004, Roger Dingledine.
 * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
3
 * Copyright (c) 2007-2010, 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"
Sebastian Hahn's avatar
Sebastian Hahn committed
15
#include "circuitlist.h"
Sebastian Hahn's avatar
Sebastian Hahn committed
16
#include "circuituse.h"
Sebastian Hahn's avatar
Sebastian Hahn committed
17
#include "config.h"
Sebastian Hahn's avatar
Sebastian Hahn committed
18
#include "connection.h"
Sebastian Hahn's avatar
Sebastian Hahn committed
19
#include "connection_edge.h"
Sebastian Hahn's avatar
Sebastian Hahn committed
20
#include "router.h"
21
#include "ht.h"
22
#ifdef HAVE_EVENT2_DNS_H
23
#include <event2/event.h>
24
25
#include <event2/dns.h>
#else
26
#include <event.h>
27
#include "eventdns.h"
28
29
30
31
#ifndef HAVE_EVDNS_SET_DEFAULT_OUTGOING_BIND_ADDRESS
#define HAVE_EVDNS_SET_DEFAULT_OUTGOING_BIND_ADDRESS
#endif
#endif
32

33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
#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()
50
51
#define evdns_base_set_option_(base, opt, val) \
  evdns_set_option((opt),(val),DNS_OPTIONS_ALL)
52
53
54
55
56
57
#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))
58
59
60
61
62
63
64
65

#elif defined(LIBEVENT_VERSION_NUMBER) && LIBEVENT_VERSION_NUMBER < 0x02000303
#define evdns_base_set_option_(base, opt, val) \
  evdns_base_set_option((base), (opt),(val),DNS_OPTIONS_ALL)

#else
#define evdns_base_set_option_ evdns_base_set_option

66
67
#endif

Roger Dingledine's avatar
Roger Dingledine committed
68
/** Longest hostname we're willing to resolve. */
69
70
#define MAX_ADDRESSLEN 256

71
72
/** How long will we wait for an answer from the resolver before we decide
 * that the resolver is wedged? */
73
74
#define RESOLVE_MAX_TIMEOUT 300

Roger Dingledine's avatar
Roger Dingledine committed
75
/** Possible outcomes from hostname lookup: permanent failure,
76
 * transient (retryable) failure, and success. */
77
78
79
80
#define DNS_RESOLVE_FAILED_TRANSIENT 1
#define DNS_RESOLVE_FAILED_PERMANENT 2
#define DNS_RESOLVE_SUCCEEDED 3

81
82
83
/** Our evdns_base; this structure handles all our name lookups. */
static struct evdns_base *the_evdns_base = NULL;

84
85
/** Have we currently configured nameservers with eventdns? */
static int nameservers_configured = 0;
86
87
/** Did our most recent attempt to configure nameservers with eventdns fail? */
static int nameserver_config_failed = 0;
88
89
90
91
92
93
/** 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;
94

Roger Dingledine's avatar
Roger Dingledine committed
95
/** Linked list of connections waiting for a DNS answer. */
96
typedef struct pending_connection_t {
97
  edge_connection_t *conn;
98
  struct pending_connection_t *next;
99
} pending_connection_t;
100

101
102
/** Value of 'magic' field for cached_resolve_t.  Used to try to catch bad
 * pointers and memory stomping. */
103
104
#define CACHED_RESOLVE_MAGIC 0x1234F00D

105
106
107
108
109
110
111
/* 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. */
112
#define CACHE_STATE_PENDING 0
113
114
115
/** 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. */
116
#define CACHE_STATE_DONE 1
117
118
/** We are caching an answer for this address. This should have no pending
 * connections, and should appear in the hash table. */
119
#define CACHE_STATE_CACHED_VALID 2
120
121
/** We are caching a failure for this address. This should have no pending
 * connections, and should appear in the hash table */
122
123
#define CACHE_STATE_CACHED_FAILED 3

Roger Dingledine's avatar
Roger Dingledine committed
124
/** A DNS request: possibly completed, possibly pending; cached_resolve
125
 * structs are stored at the OR side in a hash table, and as a linked
126
127
 * list from oldest to newest.
 */
128
typedef struct cached_resolve_t {
129
  HT_ENTRY(cached_resolve_t) node;
130
  uint32_t magic;
131
  char address[MAX_ADDRESSLEN]; /**< The hostname to be resolved. */
132
  union {
133
134
135
136
    struct {
      struct in6_addr addr6; /**< IPv6 addr for <b>address</b>. */
      uint32_t addr;  /**< IPv4 addr for <b>address</b>. */
    } a;
137
138
    char *hostname; /**< Hostname for <b>address</b> (if a reverse lookup) */
  } result;
139
  uint8_t state; /**< Is this cached entry pending/done/valid/failed? */
140
  uint8_t is_reverse; /**< Is this a reverse (addr-to-hostname) lookup? */
141
  time_t expire; /**< Remove items from cache after this time. */
142
  uint32_t ttl; /**< What TTL did the nameserver tell us? */
143
  /** Connections that want to know when we get an answer for this resolve. */
144
  pending_connection_t *pending_connections;
145
146
  /** Position of this element in the heap*/
  int minheap_idx;
147
} cached_resolve_t;
148

149
static void purge_expired_resolves(time_t now);
150
static void dns_found_answer(const char *address, uint8_t is_reverse,
151
                             uint32_t addr, const char *hostname, char outcome,
152
                             uint32_t ttl);
153
154
static void send_resolved_cell(edge_connection_t *conn, uint8_t answer_type);
static int launch_resolve(edge_connection_t *exitconn);
155
static void add_wildcarded_test_address(const char *address);
156
static int configure_nameservers(int force);
157
static int answer_is_wildcarded(const char *ip);
158
159
static int dns_resolve_impl(edge_connection_t *exitconn, int is_resolve,
                            or_circuit_t *oncirc, char **resolved_to_hostname);
160
#ifdef DEBUG_DNS_CACHE
161
static void _assert_cache_ok(void);
162
163
#define assert_cache_ok() _assert_cache_ok()
#else
164
#define assert_cache_ok() STMT_NIL
165
#endif
166
static void assert_resolve_ok(cached_resolve_t *resolve);
167

168
169
/** Hash table of cached_resolve objects. */
static HT_HEAD(cache_map, cached_resolve_t) cache_root;
170

Roger Dingledine's avatar
Roger Dingledine committed
171
/** Function to compare hashed resolves on their addresses; used to
172
 * implement hash tables. */
173
174
static INLINE int
cached_resolves_eq(cached_resolve_t *a, cached_resolve_t *b)
175
{
176
  /* make this smarter one day? */
177
  assert_resolve_ok(a); // Not b; b may be just a search.
178
179
180
  return !strncmp(a->address, b->address, MAX_ADDRESSLEN);
}

181
/** Hash function for cached_resolve objects */
182
183
184
185
static INLINE unsigned int
cached_resolve_hash(cached_resolve_t *a)
{
  return ht_string_hash(a->address);
186
187
}

188
HT_PROTOTYPE(cache_map, cached_resolve_t, node, cached_resolve_hash,
189
             cached_resolves_eq)
190
HT_GENERATE(cache_map, cached_resolve_t, node, cached_resolve_hash,
191
            cached_resolves_eq, 0.6, malloc, realloc, free)
192

193
/** Initialize the DNS cache. */
194
static void
195
init_cache_map(void)
196
{
197
  HT_INIT(cache_map, &cache_root);
198
199
}

200
/** Helper: called by eventdns when eventdns wants to log something. */
201
static void
202
evdns_log_cb(int warn, const char *msg)
203
{
204
  const char *cp;
205
206
  static int all_down = 0;
  int severity = warn ? LOG_WARN : LOG_INFO;
207
208
209
210
  if (!strcmpstart(msg, "Resolve requested for") &&
      get_options()->SafeLogging) {
    log(LOG_INFO, LD_EXIT, "eventdns: Resolve requested.");
    return;
211
212
  } else if (!strcmpstart(msg, "Search: ")) {
    return;
213
  }
214
215
  if (!strcmpstart(msg, "Nameserver ") && (cp=strstr(msg, " has failed: "))) {
    char *ns = tor_strndup(msg+11, cp-(msg+11));
216
    const char *err = strchr(cp, ':')+2;
217
    tor_assert(err);
218
219
220
    /* 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. */
221
    severity = LOG_INFO;
222
    control_event_server_status(LOG_NOTICE,
223
224
225
226
227
228
                                "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));
229
    severity = (all_down && warn) ? LOG_NOTICE : LOG_INFO;
230
    all_down = 0;
231
232
233
234
235
    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");
236
    all_down = 1;
237
  }
238
  log(severity, LD_EXIT, "eventdns: %s", msg);
239
240
}

241
242
/** Helper: passed to eventdns.c as a callback so it can generate random
 * numbers for transaction IDs and 0x20-hack coding. */
243
static void
244
_dns_randfn(char *b, size_t n)
245
{
246
  crypto_rand(b,n);
247
248
}

Roger Dingledine's avatar
Roger Dingledine committed
249
/** Initialize the DNS subsystem; called by the OR process. */
250
int
251
252
dns_init(void)
{
253
  init_cache_map();
254
  evdns_set_random_bytes_fn(_dns_randfn);
255
256
257
258
  if (server_mode(get_options())) {
    int r = configure_nameservers(1);
    return r;
  }
259
  return 0;
260
}
261

262
263
264
/** Called when DNS-related options change (or may have changed).  Returns -1
 * on failure, 0 on success. */
int
265
266
267
268
dns_reset(void)
{
  or_options_t *options = get_options();
  if (! server_mode(options)) {
269
270
271
272
273
274
275
276

    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;
      }
    }

277
278
    evdns_base_clear_nameservers_and_suspend(the_evdns_base);
    evdns_base_search_clear(the_evdns_base);
279
280
281
282
    nameservers_configured = 0;
    tor_free(resolv_conf_fname);
    resolv_conf_mtime = 0;
  } else {
283
    if (configure_nameservers(0) < 0) {
284
      return -1;
285
    }
286
  }
287
  return 0;
288
289
}

Nick Mathewson's avatar
Nick Mathewson committed
290
291
/** Return true iff the most recent attempt to initialize the DNS subsystem
 * failed. */
292
293
294
295
296
297
int
has_dns_init_failed(void)
{
  return nameserver_config_failed;
}

298
299
/** Helper: Given a TTL from a DNS response, determine what TTL to give the
 * OP that asked us to resolve it. */
300
301
302
303
304
305
306
307
308
309
310
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;
}

311
312
/** Helper: Given a TTL from a DNS response, determine how long to hold it in
 * our cache. */
313
314
315
316
317
318
319
320
321
322
323
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;
}

324
/** Helper: free storage held by an entry in the DNS cache. */
325
static void
326
_free_cached_resolve(cached_resolve_t *r)
327
{
328
329
  if (!r)
    return;
Nick Mathewson's avatar
Nick Mathewson committed
330
  while (r->pending_connections) {
331
    pending_connection_t *victim = r->pending_connections;
332
333
334
    r->pending_connections = victim->next;
    tor_free(victim);
  }
335
336
  if (r->is_reverse)
    tor_free(r->result.hostname);
337
  r->magic = 0xFF00FF00;
338
339
340
  tor_free(r);
}

341
342
343
/** 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. */
344
static int
345
_compare_cached_resolves_by_expiry(const void *_a, const void *_b)
346
{
347
  const cached_resolve_t *a = _a, *b = _b;
348
349
350
351
352
353
  if (a->expire < b->expire)
    return -1;
  else if (a->expire == b->expire)
    return 0;
  else
    return 1;
354
355
}

356
357
/** Priority queue of cached_resolve_t objects to let us know when they
 * will expire. */
358
359
static smartlist_t *cached_resolve_pqueue = NULL;

360
361
/** Set an expiry time for a cached_resolve_t, and add it to the expiry
 * priority queue */
362
363
364
365
static void
set_expiry(cached_resolve_t *resolve, time_t expires)
{
  tor_assert(resolve && resolve->expire == 0);
366
367
  if (!cached_resolve_pqueue)
    cached_resolve_pqueue = smartlist_create();
368
369
370
  resolve->expire = expires;
  smartlist_pqueue_add(cached_resolve_pqueue,
                       _compare_cached_resolves_by_expiry,
371
                       STRUCT_OFFSET(cached_resolve_t, minheap_idx),
372
373
374
                       resolve);
}

375
/** Free all storage held in the DNS cache and related structures. */
376
377
378
void
dns_free_all(void)
{
379
  cached_resolve_t **ptr, **next, *item;
380
  assert_cache_ok();
381
382
383
  if (cached_resolve_pqueue) {
    SMARTLIST_FOREACH(cached_resolve_pqueue, cached_resolve_t *, res,
      {
384
        if (res->state == CACHE_STATE_DONE)
385
386
387
          _free_cached_resolve(res);
      });
  }
388
  for (ptr = HT_START(cache_map, &cache_root); ptr != NULL; ptr = next) {
389
    item = *ptr;
390
    next = HT_NEXT_RMV(cache_map, &cache_root, ptr);
391
    _free_cached_resolve(item);
392
  }
393
  HT_CLEAR(cache_map, &cache_root);
394
  smartlist_free(cached_resolve_pqueue);
395
  cached_resolve_pqueue = NULL;
396
  tor_free(resolv_conf_fname);
397
398
}

399
400
/** Remove every cached_resolve whose <b>expire</b> time is before or
 * equal to <b>now</b> from the cache. */
401
static void
402
purge_expired_resolves(time_t now)
403
{
Nick Mathewson's avatar
Nick Mathewson committed
404
  cached_resolve_t *resolve, *removed;
405
  pending_connection_t *pend;
406
  edge_connection_t *pendconn;
407

Nick Mathewson's avatar
Nick Mathewson committed
408
  assert_cache_ok();
409
410
411
412
413
414
415
416
  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,
417
418
                         _compare_cached_resolves_by_expiry,
                         STRUCT_OFFSET(cached_resolve_t, minheap_idx));
419

420
    if (resolve->state == CACHE_STATE_PENDING) {
421
      log_debug(LD_EXIT,
422
423
                "Expiring a dns resolve %s that's still pending. Forgot to "
                "cull it? DNS resolve didn't tell us about the timeout?",
424
425
426
427
428
429
430
431
432
433
434
                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);
435
    }
436

437
    if (resolve->pending_connections) {
438
      log_debug(LD_EXIT,
439
                "Closing pending connections on timed-out DNS resolve!");
440
      tor_fragile_assert();
441
442
443
444
      while (resolve->pending_connections) {
        pend = resolve->pending_connections;
        resolve->pending_connections = pend->next;
        /* Connections should only be pending if they have no socket. */
445
        tor_assert(pend->conn->_base.s == -1);
446
        pendconn = pend->conn;
447
        connection_edge_end(pendconn, END_STREAM_REASON_TIMEOUT);
448
        circuit_detach_stream(circuit_get_by_edge_conn(pendconn), pendconn);
449
        connection_free(TO_CONN(pendconn));
450
451
        tor_free(pend);
      }
452
    }
453

454
455
456
457
458
459
460
    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).",
461
                resolve->address, (void*)resolve,
462
                removed ? removed->address : "NULL", (void*)removed);
463
464
465
      }
      tor_assert(removed == resolve);
    } else {
466
      /* This should be in state DONE. Make sure it's not in the cache. */
467
468
      cached_resolve_t *tmp = HT_FIND(cache_map, &cache_root, resolve);
      tor_assert(tmp != resolve);
469
    }
470
471
472
473
    if (resolve->is_reverse)
      tor_free(resolve->result.hostname);
    resolve->magic = 0xF0BBF0BB;
    tor_free(resolve);
474
  }
475

Nick Mathewson's avatar
Nick Mathewson committed
476
  assert_cache_ok();
477
478
}

479
480
481
/** Send a response to the RESOLVE request of a connection.
 * <b>answer_type</b> must be one of
 * RESOLVED_TYPE_(IPV4|ERROR|ERROR_TRANSIENT).
482
483
 *
 * If <b>circ</b> is provided, and we have a cached answer, send the
484
485
 * answer back along circ; otherwise, send the answer back along
 * <b>conn</b>'s attached circuit.
486
 */
487
static void
488
send_resolved_cell(edge_connection_t *conn, uint8_t answer_type)
489
490
{
  char buf[RELAY_PAYLOAD_SIZE];
491
  size_t buflen;
492
  uint32_t ttl;
493
494

  buf[0] = answer_type;
495
  ttl = dns_clip_ttl(conn->address_ttl);
496
497
498
499
500

  switch (answer_type)
    {
    case RESOLVED_TYPE_IPV4:
      buf[1] = 4;
501
      set_uint32(buf+2, tor_addr_to_ipv4n(&conn->_base.addr));
502
      set_uint32(buf+6, htonl(ttl));
503
      buflen = 10;
504
      break;
505
    /*XXXX IP6 need ipv6 implementation */
506
507
    case RESOLVED_TYPE_ERROR_TRANSIENT:
    case RESOLVED_TYPE_ERROR:
508
509
      {
        const char *errmsg = "Error resolving hostname";
510
        size_t msglen = strlen(errmsg);
511

512
513
        buf[1] = msglen;
        strlcpy(buf+2, errmsg, sizeof(buf)-2);
514
        set_uint32(buf+2+msglen, htonl(ttl));
515
516
517
        buflen = 6+msglen;
        break;
      }
518
519
    default:
      tor_assert(0);
520
      return;
521
    }
522
  // log_notice(LD_EXIT, "Sending a regular RESOLVED reply: ");
Roger Dingledine's avatar
Roger Dingledine committed
523

524
  connection_edge_send_command(conn, RELAY_COMMAND_RESOLVED, buf, buflen);
525
526
}

527
528
529
/** 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.
530
531
532
 *
 * If <b>circ</b> is provided, and we have a cached answer, send the
 * answer back along circ; otherwise, send the answer back along
533
 * <b>conn</b>'s attached circuit.
534
535
 */
static void
536
send_resolved_hostname_cell(edge_connection_t *conn, const char *hostname)
537
538
539
540
541
{
  char buf[RELAY_PAYLOAD_SIZE];
  size_t buflen;
  uint32_t ttl;
  size_t namelen = strlen(hostname);
542
  tor_assert(hostname);
543
544
545
546
547
548
549
550
551
552

  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;

553
  // log_notice(LD_EXIT, "Sending a reply RESOLVED reply: %s", hostname);
554
  connection_edge_send_command(conn, RELAY_COMMAND_RESOLVED, buf, buflen);
555
  // log_notice(LD_EXIT, "Sent");
556
557
}

Nick Mathewson's avatar
Nick Mathewson committed
558
559
/** 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
560
 * If resolve failed, free exitconn and return -1.
561
 *
562
563
564
565
566
 * (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.)
 *
567
 * If we have a cached answer, send the answer back along <b>exitconn</b>'s
568
 * circuit.
569
 *
570
571
572
573
574
 * 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.
575
576
577
578
579
580
 *
 * 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.
581
 */
582
int
583
dns_resolve(edge_connection_t *exitconn)
584
585
586
587
588
589
{
  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;

590
591
  r = dns_resolve_impl(exitconn, is_resolve, oncirc, &hostname);

592
593
  switch (r) {
    case 1:
594
595
      /* We got an answer without a lookup -- either the answer was
       * cached, or it was obvious (like an IP address). */
596
      if (is_resolve) {
597
        /* Send the answer back right now, and detach. */
598
599
600
601
        if (hostname)
          send_resolved_hostname_cell(exitconn, hostname);
        else
          send_resolved_cell(exitconn, RESOLVED_TYPE_IPV4);
602
        exitconn->on_circuit = NULL;
603
      } else {
604
605
        /* Add to the n_streams list; the calling function will send back a
         * connected cell. */
606
607
608
609
610
        exitconn->next_stream = oncirc->n_streams;
        oncirc->n_streams = exitconn;
      }
      break;
    case 0:
611
612
      /* The request is pending: add the connection into the linked list of
       * resolving_streams on this circuit. */
613
614
615
616
617
618
      exitconn->_base.state = EXIT_CONN_STATE_RESOLVING;
      exitconn->next_stream = oncirc->resolving_streams;
      oncirc->resolving_streams = exitconn;
      break;
    case -2:
    case -1:
619
      /* The request failed before it could start: cancel this connection,
620
       * and stop everybody waiting for the same connection. */
621
622
623
624
      if (is_resolve) {
        send_resolved_cell(exitconn,
             (r == -1) ? RESOLVED_TYPE_ERROR : RESOLVED_TYPE_ERROR_TRANSIENT);
      }
625

626
      exitconn->on_circuit = NULL;
627
628
629

      dns_cancel_pending_resolve(exitconn->_base.address);

630
      if (!exitconn->_base.marked_for_close) {
631
        connection_free(TO_CONN(exitconn));
632
        // XXX ... and we just leak exitconn otherwise? -RD
633
634
635
        // 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
636
        // "<armadev> If that's true, there are other bugs around, where we
637
        //  don't check if it's marked, and will end up double-freeing."
638
639
        // On the other hand, I don't know of any actual bugs here, so this
        // shouldn't be holding up the rc. -RD
640
      }
641
642
643
644
645
646
647
648
649
650
651
652
653
654
      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
655
656
657
 * 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.
658
659
660
661
 */
static int
dns_resolve_impl(edge_connection_t *exitconn, int is_resolve,
                 or_circuit_t *oncirc, char **hostname_out)
662
{
663
664
665
  cached_resolve_t *resolve;
  cached_resolve_t search;
  pending_connection_t *pending_connection;
666
  routerinfo_t *me;
667
  tor_addr_t addr;
668
  time_t now = time(NULL);
669
670
  uint8_t is_reverse = 0;
  int r;
671
672
  assert_connection_ok(TO_CONN(exitconn), 0);
  tor_assert(exitconn->_base.s == -1);
673
  assert_cache_ok();
674
  tor_assert(oncirc);
675

676
  /* first check if exitconn->_base.address is an IP. If so, we already
677
   * know the answer. */
678
  if (tor_addr_from_str(&addr, exitconn->_base.address) >= 0) {
679
    if (tor_addr_family(&addr) == AF_INET) {
680
      tor_addr_copy(&exitconn->_base.addr, &addr);
681
682
683
684
685
686
      exitconn->address_ttl = DEFAULT_DNS_TTL;
      return 1;
    } else {
      /* XXXX IPv6 */
      return -1;
    }
687
  }
688

689
690
691
692
693
  /* 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;
  }
694
695
696
697
698
699
  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;
  }
700
701

  /* then take this opportunity to see if there are any expired
702
   * resolves in the hash table. */
703
  purge_expired_resolves(now);
704

705
706
  /* lower-case exitconn->_base.address, so it's in canonical form */
  tor_strlower(exitconn->_base.address);
707

708
709
  /* 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
710
   * connection.
711
   */
712
713
  if ((r = tor_addr_parse_reverse_lookup_name(&addr, exitconn->_base.address,
                                              AF_UNSPEC, 0)) != 0) {
714
    if (r == 1) {
715
      is_reverse = 1;
716
717
      if (tor_addr_is_internal(&addr, 0)) /* internal address? */
        return -1;
718
    }
719
720
721
722
723
724
725
726
727
728
729
730
731

    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;
    }
732
    //log_notice(LD_EXIT, "Looks like an address %s",
Roger Dingledine's avatar
Roger Dingledine committed
733
    //exitconn->_base.address);
734
735
  }

736
  /* now check the hash table to see if 'address' is already there. */
737
  strlcpy(search.address, exitconn->_base.address, sizeof(search.address));
738
  resolve = HT_FIND(cache_map, &cache_root, &search);
739
  if (resolve && resolve->expire > now) { /* already there */
740
    switch (resolve->state) {
741
742
      case CACHE_STATE_PENDING:
        /* add us to the pending list */
743
        pending_connection = tor_malloc_zero(
744
                                      sizeof(pending_connection_t));
745
        pending_connection->conn = exitconn;
Roger Dingledine's avatar
   
Roger Dingledine committed
746
747
        pending_connection->next = resolve->pending_connections;
        resolve->pending_connections = pending_connection;
748
        log_debug(LD_EXIT,"Connection (fd %d) waiting for pending DNS "
749
750
                  "resolve of %s", exitconn->_base.s,
                  escaped_safe_str(exitconn->_base.address));
Roger Dingledine's avatar
   
Roger Dingledine committed
751
        return 0;
752
      case CACHE_STATE_CACHED_VALID:
753
        log_debug(LD_EXIT,"Connection (fd %d) found cached answer for %s",
754
                  exitconn->_base.s,
755
756
757
758
                  escaped_safe_str(resolve->address));
        exitconn->address_ttl = resolve->ttl;
        if (resolve->is_reverse) {
          tor_assert(is_resolve);
759
          *hostname_out = tor_strdup(resolve->result.hostname);
760
        } else {
761
          tor_addr_from_ipv4h(&exitconn->_base.addr, resolve->result.a.addr);
762
        }
763
        return 1;
764
      case CACHE_STATE_CACHED_FAILED:
765
        log_debug(LD_EXIT,"Connection (fd %d) found cached error for %s",
766
767
                  exitconn->_base.s,
                  escaped_safe_str(exitconn->_base.address));
768
        return -1;
769
770
771
      case CACHE_STATE_DONE:
        log_err(LD_BUG, "Found a 'DONE' dns resolve still in the cache.");
        tor_fragile_assert();
772
    }
Roger Dingledine's avatar
Roger Dingledine committed
773
    tor_assert(0);
Roger Dingledine's avatar
Roger Dingledine committed
774
  }
775
  tor_assert(!resolve);
Roger Dingledine's avatar
Roger Dingledine committed
776
  /* not there, need to add it */
777
  resolve = tor_malloc_zero(sizeof(cached_resolve_t));
778
  resolve->magic = CACHED_RESOLVE_MAGIC;
Roger Dingledine's avatar
Roger Dingledine committed
779
  resolve->state = CACHE_STATE_PENDING;
780
  resolve->minheap_idx = -1;
781
  resolve->is_reverse = is_reverse;
782
  strlcpy(resolve->address, exitconn->_base.address, sizeof(resolve->address));
Roger Dingledine's avatar
Roger Dingledine committed
783

784
  /* add this connection to the pending list */
785
  pending_connection = tor_malloc_zero(sizeof(pending_connection_t));
Roger Dingledine's avatar
Roger Dingledine committed
786
787
788
  pending_connection->conn = exitconn;
  resolve->pending_connections = pending_connection;

789
  /* Add this resolve to the cache and priority queue. */
790
  HT_INSERT(cache_map, &cache_root, resolve);
791
  set_expiry(resolve, now + RESOLVE_MAX_TIMEOUT);
792

793
  log_debug(LD_EXIT,"Launching %s.",
794
            escaped_safe_str(exitconn->_base.address));
795
  assert_cache_ok();
796

797
  return launch_resolve(exitconn);
798
799
}

800
/** Log an error and abort if conn is waiting for a DNS resolve.
801
 */
802
void
803
assert_connection_edge_not_dns_pending(edge_connection_t *conn)
804
{
805
  pending_connection_t *pend;
806
  cached_resolve_t search;
807

808
809
810
811
812
813
814
815
816
817
818
#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;
819
  HT_FOREACH(resolve, cache_map, &cache_root) {
820
    for (pend = (*resolve)->pending_connections; pend; pend = pend->next) {
821
822
      tor_assert(pend->conn != conn);
    }
823
  }
824
#endif
825
}
826

827
828
829
830
831
832
833
/** 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;
834

835
836
837
838
  HT_FOREACH(resolve, cache_map, &cache_root) {
    for (pend = (*resolve)->pending_connections;
         pend;
         pend = pend->next) {
839
840
841
      assert_connection_ok(TO_CONN(pend->conn), 0);
      tor_assert(pend->conn->_base.s == -1);
      tor_assert(!connection_in_array(TO_CONN(pend->conn)));
842
    }
843
844
845
  }
}

Nick Mathewson's avatar
Nick Mathewson committed
846
/** Remove <b>conn</b> from the list of connections waiting for conn-\>address.
847
 */
848
void
849
connection_dns_remove(edge_connection_t *conn)
850
{
851
852
853
  pending_connection_t *pend, *victim;
  cached_resolve_t search;
  cached_resolve_t *resolve;
854

855
856
  tor_assert(conn->_base.type == CONN_TYPE_EXIT);
  tor_assert(conn->_base.state == EXIT_CONN_STATE_RESOLVING);
857

858
  strlcpy(search.address, conn->_base.address, sizeof(search.address));
859

860
  resolve = HT_FIND(cache_map, &cache_root, &search);
861
  if (!resolve) {
862
    log_notice(LD_BUG, "Address %s is not pending. Dropping.",
863
               escaped_safe_str(conn->_base.address));
864
865
866
    return;
  }

Roger Dingledine's avatar
Roger Dingledine committed
867
  tor_assert(resolve->pending_connections);
868
  assert_connection_ok(TO_CONN(conn),0);
869
870
871

  pend = resolve->pending_connections;

872
  if (pend->conn == conn) {
873
    resolve->pending_connections = pend->next;
874
    tor_free(pend);
875
    log_debug(LD_EXIT, "First connection (fd %d) no longer waiting "
876
              "for resolve of %s",
877
              conn->_base.s,