dns.c 67.4 KB
Newer Older
Roger Dingledine's avatar
Roger Dingledine committed
1
/* Copyright 2003-2004 Roger Dingledine.
Roger Dingledine's avatar
Roger Dingledine committed
2
 * Copyright 2004-2006 Roger Dingledine, Nick Mathewson. */
3
4
/* See LICENSE for licensing information */
/* $Id$ */
5
6
const char dns_c_id[] =
  "$Id$";
7

Roger Dingledine's avatar
Roger Dingledine committed
8
9
/**
 * \file dns.c
10
 * \brief Implements a local cache for DNS results for Tor servers.
11
 * We provide two asynchronous backend implementations:
12
13
14
15
16
17
 *   1) A farm of 'DNS worker' threads or processes to perform DNS lookups for
 *      onion routers and cache the results.
 *   2) A wrapper around Adam Langley's eventdns.c code, to send requests
 *      to the nameservers asynchronously.
 * (We can't just use gethostbyname() and friends because we really need to
 * be nonblocking.)
Roger Dingledine's avatar
Roger Dingledine committed
18
 **/
19

20
#include "or.h"
21
#include "../common/ht.h"
22
23
24
#ifdef USE_EVENTDNS
#include "eventdns.h"
#endif
25

Roger Dingledine's avatar
Roger Dingledine committed
26
/** Longest hostname we're willing to resolve. */
27
28
#define MAX_ADDRESSLEN 256

Roger Dingledine's avatar
Roger Dingledine committed
29
/** Maximum DNS processes to spawn. */
30
#define MAX_DNSWORKERS 100
Roger Dingledine's avatar
Roger Dingledine committed
31
/** Minimum DNS processes to spawn. */
32
#define MIN_DNSWORKERS 3
33

Roger Dingledine's avatar
Roger Dingledine committed
34
/** If more than this many processes are idle, shut down the extras. */
35
#define MAX_IDLE_DNSWORKERS 10
36

37
38
/** How long will we wait for an answer from the resolver before we decide
 * that the resolver is wedged? */
39
40
#define RESOLVE_MAX_TIMEOUT 300

Roger Dingledine's avatar
Roger Dingledine committed
41
/** Possible outcomes from hostname lookup: permanent failure,
42
 * transient (retryable) failure, and success. */
43
44
45
46
#define DNS_RESOLVE_FAILED_TRANSIENT 1
#define DNS_RESOLVE_FAILED_PERMANENT 2
#define DNS_RESOLVE_SUCCEEDED 3

47
#ifndef USE_EVENTDNS
48
/** How many dnsworkers we have running right now. */
49
static int num_dnsworkers=0;
50
/** How many of the running dnsworkers have an assigned task right now. */
51
52
53
static int num_dnsworkers_busy=0;
/** When did we last rotate the dnsworkers? */
static time_t last_rotation_time=0;
54
55
56
57
58
59
60
61
62
#else
/** 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;
63
#endif
64

Roger Dingledine's avatar
Roger Dingledine committed
65
/** Linked list of connections waiting for a DNS answer. */
66
typedef struct pending_connection_t {
67
  edge_connection_t *conn;
68
  struct pending_connection_t *next;
69
} pending_connection_t;
70

71
/** DOCDOC */
72
73
#define CACHED_RESOLVE_MAGIC 0x1234F00D

74
75
76
77
78
79
80
/* 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. */
81
#define CACHE_STATE_PENDING 0
82
83
84
/** 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. */
85
#define CACHE_STATE_DONE 1
86
87
/** We are caching an answer for this address. This should have no pending
 * connections, and should appear in the hash table. */
88
#define CACHE_STATE_CACHED_VALID 2
89
90
/** We are caching a failure for this address. This should have no pending
 * connections, and should appear in the hash table */
91
92
#define CACHE_STATE_CACHED_FAILED 3

Roger Dingledine's avatar
Roger Dingledine committed
93
/** A DNS request: possibly completed, possibly pending; cached_resolve
94
 * structs are stored at the OR side in a hash table, and as a linked
95
96
 * list from oldest to newest.
 */
97
typedef struct cached_resolve_t {
98
  HT_ENTRY(cached_resolve_t) node;
99
  uint32_t magic;
100
  char address[MAX_ADDRESSLEN]; /**< The hostname to be resolved. */
101
102
103
104
  union {
    uint32_t addr;  /**< IPv4 addr for <b>address</b>. */
    char *hostname; /**< Hostname for <b>address</b> (if a reverse lookup) */
  } result;
105
  uint8_t state; /**< Is this cached entry pending/done/valid/failed? */
106
  uint8_t is_reverse; /**< Is this a reverse (addr-to-hostname) lookup? */
107
  time_t expire; /**< Remove items from cache after this time. */
108
  uint32_t ttl; /**< What TTL did the nameserver tell us? */
109
  /** Connections that want to know when we get an answer for this resolve. */
110
111
  pending_connection_t *pending_connections;
} cached_resolve_t;
112

113
static void purge_expired_resolves(time_t now);
114
115
static void dns_found_answer(const char *address, int is_reverse,
                             uint32_t addr, const char *hostname, char outcome,
116
                             uint32_t ttl);
117
static void send_resolved_cell(edge_connection_t *conn, or_circuit_t *circ,
Roger Dingledine's avatar
Roger Dingledine committed
118
                               uint8_t answer_type);
119
static int launch_resolve(edge_connection_t *exitconn, or_circuit_t *circ);
120
#ifndef USE_EVENTDNS
121
static void dnsworkers_rotate(void);
122
static void dnsworker_main(void *data);
123
static int spawn_dnsworker(void);
124
static int spawn_enough_dnsworkers(void);
125
#else
126
static void add_wildcarded_test_address(const char *address);
127
static int configure_nameservers(int force);
128
static int answer_is_wildcarded(const char *ip);
129
#endif
130
#ifdef DEBUG_DNS_CACHE
131
static void _assert_cache_ok(void);
132
133
#define assert_cache_ok() _assert_cache_ok()
#else
134
#define assert_cache_ok() do {} while (0)
135
#endif
136
static void assert_resolve_ok(cached_resolve_t *resolve);
137

138
139
/** Hash table of cached_resolve objects. */
static HT_HEAD(cache_map, cached_resolve_t) cache_root;
140

Roger Dingledine's avatar
Roger Dingledine committed
141
/** Function to compare hashed resolves on their addresses; used to
142
 * implement hash tables. */
143
144
static INLINE int
cached_resolves_eq(cached_resolve_t *a, cached_resolve_t *b)
145
{
146
  /* make this smarter one day? */
147
  assert_resolve_ok(a); // Not b; b may be just a search.
148
149
150
  return !strncmp(a->address, b->address, MAX_ADDRESSLEN);
}

151
/** Hash function for cached_resolve objects */
152
153
154
155
static INLINE unsigned int
cached_resolve_hash(cached_resolve_t *a)
{
  return ht_string_hash(a->address);
156
157
}

158
HT_PROTOTYPE(cache_map, cached_resolve_t, node, cached_resolve_hash,
159
             cached_resolves_eq);
160
HT_GENERATE(cache_map, cached_resolve_t, node, cached_resolve_hash,
161
            cached_resolves_eq, 0.6, malloc, realloc, free);
162

163
/** Initialize the DNS cache. */
164
static void
165
init_cache_map(void)
166
{
167
  HT_INIT(cache_map, &cache_root);
168
169
}

170
#ifdef USE_EVENTDNS
171
/** Helper: called by eventdns when eventdns wants to log something. */
172
static void
173
evdns_log_cb(int warn, const char *msg)
174
{
175
  const char *cp;
176
177
  static int all_down = 0;
  int severity = warn ? LOG_WARN : LOG_INFO;
178
179
180
181
  if (!strcmpstart(msg, "Resolve requested for") &&
      get_options()->SafeLogging) {
    log(LOG_INFO, LD_EXIT, "eventdns: Resolve requested.");
    return;
182
183
  } else if (!strcmpstart(msg, "Search: ")) {
    return;
184
  }
185
186
187
  if (!strcmpstart(msg, "Nameserver ") && (cp=strstr(msg, " has failed: "))) {
    char *ns = tor_strndup(msg+11, cp-(msg+11));
    const char *err = strchr(cp, ':'+2);
188
189
190
    /* 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. */
191
    severity = LOG_INFO;
192
    control_event_server_status(LOG_NOTICE,
193
194
195
196
197
198
                                "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));
199
    severity = (all_down && warn) ? LOG_NOTICE : LOG_INFO;
200
    all_down = 0;
201
202
203
204
205
    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");
206
    all_down = 1;
207
  }
208
  log(severity, LD_EXIT, "eventdns: %s", msg);
209
210
211
}
#endif

Roger Dingledine's avatar
Roger Dingledine committed
212
/** Initialize the DNS subsystem; called by the OR process. */
213
int
214
215
dns_init(void)
{
216
  init_cache_map();
217
#ifdef USE_EVENTDNS
218
  if (server_mode(get_options()))
219
220
221
    return configure_nameservers(1);
#else
  dnsworkers_rotate();
222
#endif
223
  return 0;
224
}
225

226
227
228
/** Called when DNS-related options change (or may have changed).  Returns -1
 * on failure, 0 on success. */
int
229
230
231
232
233
dns_reset(void)
{
#ifdef USE_EVENTDNS
  or_options_t *options = get_options();
  if (! server_mode(options)) {
234
235
    evdns_clear_nameservers_and_suspend();
    evdns_search_clear();
236
237
238
239
240
    nameservers_configured = 0;
    tor_free(resolv_conf_fname);
    resolv_conf_mtime = 0;
  } else {
    if (configure_nameservers(0) < 0)
241
      return -1;
242
243
244
245
246
247
  }
#else
  dnsworkers_rotate();
#endif
}

248
249
/** Helper: Given a TTL from a DNS response, determine what TTL to give the
 * OP that asked us to resolve it. */
250
251
252
253
254
255
256
257
258
259
260
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;
}

261
262
/** Helper: Given a TTL from a DNS response, determine how long to hold it in
 * our cache. */
263
264
265
266
267
268
269
270
271
272
273
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;
}

274
/** Helper: free storage held by an entry in the DNS cache. */
275
static void
276
_free_cached_resolve(cached_resolve_t *r)
277
{
Nick Mathewson's avatar
Nick Mathewson committed
278
  while (r->pending_connections) {
279
    pending_connection_t *victim = r->pending_connections;
280
281
282
    r->pending_connections = victim->next;
    tor_free(victim);
  }
283
284
  if (r->is_reverse)
    tor_free(r->result.hostname);
285
  r->magic = 0xFF00FF00;
286
287
288
  tor_free(r);
}

289
290
291
/** 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. */
292
static int
293
_compare_cached_resolves_by_expiry(const void *_a, const void *_b)
294
{
295
  const cached_resolve_t *a = _a, *b = _b;
296
  return a->expire - b->expire;
297
298
}

299
300
/** Priority queue of cached_resolve_t objects to let us know when they
 * will expire. */
301
302
static smartlist_t *cached_resolve_pqueue = NULL;

303
304
/** Set an expiry time for a cached_resolve_t, and add it to the expiry
 * priority queue */
305
306
307
308
static void
set_expiry(cached_resolve_t *resolve, time_t expires)
{
  tor_assert(resolve && resolve->expire == 0);
309
310
  if (!cached_resolve_pqueue)
    cached_resolve_pqueue = smartlist_create();
311
312
313
314
315
316
  resolve->expire = expires;
  smartlist_pqueue_add(cached_resolve_pqueue,
                       _compare_cached_resolves_by_expiry,
                       resolve);
}

317
/** Free all storage held in the DNS cache and related structures. */
318
319
320
void
dns_free_all(void)
{
321
  cached_resolve_t **ptr, **next, *item;
322
323
324
  if (cached_resolve_pqueue) {
    SMARTLIST_FOREACH(cached_resolve_pqueue, cached_resolve_t *, res,
      {
Roger Dingledine's avatar
Roger Dingledine committed
325
        /* XXXX012 The hash lookups here could be quite slow; remove them
326
327
         * once we're happy. (Leave them in for at least 0.1.2.7-alpha, so they
         * get some testing.) -NM */
328
        if (res->state == CACHE_STATE_DONE) {
329
330
          cached_resolve_t *found = HT_FIND(cache_map, &cache_root, res);
          tor_assert(!found || found != res);
331
332
333
334
335
336
337
          _free_cached_resolve(res);
        } else {
          cached_resolve_t *found = HT_FIND(cache_map, &cache_root, res);
          tor_assert(found);
        }
      });
  }
338
  for (ptr = HT_START(cache_map, &cache_root); ptr != NULL; ptr = next) {
339
    item = *ptr;
340
    next = HT_NEXT_RMV(cache_map, &cache_root, ptr);
341
    _free_cached_resolve(item);
342
  }
343
  HT_CLEAR(cache_map, &cache_root);
344
345
  if (cached_resolve_pqueue)
    smartlist_free(cached_resolve_pqueue);
346
  cached_resolve_pqueue = NULL;
347
348
349
#ifdef USE_EVENTDNS
  tor_free(resolv_conf_fname);
#endif
350
351
}

Nick Mathewson's avatar
Nick Mathewson committed
352
/** Remove every cached_resolve whose <b>expire</b> time is before <b>now</b>
353
 * from the cache. */
354
static void
355
purge_expired_resolves(time_t now)
356
{
Nick Mathewson's avatar
Nick Mathewson committed
357
  cached_resolve_t *resolve, *removed;
358
  pending_connection_t *pend;
359
  edge_connection_t *pendconn;
360

Nick Mathewson's avatar
Nick Mathewson committed
361
  assert_cache_ok();
362
363
364
365
366
367
368
369
370
371
  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);

372
    if (resolve->state == CACHE_STATE_PENDING) {
373
      log_debug(LD_EXIT,
374
375
                "Expiring a dns resolve %s that's still pending. Forgot to "
                "cull it? DNS resolve didn't tell us about the timeout?",
376
377
378
379
380
381
382
383
384
385
386
                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);
387
    }
388

389
    if (resolve->pending_connections) {
390
      log_debug(LD_EXIT,
391
                "Closing pending connections on timed-out DNS resolve!");
392
      tor_fragile_assert();
393
394
395
396
      while (resolve->pending_connections) {
        pend = resolve->pending_connections;
        resolve->pending_connections = pend->next;
        /* Connections should only be pending if they have no socket. */
397
        tor_assert(pend->conn->_base.s == -1);
398
        pendconn = pend->conn;
399
        connection_edge_end(pendconn, END_STREAM_REASON_TIMEOUT,
400
                            pendconn->cpath_layer);
401
        circuit_detach_stream(circuit_get_by_edge_conn(pendconn), pendconn);
402
        connection_free(TO_CONN(pendconn));
403
404
        tor_free(pend);
      }
405
    }
406

407
408
409
410
411
412
413
    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).",
414
415
                resolve->address, (void*)resolve,
                removed ? removed->address : "NULL", (void*)remove);
416
417
      }
      tor_assert(removed == resolve);
418
419
      if (resolve->is_reverse)
        tor_free(resolve->result.hostname);
420
421
422
      resolve->magic = 0xF0BBF0BB;
      tor_free(resolve);
    } else {
423
      /* This should be in state DONE. Make sure it's not in the cache. */
424
425
      cached_resolve_t *tmp = HT_FIND(cache_map, &cache_root, resolve);
      tor_assert(tmp != resolve);
426
    }
427
  }
428

Nick Mathewson's avatar
Nick Mathewson committed
429
  assert_cache_ok();
430
431
}

432
433
434
/** Send a response to the RESOLVE request of a connection.
 * <b>answer_type</b> must be one of
 * RESOLVED_TYPE_(IPV4|ERROR|ERROR_TRANSIENT).
435
436
 *
 * If <b>circ</b> is provided, and we have a cached answer, send the
437
438
 * answer back along circ; otherwise, send the answer back along
 * <b>conn</b>'s attached circuit.
439
 */
440
static void
441
send_resolved_cell(edge_connection_t *conn, or_circuit_t *circ,
Roger Dingledine's avatar
Roger Dingledine committed
442
                   uint8_t answer_type)
443
444
{
  char buf[RELAY_PAYLOAD_SIZE];
445
  size_t buflen;
446
  uint32_t ttl;
447
448

  buf[0] = answer_type;
449
  ttl = dns_clip_ttl(conn->address_ttl);
450
451
452
453
454

  switch (answer_type)
    {
    case RESOLVED_TYPE_IPV4:
      buf[1] = 4;
455
      set_uint32(buf+2, htonl(conn->_base.addr));
456
      set_uint32(buf+6, htonl(ttl));
457
      buflen = 10;
458
459
460
      break;
    case RESOLVED_TYPE_ERROR_TRANSIENT:
    case RESOLVED_TYPE_ERROR:
461
462
463
      {
        const char *errmsg = "Error resolving hostname";
        int msglen = strlen(errmsg);
464

465
466
        buf[1] = msglen;
        strlcpy(buf+2, errmsg, sizeof(buf)-2);
467
        set_uint32(buf+2+msglen, htonl(ttl));
468
469
470
        buflen = 6+msglen;
        break;
      }
471
472
    default:
      tor_assert(0);
473
      return;
474
    }
475
  // log_notice(LD_EXIT, "Sending a regular RESOLVED reply: ");
Roger Dingledine's avatar
Roger Dingledine committed
476

477
478
479
480
481
482
483
  if (!circ) {
    circuit_t *tmp = circuit_get_by_edge_conn(conn);
    if (! CIRCUIT_IS_ORIGIN(tmp))
      circ = TO_OR_CIRCUIT(tmp);
  }

  connection_edge_send_command(conn, TO_CIRCUIT(circ),
484
485
486
487
                               RELAY_COMMAND_RESOLVED, buf, buflen,
                               conn->cpath_layer);
}

488
489
490
/** 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.
491
492
493
 *
 * If <b>circ</b> is provided, and we have a cached answer, send the
 * answer back along circ; otherwise, send the answer back along
494
 * <b>conn</b>'s attached circuit.
495
496
 */
static void
497
send_resolved_hostname_cell(edge_connection_t *conn, or_circuit_t *circ,
Roger Dingledine's avatar
Roger Dingledine committed
498
                            const char *hostname)
499
500
501
502
503
{
  char buf[RELAY_PAYLOAD_SIZE];
  size_t buflen;
  uint32_t ttl;
  size_t namelen = strlen(hostname);
504
  tor_assert(hostname);
505
506
507
508
509
510
511
512
513
514

  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;

515
516
517
518
519
520
  if (!circ) {
    circuit_t *tmp = circuit_get_by_edge_conn(conn);
    if (! CIRCUIT_IS_ORIGIN(tmp))
      circ = TO_OR_CIRCUIT(tmp);
  }

521
  // log_notice(LD_EXIT, "Sending a reply RESOLVED reply: %s", hostname);
522
  connection_edge_send_command(conn, TO_CIRCUIT(circ),
523
524
                               RELAY_COMMAND_RESOLVED, buf, buflen,
                               conn->cpath_layer);
525
  // log_notice(LD_EXIT, "Sent");
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
}

/** 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. */

550
  memcpy(buf, address, len);
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
  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
570
571
/** 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.
572
 * If resolve failed, unlink exitconn if needed, free it, and return -1.
573
 *
574
575
 * If <b>oncirc</b> is provided, and this is a resolve request, we have
 * a cached answer, send the answer back along oncirc; otherwise, send
576
577
 * the answer back along <b>exitconn</b>'s attached circuit.
 *
578
579
580
581
582
583
 * 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.
 */
584
int
585
dns_resolve(edge_connection_t *exitconn, or_circuit_t *oncirc)
586
{
587
588
589
  cached_resolve_t *resolve;
  cached_resolve_t search;
  pending_connection_t *pending_connection;
590
  circuit_t *circ;
591
  struct in_addr in;
592
  time_t now = time(NULL);
593
  int is_reverse = 0, is_resolve, r;
594
595
  assert_connection_ok(TO_CONN(exitconn), 0);
  tor_assert(exitconn->_base.s == -1);
596

597
598
  assert_cache_ok();

599
  is_resolve = exitconn->_base.purpose == EXIT_PURPOSE_RESOLVE;
600

601
  /* first check if exitconn->_base.address is an IP. If so, we already
602
   * know the answer. */
603
604
  if (tor_inet_aton(exitconn->_base.address, &in) != 0) {
    exitconn->_base.addr = ntohl(in.s_addr);
605
    exitconn->address_ttl = DEFAULT_DNS_TTL;
606
    if (is_resolve)
607
      send_resolved_cell(exitconn, oncirc, RESOLVED_TYPE_IPV4);
608
    return 1;
609
  }
610
611
612
613
614
615
616
617
618
619
620
621
622
623
  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));
    if (is_resolve)
      send_resolved_cell(exitconn, oncirc, RESOLVED_TYPE_ERROR);
    /* XXXX012 send error in connect case? -NM */
    circ = circuit_get_by_edge_conn(exitconn);
    if (circ)
      circuit_detach_stream(circ, exitconn);
    if (!exitconn->_base.marked_for_close)
      connection_free(TO_CONN(exitconn));
    return -1;
  }
624
625

  /* then take this opportunity to see if there are any expired
626
   * resolves in the hash table. */
627
  purge_expired_resolves(now);
628

629
630
  /* lower-case exitconn->_base.address, so it's in canonical form */
  tor_strlower(exitconn->_base.address);
631

632
633
  /* 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
634
   * connection.
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
   */
  if ((r = parse_inaddr_arpa_address(exitconn->_base.address, NULL)) != 0) {
    if (r == 1)
      is_reverse = 1;

#ifdef USE_EVENTDNS
    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));
#else
    if (1) {
      log_info(LD_PROTOCOL, "Dnsworker code does not support in-addr.arpa "
               "domain, but received a request for \"%s\"; sending error.",
               escaped_safe_str(exitconn->_base.address));
#endif

      if (exitconn->_base.purpose == EXIT_PURPOSE_RESOLVE)
658
        send_resolved_cell(exitconn, oncirc, RESOLVED_TYPE_ERROR);
659
660
661
662
663
664
665
      circ = circuit_get_by_edge_conn(exitconn);
      if (circ)
        circuit_detach_stream(circ, exitconn);
      if (!exitconn->_base.marked_for_close)
        connection_free(TO_CONN(exitconn));
      return -1;
    }
666
    //log_notice(LD_EXIT, "Looks like an address %s",
Roger Dingledine's avatar
Roger Dingledine committed
667
    //exitconn->_base.address);
668
669
  }

670
  /* now check the hash table to see if 'address' is already there. */
671
  strlcpy(search.address, exitconn->_base.address, sizeof(search.address));
672
  resolve = HT_FIND(cache_map, &cache_root, &search);
673
  if (resolve && resolve->expire > now) { /* already there */
674
    switch (resolve->state) {
675
676
      case CACHE_STATE_PENDING:
        /* add us to the pending list */
677
        pending_connection = tor_malloc_zero(
678
                                      sizeof(pending_connection_t));
679
        pending_connection->conn = exitconn;
Roger Dingledine's avatar
   
Roger Dingledine committed
680
681
        pending_connection->next = resolve->pending_connections;
        resolve->pending_connections = pending_connection;
682
        log_debug(LD_EXIT,"Connection (fd %d) waiting for pending DNS "
683
684
                  "resolve of %s", exitconn->_base.s,
                  escaped_safe_str(exitconn->_base.address));
685
        exitconn->_base.state = EXIT_CONN_STATE_RESOLVING;
Roger Dingledine's avatar
   
Roger Dingledine committed
686
        return 0;
687
      case CACHE_STATE_CACHED_VALID:
688
        log_debug(LD_EXIT,"Connection (fd %d) found cached answer for %s",
689
                  exitconn->_base.s,
690
691
692
693
                  escaped_safe_str(resolve->address));
        exitconn->address_ttl = resolve->ttl;
        if (resolve->is_reverse) {
          tor_assert(is_resolve);
694
          send_resolved_hostname_cell(exitconn, oncirc,
Roger Dingledine's avatar
Roger Dingledine committed
695
                                      resolve->result.hostname);
696
697
698
        } else {
          exitconn->_base.addr = resolve->result.addr;
          if (is_resolve)
699
            send_resolved_cell(exitconn, oncirc, RESOLVED_TYPE_IPV4);
700
        }
701
        return 1;
702
      case CACHE_STATE_CACHED_FAILED:
703
        log_debug(LD_EXIT,"Connection (fd %d) found cached error for %s",
704
705
                  exitconn->_base.s,
                  escaped_safe_str(exitconn->_base.address));
706
        /*  XXXX012 send back indication of failure for connect case? -NM*/
707
        if (is_resolve)
708
          send_resolved_cell(exitconn, oncirc, RESOLVED_TYPE_ERROR);
709
        circ = circuit_get_by_edge_conn(exitconn);
710
711
        if (circ)
          circuit_detach_stream(circ, exitconn);
712
713
        if (!exitconn->_base.marked_for_close)
          connection_free(TO_CONN(exitconn));
714
        return -1;
715
716
717
      case CACHE_STATE_DONE:
        log_err(LD_BUG, "Found a 'DONE' dns resolve still in the cache.");
        tor_fragile_assert();
718
    }
Roger Dingledine's avatar
Roger Dingledine committed
719
    tor_assert(0);
Roger Dingledine's avatar
Roger Dingledine committed
720
721
  }
  /* not there, need to add it */
722
  resolve = tor_malloc_zero(sizeof(cached_resolve_t));
723
  resolve->magic = CACHED_RESOLVE_MAGIC;
Roger Dingledine's avatar
Roger Dingledine committed
724
  resolve->state = CACHE_STATE_PENDING;
725
  resolve->is_reverse = is_reverse;
726
  strlcpy(resolve->address, exitconn->_base.address, sizeof(resolve->address));
Roger Dingledine's avatar
Roger Dingledine committed
727

728
  /* add this connection to the pending list */
729
  pending_connection = tor_malloc_zero(sizeof(pending_connection_t));
Roger Dingledine's avatar
Roger Dingledine committed
730
731
  pending_connection->conn = exitconn;
  resolve->pending_connections = pending_connection;
732
  exitconn->_base.state = EXIT_CONN_STATE_RESOLVING;
Roger Dingledine's avatar
Roger Dingledine committed
733

734
  /* Add this resolve to the cache and priority queue. */
735
  HT_INSERT(cache_map, &cache_root, resolve);
736
  set_expiry(resolve, now + RESOLVE_MAX_TIMEOUT);
737

738
  log_debug(LD_EXIT,"Launching %s.",
739
            escaped_safe_str(exitconn->_base.address));
740
  assert_cache_ok();
741
  return launch_resolve(exitconn, oncirc);
742
743
}

744
/** Log an error and abort if conn is waiting for a DNS resolve.
745
 */
746
void
747
assert_connection_edge_not_dns_pending(edge_connection_t *conn)
748
{
749
750
  pending_connection_t *pend;
  cached_resolve_t **resolve;
751

752
753
754
755
756
757
  HT_FOREACH(resolve, cache_map, &cache_root) {
    for (pend = (*resolve)->pending_connections;
         pend;
         pend = pend->next) {
      tor_assert(pend->conn != conn);
    }
758
  }
759
}
760

761
762
763
764
765
766
767
/** 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;
768

769
770
771
772
  HT_FOREACH(resolve, cache_map, &cache_root) {
    for (pend = (*resolve)->pending_connections;
         pend;
         pend = pend->next) {
773
774
775
      assert_connection_ok(TO_CONN(pend->conn), 0);
      tor_assert(pend->conn->_base.s == -1);
      tor_assert(!connection_in_array(TO_CONN(pend->conn)));
776
    }
777
778
779
  }
}

Nick Mathewson's avatar
Nick Mathewson committed
780
/** Remove <b>conn</b> from the list of connections waiting for conn-\>address.
781
 */
782
void
783
connection_dns_remove(edge_connection_t *conn)
784
{
785
786
787
  pending_connection_t *pend, *victim;
  cached_resolve_t search;
  cached_resolve_t *resolve;
788

789
790
  tor_assert(conn->_base.type == CONN_TYPE_EXIT);
  tor_assert(conn->_base.state == EXIT_CONN_STATE_RESOLVING);
791

792
  strlcpy(search.address, conn->_base.address, sizeof(search.address));
793

794
  resolve = HT_FIND(cache_map, &cache_root, &search);
795
  if (!resolve) {
796
    log_notice(LD_BUG, "Address %s is not pending. Dropping.",
797
               escaped_safe_str(conn->_base.address));
798
799
800
    return;
  }

Roger Dingledine's avatar
Roger Dingledine committed
801
  tor_assert(resolve->pending_connections);
802
  assert_connection_ok(TO_CONN(conn),0);
803
804
805

  pend = resolve->pending_connections;

806
  if (pend->conn == conn) {
807
    resolve->pending_connections = pend->next;
808
    tor_free(pend);
809
    log_debug(LD_EXIT, "First connection (fd %d) no longer waiting "
810
              "for resolve of %s",
811
              conn->_base.s, escaped_safe_str(conn->_base.address));
812
813
    return;
  } else {
814
815
    for ( ; pend->next; pend = pend->next) {
      if (pend->next->conn == conn) {
816
817
        victim = pend->next;
        pend->next = victim->next;
818
        tor_free(victim);
819
        log_debug(LD_EXIT,
820
                  "Connection (fd %d) no longer waiting for resolve of %s",
821
                  conn->_base.s, escaped_safe_str(conn->_base.address));
822
823
824
        return; /* more are pending */
      }
    }
Roger Dingledine's avatar
Roger Dingledine committed
825
    tor_assert(0); /* not reachable unless onlyconn not in pending list */
826
827
828
  }
}

Nick Mathewson's avatar
Nick Mathewson committed
829
830
831
/** 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.
832
 */
833
void
834
dns_cancel_pending_resolve(const char *address)
835
{
836
837
  pending_connection_t *pend;
  cached_resolve_t search;
838
  cached_resolve_t *resolve, *tmp;
839
  edge_connection_t *pendconn;
840
  circuit_t *circ;
841

Nick Mathewson's avatar
Nick Mathewson committed
842
  strlcpy(search.address, address, sizeof(search.address));
843

844
  resolve = HT_FIND(cache_map, &cache_root, &search);
845
  if (!resolve || resolve->state != CACHE_STATE_PENDING) {
846
847
    log_notice(LD_BUG,"Address %s is not pending. Dropping.",
               escaped_safe_str(address));
848
849
850
    return;
  }

851
852
  if (!resolve->pending_connections) {
    /* XXX this should never trigger, but sometimes it does */
853
    log_warn(LD_BUG,
854
855
             "Bug: Address %s is pending but has no pending connections!",
             escaped_safe_str(address));
856
    tor_fragile_assert();
857
858
    return;
  }
Roger Dingledine's avatar
Roger Dingledine committed
859
  tor_assert(resolve->pending_connections);
860

861
  /* mark all pending connections to fail */
862
  log_debug(LD_EXIT,
863
864
             "Failing all connections waiting on DNS resolve of %s",
             escaped_safe_str(address));
865
  while (resolve->pending_connections) {
866
    pend = resolve->pending_connections;
867
    pend->conn->_base.state = EXIT_CONN_STATE_RESOLVEFAILED;
868
    pendconn = pend->conn;
869
870
871
    assert_connection_ok(TO_CONN(pendconn), 0);
    tor_assert(pendconn->_base.s == -1);
    if (!pendconn->_base.marked_for_close) {
872
873
      connection_edge_end(pendconn, END_STREAM_REASON_RESOURCELIMIT,
                          pendconn->cpath_layer);
874
    }
875
    circ = circuit_get_by_edge_conn(pendconn);
Roger Dingledine's avatar