dns.c 53 KB
Newer Older
Roger Dingledine's avatar
Roger Dingledine committed
1
/* Copyright 2003-2004 Roger Dingledine.
2
 * Copyright 2004-2007 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
 * This is implemetned as a wrapper around Adam Langley's eventdns.c code.
12
13
 * (We can't just use gethostbyname() and friends because we really need to
 * be nonblocking.)
Roger Dingledine's avatar
Roger Dingledine committed
14
 **/
15

16
#include "or.h"
17
#include "../common/ht.h"
18
#include "eventdns.h"
19

Roger Dingledine's avatar
Roger Dingledine committed
20
/** Longest hostname we're willing to resolve. */
21
22
#define MAX_ADDRESSLEN 256

23
24
/** How long will we wait for an answer from the resolver before we decide
 * that the resolver is wedged? */
25
26
#define RESOLVE_MAX_TIMEOUT 300

Roger Dingledine's avatar
Roger Dingledine committed
27
/** Possible outcomes from hostname lookup: permanent failure,
28
 * transient (retryable) failure, and success. */
29
30
31
32
#define DNS_RESOLVE_FAILED_TRANSIENT 1
#define DNS_RESOLVE_FAILED_PERMANENT 2
#define DNS_RESOLVE_SUCCEEDED 3

33
34
35
36
37
38
39
40
/** 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;
41

Roger Dingledine's avatar
Roger Dingledine committed
42
/** Linked list of connections waiting for a DNS answer. */
43
typedef struct pending_connection_t {
44
  edge_connection_t *conn;
45
  struct pending_connection_t *next;
46
} pending_connection_t;
47

48
49
/** Value of 'magic' field for cached_resolve_t.  Used to try to catch bad
 * pointers and memory stomping. */
50
51
#define CACHED_RESOLVE_MAGIC 0x1234F00D

52
53
54
55
56
57
58
/* 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. */
59
#define CACHE_STATE_PENDING 0
60
61
62
/** 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. */
63
#define CACHE_STATE_DONE 1
64
65
/** We are caching an answer for this address. This should have no pending
 * connections, and should appear in the hash table. */
66
#define CACHE_STATE_CACHED_VALID 2
67
68
/** We are caching a failure for this address. This should have no pending
 * connections, and should appear in the hash table */
69
70
#define CACHE_STATE_CACHED_FAILED 3

Roger Dingledine's avatar
Roger Dingledine committed
71
/** A DNS request: possibly completed, possibly pending; cached_resolve
72
 * structs are stored at the OR side in a hash table, and as a linked
73
74
 * list from oldest to newest.
 */
75
typedef struct cached_resolve_t {
76
  HT_ENTRY(cached_resolve_t) node;
77
  uint32_t magic;
78
  char address[MAX_ADDRESSLEN]; /**< The hostname to be resolved. */
79
80
81
82
  union {
    uint32_t addr;  /**< IPv4 addr for <b>address</b>. */
    char *hostname; /**< Hostname for <b>address</b> (if a reverse lookup) */
  } result;
83
  uint8_t state; /**< Is this cached entry pending/done/valid/failed? */
84
  uint8_t is_reverse; /**< Is this a reverse (addr-to-hostname) lookup? */
85
  time_t expire; /**< Remove items from cache after this time. */
86
  uint32_t ttl; /**< What TTL did the nameserver tell us? */
87
  /** Connections that want to know when we get an answer for this resolve. */
88
89
  pending_connection_t *pending_connections;
} cached_resolve_t;
90

91
static void purge_expired_resolves(time_t now);
92
93
static void dns_found_answer(const char *address, int is_reverse,
                             uint32_t addr, const char *hostname, char outcome,
94
                             uint32_t ttl);
95
static void send_resolved_cell(edge_connection_t *conn, or_circuit_t *circ,
Roger Dingledine's avatar
Roger Dingledine committed
96
                               uint8_t answer_type);
97
static int launch_resolve(edge_connection_t *exitconn, or_circuit_t *circ);
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
#ifdef DEBUG_DNS_CACHE
102
static void _assert_cache_ok(void);
103
104
#define assert_cache_ok() _assert_cache_ok()
#else
105
#define assert_cache_ok() do {} while (0)
106
#endif
107
static void assert_resolve_ok(cached_resolve_t *resolve);
108

109
110
/** Hash table of cached_resolve objects. */
static HT_HEAD(cache_map, cached_resolve_t) cache_root;
111

Roger Dingledine's avatar
Roger Dingledine committed
112
/** Function to compare hashed resolves on their addresses; used to
113
 * implement hash tables. */
114
115
static INLINE int
cached_resolves_eq(cached_resolve_t *a, cached_resolve_t *b)
116
{
117
  /* make this smarter one day? */
118
  assert_resolve_ok(a); // Not b; b may be just a search.
119
120
121
  return !strncmp(a->address, b->address, MAX_ADDRESSLEN);
}

122
/** Hash function for cached_resolve objects */
123
124
125
126
static INLINE unsigned int
cached_resolve_hash(cached_resolve_t *a)
{
  return ht_string_hash(a->address);
127
128
}

129
HT_PROTOTYPE(cache_map, cached_resolve_t, node, cached_resolve_hash,
130
             cached_resolves_eq);
131
HT_GENERATE(cache_map, cached_resolve_t, node, cached_resolve_hash,
132
            cached_resolves_eq, 0.6, malloc, realloc, free);
133

134
/** Initialize the DNS cache. */
135
static void
136
init_cache_map(void)
137
{
138
  HT_INIT(cache_map, &cache_root);
139
140
}

141
/** Helper: called by eventdns when eventdns wants to log something. */
142
static void
143
evdns_log_cb(int warn, const char *msg)
144
{
145
  const char *cp;
146
147
  static int all_down = 0;
  int severity = warn ? LOG_WARN : LOG_INFO;
148
149
150
151
  if (!strcmpstart(msg, "Resolve requested for") &&
      get_options()->SafeLogging) {
    log(LOG_INFO, LD_EXIT, "eventdns: Resolve requested.");
    return;
152
153
  } else if (!strcmpstart(msg, "Search: ")) {
    return;
154
  }
155
156
157
  if (!strcmpstart(msg, "Nameserver ") && (cp=strstr(msg, " has failed: "))) {
    char *ns = tor_strndup(msg+11, cp-(msg+11));
    const char *err = strchr(cp, ':'+2);
158
159
160
    /* 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. */
161
    severity = LOG_INFO;
162
    control_event_server_status(LOG_NOTICE,
163
164
165
166
167
168
                                "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));
169
    severity = (all_down && warn) ? LOG_NOTICE : LOG_INFO;
170
    all_down = 0;
171
172
173
174
175
    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");
176
    all_down = 1;
177
  }
178
  log(severity, LD_EXIT, "eventdns: %s", msg);
179
180
}

Roger Dingledine's avatar
Roger Dingledine committed
181
/** Initialize the DNS subsystem; called by the OR process. */
182
int
183
184
dns_init(void)
{
185
  init_cache_map();
186
  if (server_mode(get_options()))
187
    return configure_nameservers(1);
188
  return 0;
189
}
190

191
192
193
/** Called when DNS-related options change (or may have changed).  Returns -1
 * on failure, 0 on success. */
int
194
195
196
197
dns_reset(void)
{
  or_options_t *options = get_options();
  if (! server_mode(options)) {
198
199
    evdns_clear_nameservers_and_suspend();
    evdns_search_clear();
200
201
202
203
204
    nameservers_configured = 0;
    tor_free(resolv_conf_fname);
    resolv_conf_mtime = 0;
  } else {
    if (configure_nameservers(0) < 0)
205
      return -1;
206
  }
207
  return 0;
208
209
}

210
211
/** Helper: Given a TTL from a DNS response, determine what TTL to give the
 * OP that asked us to resolve it. */
212
213
214
215
216
217
218
219
220
221
222
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;
}

223
224
/** Helper: Given a TTL from a DNS response, determine how long to hold it in
 * our cache. */
225
226
227
228
229
230
231
232
233
234
235
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;
}

236
/** Helper: free storage held by an entry in the DNS cache. */
237
static void
238
_free_cached_resolve(cached_resolve_t *r)
239
{
Nick Mathewson's avatar
Nick Mathewson committed
240
  while (r->pending_connections) {
241
    pending_connection_t *victim = r->pending_connections;
242
243
244
    r->pending_connections = victim->next;
    tor_free(victim);
  }
245
246
  if (r->is_reverse)
    tor_free(r->result.hostname);
247
  r->magic = 0xFF00FF00;
248
249
250
  tor_free(r);
}

251
252
253
/** 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. */
254
static int
255
_compare_cached_resolves_by_expiry(const void *_a, const void *_b)
256
{
257
  const cached_resolve_t *a = _a, *b = _b;
258
  return a->expire - b->expire;
259
260
}

261
262
/** Priority queue of cached_resolve_t objects to let us know when they
 * will expire. */
263
264
static smartlist_t *cached_resolve_pqueue = NULL;

265
266
/** Set an expiry time for a cached_resolve_t, and add it to the expiry
 * priority queue */
267
268
269
270
static void
set_expiry(cached_resolve_t *resolve, time_t expires)
{
  tor_assert(resolve && resolve->expire == 0);
271
272
  if (!cached_resolve_pqueue)
    cached_resolve_pqueue = smartlist_create();
273
274
275
276
277
278
  resolve->expire = expires;
  smartlist_pqueue_add(cached_resolve_pqueue,
                       _compare_cached_resolves_by_expiry,
                       resolve);
}

279
/** Free all storage held in the DNS cache and related structures. */
280
281
282
void
dns_free_all(void)
{
283
  cached_resolve_t **ptr, **next, *item;
284
  assert_cache_ok();
285
286
287
  if (cached_resolve_pqueue) {
    SMARTLIST_FOREACH(cached_resolve_pqueue, cached_resolve_t *, res,
      {
288
        if (res->state == CACHE_STATE_DONE)
289
290
291
          _free_cached_resolve(res);
      });
  }
292
  for (ptr = HT_START(cache_map, &cache_root); ptr != NULL; ptr = next) {
293
    item = *ptr;
294
    next = HT_NEXT_RMV(cache_map, &cache_root, ptr);
295
    _free_cached_resolve(item);
296
  }
297
  HT_CLEAR(cache_map, &cache_root);
298
299
  if (cached_resolve_pqueue)
    smartlist_free(cached_resolve_pqueue);
300
  cached_resolve_pqueue = NULL;
301
  tor_free(resolv_conf_fname);
302
303
}

Nick Mathewson's avatar
Nick Mathewson committed
304
/** Remove every cached_resolve whose <b>expire</b> time is before <b>now</b>
305
 * from the cache. */
306
static void
307
purge_expired_resolves(time_t now)
308
{
Nick Mathewson's avatar
Nick Mathewson committed
309
  cached_resolve_t *resolve, *removed;
310
  pending_connection_t *pend;
311
  edge_connection_t *pendconn;
312

Nick Mathewson's avatar
Nick Mathewson committed
313
  assert_cache_ok();
314
315
316
317
318
319
320
321
322
323
  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);

324
    if (resolve->state == CACHE_STATE_PENDING) {
325
      log_debug(LD_EXIT,
326
327
                "Expiring a dns resolve %s that's still pending. Forgot to "
                "cull it? DNS resolve didn't tell us about the timeout?",
328
329
330
331
332
333
334
335
336
337
338
                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);
339
    }
340

341
    if (resolve->pending_connections) {
342
      log_debug(LD_EXIT,
343
                "Closing pending connections on timed-out DNS resolve!");
344
      tor_fragile_assert();
345
346
347
348
      while (resolve->pending_connections) {
        pend = resolve->pending_connections;
        resolve->pending_connections = pend->next;
        /* Connections should only be pending if they have no socket. */
349
        tor_assert(pend->conn->_base.s == -1);
350
        pendconn = pend->conn;
351
        connection_edge_end(pendconn, END_STREAM_REASON_TIMEOUT,
352
                            pendconn->cpath_layer);
353
        circuit_detach_stream(circuit_get_by_edge_conn(pendconn), pendconn);
354
        connection_free(TO_CONN(pendconn));
355
356
        tor_free(pend);
      }
357
    }
358

359
360
361
362
363
364
365
    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).",
366
367
                resolve->address, (void*)resolve,
                removed ? removed->address : "NULL", (void*)remove);
368
369
      }
      tor_assert(removed == resolve);
370
371
      if (resolve->is_reverse)
        tor_free(resolve->result.hostname);
372
373
374
      resolve->magic = 0xF0BBF0BB;
      tor_free(resolve);
    } else {
375
      /* This should be in state DONE. Make sure it's not in the cache. */
376
377
      cached_resolve_t *tmp = HT_FIND(cache_map, &cache_root, resolve);
      tor_assert(tmp != resolve);
378
    }
379
  }
380

Nick Mathewson's avatar
Nick Mathewson committed
381
  assert_cache_ok();
382
383
}

384
385
386
/** Send a response to the RESOLVE request of a connection.
 * <b>answer_type</b> must be one of
 * RESOLVED_TYPE_(IPV4|ERROR|ERROR_TRANSIENT).
387
388
 *
 * If <b>circ</b> is provided, and we have a cached answer, send the
389
390
 * answer back along circ; otherwise, send the answer back along
 * <b>conn</b>'s attached circuit.
391
 */
392
static void
393
send_resolved_cell(edge_connection_t *conn, or_circuit_t *circ,
Roger Dingledine's avatar
Roger Dingledine committed
394
                   uint8_t answer_type)
395
396
{
  char buf[RELAY_PAYLOAD_SIZE];
397
  size_t buflen;
398
  uint32_t ttl;
399
400

  buf[0] = answer_type;
401
  ttl = dns_clip_ttl(conn->address_ttl);
402
403
404
405
406

  switch (answer_type)
    {
    case RESOLVED_TYPE_IPV4:
      buf[1] = 4;
407
      set_uint32(buf+2, htonl(conn->_base.addr));
408
      set_uint32(buf+6, htonl(ttl));
409
      buflen = 10;
410
411
412
      break;
    case RESOLVED_TYPE_ERROR_TRANSIENT:
    case RESOLVED_TYPE_ERROR:
413
414
415
      {
        const char *errmsg = "Error resolving hostname";
        int msglen = strlen(errmsg);
416

417
418
        buf[1] = msglen;
        strlcpy(buf+2, errmsg, sizeof(buf)-2);
419
        set_uint32(buf+2+msglen, htonl(ttl));
420
421
422
        buflen = 6+msglen;
        break;
      }
423
424
    default:
      tor_assert(0);
425
      return;
426
    }
427
  // log_notice(LD_EXIT, "Sending a regular RESOLVED reply: ");
Roger Dingledine's avatar
Roger Dingledine committed
428

429
430
431
432
433
434
435
  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),
436
437
438
439
                               RELAY_COMMAND_RESOLVED, buf, buflen,
                               conn->cpath_layer);
}

440
441
442
/** 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.
443
444
445
 *
 * If <b>circ</b> is provided, and we have a cached answer, send the
 * answer back along circ; otherwise, send the answer back along
446
 * <b>conn</b>'s attached circuit.
447
448
 */
static void
449
send_resolved_hostname_cell(edge_connection_t *conn, or_circuit_t *circ,
Roger Dingledine's avatar
Roger Dingledine committed
450
                            const char *hostname)
451
452
453
454
455
{
  char buf[RELAY_PAYLOAD_SIZE];
  size_t buflen;
  uint32_t ttl;
  size_t namelen = strlen(hostname);
456
  tor_assert(hostname);
457
458
459
460
461
462
463
464
465
466

  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;

467
468
469
470
471
472
  if (!circ) {
    circuit_t *tmp = circuit_get_by_edge_conn(conn);
    if (! CIRCUIT_IS_ORIGIN(tmp))
      circ = TO_OR_CIRCUIT(tmp);
  }

473
  // log_notice(LD_EXIT, "Sending a reply RESOLVED reply: %s", hostname);
474
  connection_edge_send_command(conn, TO_CIRCUIT(circ),
475
476
                               RELAY_COMMAND_RESOLVED, buf, buflen,
                               conn->cpath_layer);
477
  // log_notice(LD_EXIT, "Sent");
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
}

/** 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. */

502
  memcpy(buf, address, len);
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
  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
522
523
/** 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.
524
 * If resolve failed, unlink exitconn if needed, free it, and return -1.
525
 *
526
527
528
529
530
 * (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.)
 *
531
532
 * 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
533
534
 * the answer back along <b>exitconn</b>'s attached circuit.
 *
535
536
537
538
539
540
 * 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.
 */
541
int
542
dns_resolve(edge_connection_t *exitconn, or_circuit_t *oncirc)
543
{
544
545
546
  cached_resolve_t *resolve;
  cached_resolve_t search;
  pending_connection_t *pending_connection;
547
  circuit_t *circ;
548
  struct in_addr in;
549
  time_t now = time(NULL);
550
  int is_reverse = 0, is_resolve, r;
551
552
  assert_connection_ok(TO_CONN(exitconn), 0);
  tor_assert(exitconn->_base.s == -1);
553

554
555
  assert_cache_ok();

556
  is_resolve = exitconn->_base.purpose == EXIT_PURPOSE_RESOLVE;
557

558
  /* first check if exitconn->_base.address is an IP. If so, we already
559
   * know the answer. */
560
561
  if (tor_inet_aton(exitconn->_base.address, &in) != 0) {
    exitconn->_base.addr = ntohl(in.s_addr);
562
    exitconn->address_ttl = DEFAULT_DNS_TTL;
563
    if (is_resolve)
564
      send_resolved_cell(exitconn, oncirc, RESOLVED_TYPE_IPV4);
565
    return 1;
566
  }
567
568
569
570
571
572
573
574
575
576
577
578
579
  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);
    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;
  }
580
581

  /* then take this opportunity to see if there are any expired
582
   * resolves in the hash table. */
583
  purge_expired_resolves(now);
584

585
586
  /* lower-case exitconn->_base.address, so it's in canonical form */
  tor_strlower(exitconn->_base.address);
587

588
589
  /* 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
590
   * connection.
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
   */
  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));

      if (exitconn->_base.purpose == EXIT_PURPOSE_RESOLVE)
607
        send_resolved_cell(exitconn, oncirc, RESOLVED_TYPE_ERROR);
608
609
610
611
612
613
614
      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;
    }
615
    //log_notice(LD_EXIT, "Looks like an address %s",
Roger Dingledine's avatar
Roger Dingledine committed
616
    //exitconn->_base.address);
617
618
  }

619
  /* now check the hash table to see if 'address' is already there. */
620
  strlcpy(search.address, exitconn->_base.address, sizeof(search.address));
621
  resolve = HT_FIND(cache_map, &cache_root, &search);
622
  if (resolve && resolve->expire > now) { /* already there */
623
    switch (resolve->state) {
624
625
      case CACHE_STATE_PENDING:
        /* add us to the pending list */
626
        pending_connection = tor_malloc_zero(
627
                                      sizeof(pending_connection_t));
628
        pending_connection->conn = exitconn;
Roger Dingledine's avatar
   
Roger Dingledine committed
629
630
        pending_connection->next = resolve->pending_connections;
        resolve->pending_connections = pending_connection;
631
        log_debug(LD_EXIT,"Connection (fd %d) waiting for pending DNS "
632
633
                  "resolve of %s", exitconn->_base.s,
                  escaped_safe_str(exitconn->_base.address));
634
        exitconn->_base.state = EXIT_CONN_STATE_RESOLVING;
Roger Dingledine's avatar
   
Roger Dingledine committed
635
        return 0;
636
      case CACHE_STATE_CACHED_VALID:
637
        log_debug(LD_EXIT,"Connection (fd %d) found cached answer for %s",
638
                  exitconn->_base.s,
639
640
641
642
                  escaped_safe_str(resolve->address));
        exitconn->address_ttl = resolve->ttl;
        if (resolve->is_reverse) {
          tor_assert(is_resolve);
643
          send_resolved_hostname_cell(exitconn, oncirc,
Roger Dingledine's avatar
Roger Dingledine committed
644
                                      resolve->result.hostname);
645
646
647
        } else {
          exitconn->_base.addr = resolve->result.addr;
          if (is_resolve)
648
            send_resolved_cell(exitconn, oncirc, RESOLVED_TYPE_IPV4);
649
        }
650
        return 1;
651
      case CACHE_STATE_CACHED_FAILED:
652
        log_debug(LD_EXIT,"Connection (fd %d) found cached error for %s",
653
654
                  exitconn->_base.s,
                  escaped_safe_str(exitconn->_base.address));
655
        if (is_resolve)
656
          send_resolved_cell(exitconn, oncirc, RESOLVED_TYPE_ERROR);
657
        circ = circuit_get_by_edge_conn(exitconn);
658
659
        if (circ)
          circuit_detach_stream(circ, exitconn);
660
661
        if (!exitconn->_base.marked_for_close)
          connection_free(TO_CONN(exitconn));
662
        return -1;
663
664
665
      case CACHE_STATE_DONE:
        log_err(LD_BUG, "Found a 'DONE' dns resolve still in the cache.");
        tor_fragile_assert();
666
    }
Roger Dingledine's avatar
Roger Dingledine committed
667
    tor_assert(0);
Roger Dingledine's avatar
Roger Dingledine committed
668
669
  }
  /* not there, need to add it */
670
  resolve = tor_malloc_zero(sizeof(cached_resolve_t));
671
  resolve->magic = CACHED_RESOLVE_MAGIC;
Roger Dingledine's avatar
Roger Dingledine committed
672
  resolve->state = CACHE_STATE_PENDING;
673
  resolve->is_reverse = is_reverse;
674
  strlcpy(resolve->address, exitconn->_base.address, sizeof(resolve->address));
Roger Dingledine's avatar
Roger Dingledine committed
675

676
  /* add this connection to the pending list */
677
  pending_connection = tor_malloc_zero(sizeof(pending_connection_t));
Roger Dingledine's avatar
Roger Dingledine committed
678
679
  pending_connection->conn = exitconn;
  resolve->pending_connections = pending_connection;
680
  exitconn->_base.state = EXIT_CONN_STATE_RESOLVING;
Roger Dingledine's avatar
Roger Dingledine committed
681

682
  /* Add this resolve to the cache and priority queue. */
683
  HT_INSERT(cache_map, &cache_root, resolve);
684
  set_expiry(resolve, now + RESOLVE_MAX_TIMEOUT);
685

686
  log_debug(LD_EXIT,"Launching %s.",
687
            escaped_safe_str(exitconn->_base.address));
688
  assert_cache_ok();
689
  return launch_resolve(exitconn, oncirc);
690
691
}

692
/** Log an error and abort if conn is waiting for a DNS resolve.
693
 */
694
void
695
assert_connection_edge_not_dns_pending(edge_connection_t *conn)
696
{
697
698
  pending_connection_t *pend;
  cached_resolve_t **resolve;
699

700
701
702
703
704
705
  HT_FOREACH(resolve, cache_map, &cache_root) {
    for (pend = (*resolve)->pending_connections;
         pend;
         pend = pend->next) {
      tor_assert(pend->conn != conn);
    }
706
  }
707
}
708

709
710
711
712
713
714
715
/** 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;
716

717
718
719
720
  HT_FOREACH(resolve, cache_map, &cache_root) {
    for (pend = (*resolve)->pending_connections;
         pend;
         pend = pend->next) {
721
722
723
      assert_connection_ok(TO_CONN(pend->conn), 0);
      tor_assert(pend->conn->_base.s == -1);
      tor_assert(!connection_in_array(TO_CONN(pend->conn)));
724
    }
725
726
727
  }
}

Nick Mathewson's avatar
Nick Mathewson committed
728
/** Remove <b>conn</b> from the list of connections waiting for conn-\>address.
729
 */
730
void
731
connection_dns_remove(edge_connection_t *conn)
732
{
733
734
735
  pending_connection_t *pend, *victim;
  cached_resolve_t search;
  cached_resolve_t *resolve;
736

737
738
  tor_assert(conn->_base.type == CONN_TYPE_EXIT);
  tor_assert(conn->_base.state == EXIT_CONN_STATE_RESOLVING);
739

740
  strlcpy(search.address, conn->_base.address, sizeof(search.address));
741

742
  resolve = HT_FIND(cache_map, &cache_root, &search);
743
  if (!resolve) {
744
    log_notice(LD_BUG, "Address %s is not pending. Dropping.",
745
               escaped_safe_str(conn->_base.address));
746
747
748
    return;
  }

Roger Dingledine's avatar
Roger Dingledine committed
749
  tor_assert(resolve->pending_connections);
750
  assert_connection_ok(TO_CONN(conn),0);
751
752
753

  pend = resolve->pending_connections;

754
  if (pend->conn == conn) {
755
    resolve->pending_connections = pend->next;
756
    tor_free(pend);
757
    log_debug(LD_EXIT, "First connection (fd %d) no longer waiting "
758
              "for resolve of %s",
759
              conn->_base.s, escaped_safe_str(conn->_base.address));
760
761
    return;
  } else {
762
763
    for ( ; pend->next; pend = pend->next) {
      if (pend->next->conn == conn) {
764
765
        victim = pend->next;
        pend->next = victim->next;
766
        tor_free(victim);
767
        log_debug(LD_EXIT,
768
                  "Connection (fd %d) no longer waiting for resolve of %s",
769
                  conn->_base.s, escaped_safe_str(conn->_base.address));
770
771
772
        return; /* more are pending */
      }
    }
Roger Dingledine's avatar
Roger Dingledine committed
773
    tor_assert(0); /* not reachable unless onlyconn not in pending list */
774
775
776
  }
}

Nick Mathewson's avatar
Nick Mathewson committed
777
778
779
/** 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.
780
 */
781
void
782
dns_cancel_pending_resolve(const char *address)
783
{
784
785
  pending_connection_t *pend;
  cached_resolve_t search;
786
  cached_resolve_t *resolve, *tmp;
787
  edge_connection_t *pendconn;
788
  circuit_t *circ;
789

Nick Mathewson's avatar
Nick Mathewson committed
790
  strlcpy(search.address, address, sizeof(search.address));
791

792
  resolve = HT_FIND(cache_map, &cache_root, &search);
793
  if (!resolve || resolve->state != CACHE_STATE_PENDING) {
794
795
    log_notice(LD_BUG,"Address %s is not pending. Dropping.",
               escaped_safe_str(address));
796
797
798
    return;
  }

799
800
  if (!resolve->pending_connections) {
    /* XXX this should never trigger, but sometimes it does */
801
    log_warn(LD_BUG,
802
             "Address %s is pending but has no pending connections!",
803
             escaped_safe_str(address));
804
    tor_fragile_assert();
805
806
    return;
  }
Roger Dingledine's avatar
Roger Dingledine committed
807
  tor_assert(resolve->pending_connections);
808

809
  /* mark all pending connections to fail */
810
  log_debug(LD_EXIT,
811
812
             "Failing all connections waiting on DNS resolve of %s",
             escaped_safe_str(address));
813
  while (resolve->pending_connections) {
814
    pend = resolve->pending_connections;
815
    pend->conn->_base.state = EXIT_CONN_STATE_RESOLVEFAILED;
816
    pendconn = pend->conn;
817
818
819
    assert_connection_ok(TO_CONN(pendconn), 0);
    tor_assert(pendconn->_base.s == -1);
    if (!pendconn->_base.marked_for_close) {
820
821
      connection_edge_end(pendconn, END_STREAM_REASON_RESOURCELIMIT,
                          pendconn->cpath_layer);
822
    }
823
    circ = circuit_get_by_edge_conn(pendconn);
824
825
    if (circ)
      circuit_detach_stream(circ, pendconn);
826
827
    if (!pendconn->_base.marked_for_close)
      connection_free(TO_CONN(pendconn));
828
829
    resolve->pending_connections = pend->next;
    tor_free(pend);
830
831
  }

Nick Mathewson's avatar
Nick Mathewson committed
832
  tmp = HT_REMOVE(cache_map, &cache_root, resolve);
833
834
835
  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).",
836
837
            resolve->address, (void*)resolve,
            tmp ? tmp->address : "NULL", (void*)tmp);
838
  }
Nick Mathewson's avatar
Nick Mathewson committed
839
  tor_assert(tmp == resolve);
840
841

  resolve->state = CACHE_STATE_DONE;
842
843
}

844
/** Helper: adds an entry to the DNS cache mapping <b>address</b> to the ipv4
845
846
 * address <b>addr</b> (if is_reverse is 0) or the hostname <b>hostname</b> (if
 * is_reverse is 1).  <b>ttl</b> is a cache ttl; <b>outcome</b> is one of
847
848
 * DNS_RESOLVE_{FAILED_TRANSIENT|FAILED_PERMANENT|SUCCEEDED}.
 **/
849
static void
850
851
add_answer_to_cache(const char *address, int is_reverse, uint32_t addr,
                    const char *hostname, char outcome, uint32_t ttl)
852
853
854
855
856
{
  cached_resolve_t *resolve;
  if (outcome == DNS_RESOLVE_FAILED_TRANSIENT)
    return;

857
858
859
860
  //log_notice(LD_EXIT, "Adding to cache: %s -> %s (%lx, %s), %d",
  //           address, is_reverse?"(reverse)":"", (unsigned long)addr,
  //           hostname?hostname:"NULL",(int)outcome);

861
862
863
864
865
  resolve = tor_malloc_zero(sizeof(cached_resolve_t));
  resolve->magic = CACHED_RESOLVE_MAGIC;
  resolve->state = (outcome == DNS_RESOLVE_SUCCEEDED) ?
    CACHE_STATE_CACHED_VALID : CACHE_STATE_CACHED_FAILED;
  strlcpy(resolve->address, address, sizeof(resolve->address));
866
  resolve->is_reverse = is_reverse;
867
  if (is_reverse) {
868
869
870
871
872
873
874
    if (outcome == DNS_RESOLVE_SUCCEEDED) {
      tor_assert(hostname);
      resolve->result.hostname = tor_strdup(hostname);
    } else {
      tor_assert(! hostname);</