dns.c 30.3 KB
Newer Older
Roger Dingledine's avatar
Roger Dingledine committed
1
/* Copyright 2003-2004 Roger Dingledine.
Nick Mathewson's avatar
Nick Mathewson committed
2
 * Copyright 2004-2005 Roger Dingledine, Nick Mathewson. */
3
4
/* See LICENSE for licensing information */
/* $Id$ */
5
const char dns_c_id[] = "$Id$";
6

Roger Dingledine's avatar
Roger Dingledine committed
7
8
/**
 * \file dns.c
9
10
11
12
 * \brief Implements a farm of 'DNS worker' threads or processes to
 * perform DNS lookups for onion routers and cache the results.
 * [This needs to be done in the background because of the lack of a
 * good, ubiquitous asynchronous DNS implementation.]
Roger Dingledine's avatar
Roger Dingledine committed
13
 **/
14

15
16
17
18
19
/* See http://elvin.dstc.com/ListArchive/elvin-dev/archive/2001/09/msg00027.html
 * for some approaches to asynchronous dns. We will want to switch once one of
 * them becomes more commonly available.
 */

20
#include "or.h"
21
#include "tree.h"
22

Roger Dingledine's avatar
Roger Dingledine committed
23
/** Longest hostname we're willing to resolve. */
24
25
#define MAX_ADDRESSLEN 256

Roger Dingledine's avatar
Roger Dingledine committed
26
/** Maximum DNS processes to spawn. */
27
#define MAX_DNSWORKERS 100
Roger Dingledine's avatar
Roger Dingledine committed
28
/** Minimum DNS processes to spawn. */
29
#define MIN_DNSWORKERS 3
30

Roger Dingledine's avatar
Roger Dingledine committed
31
/** If more than this many processes are idle, shut down the extras. */
32
#define MAX_IDLE_DNSWORKERS 10
33

Roger Dingledine's avatar
Roger Dingledine committed
34
/** Possible outcomes from hostname lookup: permanent failure,
35
 * transient (retryable) failure, and success. */
36
37
38
39
#define DNS_RESOLVE_FAILED_TRANSIENT 1
#define DNS_RESOLVE_FAILED_PERMANENT 2
#define DNS_RESOLVE_SUCCEEDED 3

40
/** How many dnsworkers we have running right now. */
41
static int num_dnsworkers=0;
42
/** How many of the running dnsworkers have an assigned task right now. */
43
44
45
static int num_dnsworkers_busy=0;
/** When did we last rotate the dnsworkers? */
static time_t last_rotation_time=0;
46

Roger Dingledine's avatar
Roger Dingledine committed
47
/** Linked list of connections waiting for a DNS answer. */
48
49
typedef struct pending_connection_t {
  connection_t *conn;
50
  struct pending_connection_t *next;
51
} pending_connection_t;
52

Roger Dingledine's avatar
Roger Dingledine committed
53
/** A DNS request: possibly completed, possibly pending; cached_resolve
54
55
56
 * structs are stored at the OR side in a splay tree, and as a linked
 * list from oldest to newest.
 */
57
58
typedef struct cached_resolve_t {
  SPLAY_ENTRY(cached_resolve_t) node;
59
  char address[MAX_ADDRESSLEN]; /**< The hostname to be resolved. */
60
  uint32_t addr; /**< IPv4 addr for <b>address</b>. */
61
  char state; /**< 0 is pending; 1 means answer is valid; 2 means resolve failed. */
62
63
64
#define CACHE_STATE_PENDING 0
#define CACHE_STATE_VALID 1
#define CACHE_STATE_FAILED 2
65
  uint32_t expire; /**< Remove items from cache after this time. */
66
67
68
  pending_connection_t *pending_connections;
  struct cached_resolve_t *next;
} cached_resolve_t;
69

70
71
static void purge_expired_resolves(uint32_t now);
static int assign_to_dnsworker(connection_t *exitconn);
72
static void dns_purge_resolve(cached_resolve_t *resolve);
73
static void dns_found_answer(char *address, uint32_t addr, char outcome);
Nick Mathewson's avatar
Nick Mathewson committed
74
static int dnsworker_main(void *data);
75
76
static int spawn_dnsworker(void);
static void spawn_enough_dnsworkers(void);
77
static void send_resolved_cell(connection_t *conn, uint8_t answer_type);
78

79
/** Splay tree of cached_resolve objects. */
80
static SPLAY_HEAD(cache_tree, cached_resolve_t) cache_root;
81

Roger Dingledine's avatar
Roger Dingledine committed
82
/** Function to compare hashed resolves on their addresses; used to
83
 * implement splay trees. */
84
85
static int compare_cached_resolves(cached_resolve_t *a,
                                   cached_resolve_t *b) {
86
  /* make this smarter one day? */
87
  return strncmp(a->address, b->address, MAX_ADDRESSLEN);
88
89
}

90
91
SPLAY_PROTOTYPE(cache_tree, cached_resolve_t, node, compare_cached_resolves);
SPLAY_GENERATE(cache_tree, cached_resolve_t, node, compare_cached_resolves);
92

93
/** Initialize the DNS cache. */
94
95
96
static void
init_cache_tree(void)
{
97
98
99
  SPLAY_INIT(&cache_root);
}

Roger Dingledine's avatar
Roger Dingledine committed
100
/** Initialize the DNS subsystem; called by the OR process. */
101
102
103
void
dns_init(void)
{
104
  init_cache_tree();
105
  dnsworkers_rotate();
106
}
107

108
/** Helper: free storage held by an entry in the DNS cache. */
109
static void
110
_free_cached_resolve(cached_resolve_t *r)
111
{
Nick Mathewson's avatar
Nick Mathewson committed
112
  while (r->pending_connections) {
113
    pending_connection_t *victim = r->pending_connections;
114
115
116
117
118
119
    r->pending_connections = victim->next;
    tor_free(victim);
  }
  tor_free(r);
}

120
/** Free all storage held in the DNS cache */
121
122
123
void
dns_free_all(void)
{
124
  cached_resolve_t *ptr, *next;
125
126
127
128
129
130
131
  for (ptr = SPLAY_MIN(cache_tree, &cache_root); ptr != NULL; ptr = next) {
    next = SPLAY_NEXT(cache_tree, &cache_root, ptr);
    SPLAY_REMOVE(cache_tree, &cache_root, ptr);
    _free_cached_resolve(ptr);
  }
}

132
/** Linked list of resolved addresses, oldest to newest. */
133
134
static cached_resolve_t *oldest_cached_resolve = NULL;
static cached_resolve_t *newest_cached_resolve = NULL;
135

Nick Mathewson's avatar
Nick Mathewson committed
136
/** Remove every cached_resolve whose <b>expire</b> time is before <b>now</b>
137
 * from the cache. */
138
139
140
static void
purge_expired_resolves(uint32_t now)
{
141
142
  cached_resolve_t *resolve;
  pending_connection_t *pend;
143
  connection_t *pendconn;
144
145
146
147

  /* this is fast because the linked list
   * oldest_cached_resolve is ordered by when they came in.
   */
148
  while (oldest_cached_resolve && (oldest_cached_resolve->expire < now)) {
149
    resolve = oldest_cached_resolve;
Roger Dingledine's avatar
Roger Dingledine committed
150
    log(LOG_DEBUG,"Forgetting old cached resolve (address %s, expires %lu)",
151
        safe_str(resolve->address), (unsigned long)resolve->expire);
152
    if (resolve->state == CACHE_STATE_PENDING) {
153
      log_fn(LOG_WARN,"Bug: Expiring a dns resolve ('%s') that's still pending. Forgot to cull it?", safe_str(resolve->address));
154
      tor_fragile_assert();
155
156
157
    }
    if (resolve->pending_connections) {
      log_fn(LOG_WARN, "Closing pending connections on expiring DNS resolve!");
158
      tor_fragile_assert();
159
160
161
162
163
164
      while (resolve->pending_connections) {
        pend = resolve->pending_connections;
        resolve->pending_connections = pend->next;
        /* Connections should only be pending if they have no socket. */
        tor_assert(pend->conn->s == -1);
        pendconn = pend->conn;
165
        connection_edge_end(pendconn, END_STREAM_REASON_TIMEOUT,
166
                            pendconn->cpath_layer);
167
        circuit_detach_stream(circuit_get_by_edge_conn(pendconn), pendconn);
168
169
170
        connection_free(pendconn);
        tor_free(pend);
      }
171
    }
172
    oldest_cached_resolve = resolve->next;
173
    if (!oldest_cached_resolve) /* if there are no more, */
174
175
      newest_cached_resolve = NULL; /* then make sure the list's tail knows that too */
    SPLAY_REMOVE(cache_tree, &cache_root, resolve);
176
    tor_free(resolve);
177
178
179
  }
}

180
181
182
183
/** Send a response to the RESOVLE request of a connection. answer_type must
 *  be one of RESOLVED_TYPE_(IPV4|ERROR|ERROR_TRANSIENT) */
static void
send_resolved_cell(connection_t *conn, uint8_t answer_type)
184
185
{
  char buf[RELAY_PAYLOAD_SIZE];
186
  size_t buflen;
187
188
189
190
191
192
193
194

  buf[0] = answer_type;

  switch (answer_type)
    {
    case RESOLVED_TYPE_IPV4:
      buf[1] = 4;
      set_uint32(buf+2, htonl(conn->addr));
195
196
      set_uint32(buf+6, htonl(MAX_DNS_ENTRY_AGE)); /*XXXX send a real TTL*/
      buflen = 10;
197
198
199
      break;
    case RESOLVED_TYPE_ERROR_TRANSIENT:
    case RESOLVED_TYPE_ERROR:
200
201
202
203
204
205
206
207
208
209
      {
        const char *errmsg = "Error resolving hostname";
        int msglen = strlen(errmsg);
        int ttl = (answer_type == RESOLVED_TYPE_ERROR ? MAX_DNS_ENTRY_AGE : 0);
        buf[1] = msglen;
        strlcpy(buf+2, errmsg, sizeof(buf)-2);
        set_uint32(buf+2+msglen, htonl((uint32_t)ttl));
        buflen = 6+msglen;
        break;
      }
210
211
212
    default:
      tor_assert(0);
    }
213
  connection_edge_send_command(conn, circuit_get_by_edge_conn(conn),
214
215
216
217
                               RELAY_COMMAND_RESOLVED, buf, buflen,
                               conn->cpath_layer);
}

218
219
220
/** Link <b>r</b> into the tree of address-to-result mappings, and add it to
 * the linked list of resolves-by-age. */
static void
221
insert_resolve(cached_resolve_t *r)
222
223
224
225
226
227
228
229
230
231
232
233
{
  /* add us to the linked list of resolves */
  if (!oldest_cached_resolve) {
    oldest_cached_resolve = r;
  } else {
    newest_cached_resolve->next = r;
  }
  newest_cached_resolve = r;

  SPLAY_INSERT(cache_tree, &cache_root, r);
}

Nick Mathewson's avatar
Nick Mathewson committed
234
235
/** 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.
236
 * If resolve failed, unlink exitconn if needed, free it, and return -1.
237
238
239
240
241
242
243
 *
 * 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.
 */
244
245
246
int
dns_resolve(connection_t *exitconn)
{
247
248
249
  cached_resolve_t *resolve;
  cached_resolve_t search;
  pending_connection_t *pending_connection;
250
  struct in_addr in;
251
  circuit_t *circ;
252
  uint32_t now = time(NULL);
253
  assert_connection_ok(exitconn, 0);
254
  tor_assert(exitconn->s == -1);
255

256
257
258
259
  /* first check if exitconn->address is an IP. If so, we already
   * know the answer. */
  if (tor_inet_aton(exitconn->address, &in) != 0) {
    exitconn->addr = ntohl(in.s_addr);
260
261
    if (exitconn->purpose == EXIT_PURPOSE_RESOLVE)
      send_resolved_cell(exitconn, RESOLVED_TYPE_IPV4);
262
    return 1;
263
264
265
266
  }

  /* then take this opportunity to see if there are any expired
   * resolves in the tree. */
267
  purge_expired_resolves(now);
268

269
270
271
  /* lower-case exitconn->address, so it's in canonical form */
  tor_strlower(exitconn->address);

272
  /* now check the tree to see if 'address' is already there. */
Nick Mathewson's avatar
Nick Mathewson committed
273
  strlcpy(search.address, exitconn->address, sizeof(search.address));
Roger Dingledine's avatar
   
Roger Dingledine committed
274
  resolve = SPLAY_FIND(cache_tree, &cache_root, &search);
275
276
  if (resolve) { /* already there */
    switch (resolve->state) {
277
278
      case CACHE_STATE_PENDING:
        /* add us to the pending list */
279
        pending_connection = tor_malloc_zero(
280
                                      sizeof(pending_connection_t));
281
        pending_connection->conn = exitconn;
Roger Dingledine's avatar
   
Roger Dingledine committed
282
283
        pending_connection->next = resolve->pending_connections;
        resolve->pending_connections = pending_connection;
284
        log_fn(LOG_DEBUG,"Connection (fd %d) waiting for pending DNS resolve of '%s'",
285
               exitconn->s, safe_str(exitconn->address));
286
        exitconn->state = EXIT_CONN_STATE_RESOLVING;
Roger Dingledine's avatar
   
Roger Dingledine committed
287
        return 0;
288
      case CACHE_STATE_VALID:
289
        exitconn->addr = resolve->addr;
290
        log_fn(LOG_DEBUG,"Connection (fd %d) found cached answer for '%s'",
291
               exitconn->s, safe_str(exitconn->address));
292
293
        if (exitconn->purpose == EXIT_PURPOSE_RESOLVE)
          send_resolved_cell(exitconn, RESOLVED_TYPE_IPV4);
294
        return 1;
295
      case CACHE_STATE_FAILED:
296
        log_fn(LOG_DEBUG,"Connection (fd %d) found cached error for '%s'",
297
               exitconn->s, safe_str(exitconn->address));
298
299
        if (exitconn->purpose == EXIT_PURPOSE_RESOLVE)
          send_resolved_cell(exitconn, RESOLVED_TYPE_ERROR);
300
        circ = circuit_get_by_edge_conn(exitconn);
301
302
        if (circ)
          circuit_detach_stream(circ, exitconn);
303
304
        if (!exitconn->marked_for_close)
          connection_free(exitconn);
305
306
        return -1;
    }
Roger Dingledine's avatar
Roger Dingledine committed
307
    tor_assert(0);
Roger Dingledine's avatar
Roger Dingledine committed
308
309
  }
  /* not there, need to add it */
310
  resolve = tor_malloc_zero(sizeof(cached_resolve_t));
Roger Dingledine's avatar
Roger Dingledine committed
311
  resolve->state = CACHE_STATE_PENDING;
312
  resolve->expire = now + MAX_DNS_ENTRY_AGE;
Nick Mathewson's avatar
Nick Mathewson committed
313
  strlcpy(resolve->address, exitconn->address, sizeof(resolve->address));
Roger Dingledine's avatar
Roger Dingledine committed
314
315

  /* add us to the pending list */
316
  pending_connection = tor_malloc_zero(sizeof(pending_connection_t));
Roger Dingledine's avatar
Roger Dingledine committed
317
318
  pending_connection->conn = exitconn;
  resolve->pending_connections = pending_connection;
319
  exitconn->state = EXIT_CONN_STATE_RESOLVING;
Roger Dingledine's avatar
Roger Dingledine committed
320

321
  insert_resolve(resolve);
Roger Dingledine's avatar
Roger Dingledine committed
322
  return assign_to_dnsworker(exitconn);
323
324
}

Roger Dingledine's avatar
Roger Dingledine committed
325
/** Find or spawn a dns worker process to handle resolving
Nick Mathewson's avatar
Nick Mathewson committed
326
 * <b>exitconn</b>-\>address; tell that dns worker to begin resolving.
327
 */
328
329
330
static int
assign_to_dnsworker(connection_t *exitconn)
{
331
332
  connection_t *dnsconn;
  unsigned char len;
333

Roger Dingledine's avatar
Roger Dingledine committed
334
  tor_assert(exitconn->state == EXIT_CONN_STATE_RESOLVING);
335
  tor_assert(exitconn->s == -1);
336

Roger Dingledine's avatar
Roger Dingledine committed
337
  spawn_enough_dnsworkers(); /* respawn here, to be sure there are enough */
338

339
  dnsconn = connection_get_by_type_state(CONN_TYPE_DNSWORKER, DNSWORKER_STATE_IDLE);
340

341
  if (!dnsconn) {
Roger Dingledine's avatar
Roger Dingledine committed
342
    log_fn(LOG_WARN,"no idle dns workers. Failing.");
343
344
    if (exitconn->purpose == EXIT_PURPOSE_RESOLVE)
      send_resolved_cell(exitconn, RESOLVED_TYPE_ERROR_TRANSIENT);
345
    dns_cancel_pending_resolve(exitconn->address); /* also sends end and frees! */
346
    return -1;
347
348
  }

349
  log_fn(LOG_DEBUG, "Connection (fd %d) needs to resolve '%s'; assigning to DNSWorker (fd %d)",
350
         exitconn->s, safe_str(exitconn->address), dnsconn->s);
351

352
  tor_free(dnsconn->address);
353
  dnsconn->address = tor_strdup(exitconn->address);
354
  dnsconn->state = DNSWORKER_STATE_BUSY;
Roger Dingledine's avatar
Roger Dingledine committed
355
  num_dnsworkers_busy++;
356

357
  len = strlen(dnsconn->address);
358
  connection_write_to_buf((char*)&len, 1, dnsconn);
359
  connection_write_to_buf(dnsconn->address, len, dnsconn);
360
361
362
363

  return 0;
}

Nick Mathewson's avatar
Nick Mathewson committed
364
/** Remove <b>conn</b> from the list of connections waiting for conn-\>address.
365
 */
366
367
void
connection_dns_remove(connection_t *conn)
368
{
369
370
371
  pending_connection_t *pend, *victim;
  cached_resolve_t search;
  cached_resolve_t *resolve;
372

373
374
375
  tor_assert(conn->type == CONN_TYPE_EXIT);
  tor_assert(conn->state == EXIT_CONN_STATE_RESOLVING);

Nick Mathewson's avatar
Nick Mathewson committed
376
  strlcpy(search.address, conn->address, sizeof(search.address));
377
378

  resolve = SPLAY_FIND(cache_tree, &cache_root, &search);
379
  if (!resolve) {
380
    log_fn(LOG_NOTICE,"Address '%s' is not pending. Dropping.", safe_str(conn->address));
381
382
383
    return;
  }

Roger Dingledine's avatar
Roger Dingledine committed
384
  tor_assert(resolve->pending_connections);
385
386
387
388
  assert_connection_ok(conn,0);

  pend = resolve->pending_connections;

389
  if (pend->conn == conn) {
390
    resolve->pending_connections = pend->next;
391
    tor_free(pend);
392
    log_fn(LOG_DEBUG, "First connection (fd %d) no longer waiting for resolve of '%s'",
393
           conn->s, safe_str(conn->address));
394
395
    return;
  } else {
396
397
    for ( ; pend->next; pend = pend->next) {
      if (pend->next->conn == conn) {
398
399
        victim = pend->next;
        pend->next = victim->next;
400
        tor_free(victim);
401
        log_fn(LOG_DEBUG, "Connection (fd %d) no longer waiting for resolve of '%s'",
402
               conn->s, safe_str(conn->address));
403
404
405
        return; /* more are pending */
      }
    }
Roger Dingledine's avatar
Roger Dingledine committed
406
    tor_assert(0); /* not reachable unless onlyconn not in pending list */
407
408
409
  }
}

Roger Dingledine's avatar
Roger Dingledine committed
410
/** Log an error and abort if conn is waiting for a DNS resolve.
411
 */
412
413
414
void
assert_connection_edge_not_dns_pending(connection_t *conn)
{
415
416
  pending_connection_t *pend;
  cached_resolve_t *resolve;
417
418

  SPLAY_FOREACH(resolve, cache_tree, &cache_root) {
419
    for (pend = resolve->pending_connections;
420
421
         pend;
         pend = pend->next) {
Roger Dingledine's avatar
Roger Dingledine committed
422
      tor_assert(pend->conn != conn);
423
424
425
426
    }
  }
}

Roger Dingledine's avatar
Roger Dingledine committed
427
/** Log an error and abort if any connection waiting for a DNS resolve is
428
 * corrupted. */
429
430
431
void
assert_all_pending_dns_resolves_ok(void)
{
432
433
  pending_connection_t *pend;
  cached_resolve_t *resolve;
434
435

  SPLAY_FOREACH(resolve, cache_tree, &cache_root) {
436
    for (pend = resolve->pending_connections;
437
438
         pend;
         pend = pend->next) {
439
      assert_connection_ok(pend->conn, 0);
440
441
      tor_assert(pend->conn->s == -1);
      tor_assert(!connection_in_array(pend->conn));
442
443
444
445
    }
  }
}

Nick Mathewson's avatar
Nick Mathewson committed
446
447
448
/** 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.
449
 */
450
451
452
void
dns_cancel_pending_resolve(char *address)
{
453
454
455
  pending_connection_t *pend;
  cached_resolve_t search;
  cached_resolve_t *resolve;
456
  connection_t *pendconn;
457
  circuit_t *circ;
458

Nick Mathewson's avatar
Nick Mathewson committed
459
  strlcpy(search.address, address, sizeof(search.address));
460
461

  resolve = SPLAY_FIND(cache_tree, &cache_root, &search);
462
  if (!resolve) {
463
    log_fn(LOG_NOTICE,"Address '%s' is not pending. Dropping.", safe_str(address));
464
465
466
    return;
  }

467
468
  if (!resolve->pending_connections) {
    /* XXX this should never trigger, but sometimes it does */
469
470
    log_fn(LOG_WARN,"Bug: Address '%s' is pending but has no pending connections!",
           safe_str(address));
471
    tor_fragile_assert();
472
473
    return;
  }
Roger Dingledine's avatar
Roger Dingledine committed
474
  tor_assert(resolve->pending_connections);
475

476
477
  /* mark all pending connections to fail */
  log_fn(LOG_DEBUG, "Failing all connections waiting on DNS resolve of '%s'",
478
         safe_str(address));
479
  while (resolve->pending_connections) {
480
    pend = resolve->pending_connections;
481
    pend->conn->state = EXIT_CONN_STATE_RESOLVEFAILED;
482
    pendconn = pend->conn;
483
    tor_assert(pendconn->s == -1);
484
    if (!pendconn->marked_for_close) {
485
486
      connection_edge_end(pendconn, END_STREAM_REASON_RESOURCELIMIT,
                          pendconn->cpath_layer);
487
    }
488
    circ = circuit_get_by_edge_conn(pendconn);
489
490
    if (circ)
      circuit_detach_stream(circ, pendconn);
491
    connection_free(pendconn);
492
493
    resolve->pending_connections = pend->next;
    tor_free(pend);
494
495
  }

496
497
498
  dns_purge_resolve(resolve);
}

Nick Mathewson's avatar
Nick Mathewson committed
499
/** Remove <b>resolve</b> from the cache.
500
 */
501
static void
502
dns_purge_resolve(cached_resolve_t *resolve)
503
{
504
  cached_resolve_t *tmp;
505

506
  /* remove resolve from the linked list */
507
  if (resolve == oldest_cached_resolve) {
508
    oldest_cached_resolve = resolve->next;
509
    if (oldest_cached_resolve == NULL)
510
      newest_cached_resolve = NULL;
511
  } else {
512
    /* FFFF make it a doubly linked list if this becomes too slow */
513
    for (tmp=oldest_cached_resolve; tmp && tmp->next != resolve; tmp=tmp->next) ;
Roger Dingledine's avatar
Roger Dingledine committed
514
    tor_assert(tmp); /* it's got to be in the list, or we screwed up somewhere else */
515
516
    tmp->next = resolve->next; /* unlink it */

517
    if (newest_cached_resolve == resolve)
518
      newest_cached_resolve = tmp;
519
  }
520
521
522
523

  /* remove resolve from the tree */
  SPLAY_REMOVE(cache_tree, &cache_root, resolve);

524
  tor_free(resolve);
525
526
}

Roger Dingledine's avatar
Roger Dingledine committed
527
/** Called on the OR side when a DNS worker tells us the outcome of a DNS
528
 * resolve: tell all pending connections about the result of the lookup, and
Nick Mathewson's avatar
Nick Mathewson committed
529
530
531
532
 * cache the value.  (<b>address</b> is a NUL-terminated string containing the
 * address to look up; <b>addr</b> is an IPv4 address in host order;
 * <b>outcome</b> is one of
 * DNS_RESOLVE_{FAILED_TRANSIENT|FAILED_PERMANENT|SUCCEEDED}.
533
 */
534
535
536
static void
dns_found_answer(char *address, uint32_t addr, char outcome)
{
537
538
539
  pending_connection_t *pend;
  cached_resolve_t search;
  cached_resolve_t *resolve;
540
  connection_t *pendconn;
541
  circuit_t *circ;
542

Nick Mathewson's avatar
Nick Mathewson committed
543
  strlcpy(search.address, address, sizeof(search.address));
544
545

  resolve = SPLAY_FIND(cache_tree, &cache_root, &search);
546
  if (!resolve) {
547
548
    log_fn(LOG_INFO,"Resolved unasked address '%s'; caching anyway.",
           safe_str(address));
549
    resolve = tor_malloc_zero(sizeof(cached_resolve_t));
550
551
552
553
554
    resolve->state = (outcome == DNS_RESOLVE_SUCCEEDED) ?
      CACHE_STATE_VALID : CACHE_STATE_FAILED;
    resolve->addr = addr;
    resolve->expire = time(NULL) + MAX_DNS_ENTRY_AGE;
    insert_resolve(resolve);
555
    return;
556
557
  }

558
  if (resolve->state != CACHE_STATE_PENDING) {
559
560
    /* XXXX Maybe update addr? or check addr for consistency? Or let
     * VALID replace FAILED? */
Roger Dingledine's avatar
Roger Dingledine committed
561
    log_fn(LOG_NOTICE, "Resolved '%s' which was already resolved; ignoring",
562
           safe_str(address));
Roger Dingledine's avatar
Roger Dingledine committed
563
    tor_assert(resolve->pending_connections == NULL);
564
565
566
567
568
569
    return;
  }
  /* Removed this assertion: in fact, we'll sometimes get a double answer
   * to the same question.  This can happen when we ask one worker to resolve
   * X.Y.Z., then we cancel the request, and then we ask another worker to
   * resolve X.Y.Z. */
Roger Dingledine's avatar
Roger Dingledine committed
570
  /* tor_assert(resolve->state == CACHE_STATE_PENDING); */
571

572
  resolve->addr = addr;
573
  if (outcome == DNS_RESOLVE_SUCCEEDED)
574
575
576
577
    resolve->state = CACHE_STATE_VALID;
  else
    resolve->state = CACHE_STATE_FAILED;

578
  while (resolve->pending_connections) {
579
    pend = resolve->pending_connections;
580
    assert_connection_ok(pend->conn,time(NULL));
581
    pend->conn->addr = resolve->addr;
582
583
    pendconn = pend->conn; /* don't pass complex things to the
                              connection_mark_for_close macro */
584

585
    if (resolve->state == CACHE_STATE_FAILED) {
586
      /* prevent double-remove. */
587
      pendconn->state = EXIT_CONN_STATE_RESOLVEFAILED;
588
      if (pendconn->purpose == EXIT_PURPOSE_CONNECT) {
589
590
        connection_edge_end(pendconn, END_STREAM_REASON_RESOLVEFAILED, pendconn->cpath_layer);
        /* This detach must happen after we send the end cell. */
591
        circuit_detach_stream(circuit_get_by_edge_conn(pendconn), pendconn);
592
      } else {
593
        send_resolved_cell(pendconn, RESOLVED_TYPE_ERROR);
594
        /* This detach must happen after we send the resolved cell. */
595
        circuit_detach_stream(circuit_get_by_edge_conn(pendconn), pendconn);
596
      }
597
      connection_free(pendconn);
Roger Dingledine's avatar
Roger Dingledine committed
598
    } else {
599
600
601
602
      if (pendconn->purpose == EXIT_PURPOSE_CONNECT) {
        /* prevent double-remove. */
        pend->conn->state = EXIT_CONN_STATE_CONNECTING;

603
        circ = circuit_get_by_edge_conn(pend->conn);
604
605
606
607
608
        tor_assert(circ);
        /* unlink pend->conn from resolving_streams, */
        circuit_detach_stream(circ, pend->conn);
        /* and link it to n_streams */
        pend->conn->next_stream = circ->n_streams;
609
        pend->conn->on_circuit = circ;
610
611
612
613
614
615
616
617
        circ->n_streams = pend->conn;

        connection_exit_connect(pend->conn);
      } else {
        /* prevent double-remove.  This isn't really an accurate state,
         * but it does the right thing. */
        pendconn->state = EXIT_CONN_STATE_RESOLVEFAILED;
        send_resolved_cell(pendconn, RESOLVED_TYPE_IPV4);
618
        circ = circuit_get_by_edge_conn(pendconn);
619
620
621
622
        tor_assert(circ);
        circuit_detach_stream(circ, pendconn);
        connection_free(pendconn);
      }
Roger Dingledine's avatar
Roger Dingledine committed
623
    }
624
625
    resolve->pending_connections = pend->next;
    tor_free(pend);
626
  }
627

628
  if (outcome == DNS_RESOLVE_FAILED_TRANSIENT) { /* remove from cache */
629
630
    dns_purge_resolve(resolve);
  }
631
632
}

633
634
/******************************************************************/

Nick Mathewson's avatar
Nick Mathewson committed
635
/*
636
 * Connection between OR and dnsworker
Nick Mathewson's avatar
Nick Mathewson committed
637
 */
638

Roger Dingledine's avatar
Roger Dingledine committed
639
/** Write handler: called when we've pushed a request to a dnsworker. */
640
641
642
int
connection_dns_finished_flushing(connection_t *conn)
{
643
644
  tor_assert(conn);
  tor_assert(conn->type == CONN_TYPE_DNSWORKER);
645
646
647
648
  connection_stop_writing(conn);
  return 0;
}

649
650
651
int
connection_dns_reached_eof(connection_t *conn)
{
652
  log_fn(LOG_WARN,"Read eof. Worker died unexpectedly.");
653
  if (conn->state == DNSWORKER_STATE_BUSY) {
654
655
656
657
    /* don't cancel the resolve here -- it would be cancelled in
     * connection_about_to_close_connection(), since conn is still
     * in state BUSY
     */
658
659
660
661
662
663
664
665
    num_dnsworkers_busy--;
  }
  num_dnsworkers--;
  connection_mark_for_close(conn);
  return 0;
}

/** Read handler: called when we get data from a dnsworker. See
666
667
 * if we have a complete answer.  If so, call dns_found_answer on the
 * result.  If not, wait.  Returns 0. */
668
669
670
int
connection_dns_process_inbuf(connection_t *conn)
{
671
  char success;
672
  uint32_t addr;
673

674
675
  tor_assert(conn);
  tor_assert(conn->type == CONN_TYPE_DNSWORKER);
676

677
  if (conn->state != DNSWORKER_STATE_BUSY && buf_datalen(conn->inbuf)) {
678
    log_fn(LOG_WARN,"Bug: read data (%d bytes) from an idle dns worker (fd %d, address '%s'). Please report.",
679
           (int)buf_datalen(conn->inbuf), conn->s, safe_str(conn->address));
680
    tor_fragile_assert();
681
682
683
684
685
686
687
688

    /* Pull it off the buffer anyway, or it will just stay there.
     * Keep pulling things off because sometimes we get several
     * answers at once (!). */
    while (buf_datalen(conn->inbuf)) {
      connection_fetch_from_buf(&success,1,conn);
      connection_fetch_from_buf((char *)&addr,sizeof(uint32_t),conn);
      log_fn(LOG_WARN,"Discarding idle dns answer (success %d, addr %d.)",
689
             success, addr); // XXX safe_str
690
    }
691
692
    return 0;
  }
693
  if (buf_datalen(conn->inbuf) < 5) /* entire answer available? */
694
    return 0; /* not yet */
695
  tor_assert(conn->state == DNSWORKER_STATE_BUSY);
Roger Dingledine's avatar
Roger Dingledine committed
696
  tor_assert(buf_datalen(conn->inbuf) == 5);
697

698
699
  connection_fetch_from_buf(&success,1,conn);
  connection_fetch_from_buf((char *)&addr,sizeof(uint32_t),conn);
700

701
  log_fn(LOG_DEBUG, "DNSWorker (fd %d) returned answer for '%s'",
702
         conn->s, safe_str(conn->address));
703

Roger Dingledine's avatar
Roger Dingledine committed
704
705
  tor_assert(success >= DNS_RESOLVE_FAILED_TRANSIENT);
  tor_assert(success <= DNS_RESOLVE_SUCCEEDED);
706
  dns_found_answer(conn->address, ntohl(addr), success);
707

708
  tor_free(conn->address);
709
  conn->address = tor_strdup("<idle>");
710
  conn->state = DNSWORKER_STATE_IDLE;
Roger Dingledine's avatar
Roger Dingledine committed
711
  num_dnsworkers_busy--;
712
713
714
715
716
  if (conn->timestamp_created < last_rotation_time) {
    connection_mark_for_close(conn);
    num_dnsworkers--;
    spawn_enough_dnsworkers();
  }
717
718
719
  return 0;
}

720
721
722
/** Close and re-open all idle dnsworkers; schedule busy ones to be closed
 * and re-opened once they're no longer busy.
 **/
723
724
void
dnsworkers_rotate(void)
725
726
727
728
729
730
731
732
{
  connection_t *dnsconn;
  while ((dnsconn = connection_get_by_type_state(CONN_TYPE_DNSWORKER,
                                                 DNSWORKER_STATE_IDLE))) {
    connection_mark_for_close(dnsconn);
    num_dnsworkers--;
  }
  last_rotation_time = time(NULL);
733
734
  if (server_mode(get_options()))
    spawn_enough_dnsworkers();
735
736
}

Roger Dingledine's avatar
Roger Dingledine committed
737
/** Implementation for DNS workers; this code runs in a separate
738
739
740
 * execution context.  It takes as its argument an fdarray as returned
 * by socketpair(), and communicates via fdarray[1].  The protocol is
 * as follows:
Nick Mathewson's avatar
Nick Mathewson committed
741
742
743
744
745
746
 *    - The OR says:
 *         - ADDRESSLEN [1 byte]
 *         - ADDRESS    [ADDRESSLEN bytes]
 *    - The DNS worker does the lookup, and replies:
 *         - OUTCOME    [1 byte]
 *         - IP         [4 bytes]
747
748
749
750
751
752
753
 *
 * OUTCOME is one of DNS_RESOLVE_{FAILED_TRANSIENT|FAILED_PERMANENT|SUCCEEDED}.
 * IP is in host order.
 *
 * The dnsworker runs indefinitely, until its connection is closed or an error
 * occurs.
 */
754
755
756
static int
dnsworker_main(void *data)
{
757
758
  char address[MAX_ADDRESSLEN];
  unsigned char address_len;
759
  char answer[5];
Roger Dingledine's avatar
Roger Dingledine committed
760
  uint32_t ip;
761
  int *fdarray = data;
Roger Dingledine's avatar
Roger Dingledine committed
762
  int fd;
763
  int result;
764

765
766
  /* log_fn(LOG_NOTICE,"After spawn: fdarray @%d has %d:%d", (int)fdarray, fdarray[0],fdarray[1]); */

767
  fd = fdarray[1]; /* this side is ours */
768
#ifndef TOR_IS_MULTITHREADED
769
  tor_close_socket(fdarray[0]); /* this is the side of the socketpair the parent uses */
770
  tor_free_all(1); /* so the child doesn't hold the parent's fd's open */
771
  handle_signals(0); /* ignore interrupts from the keyboard, etc */
772
773
#endif
  tor_free(data);
774

775
  for (;;) {
776
    int r;
777

778
779
780
781
782
783
784
    if ((r = recv(fd, &address_len, 1, 0)) != 1) {
      if (r == 0) {
        log_fn(LOG_INFO,"DNS worker exiting because Tor process closed connection (either pruned idle dnsworker or died).");
      } else {
        log_fn(LOG_INFO,"DNS worker exiting because of error on connection to Tor process.");
        log_fn(LOG_INFO,"(Error on %d was %s)", fd, tor_socket_strerror(tor_socket_errno(fd)));
      }
785
      tor_close_socket(fd);
786
      spawn_exit();
787
788
    }

789
    if (address_len && read_all(fd, address, address_len, 1) != address_len) {
790
      log_fn(LOG_ERR,"read hostname failed. Child exiting.");
791
      tor_close_socket(fd);
792
      spawn_exit();
793
    }
794
    address[address_len] = 0; /* null terminate it */
795

796
797
798
799
800
    result = tor_lookup_hostname(address, &ip);
    /* Make 0.0.0.0 an error, so that we can use "0" to mean "no addr") */
    if (!ip)
      result = -1;
    switch (result) {
801
      case 1:
802
        /* XXX result can never be 1, because we set it to -1 above on error */
803
        log_fn(LOG_INFO,"Could not resolve dest addr %s (transient).",safe_str(address));
804
        answer[0] = DNS_RESOLVE_FAILED_TRANSIENT;
805
806
        break;
      case -1:
807
        log_fn(LOG_INFO,"Could not resolve dest addr %s (permanent).",safe_str(address));
808
        answer[0] = DNS_RESOLVE_FAILED_PERMANENT;
809
        break;
810
      case 0:
811
        log_fn(LOG_INFO,"Resolved address '%s'.",safe_str(address));
812
        answer[0] = DNS_RESOLVE_SUCCEEDED;
813
        break;
814
    }
Roger Dingledine's avatar
Roger Dingledine committed
815
    set_uint32(answer+1, ip);
816
    if (write_all(fd, answer, 5, 1) != 5) {
817
      log_fn(LOG_ERR,"writing answer failed. Child exiting.");
818
      tor_close_socket(fd);
819
820
      spawn_exit();
    }
821
  }