dns.c 26.4 KB
Newer Older
1
2
3
4
/* Copyright 2003 Roger Dingledine. */
/* See LICENSE for licensing information */
/* $Id$ */

Roger Dingledine's avatar
Roger Dingledine committed
5
6
7
8
/**
 * \file dns.c
 * \brief Resolve hostnames in separate processes.
 **/
9

10
11
12
13
14
/* 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.
 */

15
#include "or.h"
16
#include "tree.h"
17

18
extern or_options_t options; /* command-line and config-file options */
Roger Dingledine's avatar
Roger Dingledine committed
19

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

Roger Dingledine's avatar
Roger Dingledine committed
23
/** Maximum DNS processes to spawn. */
24
#define MAX_DNSWORKERS 100
Roger Dingledine's avatar
Roger Dingledine committed
25
/** Minimum DNS processes to spawn. */
26
#define MIN_DNSWORKERS 3
27

Roger Dingledine's avatar
Roger Dingledine committed
28
/** If more than this many processes are idle, shut down the extras. */
29
#define MAX_IDLE_DNSWORKERS 10
30

Roger Dingledine's avatar
Roger Dingledine committed
31
/** Possible outcomes from hostname lookup: permanent failure,
32
 * transient (retryable) failure, and success. */
33
34
35
36
#define DNS_RESOLVE_FAILED_TRANSIENT 1
#define DNS_RESOLVE_FAILED_PERMANENT 2
#define DNS_RESOLVE_SUCCEEDED 3

37
/** How many dnsworkers we have running right now. */
38
static int num_dnsworkers=0;
39
/** How many of the running dnsworkers have an assigned task right now. */
40
41
42
static int num_dnsworkers_busy=0;
/** When did we last rotate the dnsworkers? */
static time_t last_rotation_time=0;
43

Roger Dingledine's avatar
Roger Dingledine committed
44
/** Linked list of connections waiting for a DNS answer. */
45
46
47
48
49
struct pending_connection_t {
  struct connection_t *conn;
  struct pending_connection_t *next;
};

Roger Dingledine's avatar
Roger Dingledine committed
50
/** A DNS request: possibly completed, possibly pending; cached_resolve
51
52
53
 * structs are stored at the OR side in a splay tree, and as a linked
 * list from oldest to newest.
 */
54
55
struct cached_resolve {
  SPLAY_ENTRY(cached_resolve) node;
56
  char address[MAX_ADDRESSLEN]; /**< The hostname to be resolved. */
57
  uint32_t addr; /**< IPv4 addr for <b>address</b>. */
58
  char state; /**< 0 is pending; 1 means answer is valid; 2 means resolve failed. */
59
60
61
#define CACHE_STATE_PENDING 0
#define CACHE_STATE_VALID 1
#define CACHE_STATE_FAILED 2
62
  uint32_t expire; /**< Remove items from cache after this time. */
63
64
65
66
  struct pending_connection_t *pending_connections;
  struct cached_resolve *next;
};

67
68
69
70
static void purge_expired_resolves(uint32_t now);
static int assign_to_dnsworker(connection_t *exitconn);
static void dns_purge_resolve(struct cached_resolve *resolve);
static void dns_found_answer(char *address, uint32_t addr, char outcome);
Nick Mathewson's avatar
Nick Mathewson committed
71
static int dnsworker_main(void *data);
72
73
static int spawn_dnsworker(void);
static void spawn_enough_dnsworkers(void);
74
static void send_resolved_cell(connection_t *conn, uint8_t answer_type);
75

76
/** Splay tree of cached_resolve objects. */
77
static SPLAY_HEAD(cache_tree, cached_resolve) cache_root;
78

Roger Dingledine's avatar
Roger Dingledine committed
79
/** Function to compare hashed resolves on their addresses; used to
80
 * implement splay trees. */
81
82
static int compare_cached_resolves(struct cached_resolve *a,
                                   struct cached_resolve *b) {
83
  /* make this smarter one day? */
84
  return strncasecmp(a->address, b->address, MAX_ADDRESSLEN);
85
86
87
88
89
}

SPLAY_PROTOTYPE(cache_tree, cached_resolve, node, compare_cached_resolves);
SPLAY_GENERATE(cache_tree, cached_resolve, node, compare_cached_resolves);

90
/** Initialize the DNS cache. */
91
static void init_cache_tree(void) {
92
93
94
  SPLAY_INIT(&cache_root);
}

Roger Dingledine's avatar
Roger Dingledine committed
95
/** Initialize the DNS subsystem; called by the OR process. */
96
97
void dns_init(void) {
  init_cache_tree();
98
  last_rotation_time=time(NULL);
Roger Dingledine's avatar
Roger Dingledine committed
99
  spawn_enough_dnsworkers();
100
}
101

102
/** Linked list of resolved addresses, oldest to newest. */
Roger Dingledine's avatar
Roger Dingledine committed
103
104
static struct cached_resolve *oldest_cached_resolve = NULL;
static struct cached_resolve *newest_cached_resolve = NULL;
105

Nick Mathewson's avatar
Nick Mathewson committed
106
/** Remove every cached_resolve whose <b>expire</b> time is before <b>now</b>
107
 * from the cache. */
108
109
static void purge_expired_resolves(uint32_t now) {
  struct cached_resolve *resolve;
110
111
  struct pending_connection_t *pend;
  connection_t *pendconn;
112
113
114
115
116
117

  /* this is fast because the linked list
   * oldest_cached_resolve is ordered by when they came in.
   */
  while(oldest_cached_resolve && (oldest_cached_resolve->expire < now)) {
    resolve = oldest_cached_resolve;
118
    log(LOG_DEBUG,"Forgetting old cached resolve (expires %lu)", (unsigned long)resolve->expire);
119
120
    if(resolve->state == CACHE_STATE_PENDING) {
      log_fn(LOG_WARN,"Expiring a dns resolve that's still pending. Forgot to cull it?");
121
122
123
124
125
126
127
128
129
130
131
    }
    if (resolve->pending_connections) {
      log_fn(LOG_WARN, "Closing pending connections on expiring DNS resolve!");
      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;
        connection_edge_end(pendconn, END_STREAM_REASON_MISC,
                            pendconn->cpath_layer);
132
        circuit_detach_stream(circuit_get_by_conn(pendconn), pendconn);
133
134
135
        connection_free(pendconn);
        tor_free(pend);
      }
136
    }
137
138
139
140
    oldest_cached_resolve = resolve->next;
    if(!oldest_cached_resolve) /* if there are no more, */
      newest_cached_resolve = NULL; /* then make sure the list's tail knows that too */
    SPLAY_REMOVE(cache_tree, &cache_root, resolve);
141
    tor_free(resolve);
142
143
144
  }
}

145
146
147
static void send_resolved_cell(connection_t *conn, uint8_t answer_type)
{
  char buf[RELAY_PAYLOAD_SIZE];
148
  size_t buflen;
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172

  buf[0] = answer_type;

  switch (answer_type)
    {
    case RESOLVED_TYPE_IPV4:
      buf[1] = 4;
      set_uint32(buf+2, htonl(conn->addr));
      buflen = 6;
      break;
    case RESOLVED_TYPE_ERROR_TRANSIENT:
    case RESOLVED_TYPE_ERROR:
      buf[1] = 24; /* length of "error resolving hostname" */
      strcpy(buf+2, "error resolving hostname");
      buflen = 26;
      break;
    default:
      tor_assert(0);
    }
  connection_edge_send_command(conn, circuit_get_by_conn(conn),
                               RELAY_COMMAND_RESOLVED, buf, buflen,
                               conn->cpath_layer);
}

Nick Mathewson's avatar
Nick Mathewson committed
173
174
/** 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.
175
 * If resolve failed, return -1.
176
177
178
179
180
181
182
183
184
 *
 * 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.
 */
int dns_resolve(connection_t *exitconn) {
  struct cached_resolve *resolve;
Roger Dingledine's avatar
   
Roger Dingledine committed
185
  struct cached_resolve search;
186
  struct pending_connection_t *pending_connection;
187
  struct in_addr in;
188
  uint32_t now = time(NULL);
189
  assert_connection_ok(exitconn, 0);
190
  tor_assert(exitconn->s == -1);
191

192
193
194
195
196
  /* 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);
    return 1;
197
198
199
200
  }

  /* then take this opportunity to see if there are any expired
   * resolves in the tree. */
201
  purge_expired_resolves(now);
202

203
204
  /* now check the tree to see if 'address' is already there. */
  strncpy(search.address, exitconn->address, MAX_ADDRESSLEN);
205
  search.address[MAX_ADDRESSLEN-1] = 0;
Roger Dingledine's avatar
   
Roger Dingledine committed
206
  resolve = SPLAY_FIND(cache_tree, &cache_root, &search);
207
  if(resolve) { /* already there */
208
209
210
    switch(resolve->state) {
      case CACHE_STATE_PENDING:
        /* add us to the pending list */
211
212
        pending_connection = tor_malloc_zero(
                                      sizeof(struct pending_connection_t));
213
        pending_connection->conn = exitconn;
Roger Dingledine's avatar
   
Roger Dingledine committed
214
215
        pending_connection->next = resolve->pending_connections;
        resolve->pending_connections = pending_connection;
216
217
        log_fn(LOG_DEBUG,"Connection (fd %d) waiting for pending DNS resolve of '%s'",
               exitconn->s, exitconn->address);
218
        exitconn->state = EXIT_CONN_STATE_RESOLVING;
Roger Dingledine's avatar
   
Roger Dingledine committed
219
        return 0;
220
      case CACHE_STATE_VALID:
221
        exitconn->addr = resolve->addr;
222
223
        log_fn(LOG_DEBUG,"Connection (fd %d) found cached answer for '%s'",
               exitconn->s, exitconn->address);
224
225
        if (exitconn->purpose == EXIT_PURPOSE_RESOLVE)
          send_resolved_cell(exitconn, RESOLVED_TYPE_IPV4);
226
        return 1;
227
      case CACHE_STATE_FAILED:
228
229
        log_fn(LOG_DEBUG,"Connection (fd %d) found cached error for '%s'",
               exitconn->s, exitconn->address);
230
231
        if (exitconn->purpose == EXIT_PURPOSE_RESOLVE)
          send_resolved_cell(exitconn, RESOLVED_TYPE_ERROR);
232
233
        return -1;
    }
Roger Dingledine's avatar
Roger Dingledine committed
234
    tor_assert(0);
Roger Dingledine's avatar
Roger Dingledine committed
235
236
237
238
  }
  /* not there, need to add it */
  resolve = tor_malloc_zero(sizeof(struct cached_resolve));
  resolve->state = CACHE_STATE_PENDING;
239
240
  resolve->expire = now + MAX_DNS_ENTRY_AGE;
  strncpy(resolve->address, exitconn->address, MAX_ADDRESSLEN);
241
  resolve->address[MAX_ADDRESSLEN-1] = 0;
Roger Dingledine's avatar
Roger Dingledine committed
242
243

  /* add us to the pending list */
244
  pending_connection = tor_malloc_zero(sizeof(struct pending_connection_t));
Roger Dingledine's avatar
Roger Dingledine committed
245
246
  pending_connection->conn = exitconn;
  resolve->pending_connections = pending_connection;
247
  exitconn->state = EXIT_CONN_STATE_RESOLVING;
Roger Dingledine's avatar
Roger Dingledine committed
248
249
250
251
252
253

  /* add us to the linked list of resolves */
  if (!oldest_cached_resolve) {
    oldest_cached_resolve = resolve;
  } else {
    newest_cached_resolve->next = resolve;
254
  }
Roger Dingledine's avatar
Roger Dingledine committed
255
  newest_cached_resolve = resolve;
256

Roger Dingledine's avatar
Roger Dingledine committed
257
258
  SPLAY_INSERT(cache_tree, &cache_root, resolve);
  return assign_to_dnsworker(exitconn);
259
260
}

Roger Dingledine's avatar
Roger Dingledine committed
261
/** Find or spawn a dns worker process to handle resolving
Nick Mathewson's avatar
Nick Mathewson committed
262
 * <b>exitconn</b>-\>address; tell that dns worker to begin resolving.
263
 */
Roger Dingledine's avatar
Roger Dingledine committed
264
static int assign_to_dnsworker(connection_t *exitconn) {
265
266
  connection_t *dnsconn;
  unsigned char len;
267

Roger Dingledine's avatar
Roger Dingledine committed
268
  tor_assert(exitconn->state == EXIT_CONN_STATE_RESOLVING);
269
  tor_assert(exitconn->s == -1);
270

Roger Dingledine's avatar
Roger Dingledine committed
271
  spawn_enough_dnsworkers(); /* respawn here, to be sure there are enough */
272

273
  dnsconn = connection_get_by_type_state(CONN_TYPE_DNSWORKER, DNSWORKER_STATE_IDLE);
274
275

  if(!dnsconn) {
Roger Dingledine's avatar
Roger Dingledine committed
276
    log_fn(LOG_WARN,"no idle dns workers. Failing.");
277
    dns_cancel_pending_resolve(exitconn->address);
278
    send_resolved_cell(exitconn, RESOLVED_TYPE_ERROR_TRANSIENT);
279
    return -1;
280
281
  }

282
283
284
  log_fn(LOG_DEBUG, "Connection (fd %d) needs to resolve '%s'; assigning to DNSWorker (fd %d)",
         exitconn->s, exitconn->address, dnsconn->s);

285
  tor_free(dnsconn->address);
286
  dnsconn->address = tor_strdup(exitconn->address);
287
  dnsconn->state = DNSWORKER_STATE_BUSY;
Roger Dingledine's avatar
Roger Dingledine committed
288
  num_dnsworkers_busy++;
289

290
  len = strlen(dnsconn->address);
291
292
  connection_write_to_buf(&len, 1, dnsconn);
  connection_write_to_buf(dnsconn->address, len, dnsconn);
293

Roger Dingledine's avatar
Roger Dingledine committed
294
//  log_fn(LOG_DEBUG,"submitted '%s'", exitconn->address);
295
296
297
  return 0;
}

Nick Mathewson's avatar
Nick Mathewson committed
298
/** Remove <b>conn</b> from the list of connections waiting for conn-\>address.
299
 */
300
301
302
303
304
305
void connection_dns_remove(connection_t *conn)
{
  struct pending_connection_t *pend, *victim;
  struct cached_resolve search;
  struct cached_resolve *resolve;

306
307
308
  tor_assert(conn->type == CONN_TYPE_EXIT);
  tor_assert(conn->state == EXIT_CONN_STATE_RESOLVING);

309
310
311
312
313
314
315
316
317
  strncpy(search.address, conn->address, MAX_ADDRESSLEN);
  search.address[MAX_ADDRESSLEN-1] = 0;

  resolve = SPLAY_FIND(cache_tree, &cache_root, &search);
  if(!resolve) {
    log_fn(LOG_WARN,"Address '%s' is not pending. Dropping.", conn->address);
    return;
  }

Roger Dingledine's avatar
Roger Dingledine committed
318
  tor_assert(resolve->pending_connections);
319
320
321
322
323
324
  assert_connection_ok(conn,0);

  pend = resolve->pending_connections;

  if(pend->conn == conn) {
    resolve->pending_connections = pend->next;
325
    tor_free(pend);
326
    log_fn(LOG_DEBUG, "First connection (fd %d) no longer waiting for resolve of '%s'",
327
328
329
330
331
332
333
           conn->s, conn->address);
    return;
  } else {
    for( ; pend->next; pend = pend->next) {
      if(pend->next->conn == conn) {
        victim = pend->next;
        pend->next = victim->next;
334
        tor_free(victim);
335
336
337
338
339
        log_fn(LOG_DEBUG, "Connection (fd %d) no longer waiting for resolve of '%s'",
               conn->s, conn->address);
        return; /* more are pending */
      }
    }
Roger Dingledine's avatar
Roger Dingledine committed
340
    tor_assert(0); /* not reachable unless onlyconn not in pending list */
341
342
343
  }
}

Roger Dingledine's avatar
Roger Dingledine committed
344
/** Log an error and abort if conn is waiting for a DNS resolve.
345
 */
346
347
348
349
350
351
352
353
void assert_connection_edge_not_dns_pending(connection_t *conn) {
  struct pending_connection_t *pend;
  struct cached_resolve *resolve;

  SPLAY_FOREACH(resolve, cache_tree, &cache_root) {
    for(pend = resolve->pending_connections;
        pend;
        pend = pend->next) {
Roger Dingledine's avatar
Roger Dingledine committed
354
      tor_assert(pend->conn != conn);
355
356
357
358
    }
  }
}

Roger Dingledine's avatar
Roger Dingledine committed
359
/** Log an error and abort if any connection waiting for a DNS resolve is
360
 * corrupted. */
361
362
363
364
365
366
367
368
369
void assert_all_pending_dns_resolves_ok(void) {
  struct pending_connection_t *pend;
  struct cached_resolve *resolve;

  SPLAY_FOREACH(resolve, cache_tree, &cache_root) {
    for(pend = resolve->pending_connections;
        pend;
        pend = pend->next) {
      assert_connection_ok(pend->conn, 0);
370
371
      tor_assert(pend->conn->s == -1);
      tor_assert(!connection_in_array(pend->conn));
372
373
374
375
    }
  }
}

Nick Mathewson's avatar
Nick Mathewson committed
376
377
378
/** 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.
379
 */
380
381
void dns_cancel_pending_resolve(char *address) {
  struct pending_connection_t *pend;
382
  struct cached_resolve search;
383
  struct cached_resolve *resolve;
384
  connection_t *pendconn;
385

386
  strncpy(search.address, address, MAX_ADDRESSLEN);
387
  search.address[MAX_ADDRESSLEN-1] = 0;
388
389
390

  resolve = SPLAY_FIND(cache_tree, &cache_root, &search);
  if(!resolve) {
391
    log_fn(LOG_WARN,"Address '%s' is not pending. Dropping.", address);
392
393
394
    return;
  }

Roger Dingledine's avatar
Roger Dingledine committed
395
  tor_assert(resolve->pending_connections);
396

397
398
399
400
  /* mark all pending connections to fail */
  log_fn(LOG_DEBUG, "Failing all connections waiting on DNS resolve of '%s'",
         address);
  while(resolve->pending_connections) {
401
    pend = resolve->pending_connections;
402
    pend->conn->state = EXIT_CONN_STATE_RESOLVEFAILED;
403
    pendconn = pend->conn;
404
    tor_assert(pendconn->s == -1);
405
406
407
    if(!pendconn->marked_for_close) {
      connection_edge_end(pendconn, END_STREAM_REASON_MISC, pendconn->cpath_layer);
    }
408
    circuit_detach_stream(circuit_get_by_conn(pendconn), pendconn);
409
    connection_free(pendconn);
410
411
    resolve->pending_connections = pend->next;
    tor_free(pend);
412
413
  }

414
415
416
  dns_purge_resolve(resolve);
}

Nick Mathewson's avatar
Nick Mathewson committed
417
/** Remove <b>resolve</b> from the cache.
418
 */
419
420
421
static void dns_purge_resolve(struct cached_resolve *resolve) {
  struct cached_resolve *tmp;

422
423
424
425
426
  /* remove resolve from the linked list */
  if(resolve == oldest_cached_resolve) {
    oldest_cached_resolve = resolve->next;
    if(oldest_cached_resolve == NULL)
      newest_cached_resolve = NULL;
427
  } else {
428
429
    /* FFFF make it a doubly linked list if this becomes too slow */
    for(tmp=oldest_cached_resolve; tmp && tmp->next != resolve; tmp=tmp->next) ;
Roger Dingledine's avatar
Roger Dingledine committed
430
    tor_assert(tmp); /* it's got to be in the list, or we screwed up somewhere else */
431
432
433
434
    tmp->next = resolve->next; /* unlink it */

    if(newest_cached_resolve == resolve)
      newest_cached_resolve = tmp;
435
  }
436
437
438
439

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

440
  tor_free(resolve);
441
442
}

Roger Dingledine's avatar
Roger Dingledine committed
443
/** Called on the OR side when a DNS worker tells us the outcome of a DNS
444
 * resolve: tell all pending connections about the result of the lookup, and
Nick Mathewson's avatar
Nick Mathewson committed
445
446
447
448
 * 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}.
449
 */
450
static void dns_found_answer(char *address, uint32_t addr, char outcome) {
451
452
453
  struct pending_connection_t *pend;
  struct cached_resolve search;
  struct cached_resolve *resolve;
454
  connection_t *pendconn;
455
  circuit_t *circ;
456

457
  strncpy(search.address, address, MAX_ADDRESSLEN);
458
  search.address[MAX_ADDRESSLEN-1] = 0;
459
460
461

  resolve = SPLAY_FIND(cache_tree, &cache_root, &search);
  if(!resolve) {
462
    log_fn(LOG_INFO,"Resolved unasked address '%s'? Dropping.", address);
463
464
    /* XXX Why drop?  Just because we don't care now doesn't mean we shouldn't
     * XXX cache the result for later. */
465
    return;
466
467
  }

468
  if (resolve->state != CACHE_STATE_PENDING) {
469
470
    /* XXXX Maybe update addr? or check addr for consistency? Or let
     * VALID replace FAILED? */
471
472
    log_fn(LOG_WARN, "Resolved '%s' which was already resolved; ignoring",
           address);
Roger Dingledine's avatar
Roger Dingledine committed
473
    tor_assert(resolve->pending_connections == NULL);
474
475
476
477
478
479
    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
480
  /* tor_assert(resolve->state == CACHE_STATE_PENDING); */
481

482
  resolve->addr = ntohl(addr);
483
  if(outcome == DNS_RESOLVE_SUCCEEDED)
484
485
486
487
488
489
    resolve->state = CACHE_STATE_VALID;
  else
    resolve->state = CACHE_STATE_FAILED;

  while(resolve->pending_connections) {
    pend = resolve->pending_connections;
490
    assert_connection_ok(pend->conn,time(NULL));
491
    pend->conn->addr = resolve->addr;
492
493
    pendconn = pend->conn; /* don't pass complex things to the
                              connection_mark_for_close macro */
494

495
    if(resolve->state == CACHE_STATE_FAILED) {
496
      /* prevent double-remove. */
497
      pendconn->state = EXIT_CONN_STATE_RESOLVEFAILED;
498
      if (pendconn->purpose == EXIT_PURPOSE_CONNECT) {
499
500
        connection_edge_end(pendconn, END_STREAM_REASON_RESOLVEFAILED, pendconn->cpath_layer);
        /* This detach must happen after we send the end cell. */
501
502
        circuit_detach_stream(circuit_get_by_conn(pendconn), pendconn);
      } else {
503
        send_resolved_cell(pendconn, RESOLVED_TYPE_ERROR);
504
505
506
        /* This detach must happen after we send the resolved cell. */
        circuit_detach_stream(circuit_get_by_conn(pendconn), pendconn);
      }
507
      connection_free(pendconn);
Roger Dingledine's avatar
Roger Dingledine committed
508
    } else {
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
      if (pendconn->purpose == EXIT_PURPOSE_CONNECT) {
        /* prevent double-remove. */
        pend->conn->state = EXIT_CONN_STATE_CONNECTING;

        circ = circuit_get_by_conn(pend->conn);
        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;
        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);
        circ = circuit_get_by_conn(pendconn);
        tor_assert(circ);
        circuit_detach_stream(circ, pendconn);
        connection_free(pendconn);
      }
Roger Dingledine's avatar
Roger Dingledine committed
532
    }
533
534
    resolve->pending_connections = pend->next;
    tor_free(pend);
535
  }
536
537
538
539

  if(outcome == DNS_RESOLVE_FAILED_TRANSIENT) { /* remove from cache */
    dns_purge_resolve(resolve);
  }
540
541
}

542
543
/******************************************************************/

Nick Mathewson's avatar
Nick Mathewson committed
544
/*
545
 * Connection between OR and dnsworker
Nick Mathewson's avatar
Nick Mathewson committed
546
 */
547

Roger Dingledine's avatar
Roger Dingledine committed
548
/** Write handler: called when we've pushed a request to a dnsworker. */
549
int connection_dns_finished_flushing(connection_t *conn) {
Roger Dingledine's avatar
Roger Dingledine committed
550
  tor_assert(conn && conn->type == CONN_TYPE_DNSWORKER);
551
552
553
554
  connection_stop_writing(conn);
  return 0;
}

Roger Dingledine's avatar
Roger Dingledine committed
555
/** Read handler: called when we get data from a dnsworker.  If the
556
557
558
 * connection is closed, mark the dnsworker as dead.  Otherwise, see
 * if we have a complete answer.  If so, call dns_found_answer on the
 * result.  If not, wait.  Returns 0. */
559
int connection_dns_process_inbuf(connection_t *conn) {
560
  char success;
561
  uint32_t addr;
562

Roger Dingledine's avatar
Roger Dingledine committed
563
  tor_assert(conn && conn->type == CONN_TYPE_DNSWORKER);
564
565

  if(conn->inbuf_reached_eof) {
566
    log_fn(LOG_WARN,"Read eof. Worker died unexpectedly.");
567
    if(conn->state == DNSWORKER_STATE_BUSY) {
568
      dns_cancel_pending_resolve(conn->address);
Roger Dingledine's avatar
Roger Dingledine committed
569
      num_dnsworkers_busy--;
570
    }
Roger Dingledine's avatar
Roger Dingledine committed
571
    num_dnsworkers--;
572
    connection_mark_for_close(conn);
573
    return 0;
574
575
  }

576
577
578
579
  if(conn->state != DNSWORKER_STATE_BUSY) {
    log_fn(LOG_WARN,"Bug: poll() indicated than an idle dns worker was readable. Please report.");
    return 0;
  }
580
  if(buf_datalen(conn->inbuf) < 5) /* entire answer available? */
581
    return 0; /* not yet */
582
  tor_assert(conn->state == DNSWORKER_STATE_BUSY);
Roger Dingledine's avatar
Roger Dingledine committed
583
  tor_assert(buf_datalen(conn->inbuf) == 5);
584

585
586
  connection_fetch_from_buf(&success,1,conn);
  connection_fetch_from_buf((char *)&addr,sizeof(uint32_t),conn);
587

588
589
590
  log_fn(LOG_DEBUG, "DNSWorker (fd %d) returned answer for '%s'",
         conn->s, conn->address);

Roger Dingledine's avatar
Roger Dingledine committed
591
592
  tor_assert(success >= DNS_RESOLVE_FAILED_TRANSIENT);
  tor_assert(success <= DNS_RESOLVE_SUCCEEDED);
593
  dns_found_answer(conn->address, addr, success);
594

595
  tor_free(conn->address);
596
  conn->address = tor_strdup("<idle>");
597
  conn->state = DNSWORKER_STATE_IDLE;
Roger Dingledine's avatar
Roger Dingledine committed
598
  num_dnsworkers_busy--;
599
600
601
602
603
  if (conn->timestamp_created < last_rotation_time) {
    connection_mark_for_close(conn);
    num_dnsworkers--;
    spawn_enough_dnsworkers();
  }
604
605
606
  return 0;
}

607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
/** Close and re-open all idle dnsworkers; schedule busy ones to be closed
 * and re-opened once they're no longer busy.
 **/
void dnsworkers_rotate(void)
{
  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);
  spawn_enough_dnsworkers();
}

Roger Dingledine's avatar
Roger Dingledine committed
622
/** Implementation for DNS workers; this code runs in a separate
623
624
625
 * 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
626
627
628
629
630
631
 *    - The OR says:
 *         - ADDRESSLEN [1 byte]
 *         - ADDRESS    [ADDRESSLEN bytes]
 *    - The DNS worker does the lookup, and replies:
 *         - OUTCOME    [1 byte]
 *         - IP         [4 bytes]
632
633
634
635
636
637
638
 *
 * 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.
 */
Nick Mathewson's avatar
Nick Mathewson committed
639
static int dnsworker_main(void *data) {
640
641
  char address[MAX_ADDRESSLEN];
  unsigned char address_len;
642
  char answer[5];
Roger Dingledine's avatar
Roger Dingledine committed
643
  uint32_t ip;
644
  int *fdarray = data;
Roger Dingledine's avatar
Roger Dingledine committed
645
  int fd;
646
  int result;
647

648
  tor_close_socket(fdarray[0]); /* this is the side of the socketpair the parent uses */
649
  fd = fdarray[1]; /* this side is ours */
650
#ifndef MS_WINDOWS
651
  connection_free_all(); /* so the child doesn't hold the parent's fd's open */
652
#endif
653
  handle_signals(0); /* ignore interrupts from the keyboard, etc */
654
655
656

  for(;;) {

657
    if(recv(fd, &address_len, 1, 0) != 1) {
658
      log_fn(LOG_INFO,"dnsworker exiting because tor process closed connection (either pruned idle dnsworker or died).");
659
      spawn_exit();
660
661
    }

662
    if(address_len && read_all(fd, address, address_len, 1) != address_len) {
663
      log_fn(LOG_ERR,"read hostname failed. Child exiting.");
664
      spawn_exit();
665
    }
666
    address[address_len] = 0; /* null terminate it */
667

668
669
670
671
672
    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) {
673
      case 1:
674
/* XXX008 result can never be 1, because we set it to -1 above on error */
675
676
        log_fn(LOG_INFO,"Could not resolve dest addr %s (transient).",address);
        answer[0] = DNS_RESOLVE_FAILED_TRANSIENT;
677
678
        break;
      case -1:
679
680
        log_fn(LOG_INFO,"Could not resolve dest addr %s (permanent).",address);
        answer[0] = DNS_RESOLVE_FAILED_PERMANENT;
681
        break;
682
683
684
      case 0:
        log_fn(LOG_INFO,"Resolved address '%s'.",address);
        answer[0] = DNS_RESOLVE_SUCCEEDED;
685
        break;
686
    }
Roger Dingledine's avatar
Roger Dingledine committed
687
    set_uint32(answer+1, ip);
688
689
690
691
    if(write_all(fd, answer, 5, 1) != 5) {
      log_fn(LOG_ERR,"writing answer failed. Child exiting.");
      spawn_exit();
    }
692
  }
693
  return 0; /* windows wants this function to return an int */
694
695
}

Roger Dingledine's avatar
Roger Dingledine committed
696
/** Launch a new DNS worker; return 0 on success, -1 on failure.
697
 */
Roger Dingledine's avatar
Roger Dingledine committed
698
static int spawn_dnsworker(void) {
699
700
701
  int fd[2];
  connection_t *conn;

702
  if(tor_socketpair(AF_UNIX, SOCK_STREAM, 0, fd) < 0) {
703
704
    log(LOG_ERR, "Couldn't construct socketpair: %s",
        tor_socket_strerror(tor_socket_errno(-1)));
705
    tor_cleanup();
706
707
708
    exit(1);
  }

709
  spawn_func(dnsworker_main, (void*)fd);
Roger Dingledine's avatar
Roger Dingledine committed
710
  log_fn(LOG_DEBUG,"just spawned a worker.");
711
  tor_close_socket(fd[1]); /* we don't need the worker's side of the pipe */
712
713
714

  conn = connection_new(CONN_TYPE_DNSWORKER);

715
  set_socket_nonblocking(fd[0]);
716
717
718

  /* set up conn so it's got all the data we need to remember */
  conn->s = fd[0];
Roger Dingledine's avatar
Roger Dingledine committed
719
  conn->address = tor_strdup("<unused>");
720
721

  if(connection_add(conn) < 0) { /* no space, forget it */
Roger Dingledine's avatar
Roger Dingledine committed
722
    log_fn(LOG_WARN,"connection_add failed. Giving up.");
723
724
725
726
727
728
729
730
731
732
    connection_free(conn); /* this closes fd[0] */
    return -1;
  }

  conn->state = DNSWORKER_STATE_IDLE;
  connection_start_reading(conn);

  return 0; /* success */
}

Roger Dingledine's avatar
Roger Dingledine committed
733
/** If we have too many or too few DNS workers, spawn or kill some.
734
 */
Roger Dingledine's avatar
Roger Dingledine committed
735
736
static void spawn_enough_dnsworkers(void) {
  int num_dnsworkers_needed; /* aim to have 1 more than needed,
737
                           * but no less than min and no more than max */
738
739
  connection_t *dnsconn;

740
  /* XXX This may not be the best strategy. Maybe we should queue pending
741
742
743
744
745
746
   *     requests until the old ones finish or time out: otherwise, if
   *     the connection requests come fast enough, we never get any DNS done. -NM
   * XXX But if we queue them, then the adversary can pile even more
   *     queries onto us, blocking legitimate requests for even longer.
   *     Maybe we should compromise and only kill if it's been at it for
   *     more than, e.g., 2 seconds. -RD
747
   */
Roger Dingledine's avatar
Roger Dingledine committed
748
  if(num_dnsworkers_busy == MAX_DNSWORKERS) {
749
750
751
    /* We always want at least one worker idle.
     * So find the oldest busy worker and kill it.
     */
752
753
    dnsconn = connection_get_by_type_state_lastwritten(CONN_TYPE_DNSWORKER,
                                                       DNSWORKER_STATE_BUSY);
Roger Dingledine's avatar
Roger Dingledine committed
754
    tor_assert(dnsconn);
755

756
757
    log_fn(LOG_WARN, "%d DNS workers are spawned; all are busy. Killing one.",
           MAX_DNSWORKERS);
758

759
    connection_mark_for_close(dnsconn);
Roger Dingledine's avatar
Roger Dingledine committed
760
    num_dnsworkers_busy--;
761
    num_dnsworkers--;
762
  }
763

Roger Dingledine's avatar
Roger Dingledine committed
764
765
  if(num_dnsworkers_busy >= MIN_DNSWORKERS)
    num_dnsworkers_needed = num_dnsworkers_busy+1;
766
  else
Roger Dingledine's avatar
Roger Dingledine committed
767
    num_dnsworkers_needed = MIN_DNSWORKERS;
768

Roger Dingledine's avatar
Roger Dingledine committed
769
770
  while(num_dnsworkers < num_dnsworkers_needed) {
    if(spawn_dnsworker() < 0) {
Roger Dingledine's avatar
Roger Dingledine committed
771
      log(LOG_WARN,"spawn_enough_dnsworkers(): spawn failed!");
772
773
      return;
    }
Roger Dingledine's avatar
Roger Dingledine committed
774
    num_dnsworkers++;
775
776
  }

777
  while(num_dnsworkers > num_dnsworkers_busy+MAX_IDLE_DNSWORKERS) { /* too many idle? */
778
    /* cull excess workers */
779
780
    log_fn(LOG_WARN,"%d of %d dnsworkers are idle. Killing one.",
           num_dnsworkers-num_dnsworkers_needed, num_dnsworkers);
781
    dnsconn = connection_get_by_type_state(CONN_TYPE_DNSWORKER, DNSWORKER_STATE_IDLE);
Roger Dingledine's avatar
Roger Dingledine committed
782
    tor_assert(dnsconn);
783
    connection_mark_for_close(dnsconn);
Roger Dingledine's avatar
Roger Dingledine committed
784
    num_dnsworkers--;
785
  }
786
787
}

788
789
790
791
792
793
794
/*
  Local Variables:
  mode:c
  indent-tabs-mode:nil
  c-basic-offset:2
  End:
*/