dns.c 16.9 KB
Newer Older
1
2
3
4
/* Copyright 2003 Roger Dingledine. */
/* See LICENSE for licensing information */
/* $Id$ */

5
6
7
8
9
/* 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.
 */

10
#include "or.h"
11
#include "tree.h"
12

13
14
#define MAX_ADDRESSLEN 256

15
16
#define MAX_DNSWORKERS 50
#define MIN_DNSWORKERS 3
17
#define MAX_IDLE_DNSWORKERS 10
18

Roger Dingledine's avatar
Roger Dingledine committed
19
20
int num_dnsworkers=0;
int num_dnsworkers_busy=0;
21

22
static void purge_expired_resolves(uint32_t now);
Roger Dingledine's avatar
Roger Dingledine committed
23
static int assign_to_dnsworker(connection_t *exitconn);
24
static void dns_found_answer(char *address, uint32_t addr);
25
int dnsworker_main(void *data);
Roger Dingledine's avatar
Roger Dingledine committed
26
27
static int spawn_dnsworker(void);
static void spawn_enough_dnsworkers(void);
28
29
30
31
32
33
34
35

struct pending_connection_t {
  struct connection_t *conn;
  struct pending_connection_t *next;
};

struct cached_resolve {
  SPLAY_ENTRY(cached_resolve) node;
36
37
  char address[MAX_ADDRESSLEN]; /* the hostname to be resolved */
  uint32_t addr; /* in host order. I know I'm horrible for assuming ipv4 */
38
39
40
41
42
43
44
45
46
  char state; /* 0 is pending; 1 means answer is valid; 2 means resolve failed */
#define CACHE_STATE_PENDING 0
#define CACHE_STATE_VALID 1
#define CACHE_STATE_FAILED 2
  uint32_t expire; /* remove untouched items from cache after some time? */
  struct pending_connection_t *pending_connections;
  struct cached_resolve *next;
};

47
static SPLAY_HEAD(cache_tree, cached_resolve) cache_root;
48

49
50
static int compare_cached_resolves(struct cached_resolve *a,
                                   struct cached_resolve *b) {
51
  /* make this smarter one day? */
52
  return strncasecmp(a->address, b->address, MAX_ADDRESSLEN);
53
54
55
56
57
}

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

58
static void init_cache_tree(void) {
59
60
61
  SPLAY_INIT(&cache_root);
}

62
63
void dns_init(void) {
  init_cache_tree();
Roger Dingledine's avatar
Roger Dingledine committed
64
  spawn_enough_dnsworkers();
65
}
66

67
68
69
static struct cached_resolve *oldest_cached_resolve = NULL; /* linked list, */
static struct cached_resolve *newest_cached_resolve = NULL; /* oldest to newest */

70
71
72
73
74
75
76
77
static void purge_expired_resolves(uint32_t now) {
  struct cached_resolve *resolve;

  /* 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;
78
    log(LOG_DEBUG,"Forgetting old cached resolve (expires %lu)", (unsigned long)resolve->expire);
79
80
81
82
83
84
85
86
    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);
    free(resolve);
  }
}

87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
#if 0
uint32_t dns_lookup(const char *address) {
  struct in_addr in;
  uint32_t now = time(NULL);

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

  if (inet_aton(address, &in)) {
    log_fn(LOG_DEBUG, "Using static address %s (%08X)", address,
           ntohl(in.s_addr));
    return ntohl(in.s_addr);
  }

  strncpy(search.address, address, MAX_ADDRESSLEN);
103
  search.address[MAX_ADDRESSLEN-1] = 0;
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
  resolve = SPLAY_FIND(cache_tree, &cache_root, &search);
  if(resolve) { /* it's there */
    if(resolve->state == CACHE_STATE_VALID) {
      in.s_addr = htonl(resolve->addr);
      log_fn(LOG_DEBUG, "Found cached entry for address %s: %s", address,
             inet_ntoa(in));
      return resolve->addr;
    }
    log_fn(LOG_DEBUG, "Entry found for address %s but it's not valid. Returning 0.",
           address);
    return 0;
  }
  /* it's not there */
  log_fn(LOG_DEBUG, "No entry found for address %s", address);
  return 0;
}
#endif

122
/* See if we have a cache entry for 'exitconn->address'. if so,
123
124
 * if resolve valid, put it into exitconn->addr and return 1.
 * If resolve failed, return -1.
125
126
127
128
129
130
131
132
133
 *
 * 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
134
  struct cached_resolve search;
135
  struct pending_connection_t *pending_connection;
136
  uint32_t now = time(NULL);
137

138
  /* first take this opportunity to see if there are any expired
139
140
     resolves in the tree.*/
  purge_expired_resolves(now);
141

142
143
  /* now check the tree to see if 'address' is already there. */
  strncpy(search.address, exitconn->address, MAX_ADDRESSLEN);
144
  search.address[MAX_ADDRESSLEN-1] = 0;
Roger Dingledine's avatar
   
Roger Dingledine committed
145
  resolve = SPLAY_FIND(cache_tree, &cache_root, &search);
146
  if(resolve) { /* already there */
147
148
149
    switch(resolve->state) {
      case CACHE_STATE_PENDING:
        /* add us to the pending list */
150
        pending_connection = tor_malloc(sizeof(struct pending_connection_t));
151
        pending_connection->conn = exitconn;
Roger Dingledine's avatar
   
Roger Dingledine committed
152
153
        pending_connection->next = resolve->pending_connections;
        resolve->pending_connections = pending_connection;
154
155
        log_fn(LOG_DEBUG,"Connection (fd %d) waiting for pending DNS resolve of '%s'",
               exitconn->s, exitconn->address);
Roger Dingledine's avatar
   
Roger Dingledine committed
156
        return 0;
157
      case CACHE_STATE_VALID:
158
        exitconn->addr = resolve->addr;
159
160
        log_fn(LOG_DEBUG,"Connection (fd %d) found cached answer for '%s'",
               exitconn->s, exitconn->address);
161
        return 1;
162
163
164
      case CACHE_STATE_FAILED:
        return -1;
    }
Roger Dingledine's avatar
Roger Dingledine committed
165
166
167
168
169
    assert(0);
  }
  /* not there, need to add it */
  resolve = tor_malloc_zero(sizeof(struct cached_resolve));
  resolve->state = CACHE_STATE_PENDING;
170
171
  resolve->expire = now + MAX_DNS_ENTRY_AGE;
  strncpy(resolve->address, exitconn->address, MAX_ADDRESSLEN);
172
  resolve->address[MAX_ADDRESSLEN-1] = 0;
Roger Dingledine's avatar
Roger Dingledine committed
173
174
175
176
177
178
179
180
181
182
183
184

  /* add us to the pending list */
  pending_connection = tor_malloc(sizeof(struct pending_connection_t));
  pending_connection->conn = exitconn;
  pending_connection->next = resolve->pending_connections;
  resolve->pending_connections = pending_connection;

  /* add us to the linked list of resolves */
  if (!oldest_cached_resolve) {
    oldest_cached_resolve = resolve;
  } else {
    newest_cached_resolve->next = resolve;
185
  }
Roger Dingledine's avatar
Roger Dingledine committed
186
  newest_cached_resolve = resolve;
187

Roger Dingledine's avatar
Roger Dingledine committed
188
189
  SPLAY_INSERT(cache_tree, &cache_root, resolve);
  return assign_to_dnsworker(exitconn);
190
191
}

Roger Dingledine's avatar
Roger Dingledine committed
192
static int assign_to_dnsworker(connection_t *exitconn) {
193
194
  connection_t *dnsconn;
  unsigned char len;
195

Roger Dingledine's avatar
Roger Dingledine committed
196
  spawn_enough_dnsworkers(); /* respawn here, to be sure there are enough */
197

198
  dnsconn = connection_get_by_type_state(CONN_TYPE_DNSWORKER, DNSWORKER_STATE_IDLE);
199
200

  if(!dnsconn) {
Roger Dingledine's avatar
Roger Dingledine committed
201
    log_fn(LOG_WARN,"no idle dns workers. Failing.");
202
    dns_cancel_pending_resolve(exitconn->address, NULL);
203
    return -1;
204
205
  }

206
207
208
  log_fn(LOG_DEBUG, "Connection (fd %d) needs to resolve '%s'; assigning to DNSWorker (fd %d)",
         exitconn->s, exitconn->address, dnsconn->s);

Roger Dingledine's avatar
Roger Dingledine committed
209
  free(dnsconn->address);
210
  dnsconn->address = tor_strdup(exitconn->address);
211
  dnsconn->state = DNSWORKER_STATE_BUSY;
Roger Dingledine's avatar
Roger Dingledine committed
212
  num_dnsworkers_busy++;
213

214
  len = strlen(dnsconn->address);
215
216
  connection_write_to_buf(&len, 1, dnsconn);
  connection_write_to_buf(dnsconn->address, len, dnsconn);
217

Roger Dingledine's avatar
Roger Dingledine committed
218
//  log_fn(LOG_DEBUG,"submitted '%s'", exitconn->address);
219
220
221
  return 0;
}

222
223
224
225
/* if onlyconn is NULL, cancel the whole thing. if onlyconn is defined,
 * then remove onlyconn from the pending list, and if the pending list
 * is now empty, cancel the whole thing.
 */
226
void dns_cancel_pending_resolve(char *address, connection_t *onlyconn) {
227
  struct pending_connection_t *pend, *victim;
228
229
230
  struct cached_resolve search;
  struct cached_resolve *resolve, *tmp;

231
  strncpy(search.address, address, MAX_ADDRESSLEN);
232
  search.address[MAX_ADDRESSLEN-1] = 0;
233
234
235

  resolve = SPLAY_FIND(cache_tree, &cache_root, &search);
  if(!resolve) {
236
    log_fn(LOG_WARN,"Address '%s' is not pending. Dropping.", address);
237
238
239
240
    return;
  }

  assert(resolve->state == CACHE_STATE_PENDING);
241
  assert(resolve->pending_connections);
242

243
  if(onlyconn) {
244
    pend = resolve->pending_connections;
245
246
247
    if(pend->conn == onlyconn) {
      resolve->pending_connections = pend->next;
      free(pend);
248
249
      if(resolve->pending_connections) {/* more pending, don't cancel it */
        log_fn(LOG_DEBUG, "Connection (fd %d) no longer waiting for resolve of '%s'",
250
               onlyconn->s, address);
251
        return;
252
      }
253
254
255
256
257
258
    } else {
      for( ; pend->next; pend = pend->next) {
        if(pend->next->conn == onlyconn) {
          victim = pend->next;
          pend->next = victim->next;
          free(victim);
259
          log_fn(LOG_DEBUG, "Connection (fd %d) no longer waiting for resolve of '%s'",
260
                 onlyconn->s, address);
261
262
263
264
265
266
267
          return; /* more are pending */
        }
      }
      assert(0); /* not reachable unless onlyconn not in pending list */
    }
  } else {
    /* mark all pending connections to fail */
268
    log_fn(LOG_DEBUG, "Failing all connections waiting on DNS resolve of '%s'",
269
           address);
270
271
    while(resolve->pending_connections) {
      pend = resolve->pending_connections;
272
273
      if(connection_edge_end(pend->conn, END_STREAM_REASON_MISC, NULL) < 0)
        log_fn(LOG_WARN,"1: I called connection_edge_end redundantly.");
274
275
276
      resolve->pending_connections = pend->next;
      free(pend);
    }
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
  }

  /* 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;
  } else {
    /* FFFF make it a doubly linked list if this becomes too slow */
    for(tmp=oldest_cached_resolve; tmp && tmp->next != resolve; tmp=tmp->next) ;
    assert(tmp); /* it's got to be in the list, or we screwed up somewhere else */
    tmp->next = resolve->next; /* unlink it */

    if(newest_cached_resolve == resolve)
      newest_cached_resolve = tmp;
  }

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

  free(resolve);
}

300
static void dns_found_answer(char *address, uint32_t addr) {
301
302
303
304
  struct pending_connection_t *pend;
  struct cached_resolve search;
  struct cached_resolve *resolve;

305
  strncpy(search.address, address, MAX_ADDRESSLEN);
306
  search.address[MAX_ADDRESSLEN-1] = 0;
307
308
309

  resolve = SPLAY_FIND(cache_tree, &cache_root, &search);
  if(!resolve) {
310
    log_fn(LOG_INFO,"Resolved unasked address '%s'? Dropping.", address);
311
312
    /* XXX Why drop?  Just because we don't care now doesn't mean we shouldn't
     * XXX cache the result for later. */
313
    return;
314
315
  }

316
  if (resolve->state != CACHE_STATE_PENDING) {
317
318
    log_fn(LOG_WARN, "Resolved '%s' which was already resolved; ignoring",
           address);
319
320
321
322
323
324
325
    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. */
  /* assert(resolve->state == CACHE_STATE_PENDING); */
326

327
328
  resolve->addr = ntohl(addr);
  if(resolve->addr)
329
330
331
332
333
334
    resolve->state = CACHE_STATE_VALID;
  else
    resolve->state = CACHE_STATE_FAILED;

  while(resolve->pending_connections) {
    pend = resolve->pending_connections;
335
    pend->conn->addr = resolve->addr;
336
337
338
339
    if(resolve->state == CACHE_STATE_FAILED) {
      if(connection_edge_end(pend->conn, END_STREAM_REASON_RESOLVEFAILED, NULL) < 0)
        log_fn(LOG_WARN,"1: I called connection_edge_end redundantly.");
    } else
340
      connection_exit_connect(pend->conn);
341
342
343
344
345
    resolve->pending_connections = pend->next;
    free(pend);
  }
}

346
347
348
349
350
351
352
353
354
/******************************************************************/

int connection_dns_finished_flushing(connection_t *conn) {
  assert(conn && conn->type == CONN_TYPE_DNSWORKER);
  connection_stop_writing(conn);
  return 0;
}

int connection_dns_process_inbuf(connection_t *conn) {
355
  uint32_t addr;
356
357
358
359

  assert(conn && conn->type == CONN_TYPE_DNSWORKER);

  if(conn->inbuf_reached_eof) {
Roger Dingledine's avatar
Roger Dingledine committed
360
    log_fn(LOG_WARN,"Read eof. Worker dying.");
361
    if(conn->state == DNSWORKER_STATE_BUSY) {
362
      dns_cancel_pending_resolve(conn->address, NULL);
Roger Dingledine's avatar
Roger Dingledine committed
363
      num_dnsworkers_busy--;
364
    }
Roger Dingledine's avatar
Roger Dingledine committed
365
    num_dnsworkers--;
366
367
368
369
    return -1;
  }

  assert(conn->state == DNSWORKER_STATE_BUSY);
370
  if(buf_datalen(conn->inbuf) < 4) /* entire answer available? */
371
    return 0; /* not yet */
372
  assert(buf_datalen(conn->inbuf) == 4);
373

374
  connection_fetch_from_buf((char*)&addr,sizeof(addr),conn);
375

376
377
378
  log_fn(LOG_DEBUG, "DNSWorker (fd %d) returned answer for '%s'",
         conn->s, conn->address);

379
  dns_found_answer(conn->address, addr);
380
381

  free(conn->address);
382
  conn->address = tor_strdup("<idle>");
383
  conn->state = DNSWORKER_STATE_IDLE;
Roger Dingledine's avatar
Roger Dingledine committed
384
  num_dnsworkers_busy--;
385
386
387
388

  return 0;
}

389
int dnsworker_main(void *data) {
390
391
  char address[MAX_ADDRESSLEN];
  unsigned char address_len;
392
  struct hostent *rent;
393
  int *fdarray = data;
Roger Dingledine's avatar
Roger Dingledine committed
394
  int fd;
395
396
397

  close(fdarray[0]); /* this is the side of the socketpair the parent uses */
  fd = fdarray[1]; /* this side is ours */
398
  connection_free_all(); /* so the child doesn't hold the parent's fd's open */
399
/* XXX probably don't close all the fd's on MS_WINDOWS? */
400
401
402

  for(;;) {

403
    if(read(fd, &address_len, 1) != 1) {
404
      log_fn(LOG_INFO,"read length failed. Child exiting.");
405
      spawn_exit();
406
    }
407
    assert(address_len > 0);
408

409
    if(read_all(fd, address, address_len) != address_len) {
410
      log_fn(LOG_ERR,"read hostname failed. Child exiting.");
411
      spawn_exit();
412
    }
413
    address[address_len] = 0; /* null terminate it */
414

415
    rent = gethostbyname(address);
416
    if (!rent) {
417
      log_fn(LOG_INFO,"Could not resolve dest addr %s. Returning nulls.",address);
Roger Dingledine's avatar
Roger Dingledine committed
418
      if(write_all(fd, "\0\0\0\0", 4) != 4) {
419
        log_fn(LOG_ERR,"writing nulls failed. Child exiting.");
420
        spawn_exit();
421
422
423
      }
    } else {
      assert(rent->h_length == 4); /* break to remind us if we move away from ipv4 */
Roger Dingledine's avatar
Roger Dingledine committed
424
      if(write_all(fd, rent->h_addr, 4) != 4) {
425
        log_fn(LOG_INFO,"writing answer failed. Child exiting.");
426
        spawn_exit();
427
      }
428
      log_fn(LOG_INFO,"Resolved address '%s'.",address);
429
430
    }
  }
431
  return 0; /* windows wants this function to return an int */
432
433
}

Roger Dingledine's avatar
Roger Dingledine committed
434
static int spawn_dnsworker(void) {
435
436
437
  int fd[2];
  connection_t *conn;

438
  if(tor_socketpair(AF_UNIX, SOCK_STREAM, 0, fd) < 0) {
439
    log(LOG_ERR, "Couldn't construct socketpair: %s", strerror(errno));
440
441
442
    exit(1);
  }

443
  spawn_func(dnsworker_main, (void*)fd);
Roger Dingledine's avatar
Roger Dingledine committed
444
  log_fn(LOG_DEBUG,"just spawned a worker.");
445
  close(fd[1]); /* we don't need the worker's side of the pipe */
446
447
448

  conn = connection_new(CONN_TYPE_DNSWORKER);

449
  set_socket_nonblocking(fd[0]);
450
451
452

  /* 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
453
  conn->address = tor_strdup("<unused>");
454
455

  if(connection_add(conn) < 0) { /* no space, forget it */
Roger Dingledine's avatar
Roger Dingledine committed
456
    log_fn(LOG_WARN,"connection_add failed. Giving up.");
457
458
459
460
461
462
463
464
465
466
    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
467
468
static void spawn_enough_dnsworkers(void) {
  int num_dnsworkers_needed; /* aim to have 1 more than needed,
469
                           * but no less than min and no more than max */
470
471
  connection_t *dnsconn;

472
  /* XXX This may not be the best strategy. Maybe we should queue pending
473
474
475
476
477
478
   *     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
479
   */
Roger Dingledine's avatar
Roger Dingledine committed
480
  if(num_dnsworkers_busy == MAX_DNSWORKERS) {
481
482
483
    /* We always want at least one worker idle.
     * So find the oldest busy worker and kill it.
     */
484
485
    dnsconn = connection_get_by_type_state_lastwritten(CONN_TYPE_DNSWORKER,
                                                       DNSWORKER_STATE_BUSY);
486
487
    assert(dnsconn);

488
489
    log_fn(LOG_WARN, "%d DNS workers are spawned; all are busy. Killing one.",
           MAX_DNSWORKERS);
490
    /* tell the exit connection that it's failed */
491
    dns_cancel_pending_resolve(dnsconn->address, NULL);
492

493
    dnsconn->marked_for_close = 1;
Roger Dingledine's avatar
Roger Dingledine committed
494
    num_dnsworkers_busy--;
495
    num_dnsworkers--;
496
  }
497

Roger Dingledine's avatar
Roger Dingledine committed
498
499
  if(num_dnsworkers_busy >= MIN_DNSWORKERS)
    num_dnsworkers_needed = num_dnsworkers_busy+1;
500
  else
Roger Dingledine's avatar
Roger Dingledine committed
501
    num_dnsworkers_needed = MIN_DNSWORKERS;
502

Roger Dingledine's avatar
Roger Dingledine committed
503
504
  while(num_dnsworkers < num_dnsworkers_needed) {
    if(spawn_dnsworker() < 0) {
Roger Dingledine's avatar
Roger Dingledine committed
505
      log(LOG_WARN,"spawn_enough_dnsworkers(): spawn failed!");
506
507
      return;
    }
Roger Dingledine's avatar
Roger Dingledine committed
508
    num_dnsworkers++;
509
510
  }

511
  while(num_dnsworkers > num_dnsworkers_busy+MAX_IDLE_DNSWORKERS) { /* too many idle? */
512
    /* cull excess workers */
513
514
    log_fn(LOG_WARN,"%d of %d dnsworkers are idle. Killing one.",
           num_dnsworkers-num_dnsworkers_needed, num_dnsworkers);
515
516
517
    dnsconn = connection_get_by_type_state(CONN_TYPE_DNSWORKER, DNSWORKER_STATE_IDLE);
    assert(dnsconn);
    dnsconn->marked_for_close = 1;
Roger Dingledine's avatar
Roger Dingledine committed
518
    num_dnsworkers--;
519
  }
520
521
}

522
523
524
525
526
527
528
/*
  Local Variables:
  mode:c
  indent-tabs-mode:nil
  c-basic-offset:2
  End:
*/