summaryrefslogtreecommitdiff
path: root/src/resolve/resolved-dns-transaction.c
blob: 3d46c99df85f26b74b7d93b7df29376e489006ca (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/

/***
  This file is part of systemd.

  Copyright 2014 Lennart Poettering

  systemd is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.

  systemd is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/

#include "af-list.h"

#include "resolved-llmnr.h"
#include "resolved-dns-transaction.h"
#include "random-util.h"

DnsTransaction* dns_transaction_free(DnsTransaction *t) {
        DnsQuery *q;
        DnsZoneItem *i;

        if (!t)
                return NULL;

        sd_event_source_unref(t->timeout_event_source);

        dns_question_unref(t->question);
        dns_packet_unref(t->sent);
        dns_packet_unref(t->received);
        dns_answer_unref(t->cached);

        sd_event_source_unref(t->dns_ipv4_event_source);
        sd_event_source_unref(t->dns_ipv6_event_source);
        safe_close(t->dns_ipv4_fd);
        safe_close(t->dns_ipv6_fd);

        dns_server_unref(t->server);
        dns_stream_free(t->stream);

        if (t->scope) {
                LIST_REMOVE(transactions_by_scope, t->scope->transactions, t);

                if (t->id != 0)
                        hashmap_remove(t->scope->manager->dns_transactions, UINT_TO_PTR(t->id));
        }

        while ((q = set_steal_first(t->queries)))
                set_remove(q->transactions, t);
        set_free(t->queries);

        while ((i = set_steal_first(t->zone_items)))
                i->probe_transaction = NULL;
        set_free(t->zone_items);

        free(t);
        return NULL;
}

DEFINE_TRIVIAL_CLEANUP_FUNC(DnsTransaction*, dns_transaction_free);

void dns_transaction_gc(DnsTransaction *t) {
        assert(t);

        if (t->block_gc > 0)
                return;

        if (set_isempty(t->queries) && set_isempty(t->zone_items))
                dns_transaction_free(t);
}

int dns_transaction_new(DnsTransaction **ret, DnsScope *s, DnsQuestion *q) {
        _cleanup_(dns_transaction_freep) DnsTransaction *t = NULL;
        int r;

        assert(ret);
        assert(s);
        assert(q);

        r = hashmap_ensure_allocated(&s->manager->dns_transactions, NULL);
        if (r < 0)
                return r;

        t = new0(DnsTransaction, 1);
        if (!t)
                return -ENOMEM;

        t->dns_ipv4_fd = t->dns_ipv6_fd = -1;

        t->question = dns_question_ref(q);

        do
                random_bytes(&t->id, sizeof(t->id));
        while (t->id == 0 ||
               hashmap_get(s->manager->dns_transactions, UINT_TO_PTR(t->id)));

        r = hashmap_put(s->manager->dns_transactions, UINT_TO_PTR(t->id), t);
        if (r < 0) {
                t->id = 0;
                return r;
        }

        LIST_PREPEND(transactions_by_scope, s->transactions, t);
        t->scope = s;

        if (ret)
                *ret = t;

        t = NULL;

        return 0;
}

static void dns_transaction_stop(DnsTransaction *t) {
        assert(t);

        t->timeout_event_source = sd_event_source_unref(t->timeout_event_source);
        t->stream = dns_stream_free(t->stream);
}

static void dns_transaction_tentative(DnsTransaction *t, DnsPacket *p) {
        _cleanup_free_ char *pretty = NULL;
        DnsZoneItem *z;

        assert(t);
        assert(p);

        if (manager_our_packet(t->scope->manager, p) != 0)
                return;

        in_addr_to_string(p->family, &p->sender, &pretty);

        log_debug("Transaction on scope %s on %s/%s got tentative packet from %s",
                  dns_protocol_to_string(t->scope->protocol),
                  t->scope->link ? t->scope->link->name : "*",
                  t->scope->family == AF_UNSPEC ? "*" : af_to_name(t->scope->family),
                  pretty);

        /* RFC 4795, Section 4.1 says that the peer with the
         * lexicographically smaller IP address loses */
        if (memcmp(&p->sender, &p->destination, FAMILY_ADDRESS_SIZE(p->family)) >= 0) {
                log_debug("Peer has lexicographically larger IP address and thus lost in the conflict.");
                return;
        }

        log_debug("We have the lexicographically larger IP address and thus lost in the conflict.");

        t->block_gc++;
        while ((z = set_first(t->zone_items))) {
                /* First, make sure the zone item drops the reference
                 * to us */
                dns_zone_item_probe_stop(z);

                /* Secondly, report this as conflict, so that we might
                 * look for a different hostname */
                dns_zone_item_conflict(z);
        }
        t->block_gc--;

        dns_transaction_gc(t);
}

void dns_transaction_complete(DnsTransaction *t, DnsTransactionState state) {
        DnsQuery *q;
        DnsZoneItem *z;
        Iterator i;

        assert(t);
        assert(!IN_SET(state, DNS_TRANSACTION_NULL, DNS_TRANSACTION_PENDING));

        if (!IN_SET(t->state, DNS_TRANSACTION_NULL, DNS_TRANSACTION_PENDING))
                return;

        /* Note that this call might invalidate the query. Callers
         * should hence not attempt to access the query or transaction
         * after calling this function. */

        log_debug("Transaction on scope %s on %s/%s now complete with <%s>",
                  dns_protocol_to_string(t->scope->protocol),
                  t->scope->link ? t->scope->link->name : "*",
                  t->scope->family == AF_UNSPEC ? "*" : af_to_name(t->scope->family),
                  dns_transaction_state_to_string(state));

        t->state = state;

        dns_transaction_stop(t);

        /* Notify all queries that are interested, but make sure the
         * transaction isn't freed while we are still looking at it */
        t->block_gc++;
        SET_FOREACH(q, t->queries, i)
                dns_query_ready(q);
        SET_FOREACH(z, t->zone_items, i)
                dns_zone_item_ready(z);
        t->block_gc--;

        dns_transaction_gc(t);
}

static int on_stream_complete(DnsStream *s, int error) {
        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
        DnsTransaction *t;

        assert(s);
        assert(s->transaction);

        /* Copy the data we care about out of the stream before we
         * destroy it. */
        t = s->transaction;
        p = dns_packet_ref(s->read_packet);

        t->stream = dns_stream_free(t->stream);

        if (error != 0) {
                dns_transaction_complete(t, DNS_TRANSACTION_RESOURCES);
                return 0;
        }

        if (dns_packet_validate_reply(p) <= 0) {
                log_debug("Invalid LLMNR TCP packet.");
                dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
                return 0;
        }

        dns_scope_check_conflicts(t->scope, p);

        t->block_gc++;
        dns_transaction_process_reply(t, p);
        t->block_gc--;

        /* If the response wasn't useful, then complete the transition now */
        if (t->state == DNS_TRANSACTION_PENDING)
                dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);

        return 0;
}

static int dns_transaction_open_tcp(DnsTransaction *t) {
        _cleanup_(dns_server_unrefp) DnsServer *server = NULL;
        _cleanup_close_ int fd = -1;
        int r;

        assert(t);

        if (t->stream)
                return 0;

        if (t->scope->protocol == DNS_PROTOCOL_DNS)
                fd = dns_scope_tcp_socket(t->scope, AF_UNSPEC, NULL, 53, &server);
        else if (t->scope->protocol == DNS_PROTOCOL_LLMNR) {

                /* When we already received a query to this (but it was truncated), send to its sender address */
                if (t->received)
                        fd = dns_scope_tcp_socket(t->scope, t->received->family, &t->received->sender, t->received->sender_port, NULL);
                else {
                        union in_addr_union address;
                        int family = AF_UNSPEC;

                        /* Otherwise, try to talk to the owner of a
                         * the IP address, in case this is a reverse
                         * PTR lookup */
                        r = dns_question_extract_reverse_address(t->question, &family, &address);
                        if (r < 0)
                                return r;
                        if (r == 0)
                                return -EINVAL;

                        fd = dns_scope_tcp_socket(t->scope, family, &address, LLMNR_PORT, NULL);
                }
        } else
                return -EAFNOSUPPORT;

        if (fd < 0)
                return fd;

        r = dns_stream_new(t->scope->manager, &t->stream, t->scope->protocol, fd);
        if (r < 0)
                return r;

        fd = -1;

        r = dns_stream_write_packet(t->stream, t->sent);
        if (r < 0) {
                t->stream = dns_stream_free(t->stream);
                return r;
        }


        dns_server_unref(t->server);
        t->server = dns_server_ref(server);
        t->received = dns_packet_unref(t->received);
        t->stream->complete = on_stream_complete;
        t->stream->transaction = t;

        /* The interface index is difficult to determine if we are
         * connecting to the local host, hence fill this in right away
         * instead of determining it from the socket */
        if (t->scope->link)
                t->stream->ifindex = t->scope->link->ifindex;

        return 0;
}

void dns_transaction_process_reply(DnsTransaction *t, DnsPacket *p) {
        int r;

        assert(t);
        assert(p);
        assert(t->state == DNS_TRANSACTION_PENDING);

        /* Note that this call might invalidate the query. Callers
         * should hence not attempt to access the query or transaction
         * after calling this function. */

        if (t->scope->protocol == DNS_PROTOCOL_LLMNR) {
                assert(t->scope->link);

                /* For LLMNR we will not accept any packets from other
                 * interfaces */

                if (p->ifindex != t->scope->link->ifindex)
                        return;

                if (p->family != t->scope->family)
                        return;

                /* Tentative packets are not full responses but still
                 * useful for identifying uniqueness conflicts during
                 * probing. */
                if (DNS_PACKET_LLMNR_T(p)) {
                        dns_transaction_tentative(t, p);
                        return;
                }
        }

        if (t->scope->protocol == DNS_PROTOCOL_DNS) {

                /* For DNS we are fine with accepting packets on any
                 * interface, but the source IP address must be the
                 * one of the DNS server we queried */

                assert(t->server);

                if (t->server->family != p->family)
                        return;

                if (!in_addr_equal(p->family, &p->sender, &t->server->address))
                        return;

                if (p->sender_port != 53)
                        return;
        }

        if (t->received != p) {
                dns_packet_unref(t->received);
                t->received = dns_packet_ref(p);
        }

        if (p->ipproto == IPPROTO_TCP) {
                if (DNS_PACKET_TC(p)) {
                        /* Truncated via TCP? Somebody must be fucking with us */
                        dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
                        return;
                }

                if (DNS_PACKET_ID(p) != t->id) {
                        /* Not the reply to our query? Somebody must be fucking with us */
                        dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
                        return;
                }
        }

        if (DNS_PACKET_TC(p)) {
                /* Response was truncated, let's try again with good old TCP */
                r = dns_transaction_open_tcp(t);
                if (r == -ESRCH) {
                        /* No servers found? Damn! */
                        dns_transaction_complete(t, DNS_TRANSACTION_NO_SERVERS);
                        return;
                }
                if (r < 0) {
                        /* On LLMNR, if we cannot connect to the host,
                         * we immediately give up */
                        if (t->scope->protocol == DNS_PROTOCOL_LLMNR) {
                                dns_transaction_complete(t, DNS_TRANSACTION_RESOURCES);
                                return;
                        }

                        /* On DNS, couldn't send? Try immediately again, with a new server */
                        dns_scope_next_dns_server(t->scope);

                        r = dns_transaction_go(t);
                        if (r < 0) {
                                dns_transaction_complete(t, DNS_TRANSACTION_RESOURCES);
                                return;
                        }

                        return;
                }
        }

        /* Parse and update the cache */
        r = dns_packet_extract(p);
        if (r < 0) {
                dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
                return;
        }

        /* Only consider responses with equivalent query section to the request */
        if (!dns_question_is_superset(p->question, t->question) ||
            !dns_question_is_superset(t->question, p->question)) {
                dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
                return;
        }

        /* According to RFC 4795, section 2.9. only the RRs from the answer section shall be cached */
        dns_cache_put(&t->scope->cache, p->question, DNS_PACKET_RCODE(p), p->answer, DNS_PACKET_ANCOUNT(p), 0, p->family, &p->sender);

        if (DNS_PACKET_RCODE(p) == DNS_RCODE_SUCCESS)
                dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
        else
                dns_transaction_complete(t, DNS_TRANSACTION_FAILURE);
}

static int on_transaction_timeout(sd_event_source *s, usec_t usec, void *userdata) {
        DnsTransaction *t = userdata;
        int r;

        assert(s);
        assert(t);

        /* Timeout reached? Try again, with a new server */
        dns_scope_next_dns_server(t->scope);

        r = dns_transaction_go(t);
        if (r < 0)
                dns_transaction_complete(t, DNS_TRANSACTION_RESOURCES);

        return 0;
}

static int dns_transaction_make_packet(DnsTransaction *t) {
        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
        unsigned n, added = 0;
        int r;

        assert(t);

        if (t->sent)
                return 0;

        r = dns_packet_new_query(&p, t->scope->protocol, 0);
        if (r < 0)
                return r;

        for (n = 0; n < t->question->n_keys; n++) {
                r = dns_scope_good_key(t->scope, t->question->keys[n]);
                if (r < 0)
                        return r;
                if (r == 0)
                        continue;

                r = dns_packet_append_key(p, t->question->keys[n], NULL);
                if (r < 0)
                        return r;

                added++;
        }

        if (added <= 0)
                return -EDOM;

        DNS_PACKET_HEADER(p)->qdcount = htobe16(added);
        DNS_PACKET_HEADER(p)->id = t->id;

        t->sent = p;
        p = NULL;

        return 0;
}

int dns_transaction_go(DnsTransaction *t) {
        bool had_stream;
        int r;

        assert(t);

        had_stream = !!t->stream;

        dns_transaction_stop(t);

        log_debug("Excercising transaction on scope %s on %s/%s",
                  dns_protocol_to_string(t->scope->protocol),
                  t->scope->link ? t->scope->link->name : "*",
                  t->scope->family == AF_UNSPEC ? "*" : af_to_name(t->scope->family));

        if (t->n_attempts >= TRANSACTION_ATTEMPTS_MAX(t->scope->protocol)) {
                dns_transaction_complete(t, DNS_TRANSACTION_ATTEMPTS_MAX_REACHED);
                return 0;
        }

        if (t->scope->protocol == DNS_PROTOCOL_LLMNR && had_stream) {
                /* If we already tried via a stream, then we don't
                 * retry on LLMNR. See RFC 4795, Section 2.7. */
                dns_transaction_complete(t, DNS_TRANSACTION_ATTEMPTS_MAX_REACHED);
                return 0;
        }

        t->n_attempts++;
        t->server = dns_server_unref(t->server);
        t->received = dns_packet_unref(t->received);
        t->cached = dns_answer_unref(t->cached);
        t->cached_rcode = 0;

        /* Check the cache, but only if this transaction is not used
         * for probing or verifying a zone item. */
        if (set_isempty(t->zone_items)) {

                /* Before trying the cache, let's make sure we figured out a
                 * server to use. Should this cause a change of server this
                 * might flush the cache. */
                dns_scope_get_dns_server(t->scope);

                /* Let's then prune all outdated entries */
                dns_cache_prune(&t->scope->cache);

                r = dns_cache_lookup(&t->scope->cache, t->question, &t->cached_rcode, &t->cached);
                if (r < 0)
                        return r;
                if (r > 0) {
                        log_debug("Cache hit!");
                        if (t->cached_rcode == DNS_RCODE_SUCCESS)
                                dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
                        else
                                dns_transaction_complete(t, DNS_TRANSACTION_FAILURE);
                        return 0;
                }
        }

        if (t->scope->protocol == DNS_PROTOCOL_LLMNR && !t->initial_jitter) {
                usec_t jitter;

                /* RFC 4795 Section 2.7 suggests all queries should be
                 * delayed by a random time from 0 to JITTER_INTERVAL. */

                t->initial_jitter = true;

                random_bytes(&jitter, sizeof(jitter));
                jitter %= LLMNR_JITTER_INTERVAL_USEC;

                r = sd_event_add_time(
                                t->scope->manager->event,
                                &t->timeout_event_source,
                                clock_boottime_or_monotonic(),
                                now(clock_boottime_or_monotonic()) + jitter,
                                LLMNR_JITTER_INTERVAL_USEC,
                                on_transaction_timeout, t);
                if (r < 0)
                        return r;

                t->n_attempts = 0;
                t->state = DNS_TRANSACTION_PENDING;

                log_debug("Delaying LLMNR transaction for " USEC_FMT "us.", jitter);
                return 0;
        }

        log_debug("Cache miss!");

        /* Otherwise, we need to ask the network */
        r = dns_transaction_make_packet(t);
        if (r == -EDOM) {
                /* Not the right request to make on this network?
                 * (i.e. an A request made on IPv6 or an AAAA request
                 * made on IPv4, on LLMNR or mDNS.) */
                dns_transaction_complete(t, DNS_TRANSACTION_NO_SERVERS);
                return 0;
        }
        if (r < 0)
                return r;

        if (t->scope->protocol == DNS_PROTOCOL_LLMNR &&
            (dns_question_endswith(t->question, "in-addr.arpa") > 0 ||
             dns_question_endswith(t->question, "ip6.arpa") > 0)) {

                /* RFC 4795, Section 2.4. says reverse lookups shall
                 * always be made via TCP on LLMNR */
                r = dns_transaction_open_tcp(t);
        } else {
                DnsServer *server;

                /* Try via UDP, and if that fails due to large size try via TCP */
                r = dns_scope_emit(t->scope, t, t->sent, &server);
                if (r >= 0)
                        t->server = dns_server_ref(server);
                else if (r == -EMSGSIZE)
                        r = dns_transaction_open_tcp(t);
        }
        if (r == -ESRCH) {
                /* No servers to send this to? */
                dns_transaction_complete(t, DNS_TRANSACTION_NO_SERVERS);
                return 0;
        } else if (r < 0) {
                if (t->scope->protocol != DNS_PROTOCOL_DNS) {
                        dns_transaction_complete(t, DNS_TRANSACTION_RESOURCES);
                        return 0;
                }

                /* Couldn't send? Try immediately again, with a new server */
                dns_scope_next_dns_server(t->scope);

                return dns_transaction_go(t);
        }

        r = sd_event_add_time(
                        t->scope->manager->event,
                        &t->timeout_event_source,
                        clock_boottime_or_monotonic(),
                        now(clock_boottime_or_monotonic()) + TRANSACTION_TIMEOUT_USEC(t->scope->protocol), 0,
                        on_transaction_timeout, t);
        if (r < 0)
                return r;

        t->state = DNS_TRANSACTION_PENDING;
        return 1;
}

static int on_dns_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
        DnsTransaction *t = userdata;
        int r;

        assert(t);
        assert(t->scope);

        r = manager_recv(t->scope->manager, fd, DNS_PROTOCOL_DNS, &p);
        if (r <= 0)
                return r;

        if (dns_packet_validate_reply(p) > 0 &&
            DNS_PACKET_ID(p) == t->id) {
                dns_transaction_process_reply(t, p);
        } else
                log_debug("Invalid DNS packet.");

        return 0;
}

int transaction_dns_ipv4_fd(DnsTransaction *t) {
        const int one = 1;
        int r;

        assert(t);
        assert(t->scope);
        assert(t->scope->manager);

        if (t->dns_ipv4_fd >= 0)
                return t->dns_ipv4_fd;

        t->dns_ipv4_fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
        if (t->dns_ipv4_fd < 0)
                return -errno;

        r = setsockopt(t->dns_ipv4_fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof(one));
        if (r < 0) {
                r = -errno;
                goto fail;
        }

        r = sd_event_add_io(t->scope->manager->event, &t->dns_ipv4_event_source, t->dns_ipv4_fd, EPOLLIN, on_dns_packet, t);
        if (r < 0)
                goto fail;

        return t->dns_ipv4_fd;

fail:
        t->dns_ipv4_fd = safe_close(t->dns_ipv4_fd);
        return r;
}

int transaction_dns_ipv6_fd(DnsTransaction *t) {
        const int one = 1;
        int r;

        assert(t);
        assert(t->scope);
        assert(t->scope->manager);

        if (t->dns_ipv6_fd >= 0)
                return t->dns_ipv6_fd;

        t->dns_ipv6_fd = socket(AF_INET6, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
        if (t->dns_ipv6_fd < 0)
                return -errno;

        r = setsockopt(t->dns_ipv6_fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &one, sizeof(one));
        if (r < 0) {
                r = -errno;
                goto fail;
        }

        r = sd_event_add_io(t->scope->manager->event, &t->dns_ipv6_event_source, t->dns_ipv6_fd, EPOLLIN, on_dns_packet, t);
        if (r < 0)
                goto fail;

        return t->dns_ipv6_fd;

fail:
        t->dns_ipv6_fd = safe_close(t->dns_ipv6_fd);
        return r;
}

static const char* const dns_transaction_state_table[_DNS_TRANSACTION_STATE_MAX] = {
        [DNS_TRANSACTION_NULL] = "null",
        [DNS_TRANSACTION_PENDING] = "pending",
        [DNS_TRANSACTION_FAILURE] = "failure",
        [DNS_TRANSACTION_SUCCESS] = "success",
        [DNS_TRANSACTION_NO_SERVERS] = "no-servers",
        [DNS_TRANSACTION_TIMEOUT] = "timeout",
        [DNS_TRANSACTION_ATTEMPTS_MAX_REACHED] = "attempts-max-reached",
        [DNS_TRANSACTION_INVALID_REPLY] = "invalid-reply",
        [DNS_TRANSACTION_RESOURCES] = "resources",
        [DNS_TRANSACTION_ABORTED] = "aborted",
};
DEFINE_STRING_TABLE_LOOKUP(dns_transaction_state, DnsTransactionState);