summaryrefslogtreecommitdiff
path: root/src/resolve/resolved-dns-transaction.c
blob: 44267c6b2dd4b1c9dd96a8c57b28219f8d9d5fe8 (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
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
/*-*- 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 <sd-messages.h>

#include "af-list.h"
#include "alloc-util.h"
#include "dns-domain.h"
#include "fd-util.h"
#include "random-util.h"
#include "resolved-dns-cache.h"
#include "resolved-dns-transaction.h"
#include "resolved-llmnr.h"
#include "string-table.h"

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

        t->received = dns_packet_unref(t->received);
        t->answer = dns_answer_unref(t->answer);
        t->answer_rcode = 0;
        t->answer_dnssec_result = _DNSSEC_RESULT_INVALID;
        t->answer_source = _DNS_TRANSACTION_SOURCE_INVALID;
        t->answer_authenticated = false;
        t->answer_nsec_ttl = (uint32_t) -1;
}

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

        t->stream = dns_stream_free(t->stream);
        t->dns_udp_event_source = sd_event_source_unref(t->dns_udp_event_source);
        t->dns_udp_fd = safe_close(t->dns_udp_fd);
}

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

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

DnsTransaction* dns_transaction_free(DnsTransaction *t) {
        DnsQueryCandidate *c;
        DnsZoneItem *i;
        DnsTransaction *z;

        if (!t)
                return NULL;

        log_debug("Freeing transaction %" PRIu16 ".", t->id);

        dns_transaction_close_connection(t);
        dns_transaction_stop_timeout(t);

        dns_packet_unref(t->sent);
        dns_transaction_reset_answer(t);

        dns_server_unref(t->server);

        if (t->scope) {
                hashmap_remove_value(t->scope->transactions_by_key, t->key, t);
                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 ((c = set_steal_first(t->notify_query_candidates)))
                set_remove(c->transactions, t);
        set_free(t->notify_query_candidates);

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

        while ((z = set_steal_first(t->notify_transactions)))
                set_remove(z->dnssec_transactions, t);
        set_free(t->notify_transactions);

        while ((z = set_steal_first(t->dnssec_transactions))) {
                set_remove(z->notify_transactions, t);
                dns_transaction_gc(z);
        }
        set_free(t->dnssec_transactions);

        dns_answer_unref(t->validated_keys);
        dns_resource_key_unref(t->key);
        free(t->key_string);

        free(t);
        return NULL;
}

DEFINE_TRIVIAL_CLEANUP_FUNC(DnsTransaction*, dns_transaction_free);

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

        if (t->block_gc > 0)
                return true;

        if (set_isempty(t->notify_query_candidates) &&
            set_isempty(t->notify_zone_items) &&
            set_isempty(t->notify_transactions)) {
                dns_transaction_free(t);
                return false;
        }

        return true;
}

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

        assert(ret);
        assert(s);
        assert(key);

        /* Don't allow looking up invalid or pseudo RRs */
        if (!dns_type_is_valid_query(key->type))
                return -EINVAL;

        /* We only support the IN class */
        if (key->class != DNS_CLASS_IN && key->class != DNS_CLASS_ANY)
                return -EOPNOTSUPP;

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

        r = hashmap_ensure_allocated(&s->transactions_by_key, &dns_resource_key_hash_ops);
        if (r < 0)
                return r;

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

        t->dns_udp_fd = -1;
        t->answer_source = _DNS_TRANSACTION_SOURCE_INVALID;
        t->answer_dnssec_result = _DNSSEC_RESULT_INVALID;
        t->answer_nsec_ttl = (uint32_t) -1;
        t->key = dns_resource_key_ref(key);

        /* Find a fresh, unused transaction id */
        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;
        }

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

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

        s->manager->n_transactions_total ++;

        if (ret)
                *ret = t;

        t = NULL;

        return 0;
}

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 %" PRIu16 " for <%s> on scope %s on %s/%s got tentative packet from %s.",
                  t->id,
                  dns_transaction_key_string(t),
                  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->notify_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) {
        DnsQueryCandidate *c;
        DnsZoneItem *z;
        DnsTransaction *d;
        Iterator i;

        assert(t);
        assert(!DNS_TRANSACTION_IS_LIVE(state));

        if (state == DNS_TRANSACTION_DNSSEC_FAILED)
                log_struct(LOG_NOTICE,
                           LOG_MESSAGE_ID(SD_MESSAGE_DNSSEC_FAILURE),
                           LOG_MESSAGE("DNSSEC validation failed for question %s: %s", dns_transaction_key_string(t), dnssec_result_to_string(t->answer_dnssec_result)),
                           "DNS_TRANSACTION=%" PRIu16, t->id,
                           "DNS_QUESTION=%s", dns_transaction_key_string(t),
                           "DNSSEC_RESULT=%s", dnssec_result_to_string(t->answer_dnssec_result),
                           NULL);

        /* 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 %" PRIu16 " for <%s> on scope %s on %s/%s now complete with <%s> from %s (%s).",
                  t->id,
                  dns_transaction_key_string(t),
                  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->answer_source < 0 ? "none" : dns_transaction_source_to_string(t->answer_source),
                  t->answer_authenticated ? "authenticated" : "unsigned");

        t->state = state;

        dns_transaction_close_connection(t);
        dns_transaction_stop_timeout(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(c, t->notify_query_candidates, i)
                dns_query_candidate_notify(c);
        SET_FOREACH(z, t->notify_zone_items, i)
                dns_zone_item_notify(z);

        if (!set_isempty(t->notify_transactions)) {
                DnsTransaction **nt;
                unsigned j, n = 0;

                /* We need to be careful when notifying other
                 * transactions, as that might destroy other
                 * transactions in our list. Hence, in order to be
                 * able to safely iterate through the list of
                 * transactions, take a GC lock on all of them
                 * first. Then, in a second loop, notify them, but
                 * first unlock that specific transaction. */

                nt = newa(DnsTransaction*, set_size(t->notify_transactions));
                SET_FOREACH(d, t->notify_transactions, i) {
                        nt[n++] = d;
                        d->block_gc++;
                }

                assert(n == set_size(t->notify_transactions));

                for (j = 0; j < n; j++) {
                        if (set_contains(t->notify_transactions, nt[j]))
                                dns_transaction_notify(nt[j], t);

                        nt[j]->block_gc--;
                        dns_transaction_gc(nt[j]);
                }
        }

        t->block_gc--;
        dns_transaction_gc(t);
}

static int dns_transaction_pick_server(DnsTransaction *t) {
        DnsServer *server;

        assert(t);
        assert(t->scope->protocol == DNS_PROTOCOL_DNS);

        server = dns_scope_get_dns_server(t->scope);
        if (!server)
                return -ESRCH;

        t->current_features = dns_server_possible_feature_level(server);

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

        dns_server_unref(t->server);
        t->server = dns_server_ref(server);

        return 1;
}

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 (IN_SET(error, ENOTCONN, ECONNRESET, ECONNREFUSED, ECONNABORTED, EPIPE)) {
                dns_transaction_complete(t, DNS_TRANSACTION_CONNECTION_FAILURE);
                return 0;
        }

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

        if (dns_packet_validate_reply(p) <= 0) {
                log_debug("Invalid TCP reply 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. After all, we are the worst feature set now with TCP
         * sockets, and there's really no point in retrying. */
        if (t->state == DNS_TRANSACTION_PENDING)
                dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
        else
                dns_transaction_gc(t);

        return 0;
}

static int dns_transaction_open_tcp(DnsTransaction *t) {
        _cleanup_close_ int fd = -1;
        int r;

        assert(t);

        dns_transaction_close_connection(t);

        switch (t->scope->protocol) {

        case DNS_PROTOCOL_DNS:
                r = dns_transaction_pick_server(t);
                if (r < 0)
                        return r;

                r = dns_server_adjust_opt(t->server, t->sent, t->current_features);
                if (r < 0)
                        return r;

                fd = dns_scope_socket_tcp(t->scope, AF_UNSPEC, NULL, t->server, 53);
                break;

        case DNS_PROTOCOL_LLMNR:
                /* When we already received a reply to this (but it was truncated), send to its sender address */
                if (t->received)
                        fd = dns_scope_socket_tcp(t->scope, t->received->family, &t->received->sender, NULL, t->received->sender_port);
                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_name_address(DNS_RESOURCE_KEY_NAME(t->key), &family, &address);
                        if (r < 0)
                                return r;
                        if (r == 0)
                                return -EINVAL;
                        if (family != t->scope->family)
                                return -ESRCH;

                        fd = dns_scope_socket_tcp(t->scope, family, &address, NULL, LLMNR_PORT);
                }

                break;

        default:
                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;
        }

        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;

        dns_transaction_reset_answer(t);

        t->tried_stream = true;

        return 0;
}

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

        /* For mDNS we cache whenever we get the packet, rather than
         * in each transaction. */
        if (!IN_SET(t->scope->protocol, DNS_PROTOCOL_DNS, DNS_PROTOCOL_LLMNR))
                return;

        /* We never cache if this packet is from the local host, under
         * the assumption that a locally running DNS server would
         * cache this anyway, and probably knows better when to flush
         * the cache then we could. */
        if (!DNS_PACKET_SHALL_CACHE(t->received))
                return;

        dns_cache_put(&t->scope->cache,
                      t->key,
                      t->answer_rcode,
                      t->answer,
                      t->answer_authenticated,
                      t->answer_nsec_ttl,
                      0,
                      t->received->family,
                      &t->received->sender);
}

static bool dns_transaction_dnssec_is_live(DnsTransaction *t) {
        DnsTransaction *dt;
        Iterator i;

        assert(t);

        SET_FOREACH(dt, t->dnssec_transactions, i)
                if (DNS_TRANSACTION_IS_LIVE(dt->state))
                        return true;

        return false;
}

static void dns_transaction_process_dnssec(DnsTransaction *t) {
        int r;

        assert(t);

        /* Are there ongoing DNSSEC transactions? If so, let's wait for them. */
        if (dns_transaction_dnssec_is_live(t))
                return;

        /* All our auxiliary DNSSEC transactions are complete now. Try
         * to validate our RRset now. */
        r = dns_transaction_validate_dnssec(t);
        if (r < 0) {
                dns_transaction_complete(t, DNS_TRANSACTION_RESOURCES);
                return;
        }

        if (t->answer_dnssec_result == DNSSEC_INCOMPATIBLE_SERVER &&
            t->scope->dnssec_mode == DNSSEC_YES) {
                /*  We are not in automatic downgrade mode, and the
                 *  server is bad, refuse operation. */
                dns_transaction_complete(t, DNS_TRANSACTION_DNSSEC_FAILED);
                return;
        }

        if (!IN_SET(t->answer_dnssec_result,
                    _DNSSEC_RESULT_INVALID,        /* No DNSSEC validation enabled */
                    DNSSEC_VALIDATED,              /* Answer is signed and validated successfully */
                    DNSSEC_UNSIGNED,               /* Answer is right-fully unsigned */
                    DNSSEC_INCOMPATIBLE_SERVER)) { /* Server does not do DNSSEC (Yay, we are downgrade attack vulnerable!) */
                dns_transaction_complete(t, DNS_TRANSACTION_DNSSEC_FAILED);
                return;
        }

        dns_transaction_cache_answer(t);

        if (t->answer_rcode == DNS_RCODE_SUCCESS)
                dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
        else
                dns_transaction_complete(t, DNS_TRANSACTION_RCODE_FAILURE);
}

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

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

        if (t->state != 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("Processing incoming packet on transaction %" PRIu16".", t->id);

        switch (t->scope->protocol) {

        case 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;
                }

                break;

        case DNS_PROTOCOL_MDNS:
                assert(t->scope->link);

                /* For mDNS we will not accept any packets from other interfaces */
                if (p->ifindex != t->scope->link->ifindex)
                        return;

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

                break;

        case DNS_PROTOCOL_DNS:
                /* Note that we do not need to verify the
                 * addresses/port numbers of incoming traffic, as we
                 * invoked connect() on our UDP socket in which case
                 * the kernel already does the needed verification for
                 * us. */
                break;

        default:
                assert_not_reached("Invalid DNS protocol.");
        }

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

        t->answer_source = DNS_TRANSACTION_NETWORK;

        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;
                }
        }

        assert_se(sd_event_now(t->scope->manager->event, clock_boottime_or_monotonic(), &ts) >= 0);

        switch (t->scope->protocol) {

        case DNS_PROTOCOL_DNS:
                assert(t->server);

                if (IN_SET(DNS_PACKET_RCODE(p), DNS_RCODE_FORMERR, DNS_RCODE_SERVFAIL, DNS_RCODE_NOTIMP)) {

                        /* Request failed, immediately try again with reduced features */
                        log_debug("Server returned error: %s", dns_rcode_to_string(DNS_PACKET_RCODE(p)));

                        dns_server_packet_failed(t->server, t->current_features);

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

                        return;
                } else
                        dns_server_packet_received(t->server, t->current_features, ts - t->start_usec, p->size);

                break;

        case DNS_PROTOCOL_LLMNR:
        case DNS_PROTOCOL_MDNS:
                dns_scope_packet_received(t->scope, ts - t->start_usec);
                break;

        default:
                assert_not_reached("Invalid DNS protocol.");
        }

        if (DNS_PACKET_TC(p)) {

                /* Truncated packets for mDNS are not allowed. Give up immediately. */
                if (t->scope->protocol == DNS_PROTOCOL_MDNS) {
                        dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
                        return;
                }

                /* 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 message, if it isn't parsed yet. */
        r = dns_packet_extract(p);
        if (r < 0) {
                dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
                return;
        }

        if (IN_SET(t->scope->protocol, DNS_PROTOCOL_DNS, DNS_PROTOCOL_LLMNR)) {

                /* Only consider responses with equivalent query section to the request */
                r = dns_packet_is_reply_for(p, t->key);
                if (r < 0) {
                        dns_transaction_complete(t, DNS_TRANSACTION_RESOURCES);
                        return;
                }
                if (r == 0) {
                        dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
                        return;
                }

                /* Install the answer as answer to the transaction */
                dns_answer_unref(t->answer);
                t->answer = dns_answer_ref(p->answer);
                t->answer_rcode = DNS_PACKET_RCODE(p);
                t->answer_dnssec_result = _DNSSEC_RESULT_INVALID;
                t->answer_authenticated = false;

                /* Block GC while starting requests for additional DNSSEC RRs */
                t->block_gc++;
                r = dns_transaction_request_dnssec_keys(t);
                t->block_gc--;

                /* Maybe the transaction is ready for GC'ing now? If so, free it and return. */
                if (!dns_transaction_gc(t))
                        return;

                /* Requesting additional keys might have resulted in
                 * this transaction to fail, since the auxiliary
                 * request failed for some reason. If so, we are not
                 * in pending state anymore, and we should exit
                 * quickly. */
                if (t->state != DNS_TRANSACTION_PENDING)
                        return;
                if (r < 0) {
                        dns_transaction_complete(t, DNS_TRANSACTION_RESOURCES);
                        return;
                }
                if (r > 0) {
                        /* There are DNSSEC transactions pending now. Update the state accordingly. */
                        t->state = DNS_TRANSACTION_VALIDATING;
                        dns_transaction_close_connection(t);
                        dns_transaction_stop_timeout(t);
                        return;
                }
        }

        dns_transaction_process_dnssec(t);
}

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 UDP packet, ignoring.");

        return 0;
}

static int dns_transaction_emit_udp(DnsTransaction *t) {
        int r;

        assert(t);

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

                r = dns_transaction_pick_server(t);
                if (r < 0)
                        return r;

                if (t->current_features < DNS_SERVER_FEATURE_LEVEL_UDP)
                        return -EAGAIN;

                if (r > 0 || t->dns_udp_fd < 0) { /* Server changed, or no connection yet. */
                        int fd;

                        dns_transaction_close_connection(t);

                        fd = dns_scope_socket_udp(t->scope, t->server, 53);
                        if (fd < 0)
                                return fd;

                        r = sd_event_add_io(t->scope->manager->event, &t->dns_udp_event_source, fd, EPOLLIN, on_dns_packet, t);
                        if (r < 0) {
                                safe_close(fd);
                                return r;
                        }

                        t->dns_udp_fd = fd;
                }

                r = dns_server_adjust_opt(t->server, t->sent, t->current_features);
                if (r < 0)
                        return r;
        } else
                dns_transaction_close_connection(t);

        r = dns_scope_emit_udp(t->scope, t->dns_udp_fd, t->sent);
        if (r < 0)
                return r;

        dns_transaction_reset_answer(t);

        return 0;
}

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

        assert(s);
        assert(t);

        if (!t->initial_jitter_scheduled || t->initial_jitter_elapsed) {
                /* Timeout reached? Increase the timeout for the server used */
                switch (t->scope->protocol) {

                case DNS_PROTOCOL_DNS:
                        assert(t->server);
                        dns_server_packet_lost(t->server, t->current_features, usec - t->start_usec);
                        break;

                case DNS_PROTOCOL_LLMNR:
                case DNS_PROTOCOL_MDNS:
                        dns_scope_packet_lost(t->scope, usec - t->start_usec);
                        break;

                default:
                        assert_not_reached("Invalid DNS protocol.");
                }

                if (t->initial_jitter_scheduled)
                        t->initial_jitter_elapsed = true;
        }

        log_debug("Timeout reached on transaction %" PRIu16 ".", t->id);

        /* ...and 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 usec_t transaction_get_resend_timeout(DnsTransaction *t) {
        assert(t);
        assert(t->scope);

        switch (t->scope->protocol) {

        case DNS_PROTOCOL_DNS:
                assert(t->server);
                return t->server->resend_timeout;

        case DNS_PROTOCOL_MDNS:
                assert(t->n_attempts > 0);
                return (1 << (t->n_attempts - 1)) * USEC_PER_SEC;

        case DNS_PROTOCOL_LLMNR:
                return t->scope->resend_timeout;

        default:
                assert_not_reached("Invalid DNS protocol.");
        }
}

static int dns_transaction_prepare(DnsTransaction *t, usec_t ts) {
        int r;

        assert(t);

        dns_transaction_stop_timeout(t);

        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 && t->tried_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->start_usec = ts;

        dns_transaction_reset_answer(t);

        /* Check the trust anchor. Do so only on classic DNS, since DNSSEC does not apply otherwise. */
        if (t->scope->protocol == DNS_PROTOCOL_DNS) {
                r = dns_trust_anchor_lookup_positive(&t->scope->manager->trust_anchor, t->key, &t->answer);
                if (r < 0)
                        return r;
                if (r > 0) {
                        t->answer_rcode = DNS_RCODE_SUCCESS;
                        t->answer_source = DNS_TRANSACTION_TRUST_ANCHOR;
                        t->answer_authenticated = true;
                        dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
                        return 0;
                }

                if (dns_name_is_root(DNS_RESOURCE_KEY_NAME(t->key)) &&
                    t->key->type == DNS_TYPE_DS) {

                        /* Hmm, this is a request for the root DS? A
                         * DS RR doesn't exist in the root zone, and
                         * if our trust anchor didn't know it either,
                         * this means we cannot do any DNSSEC logic
                         * anymore. */

                        if (t->scope->dnssec_mode == DNSSEC_ALLOW_DOWNGRADE) {
                                /* We are in downgrade mode. In this
                                 * case, synthesize an unsigned empty
                                 * response, so that the any lookup
                                 * depending on this one can continue
                                 * assuming there was no DS, and hence
                                 * the root zone was unsigned. */

                                t->answer_rcode = DNS_RCODE_SUCCESS;
                                t->answer_source = DNS_TRANSACTION_TRUST_ANCHOR;
                                t->answer_authenticated = false;
                                dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
                        } else
                                /* If we are not in downgrade mode,
                                 * then fail the lookup, because we
                                 * cannot reasonably answer it. There
                                 * might be DS RRs, but we don't know
                                 * them, and the DNS server won't tell
                                 * them to us (and even if it would,
                                 * we couldn't validate it and trust
                                 * it). */
                                dns_transaction_complete(t, DNS_TRANSACTION_NO_TRUST_ANCHOR);

                        return 0;
                }
        }

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

                r = dns_zone_lookup(&t->scope->zone, t->key, &t->answer, NULL, NULL);
                if (r < 0)
                        return r;
                if (r > 0) {
                        t->answer_rcode = DNS_RCODE_SUCCESS;
                        t->answer_source = DNS_TRANSACTION_ZONE;
                        t->answer_authenticated = true;
                        dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
                        return 0;
                }
        }

        /* Check the cache, but only if this transaction is not used
         * for probing or verifying a zone item. */
        if (set_isempty(t->notify_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->key, &t->answer_rcode, &t->answer, &t->answer_authenticated);
                if (r < 0)
                        return r;
                if (r > 0) {
                        t->answer_source = DNS_TRANSACTION_CACHE;
                        if (t->answer_rcode == DNS_RCODE_SUCCESS)
                                dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
                        else
                                dns_transaction_complete(t, DNS_TRANSACTION_RCODE_FAILURE);
                        return 0;
                }
        }

        return 1;
}

static int dns_transaction_make_packet_mdns(DnsTransaction *t) {

        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
        bool add_known_answers = false;
        DnsTransaction *other;
        unsigned qdcount;
        usec_t ts;
        int r;

        assert(t);
        assert(t->scope->protocol == DNS_PROTOCOL_MDNS);

        /* Discard any previously prepared packet, so we can start over and coalesce again */
        t->sent = dns_packet_unref(t->sent);

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

        r = dns_packet_append_key(p, t->key, NULL);
        if (r < 0)
                return r;

        qdcount = 1;

        if (dns_key_is_shared(t->key))
                add_known_answers = true;

        /*
         * For mDNS, we want to coalesce as many open queries in pending transactions into one single
         * query packet on the wire as possible. To achieve that, we iterate through all pending transactions
         * in our current scope, and see whether their timing contraints allow them to be sent.
         */

        assert_se(sd_event_now(t->scope->manager->event, clock_boottime_or_monotonic(), &ts) >= 0);

        LIST_FOREACH(transactions_by_scope, other, t->scope->transactions) {

                /* Skip ourselves */
                if (other == t)
                        continue;

                if (other->state != DNS_TRANSACTION_PENDING)
                        continue;

                if (other->next_attempt_after > ts)
                        continue;

                if (qdcount >= UINT16_MAX)
                        break;

                r = dns_packet_append_key(p, other->key, NULL);

                /*
                 * If we can't stuff more questions into the packet, just give up.
                 * One of the 'other' transactions will fire later and take care of the rest.
                 */
                if (r == -EMSGSIZE)
                        break;

                if (r < 0)
                        return r;

                r = dns_transaction_prepare(other, ts);
                if (r <= 0)
                        continue;

                ts += transaction_get_resend_timeout(other);

                r = sd_event_add_time(
                                other->scope->manager->event,
                                &other->timeout_event_source,
                                clock_boottime_or_monotonic(),
                                ts, 0,
                                on_transaction_timeout, other);
                if (r < 0)
                        return r;

                other->state = DNS_TRANSACTION_PENDING;
                other->next_attempt_after = ts;

                qdcount ++;

                if (dns_key_is_shared(other->key))
                        add_known_answers = true;
        }

        DNS_PACKET_HEADER(p)->qdcount = htobe16(qdcount);

        /* Append known answer section if we're asking for any shared record */
        if (add_known_answers) {
                r = dns_cache_export_shared_to_packet(&t->scope->cache, p);
                if (r < 0)
                        return r;
        }

        t->sent = p;
        p = NULL;

        return 0;
}

static int dns_transaction_make_packet(DnsTransaction *t) {
        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
        int r;

        assert(t);

        if (t->scope->protocol == DNS_PROTOCOL_MDNS)
                return dns_transaction_make_packet_mdns(t);

        if (t->sent)
                return 0;

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

        r = dns_scope_good_key(t->scope, t->key);
        if (r < 0)
                return r;
        if (r == 0)
                return -EDOM;

        r = dns_packet_append_key(p, t->key, NULL);
        if (r < 0)
                return r;

        DNS_PACKET_HEADER(p)->qdcount = htobe16(1);
        DNS_PACKET_HEADER(p)->id = t->id;

        t->sent = p;
        p = NULL;

        return 0;
}

int dns_transaction_go(DnsTransaction *t) {
        usec_t ts;
        int r;

        assert(t);

        assert_se(sd_event_now(t->scope->manager->event, clock_boottime_or_monotonic(), &ts) >= 0);

        r = dns_transaction_prepare(t, ts);
        if (r <= 0)
                return r;

        log_debug("Excercising transaction %" PRIu16 " for <%s> on scope %s on %s/%s.",
                  t->id,
                  dns_transaction_key_string(t),
                  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->initial_jitter_scheduled &&
            (t->scope->protocol == DNS_PROTOCOL_LLMNR ||
             t->scope->protocol == DNS_PROTOCOL_MDNS)) {
                usec_t jitter, accuracy;

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

                t->initial_jitter_scheduled = true;

                random_bytes(&jitter, sizeof(jitter));

                switch (t->scope->protocol) {

                case DNS_PROTOCOL_LLMNR:
                        jitter %= LLMNR_JITTER_INTERVAL_USEC;
                        accuracy = LLMNR_JITTER_INTERVAL_USEC;
                        break;

                case DNS_PROTOCOL_MDNS:
                        jitter %= MDNS_JITTER_RANGE_USEC;
                        jitter += MDNS_JITTER_MIN_USEC;
                        accuracy = MDNS_JITTER_RANGE_USEC;
                        break;
                default:
                        assert_not_reached("bad protocol");
                }

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

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

                log_debug("Delaying %s transaction for " USEC_FMT "us.", dns_protocol_to_string(t->scope->protocol), jitter);
                return 0;
        }

        /* 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_name_endswith(DNS_RESOURCE_KEY_NAME(t->key), "in-addr.arpa") > 0 ||
             dns_name_endswith(DNS_RESOURCE_KEY_NAME(t->key), "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 {
                /* Try via UDP, and if that fails due to large size or lack of
                 * support try via TCP */
                r = dns_transaction_emit_udp(t);
                if (r == -EMSGSIZE || r == -EAGAIN)
                        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);
        }

        ts += transaction_get_resend_timeout(t);

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

        t->state = DNS_TRANSACTION_PENDING;
        t->next_attempt_after = ts;

        return 1;
}

static int dns_transaction_find_cyclic(DnsTransaction *t, DnsTransaction *aux) {
        DnsTransaction *n;
        Iterator i;
        int r;

        assert(t);
        assert(aux);

        /* Try to find cyclic dependencies between transaction objects */

        if (t == aux)
                return 1;

        SET_FOREACH(n, aux->notify_transactions, i) {
                r = dns_transaction_find_cyclic(t, n);
                if (r != 0)
                        return r;
        }

        return r;
}

static int dns_transaction_add_dnssec_transaction(DnsTransaction *t, DnsResourceKey *key, DnsTransaction **ret) {
        DnsTransaction *aux;
        int r;

        assert(t);
        assert(ret);
        assert(key);

        aux = dns_scope_find_transaction(t->scope, key, true);
        if (!aux) {
                r = dns_transaction_new(&aux, t->scope, key);
                if (r < 0)
                        return r;
        } else {
                if (set_contains(t->dnssec_transactions, aux)) {
                        *ret = aux;
                        return 0;
                }

                r = dns_transaction_find_cyclic(t, aux);
                if (r < 0)
                        return r;
                if (r > 0) {
                        log_debug("Detected potential cyclic dependency, refusing to add transaction %" PRIu16 " (%s) as dependency for %" PRIu16 " (%s).",
                                  aux->id,
                                  strna(dns_transaction_key_string(aux)),
                                  t->id,
                                  strna(dns_transaction_key_string(t)));
                        return -ELOOP;
                }
        }

        r = set_ensure_allocated(&t->dnssec_transactions, NULL);
        if (r < 0)
                goto gc;

        r = set_ensure_allocated(&aux->notify_transactions, NULL);
        if (r < 0)
                goto gc;

        r = set_put(t->dnssec_transactions, aux);
        if (r < 0)
                goto gc;

        r = set_put(aux->notify_transactions, t);
        if (r < 0) {
                (void) set_remove(t->dnssec_transactions, aux);
                goto gc;
        }

        *ret = aux;
        return 1;

gc:
        dns_transaction_gc(aux);
        return r;
}

static int dns_transaction_request_dnssec_rr(DnsTransaction *t, DnsResourceKey *key) {
        _cleanup_(dns_answer_unrefp) DnsAnswer *a = NULL;
        DnsTransaction *aux;
        int r;

        assert(t);
        assert(key);

        /* Try to get the data from the trust anchor */
        r = dns_trust_anchor_lookup_positive(&t->scope->manager->trust_anchor, key, &a);
        if (r < 0)
                return r;
        if (r > 0) {
                r = dns_answer_extend(&t->validated_keys, a);
                if (r < 0)
                        return r;

                return 0;
        }

        /* This didn't work, ask for it via the network/cache then. */
        r = dns_transaction_add_dnssec_transaction(t, key, &aux);
        if (r == -ELOOP) /* This would result in a cyclic dependency */
                return 0;
        if (r < 0)
                return r;

        if (aux->state == DNS_TRANSACTION_NULL) {
                r = dns_transaction_go(aux);
                if (r < 0)
                        return r;
        }

        return 1;
}

static int dns_transaction_has_positive_answer(DnsTransaction *t, DnsAnswerFlags *flags) {
        int r;

        assert(t);

        /* Checks whether the answer is positive, i.e. either a direct
         * answer to the question, or a CNAME/DNAME for it */

        r = dns_answer_match_key(t->answer, t->key, flags);
        if (r != 0)
                return r;

        r = dns_answer_find_cname_or_dname(t->answer, t->key, NULL, flags);
        if (r != 0)
                return r;

        return false;
}

static int dns_transaction_has_unsigned_negative_answer(DnsTransaction *t) {
        int r;

        assert(t);

        /* Checks whether the answer is negative, and lacks NSEC/NSEC3
         * RRs to prove it */

        r = dns_transaction_has_positive_answer(t, NULL);
        if (r < 0)
                return r;
        if (r > 0)
                return false;

        /* Is this key explicitly listed as a negative trust anchor?
         * If so, it's nothing we need to care about */
        r = dns_trust_anchor_lookup_negative(&t->scope->manager->trust_anchor, DNS_RESOURCE_KEY_NAME(t->key));
        if (r < 0)
                return r;
        if (r > 0)
                return false;

        /* The answer does not contain any RRs that match to the
         * question. If so, let's see if there are any NSEC/NSEC3 RRs
         * included. If not, the answer is unsigned. */

        r = dns_answer_contains_nsec_or_nsec3(t->answer);
        if (r < 0)
                return r;
        if (r > 0)
                return false;

        return true;
}

static int dns_transaction_is_primary_response(DnsTransaction *t, DnsResourceRecord *rr) {
        int r;

        assert(t);
        assert(rr);

        /* Check if the specified RR is the "primary" response,
         * i.e. either matches the question precisely or is a
         * CNAME/DNAME for it, or is any kind of NSEC/NSEC3 RR */

        r = dns_resource_key_match_rr(t->key, rr, NULL);
        if (r != 0)
                return r;

        r = dns_resource_key_match_cname_or_dname(t->key, rr->key, NULL);
        if (r != 0)
                return r;

        if (rr->key->type == DNS_TYPE_NSEC3) {
                const char *p;

                p = DNS_RESOURCE_KEY_NAME(rr->key);
                r = dns_name_parent(&p);
                if (r < 0)
                        return r;
                if (r > 0) {
                        r = dns_name_endswith(DNS_RESOURCE_KEY_NAME(t->key), p);
                        if (r < 0)
                                return r;
                        if (r > 0)
                                return true;
                }
        }

        return rr->key->type == DNS_TYPE_NSEC;
}

int dns_transaction_request_dnssec_keys(DnsTransaction *t) {
        DnsResourceRecord *rr;

        int r;

        assert(t);

        /*
         * Retrieve all auxiliary RRs for the answer we got, so that
         * we can verify signatures or prove that RRs are rightfully
         * unsigned. Specifically:
         *
         * - For RRSIG we get the matching DNSKEY
         * - For DNSKEY we get the matching DS
         * - For unsigned SOA/NS we get the matching DS
         * - For unsigned CNAME/DNAME/DS we get the parent SOA RR
         * - For other unsigned RRs we get the matching SOA RR
         * - For SOA/NS/DS queries with no matching response RRs, and no NSEC/NSEC3, the parent's SOA RR
         * - For other queries with no matching response RRs, and no NSEC/NSEC3, the SOA RR
         */

        if (t->scope->dnssec_mode == DNSSEC_NO)
                return 0;

        if (t->current_features < DNS_SERVER_FEATURE_LEVEL_DO)
                return 0; /* Server doesn't do DNSSEC, there's no point in requesting any RRs then. */
        if (t->server && t->server->rrsig_missing)
                return 0; /* Server handles DNSSEC requests, but isn't augmenting responses with RRSIGs. No point in trying DNSSEC then. */

        DNS_ANSWER_FOREACH(rr, t->answer) {

                if (dns_type_is_pseudo(rr->key->type))
                        continue;

                /* If this RR is in the negative trust anchor, we don't need to validate it. */
                r = dns_trust_anchor_lookup_negative(&t->scope->manager->trust_anchor, DNS_RESOURCE_KEY_NAME(rr->key));
                if (r < 0)
                        return r;
                if (r > 0)
                        continue;

                switch (rr->key->type) {

                case DNS_TYPE_RRSIG: {
                        /* For each RRSIG we request the matching DNSKEY */
                        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *dnskey = NULL;

                        /* If this RRSIG is about a DNSKEY RR and the
                         * signer is the same as the owner, then we
                         * already have the DNSKEY, and we don't have
                         * to look for more. */
                        if (rr->rrsig.type_covered == DNS_TYPE_DNSKEY) {
                                r = dns_name_equal(rr->rrsig.signer, DNS_RESOURCE_KEY_NAME(rr->key));
                                if (r < 0)
                                        return r;
                                if (r > 0)
                                        continue;
                        }

                        /* If the signer is not a parent of our
                         * original query, then this is about an
                         * auxiliary RRset, but not anything we asked
                         * for. In this case we aren't interested,
                         * because we don't want to request additional
                         * RRs for stuff we didn't really ask for, and
                         * also to avoid request loops, where
                         * additional RRs from one transaction result
                         * in another transaction whose additonal RRs
                         * point back to the original transaction, and
                         * we deadlock. */
                        r = dns_name_endswith(DNS_RESOURCE_KEY_NAME(t->key), rr->rrsig.signer);
                        if (r < 0)
                                return r;
                        if (r == 0)
                                continue;

                        dnskey = dns_resource_key_new(rr->key->class, DNS_TYPE_DNSKEY, rr->rrsig.signer);
                        if (!dnskey)
                                return -ENOMEM;

                        log_debug("Requesting DNSKEY to validate transaction %" PRIu16" (%s, RRSIG with key tag: %" PRIu16 ").", t->id, DNS_RESOURCE_KEY_NAME(rr->key), rr->rrsig.key_tag);
                        r = dns_transaction_request_dnssec_rr(t, dnskey);
                        if (r < 0)
                                return r;
                        break;
                }

                case DNS_TYPE_DNSKEY: {
                        /* For each DNSKEY we request the matching DS */
                        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *ds = NULL;

                        /* If the DNSKEY we are looking at is not for
                         * zone we are interested in, nor any of its
                         * parents, we aren't interested, and don't
                         * request it. After all, we don't want to end
                         * up in request loops, and want to keep
                         * additional traffic down. */

                        r = dns_name_endswith(DNS_RESOURCE_KEY_NAME(t->key), DNS_RESOURCE_KEY_NAME(rr->key));
                        if (r < 0)
                                return r;
                        if (r == 0)
                                continue;

                        ds = dns_resource_key_new(rr->key->class, DNS_TYPE_DS, DNS_RESOURCE_KEY_NAME(rr->key));
                        if (!ds)
                                return -ENOMEM;

                        log_debug("Requesting DS to validate transaction %" PRIu16" (%s, DNSKEY with key tag: %" PRIu16 ").", t->id, DNS_RESOURCE_KEY_NAME(rr->key), dnssec_keytag(rr, false));
                        r = dns_transaction_request_dnssec_rr(t, ds);
                        if (r < 0)
                                return r;

                        break;
                }

                case DNS_TYPE_SOA:
                case DNS_TYPE_NS: {
                        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *ds = NULL;

                        /* For an unsigned SOA or NS, try to acquire
                         * the matching DS RR, as we are at a zone cut
                         * then, and whether a DS exists tells us
                         * whether the zone is signed. Do so only if
                         * this RR matches our original question,
                         * however. */

                        r = dns_resource_key_match_rr(t->key, rr, NULL);
                        if (r < 0)
                                return r;
                        if (r == 0)
                                continue;

                        r = dnssec_has_rrsig(t->answer, rr->key);
                        if (r < 0)
                                return r;
                        if (r > 0)
                                continue;

                        ds = dns_resource_key_new(rr->key->class, DNS_TYPE_DS, DNS_RESOURCE_KEY_NAME(rr->key));
                        if (!ds)
                                return -ENOMEM;

                        log_debug("Requesting DS to validate transaction %" PRIu16 " (%s, unsigned SOA/NS RRset).", t->id, DNS_RESOURCE_KEY_NAME(rr->key));
                        r = dns_transaction_request_dnssec_rr(t, ds);
                        if (r < 0)
                                return r;

                        break;
                }

                case DNS_TYPE_DS:
                case DNS_TYPE_CNAME:
                case DNS_TYPE_DNAME: {
                        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *soa = NULL;
                        const char *name;

                        /* CNAMEs and DNAMEs cannot be located at a
                         * zone apex, hence ask for the parent SOA for
                         * unsigned CNAME/DNAME RRs, maybe that's the
                         * apex. But do all that only if this is
                         * actually a response to our original
                         * question.
                         *
                         * Similar for DS RRs, which are signed when
                         * the parent SOA is signed. */

                        r = dns_transaction_is_primary_response(t, rr);
                        if (r < 0)
                                return r;
                        if (r == 0)
                                continue;

                        r = dnssec_has_rrsig(t->answer, rr->key);
                        if (r < 0)
                                return r;
                        if (r > 0)
                                continue;

                        name = DNS_RESOURCE_KEY_NAME(rr->key);
                        r = dns_name_parent(&name);
                        if (r < 0)
                                return r;
                        if (r == 0)
                                continue;

                        soa = dns_resource_key_new(rr->key->class, DNS_TYPE_SOA, name);
                        if (!soa)
                                return -ENOMEM;

                        log_debug("Requesting parent SOA to validate transaction %" PRIu16 " (%s, unsigned CNAME/DNAME/DS RRset).", t->id, DNS_RESOURCE_KEY_NAME(rr->key));
                        r = dns_transaction_request_dnssec_rr(t, soa);
                        if (r < 0)
                                return r;

                        break;
                }

                default: {
                        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *soa = NULL;

                        /* For other unsigned RRsets (including
                         * NSEC/NSEC3!), look for proof the zone is
                         * unsigned, by requesting the SOA RR of the
                         * zone. However, do so only if they are
                         * directly relevant to our original
                         * question. */

                        r = dns_transaction_is_primary_response(t, rr);
                        if (r < 0)
                                return r;
                        if (r == 0)
                                continue;

                        r = dnssec_has_rrsig(t->answer, rr->key);
                        if (r < 0)
                                return r;
                        if (r > 0)
                                continue;

                        soa = dns_resource_key_new(rr->key->class, DNS_TYPE_SOA, DNS_RESOURCE_KEY_NAME(rr->key));
                        if (!soa)
                                return -ENOMEM;

                        log_debug("Requesting SOA to validate transaction %" PRIu16 " (%s, unsigned non-SOA/NS RRset <%s>).", t->id, DNS_RESOURCE_KEY_NAME(rr->key), dns_resource_record_to_string(rr));
                        r = dns_transaction_request_dnssec_rr(t, soa);
                        if (r < 0)
                                return r;
                        break;
                }}
        }

        /* Above, we requested everything necessary to validate what
         * we got. Now, let's request what we need to validate what we
         * didn't get... */

        r = dns_transaction_has_unsigned_negative_answer(t);
        if (r < 0)
                return r;
        if (r > 0) {
                const char *name;

                name = DNS_RESOURCE_KEY_NAME(t->key);

                /* If this was a SOA or NS request, then this
                 * indicates that we are not at a zone apex, hence ask
                 * the parent name instead. If this was a DS request,
                 * then it's signed when the parent zone is signed,
                 * hence ask the parent in that case, too. */

                if (IN_SET(t->key->type, DNS_TYPE_SOA, DNS_TYPE_NS, DNS_TYPE_DS)) {
                        r = dns_name_parent(&name);
                        if (r < 0)
                                return r;
                        if (r > 0)
                                log_debug("Requesting parent SOA to validate transaction %" PRIu16 " (%s, unsigned empty SOA/NS/DS response).", t->id, DNS_RESOURCE_KEY_NAME(t->key));
                        else
                                name = NULL;
                } else
                        log_debug("Requesting SOA to validate transaction %" PRIu16 " (%s, unsigned empty non-SOA/NS/DS response).", t->id, DNS_RESOURCE_KEY_NAME(t->key));

                if (name) {
                        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *soa = NULL;

                        soa = dns_resource_key_new(t->key->class, DNS_TYPE_SOA, name);
                        if (!soa)
                                return -ENOMEM;

                        r = dns_transaction_request_dnssec_rr(t, soa);
                        if (r < 0)
                                return r;
                }
        }

        return dns_transaction_dnssec_is_live(t);
}

void dns_transaction_notify(DnsTransaction *t, DnsTransaction *source) {
        int r;

        assert(t);
        assert(source);

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

        /* Invoked whenever any of our auxiliary DNSSEC transactions
           completed its work. We copy any RRs from that transaction
           over into our list of validated keys -- but only if the
           answer is authenticated.

           Note that we fail our transaction if the auxiliary
           transaction failed, except on NXDOMAIN. This is because
           some broken DNS servers (Akamai...) will return NXDOMAIN
           for empty non-terminals. */

        switch (source->state) {

        case DNS_TRANSACTION_DNSSEC_FAILED:

                log_debug("Auxiliary DNSSEC RR query failed validation: %s", dnssec_result_to_string(source->answer_dnssec_result));
                t->answer_dnssec_result = source->answer_dnssec_result; /* Copy error code over */
                dns_transaction_complete(t, DNS_TRANSACTION_DNSSEC_FAILED);
                break;

        case DNS_TRANSACTION_RCODE_FAILURE:

                if (source->answer_rcode != DNS_RCODE_NXDOMAIN) {
                        log_debug("Auxiliary DNSSEC RR query failed with rcode=%i.", source->answer_rcode);
                        goto fail;
                }

                /* fall-through: NXDOMAIN is good enough for us */

        case DNS_TRANSACTION_SUCCESS:
                if (source->answer_authenticated) {
                        r = dns_answer_extend(&t->validated_keys, source->answer);
                        if (r < 0) {
                                log_error_errno(r, "Failed to merge validated DNSSEC key data: %m");
                                goto fail;
                        }
                }

                /* If the state is still PENDING, we are still in the loop
                 * that adds further DNSSEC transactions, hence don't check if
                 * we are ready yet. If the state is VALIDATING however, we
                 * should check if we are complete now. */
                if (t->state == DNS_TRANSACTION_VALIDATING)
                        dns_transaction_process_dnssec(t);
                break;

        default:
                log_debug("Auxiliary DNSSEC RR query failed with %s", dns_transaction_state_to_string(source->state));
                goto fail;
        }

        return;

fail:
        t->answer_dnssec_result = DNSSEC_FAILED_AUXILIARY;
        dns_transaction_complete(t, DNS_TRANSACTION_DNSSEC_FAILED);
}

static int dns_transaction_validate_dnskey_by_ds(DnsTransaction *t) {
        DnsResourceRecord *rr;
        int ifindex, r;

        assert(t);

        /* Add all DNSKEY RRs from the answer that are validated by DS
         * RRs from the list of validated keys to the list of
         * validated keys. */

        DNS_ANSWER_FOREACH_IFINDEX(rr, ifindex, t->answer) {

                r = dnssec_verify_dnskey_search(rr, t->validated_keys);
                if (r < 0)
                        return r;
                if (r == 0)
                        continue;

                /* If so, the DNSKEY is validated too. */
                r = dns_answer_add_extend(&t->validated_keys, rr, ifindex, DNS_ANSWER_AUTHENTICATED);
                if (r < 0)
                        return r;
        }

        return 0;
}

static int dns_transaction_requires_rrsig(DnsTransaction *t, DnsResourceRecord *rr) {
        int r;

        assert(t);
        assert(rr);

        /* Checks if the RR we are looking for must be signed with an
         * RRSIG. This is used for positive responses. */

        if (t->scope->dnssec_mode == DNSSEC_NO)
                return false;

        if (dns_type_is_pseudo(rr->key->type))
                return -EINVAL;

        r = dns_trust_anchor_lookup_negative(&t->scope->manager->trust_anchor, DNS_RESOURCE_KEY_NAME(rr->key));
        if (r < 0)
                return r;
        if (r > 0)
                return false;

        switch (rr->key->type) {

        case DNS_TYPE_RRSIG:
                /* RRSIGs are the signatures themselves, they need no signing. */
                return false;

        case DNS_TYPE_SOA:
        case DNS_TYPE_NS: {
                DnsTransaction *dt;
                Iterator i;

                /* For SOA or NS RRs we look for a matching DS transaction */

                SET_FOREACH(dt, t->dnssec_transactions, i) {

                        if (dt->key->class != rr->key->class)
                                continue;
                        if (dt->key->type != DNS_TYPE_DS)
                                continue;

                        r = dns_name_equal(DNS_RESOURCE_KEY_NAME(dt->key), DNS_RESOURCE_KEY_NAME(rr->key));
                        if (r < 0)
                                return r;
                        if (r == 0)
                                continue;

                        /* We found a DS transactions for the SOA/NS
                         * RRs we are looking at. If it discovered signed DS
                         * RRs, then we need to be signed, too. */

                        if (!dt->answer_authenticated)
                                return false;

                        return dns_answer_match_key(dt->answer, dt->key, NULL);
                }

                /* We found nothing that proves this is safe to leave
                 * this unauthenticated, hence ask inist on
                 * authentication. */
                return true;
        }

        case DNS_TYPE_DS:
        case DNS_TYPE_CNAME:
        case DNS_TYPE_DNAME: {
                const char *parent = NULL;
                DnsTransaction *dt;
                Iterator i;

                /*
                 * CNAME/DNAME RRs cannot be located at a zone apex, hence look directly for the parent SOA.
                 *
                 * DS RRs are signed if the parent is signed, hence also look at the parent SOA
                 */

                SET_FOREACH(dt, t->dnssec_transactions, i) {

                        if (dt->key->class != rr->key->class)
                                continue;
                        if (dt->key->type != DNS_TYPE_SOA)
                                continue;

                        if (!parent) {
                                parent = DNS_RESOURCE_KEY_NAME(rr->key);
                                r = dns_name_parent(&parent);
                                if (r < 0)
                                        return r;
                                if (r == 0) {
                                        if (rr->key->type == DNS_TYPE_DS)
                                                return true;

                                        /* A CNAME/DNAME without a parent? That's sooo weird. */
                                        log_debug("Transaction %" PRIu16 " claims CNAME/DNAME at root. Refusing.", t->id);
                                        return -EBADMSG;
                                }
                        }

                        r = dns_name_equal(DNS_RESOURCE_KEY_NAME(dt->key), parent);
                        if (r < 0)
                                return r;
                        if (r == 0)
                                continue;

                        return t->answer_authenticated;
                }

                return true;
        }

        default: {
                DnsTransaction *dt;
                Iterator i;

                /* Any other kind of RR (including DNSKEY/NSEC/NSEC3). Let's see if our SOA lookup was authenticated */

                SET_FOREACH(dt, t->dnssec_transactions, i) {

                        if (dt->key->class != rr->key->class)
                                continue;
                        if (dt->key->type != DNS_TYPE_SOA)
                                continue;

                        r = dns_name_equal(DNS_RESOURCE_KEY_NAME(dt->key), DNS_RESOURCE_KEY_NAME(rr->key));
                        if (r < 0)
                                return r;
                        if (r == 0)
                                continue;

                        /* We found the transaction that was supposed to find
                         * the SOA RR for us. It was successful, but found no
                         * RR for us. This means we are not at a zone cut. In
                         * this case, we require authentication if the SOA
                         * lookup was authenticated too. */
                        return t->answer_authenticated;
                }

                return true;
        }}
}

static int dns_transaction_requires_nsec(DnsTransaction *t) {
        DnsTransaction *dt;
        const char *name;
        Iterator i;
        int r;

        assert(t);

        /* Checks if we need to insist on NSEC/NSEC3 RRs for proving
         * this negative reply */

        if (t->scope->dnssec_mode == DNSSEC_NO)
                return false;

        if (dns_type_is_pseudo(t->key->type))
                return -EINVAL;

        r = dns_trust_anchor_lookup_negative(&t->scope->manager->trust_anchor, DNS_RESOURCE_KEY_NAME(t->key));
        if (r < 0)
                return r;
        if (r > 0)
                return false;

        name = DNS_RESOURCE_KEY_NAME(t->key);

        if (IN_SET(t->key->type, DNS_TYPE_SOA, DNS_TYPE_NS, DNS_TYPE_DS)) {

                /* We got a negative reply for this SOA/NS lookup? If
                 * so, then we are not at a zone apex, and thus should
                 * look at the result of the parent SOA lookup.
                 *
                 * We got a negative reply for this DS lookup? DS RRs
                 * are signed when their parent zone is signed, hence
                 * also check the parent SOA in this case. */

                r = dns_name_parent(&name);
                if (r < 0)
                        return r;
                if (r == 0)
                        return true;
        }

        /* For all other RRs we check the SOA on the same level to see
         * if it's signed. */

        SET_FOREACH(dt, t->dnssec_transactions, i) {

                if (dt->key->class != t->key->class)
                        continue;
                if (dt->key->type != DNS_TYPE_SOA)
                        continue;

                r = dns_name_equal(DNS_RESOURCE_KEY_NAME(dt->key), name);
                if (r < 0)
                        return r;
                if (r == 0)
                        continue;

                return dt->answer_authenticated;
        }

        /* If in doubt, require NSEC/NSEC3 */
        return true;
}

static int dns_transaction_dnskey_authenticated(DnsTransaction *t, DnsResourceRecord *rr) {
        DnsResourceRecord *rrsig;
        bool found = false;
        int r;

        /* Checks whether any of the DNSKEYs used for the RRSIGs for
         * the specified RRset is authenticated (i.e. has a matching
         * DS RR). */

        r = dns_trust_anchor_lookup_negative(&t->scope->manager->trust_anchor, DNS_RESOURCE_KEY_NAME(rr->key));
        if (r < 0)
                return r;
        if (r > 0)
                return false;

        DNS_ANSWER_FOREACH(rrsig, t->answer) {
                DnsTransaction *dt;
                Iterator i;

                r = dnssec_key_match_rrsig(rr->key, rrsig);
                if (r < 0)
                        return r;
                if (r == 0)
                        continue;

                SET_FOREACH(dt, t->dnssec_transactions, i) {

                        if (dt->key->class != rr->key->class)
                                continue;

                        if (dt->key->type == DNS_TYPE_DNSKEY) {

                                r = dns_name_equal(DNS_RESOURCE_KEY_NAME(dt->key), rrsig->rrsig.signer);
                                if (r < 0)
                                        return r;
                                if (r == 0)
                                        continue;

                                /* OK, we found an auxiliary DNSKEY
                                 * lookup. If that lookup is
                                 * authenticated, report this. */

                                if (dt->answer_authenticated)
                                        return true;

                                found = true;

                        } else if (dt->key->type == DNS_TYPE_DS) {

                                r = dns_name_equal(DNS_RESOURCE_KEY_NAME(dt->key), rrsig->rrsig.signer);
                                if (r < 0)
                                        return r;
                                if (r == 0)
                                        continue;

                                /* OK, we found an auxiliary DS
                                 * lookup. If that lookup is
                                 * authenticated and non-zero, we
                                 * won! */

                                if (!dt->answer_authenticated)
                                        return false;

                                return dns_answer_match_key(dt->answer, dt->key, NULL);
                        }
                }
        }

        return found ? false : -ENXIO;
}

static int dns_transaction_known_signed(DnsTransaction *t, DnsResourceRecord *rr) {
        assert(t);
        assert(rr);

        /* We know that the root domain is signed, hence if it appears
         * not to be signed, there's a problem with the DNS server */

        return rr->key->class == DNS_CLASS_IN &&
                dns_name_is_root(DNS_RESOURCE_KEY_NAME(rr->key));
}

int dns_transaction_validate_dnssec(DnsTransaction *t) {
        _cleanup_(dns_answer_unrefp) DnsAnswer *validated = NULL;
        bool dnskeys_finalized = false;
        DnsResourceRecord *rr;
        DnsAnswerFlags flags;
        int r;

        assert(t);

        /* We have now collected all DS and DNSKEY RRs in
         * t->validated_keys, let's see which RRs we can now
         * authenticate with that. */

        if (t->scope->dnssec_mode == DNSSEC_NO)
                return 0;

        /* Already validated */
        if (t->answer_dnssec_result != _DNSSEC_RESULT_INVALID)
                return 0;

        /* Our own stuff needs no validation */
        if (IN_SET(t->answer_source, DNS_TRANSACTION_ZONE, DNS_TRANSACTION_TRUST_ANCHOR)) {
                t->answer_dnssec_result = DNSSEC_VALIDATED;
                t->answer_authenticated = true;
                return 0;
        }

        /* Cached stuff is not affected by validation. */
        if (t->answer_source != DNS_TRANSACTION_NETWORK)
                return 0;

        if (t->current_features < DNS_SERVER_FEATURE_LEVEL_DO ||
            (t->server && t->server->rrsig_missing)) {
                /* The server does not support DNSSEC, or doesn't augment responses with RRSIGs. */
                t->answer_dnssec_result = DNSSEC_INCOMPATIBLE_SERVER;
                return 0;
        }

        log_debug("Validating response from transaction %" PRIu16 " (%s).", t->id, dns_transaction_key_string(t));

        /* First see if there are DNSKEYs we already known a validated DS for. */
        r = dns_transaction_validate_dnskey_by_ds(t);
        if (r < 0)
                return r;

        for (;;) {
                bool changed = false;

                DNS_ANSWER_FOREACH(rr, t->answer) {
                        DnssecResult result;

                        if (rr->key->type == DNS_TYPE_RRSIG)
                                continue;

                        r = dnssec_verify_rrset_search(t->answer, rr->key, t->validated_keys, USEC_INFINITY, &result);
                        if (r < 0)
                                return r;

                        log_debug("Looking at %s: %s", strna(dns_resource_record_to_string(rr)), dnssec_result_to_string(result));

                        if (result == DNSSEC_VALIDATED) {

                                if (rr->key->type == DNS_TYPE_DNSKEY) {
                                        /* If we just validated a
                                         * DNSKEY RRset, then let's
                                         * add these keys to the set
                                         * of validated keys for this
                                         * transaction. */

                                        r = dns_answer_copy_by_key(&t->validated_keys, t->answer, rr->key, DNS_ANSWER_AUTHENTICATED);
                                        if (r < 0)
                                                return r;

                                        /* Maybe warn the user that we
                                         * encountered a revoked
                                         * DNSKEY for a key from our
                                         * trust anchor */
                                        r = dns_trust_anchor_check_revoked(&t->scope->manager->trust_anchor, t->answer, rr->key);
                                        if (r < 0)
                                                return r;
                                }

                                /* Add the validated RRset to the new
                                 * list of validated RRsets, and
                                 * remove it from the unvalidated
                                 * RRsets. We mark the RRset as
                                 * authenticated and cacheable. */
                                r = dns_answer_move_by_key(&validated, &t->answer, rr->key, DNS_ANSWER_AUTHENTICATED|DNS_ANSWER_CACHEABLE);
                                if (r < 0)
                                        return r;

                                t->scope->manager->n_dnssec_secure++;

                                /* Exit the loop, we dropped something from the answer, start from the beginning */
                                changed = true;
                                break;

                        } else if (dnskeys_finalized) {

                                /* If we haven't read all DNSKEYs yet
                                 * a negative result of the validation
                                 * is irrelevant, as there might be
                                 * more DNSKEYs coming. */

                                if (result == DNSSEC_NO_SIGNATURE) {
                                        r = dns_transaction_requires_rrsig(t, rr);
                                        if (r < 0)
                                                return r;
                                        if (r == 0) {
                                                /* Data does not require signing. In that case, just copy it over,
                                                 * but remember that this is by no means authenticated.*/
                                                r = dns_answer_move_by_key(&validated, &t->answer, rr->key, 0);
                                                if (r < 0)
                                                        return r;

                                                t->scope->manager->n_dnssec_insecure++;

                                                changed = true;
                                                break;
                                        }

                                        r = dns_transaction_known_signed(t, rr);
                                        if (r < 0)
                                                return r;
                                        if (r > 0) {
                                                /* This is an RR we know has to be signed. If it isn't this means
                                                 * the server is not attaching RRSIGs, hence complain. */

                                                dns_server_packet_rrsig_missing(t->server);

                                                if (t->scope->dnssec_mode == DNSSEC_ALLOW_DOWNGRADE) {

                                                        /* Downgrading is OK? If so, just consider the information unsigned */

                                                        r = dns_answer_move_by_key(&validated, &t->answer, rr->key, 0);
                                                        if (r < 0)
                                                                return r;

                                                        t->scope->manager->n_dnssec_insecure++;
                                                        changed = true;
                                                        break;
                                                }

                                                /* Otherwise, fail */
                                                t->answer_dnssec_result = DNSSEC_INCOMPATIBLE_SERVER;
                                                return 0;
                                        }
                                }

                                if (IN_SET(result,
                                           DNSSEC_MISSING_KEY,
                                           DNSSEC_SIGNATURE_EXPIRED,
                                           DNSSEC_UNSUPPORTED_ALGORITHM)) {

                                        r = dns_transaction_dnskey_authenticated(t, rr);
                                        if (r < 0 && r != -ENXIO)
                                                return r;
                                        if (r == 0) {
                                                /* The DNSKEY transaction was not authenticated, this means there's
                                                 * no DS for this, which means it's OK if no keys are found for this signature. */

                                                r = dns_answer_move_by_key(&validated, &t->answer, rr->key, 0);
                                                if (r < 0)
                                                        return r;

                                                t->scope->manager->n_dnssec_insecure++;

                                                changed = true;
                                                break;
                                        }
                                }

                                if (IN_SET(result,
                                           DNSSEC_INVALID,
                                           DNSSEC_SIGNATURE_EXPIRED,
                                           DNSSEC_NO_SIGNATURE,
                                           DNSSEC_UNSUPPORTED_ALGORITHM))
                                        t->scope->manager->n_dnssec_bogus++;
                                else
                                        t->scope->manager->n_dnssec_indeterminate++;

                                r = dns_transaction_is_primary_response(t, rr);
                                if (r < 0)
                                        return r;
                                if (r > 0) {
                                        /* This is a primary response
                                         * to our question, and it
                                         * failed validation. That's
                                         * fatal. */
                                        t->answer_dnssec_result = result;
                                        return 0;
                                }

                                /* This is just some auxiliary
                                 * data. Just remove the RRset and
                                 * continue. */
                                r = dns_answer_remove_by_key(&t->answer, rr->key);
                                if (r < 0)
                                        return r;

                                /* Exit the loop, we dropped something from the answer, start from the beginning */
                                changed = true;
                                break;
                        }
                }

                if (changed)
                        continue;

                if (!dnskeys_finalized) {
                        /* OK, now we know we have added all DNSKEYs
                         * we possibly could to our validated
                         * list. Now run the whole thing once more,
                         * and strip everything we still cannot
                         * validate.
                         */
                        dnskeys_finalized = true;
                        continue;
                }

                /* We're done */
                break;
        }

        dns_answer_unref(t->answer);
        t->answer = validated;
        validated = NULL;

        /* At this point the answer only contains validated
         * RRsets. Now, let's see if it actually answers the question
         * we asked. If so, great! If it doesn't, then see if
         * NSEC/NSEC3 can prove this. */
        r = dns_transaction_has_positive_answer(t, &flags);
        if (r > 0) {
                /* Yes, it answers the question! */

                if (flags & DNS_ANSWER_AUTHENTICATED) {
                        /* The answer is fully authenticated, yay. */
                        t->answer_dnssec_result = DNSSEC_VALIDATED;
                        t->answer_rcode = DNS_RCODE_SUCCESS;
                        t->answer_authenticated = true;
                } else {
                        /* The answer is not fully authenticated. */
                        t->answer_dnssec_result = DNSSEC_UNSIGNED;
                        t->answer_authenticated = false;
                }

        } else if (r == 0) {
                DnssecNsecResult nr;
                bool authenticated = false;

                /* Bummer! Let's check NSEC/NSEC3 */
                r = dnssec_test_nsec(t->answer, t->key, &nr, &authenticated, &t->answer_nsec_ttl);
                if (r < 0)
                        return r;

                switch (nr) {

                case DNSSEC_NSEC_NXDOMAIN:
                        /* NSEC proves the domain doesn't exist. Very good. */
                        log_debug("Proved NXDOMAIN via NSEC/NSEC3 for transaction %u (%s)", t->id, dns_transaction_key_string(t));
                        t->answer_dnssec_result = DNSSEC_VALIDATED;
                        t->answer_rcode = DNS_RCODE_NXDOMAIN;
                        t->answer_authenticated = authenticated;
                        break;

                case DNSSEC_NSEC_NODATA:
                        /* NSEC proves that there's no data here, very good. */
                        log_debug("Proved NODATA via NSEC/NSEC3 for transaction %u (%s)", t->id, dns_transaction_key_string(t));
                        t->answer_dnssec_result = DNSSEC_VALIDATED;
                        t->answer_rcode = DNS_RCODE_SUCCESS;
                        t->answer_authenticated = authenticated;
                        break;

                case DNSSEC_NSEC_OPTOUT:
                        /* NSEC3 says the data might not be signed */
                        log_debug("Data is NSEC3 opt-out via NSEC/NSEC3 for transaction %u (%s)", t->id, dns_transaction_key_string(t));
                        t->answer_dnssec_result = DNSSEC_UNSIGNED;
                        t->answer_authenticated = false;
                        break;

                case DNSSEC_NSEC_NO_RR:
                        /* No NSEC data? Bummer! */

                        r = dns_transaction_requires_nsec(t);
                        if (r < 0)
                                return r;
                        if (r > 0)
                                t->answer_dnssec_result = DNSSEC_NO_SIGNATURE;
                        else {
                                t->answer_dnssec_result = DNSSEC_UNSIGNED;
                                t->answer_authenticated = false;
                        }

                        break;

                case DNSSEC_NSEC_UNSUPPORTED_ALGORITHM:
                        /* We don't know the NSEC3 algorithm used? */
                        t->answer_dnssec_result = DNSSEC_UNSUPPORTED_ALGORITHM;
                        break;

                case DNSSEC_NSEC_FOUND:
                case DNSSEC_NSEC_CNAME:
                        /* NSEC says it needs to be there, but we couldn't find it? Bummer! */
                        t->answer_dnssec_result = DNSSEC_NSEC_MISMATCH;
                        break;

                default:
                        assert_not_reached("Unexpected NSEC result.");
                }
        }

        return 1;
}

const char *dns_transaction_key_string(DnsTransaction *t) {
        assert(t);

        if (!t->key_string) {
                if (dns_resource_key_to_string(t->key, &t->key_string) < 0)
                        return "n/a";
        }

        return strstrip(t->key_string);
}

static const char* const dns_transaction_state_table[_DNS_TRANSACTION_STATE_MAX] = {
        [DNS_TRANSACTION_NULL] = "null",
        [DNS_TRANSACTION_PENDING] = "pending",
        [DNS_TRANSACTION_VALIDATING] = "validating",
        [DNS_TRANSACTION_RCODE_FAILURE] = "rcode-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_CONNECTION_FAILURE] = "connection-failure",
        [DNS_TRANSACTION_ABORTED] = "aborted",
        [DNS_TRANSACTION_DNSSEC_FAILED] = "dnssec-failed",
        [DNS_TRANSACTION_NO_TRUST_ANCHOR] = "no-trust-anchor",
};
DEFINE_STRING_TABLE_LOOKUP(dns_transaction_state, DnsTransactionState);

static const char* const dns_transaction_source_table[_DNS_TRANSACTION_SOURCE_MAX] = {
        [DNS_TRANSACTION_NETWORK] = "network",
        [DNS_TRANSACTION_CACHE] = "cache",
        [DNS_TRANSACTION_ZONE] = "zone",
        [DNS_TRANSACTION_TRUST_ANCHOR] = "trust-anchor",
};
DEFINE_STRING_TABLE_LOOKUP(dns_transaction_source, DnsTransactionSource);