about summary refs log tree commit diff
path: root/support/resolv_test.c
blob: e968c836339301beb4470735d62928d9e0e7676a (plain) (blame)
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
/* DNS test framework and libresolv redirection.
   Copyright (C) 2016-2018 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library 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.

   The GNU C Library 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 the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#include <support/resolv_test.h>

#include <arpa/inet.h>
#include <errno.h>
#include <fcntl.h>
#include <nss.h>
#include <resolv.h>
#include <search.h>
#include <stdlib.h>
#include <string.h>
#include <support/check.h>
#include <support/namespace.h>
#include <support/support.h>
#include <support/test-driver.h>
#include <support/xsocket.h>
#include <support/xthread.h>
#include <support/xunistd.h>
#include <sys/uio.h>
#include <unistd.h>

/* Response builder.  */

enum
  {
    max_response_length = 65536
  };

/* List of pointers to be freed.  The hash table implementation
   (struct hsearch_data) does not provide a way to deallocate all
   objects, so this approach is used to avoid memory leaks.  */
struct to_be_freed
{
  struct to_be_freed *next;
  void *ptr;
};

struct resolv_response_builder
{
  const unsigned char *query_buffer;
  size_t query_length;

  size_t offset;                /* Bytes written so far in buffer.  */
  ns_sect section;              /* Current section in the DNS packet.  */
  unsigned int truncate_bytes;  /* Bytes to remove at end of response. */
  bool drop;                    /* Discard generated response.  */
  bool close;                   /* Close TCP client connection.  */

  /* Offset of the two-byte RDATA length field in the currently
     written RDATA sub-structure.  0 if no RDATA is being written.  */
  size_t current_rdata_offset;

  /* Hash table for locating targets for label compression.  */
  struct hsearch_data compression_offsets;
  /* List of pointers which need to be freed.  Used for domain names
     involved in label compression.  */
  struct to_be_freed *to_be_freed;

  /* Must be last.  Not zeroed for performance reasons.  */
  unsigned char buffer[max_response_length];
};

/* Response builder. */

/* Add a pointer to the list of pointers to be freed when B is
   deallocated.  */
static void
response_push_pointer_to_free (struct resolv_response_builder *b, void *ptr)
{
  if (ptr == NULL)
    return;
  struct to_be_freed *e = xmalloc (sizeof (*e));
  *e = (struct to_be_freed) {b->to_be_freed, ptr};
  b->to_be_freed = e;
}

void
resolv_response_init (struct resolv_response_builder *b,
                      struct resolv_response_flags flags)
{
  if (b->offset > 0)
    FAIL_EXIT1 ("response_init: called at offset %zu", b->offset);
  if (b->query_length < 12)
    FAIL_EXIT1 ("response_init called for a query of size %zu",
                b->query_length);
  if (flags.rcode > 15)
    FAIL_EXIT1 ("response_init: invalid RCODE %u", flags.rcode);

  /* Copy the transaction ID.  */
  b->buffer[0] = b->query_buffer[0];
  b->buffer[1] = b->query_buffer[1];

  /* Initialize the flags.  */
  b->buffer[2] = 0x80;                       /* Mark as response.   */
  b->buffer[2] |= b->query_buffer[2] & 0x01; /* Copy the RD bit.  */
  if (flags.tc)
    b->buffer[2] |= 0x02;
  b->buffer[3] = 0x80 | flags.rcode; /* Always set RA.  */

  /* Fill in the initial section count values.  */
  b->buffer[4] = flags.qdcount >> 8;
  b->buffer[5] = flags.qdcount;
  b->buffer[6] = flags.ancount >> 8;
  b->buffer[7] = flags.ancount;
  b->buffer[8] = flags.nscount >> 8;
  b->buffer[9] = flags.nscount;
  b->buffer[10] = flags.adcount >> 8;
  b->buffer[11] = flags.adcount;

  b->offset = 12;
}

void
resolv_response_section (struct resolv_response_builder *b, ns_sect section)
{
  if (b->offset == 0)
    FAIL_EXIT1 ("resolv_response_section: response_init not called before");
  if (section < b->section)
    FAIL_EXIT1 ("resolv_response_section: cannot go back to previous section");
  b->section = section;
}

/* Add a single byte to B.  */
static inline void
response_add_byte (struct resolv_response_builder *b, unsigned char ch)
{
  if (b->offset == max_response_length)
    FAIL_EXIT1 ("DNS response exceeds 64 KiB limit");
  b->buffer[b->offset] = ch;
  ++b->offset;
}

/* Add a 16-bit word VAL to B, in big-endian format.  */
static void
response_add_16 (struct resolv_response_builder *b, uint16_t val)
{
  response_add_byte (b, val >> 8);
  response_add_byte (b, val);
}

/* Increment the pers-section record counter in the packet header.  */
static void
response_count_increment (struct resolv_response_builder *b)
{
  unsigned int offset = b->section;
  offset = 4 + 2 * offset;
  ++b->buffer[offset + 1];
  if (b->buffer[offset + 1] == 0)
    {
      /* Carry.  */
      ++b->buffer[offset];
      if (b->buffer[offset] == 0)
        /* Overflow.  */
        FAIL_EXIT1 ("too many records in section");
    }
}

void
resolv_response_add_question (struct resolv_response_builder *b,
                              const char *name, uint16_t class, uint16_t type)
{
  if (b->offset == 0)
    FAIL_EXIT1 ("resolv_response_add_question: "
                "resolv_response_init not called");
  if (b->section != ns_s_qd)
    FAIL_EXIT1 ("resolv_response_add_question: "
                "must be called in the question section");

  resolv_response_add_name (b, name);
  response_add_16 (b, type);
  response_add_16 (b, class);

  response_count_increment (b);
}

void
resolv_response_add_name (struct resolv_response_builder *b,
                          const char *const origname)
{
  /* Normalized name.  */
  char *name;
  /* Normalized name with case preserved.  */
  char *name_case;
  {
    size_t namelen = strlen (origname);
    /* Remove trailing dots.  FIXME: Handle trailing quoted dots.  */
    while (namelen > 0 && origname[namelen - 1] == '.')
      --namelen;
    name = xmalloc (namelen + 1);
    name_case = xmalloc (namelen + 1);
    /* Copy and convert to lowercase.  FIXME: This needs to normalize
       escaping as well.  */
    for (size_t i = 0; i < namelen; ++i)
      {
        char ch = origname[i];
        name_case[i] = ch;
        if ('A' <= ch && ch <= 'Z')
          ch = ch - 'A' + 'a';
        name[i] = ch;
      }
    name[namelen] = 0;
    name_case[namelen] = 0;
  }
  char *name_start = name;
  char *name_case_start = name_case;

  bool compression = false;
  while (*name)
    {
      /* Search for a previous name we can reference.  */
      ENTRY new_entry =
        {
          .key = name,
          .data = (void *) (uintptr_t) b->offset,
        };

      /* If the label can be a compression target because it is at a
         reachable offset, add it to the hash table.  */
      ACTION action;
      if (b->offset < (1 << 12))
        action = ENTER;
      else
        action = FIND;

      /* Search for known compression offsets in the hash table.  */
      ENTRY *e;
      if (hsearch_r (new_entry, action, &e, &b->compression_offsets) == 0)
        {
          if (action == FIND && errno == ESRCH)
            /* Fall through.  */
            e = NULL;
          else
            FAIL_EXIT1 ("hsearch_r failure in name compression: %m");
        }

      /* The name is known.  Reference the previous location.  */
      if (e != NULL && e->data != new_entry.data)
        {
          size_t old_offset = (uintptr_t) e->data;
          response_add_byte (b, 0xC0 | (old_offset >> 8));
          response_add_byte (b, old_offset);
          compression = true;
          break;
        }

      /* The name does not exist yet.  Write one label.  First, add
         room for the label length.  */
      size_t buffer_label_offset = b->offset;
      response_add_byte (b, 0);

      /* Copy the label.  */
      while (true)
        {
          char ch = *name_case;
          if (ch == '\0')
            break;
          ++name;
          ++name_case;
          if (ch == '.')
            break;
          /* FIXME: Handle escaping.  */
          response_add_byte (b, ch);
        }

      /* Patch in the label length.  */
      size_t label_length = b->offset - buffer_label_offset - 1;
      if (label_length == 0)
        FAIL_EXIT1 ("empty label in name compression: %s", origname);
      if (label_length > 63)
        FAIL_EXIT1 ("label too long in name compression: %s", origname);
      b->buffer[buffer_label_offset] = label_length;

      /* Continue with the tail of the name and the next label.  */
    }

  if (compression)
    {
      /* If we found an immediate match for the name, we have not put
         it into the hash table, and can free it immediately.  */
      if (name == name_start)
        free (name_start);
      else
        response_push_pointer_to_free (b, name_start);
    }
  else
    {
      /* Terminate the sequence of labels.  With compression, this is
         implicit in the compression reference.  */
      response_add_byte (b, 0);
      response_push_pointer_to_free (b, name_start);
    }

  free (name_case_start);
}

void
resolv_response_open_record (struct resolv_response_builder *b,
                             const char *name,
                             uint16_t class, uint16_t type, uint32_t ttl)
{
  if (b->section == ns_s_qd)
    FAIL_EXIT1 ("resolv_response_open_record called in question section");
  if (b->current_rdata_offset != 0)
    FAIL_EXIT1 ("resolv_response_open_record called with open record");

  resolv_response_add_name (b, name);
  response_add_16 (b, type);
  response_add_16 (b, class);
  response_add_16 (b, ttl >> 16);
  response_add_16 (b, ttl);

  b->current_rdata_offset = b->offset;
  /* Add room for the RDATA length.  */
  response_add_16 (b, 0);
}


void
resolv_response_close_record (struct resolv_response_builder *b)
{
  size_t rdata_offset = b->current_rdata_offset;
  if (rdata_offset == 0)
    FAIL_EXIT1 ("response_close_record called without open record");
  size_t rdata_length = b->offset - rdata_offset - 2;
  if (rdata_length > 65535)
    FAIL_EXIT1 ("RDATA length %zu exceeds limit", rdata_length);
  b->buffer[rdata_offset] = rdata_length >> 8;
  b->buffer[rdata_offset + 1] = rdata_length;
  response_count_increment (b);
  b->current_rdata_offset = 0;
}

void
resolv_response_add_data (struct resolv_response_builder *b,
                          const void *data, size_t length)
{
  size_t remaining = max_response_length - b->offset;
  if (remaining < length)
    FAIL_EXIT1 ("resolv_response_add_data: not enough room for %zu bytes",
                length);
  memcpy (b->buffer + b->offset, data, length);
  b->offset += length;
}

void
resolv_response_drop (struct resolv_response_builder *b)
{
  b->drop = true;
}

void
resolv_response_close (struct resolv_response_builder *b)
{
  b->close = true;
}

void
resolv_response_truncate_data (struct resolv_response_builder *b, size_t count)
{
  if (count > 65535)
    FAIL_EXIT1 ("resolv_response_truncate_data: argument too large: %zu",
                count);
  b->truncate_bytes = count;
}


size_t
resolv_response_length (const struct resolv_response_builder *b)
{
  return b->offset;
}

unsigned char *
resolv_response_buffer (const struct resolv_response_builder *b)
{
  unsigned char *result = xmalloc (b->offset);
  memcpy (result, b->buffer, b->offset);
  return result;
}

static struct resolv_response_builder *
response_builder_allocate
  (const unsigned char *query_buffer, size_t query_length)
{
  struct resolv_response_builder *b = xmalloc (sizeof (*b));
  memset (b, 0, offsetof (struct resolv_response_builder, buffer));
  b->query_buffer = query_buffer;
  b->query_length = query_length;
  TEST_VERIFY_EXIT (hcreate_r (10000, &b->compression_offsets) != 0);
  return b;
}

static void
response_builder_free (struct resolv_response_builder *b)
{
  struct to_be_freed *current = b->to_be_freed;
  while (current != NULL)
    {
      struct to_be_freed *next = current->next;
      free (current->ptr);
      free (current);
      current = next;
    }
  hdestroy_r (&b->compression_offsets);
  free (b);
}

/* DNS query processing. */

/* Data extracted from the question section of a DNS packet.  */
struct query_info
{
  char qname[MAXDNAME];
  uint16_t qclass;
  uint16_t qtype;
  struct resolv_edns_info edns;
};

/* Update *INFO from the specified DNS packet.  */
static void
parse_query (struct query_info *info,
             const unsigned char *buffer, size_t length)
{
  HEADER hd;
  _Static_assert (sizeof (hd) == 12, "DNS header size");
  if (length < sizeof (hd))
    FAIL_EXIT1 ("malformed DNS query: too short: %zu bytes", length);
  memcpy (&hd, buffer, sizeof (hd));

  if (ntohs (hd.qdcount) != 1)
    FAIL_EXIT1 ("malformed DNS query: wrong question count: %d",
                (int) ntohs (hd.qdcount));
  if (ntohs (hd.ancount) != 0)
    FAIL_EXIT1 ("malformed DNS query: wrong answer count: %d",
                (int) ntohs (hd.ancount));
  if (ntohs (hd.nscount) != 0)
    FAIL_EXIT1 ("malformed DNS query: wrong authority count: %d",
                (int) ntohs (hd.nscount));
  if (ntohs (hd.arcount) > 1)
    FAIL_EXIT1 ("malformed DNS query: wrong additional count: %d",
                (int) ntohs (hd.arcount));

  int ret = dn_expand (buffer, buffer + length, buffer + sizeof (hd),
                       info->qname, sizeof (info->qname));
  if (ret < 0)
    FAIL_EXIT1 ("malformed DNS query: cannot uncompress QNAME");

  /* Obtain QTYPE and QCLASS.  */
  size_t remaining = length - (12 + ret);
  struct
  {
    uint16_t qtype;
    uint16_t qclass;
  } qtype_qclass;
  if (remaining < sizeof (qtype_qclass))
    FAIL_EXIT1 ("malformed DNS query: "
                "query lacks QCLASS/QTYPE, QNAME: %s", info->qname);
  memcpy (&qtype_qclass, buffer + 12 + ret, sizeof (qtype_qclass));
  info->qclass = ntohs (qtype_qclass.qclass);
  info->qtype = ntohs (qtype_qclass.qtype);

  memset (&info->edns, 0, sizeof (info->edns));
  if (ntohs (hd.arcount) > 0)
    {
      /* Parse EDNS record.  */
      struct __attribute__ ((packed, aligned (1)))
      {
        uint8_t root;
        uint16_t rtype;
        uint16_t payload;
        uint8_t edns_extended_rcode;
        uint8_t edns_version;
        uint16_t flags;
        uint16_t rdatalen;
      } rr;
      _Static_assert (sizeof (rr) == 11, "EDNS record size");

      if (remaining < 4 + sizeof (rr))
        FAIL_EXIT1 ("mailformed DNS query: no room for EDNS record");
      memcpy (&rr, buffer + 12 + ret + 4, sizeof (rr));
      if (rr.root != 0)
        FAIL_EXIT1 ("malformed DNS query: invalid OPT RNAME: %d\n", rr.root);
      if (rr.rtype != htons (41))
        FAIL_EXIT1 ("malformed DNS query: invalid OPT type: %d\n",
                    ntohs (rr.rtype));
      info->edns.active = true;
      info->edns.extended_rcode = rr.edns_extended_rcode;
      info->edns.version = rr.edns_version;
      info->edns.flags = ntohs (rr.flags);
      info->edns.payload_size = ntohs (rr.payload);
    }
}


/* Main testing framework.  */

/* Per-server information.  One struct is allocated for each test
   server.  */
struct resolv_test_server
{
  /* Local address of the server.  UDP and TCP use the same port.  */
  struct sockaddr_in address;

  /* File descriptor of the UDP server, or -1 if this server is
     disabled.  */
  int socket_udp;

  /* File descriptor of the TCP server, or -1 if this server is
     disabled.  */
  int socket_tcp;

  /* Counter of the number of responses processed so far.  */
  size_t response_number;

  /* Thread handles for the server threads (if not disabled in the
     configuration).  */
  pthread_t thread_udp;
  pthread_t thread_tcp;
};

/* Main struct for keeping track of libresolv redirection and
   testing.  */
struct resolv_test
{
  /* After initialization, any access to the struct must be performed
     while this lock is acquired.  */
  pthread_mutex_t lock;

  /* Data for each test server. */
  struct resolv_test_server servers[resolv_max_test_servers];

  /* Used if config.single_thread_udp is true.  */
  pthread_t thread_udp_single;

  struct resolv_redirect_config config;
  bool termination_requested;
};

/* Function implementing a server thread.  */
typedef void (*thread_callback) (struct resolv_test *, int server_index);

/* Storage for thread-specific data, for passing to the
   thread_callback function.  */
struct thread_closure
{
  struct resolv_test *obj;      /* Current test object.  */
  thread_callback callback;     /* Function to call.  */
  int server_index;             /* Index of the implemented server.  */
};

/* Wrap response_callback as a function which can be passed to
   pthread_create.  */
static void *
thread_callback_wrapper (void *arg)
{
  struct thread_closure *closure = arg;
  closure->callback (closure->obj, closure->server_index);
  free (closure);
  return NULL;
}

/* Start a server thread for the specified SERVER_INDEX, implemented
   by CALLBACK.  */
static pthread_t
start_server_thread (struct resolv_test *obj, int server_index,
                     thread_callback callback)
{
  struct thread_closure *closure = xmalloc (sizeof (*closure));
  *closure = (struct thread_closure)
    {
      .obj = obj,
      .callback = callback,
      .server_index = server_index,
    };
  return xpthread_create (NULL, thread_callback_wrapper, closure);
}

/* Process one UDP query.  Return false if a termination requested has
   been detected.  */
static bool
server_thread_udp_process_one (struct resolv_test *obj, int server_index)
{
  unsigned char query[512];
  struct sockaddr_storage peer;
  socklen_t peerlen = sizeof (peer);
  size_t length = xrecvfrom (obj->servers[server_index].socket_udp,
                             query, sizeof (query), 0,
                             (struct sockaddr *) &peer, &peerlen);
  /* Check for termination.  */
  {
    bool termination_requested;
    xpthread_mutex_lock (&obj->lock);
    termination_requested = obj->termination_requested;
    xpthread_mutex_unlock (&obj->lock);
    if (termination_requested)
      return false;
  }


  struct query_info qinfo;
  parse_query (&qinfo, query, length);
  if (test_verbose > 0)
    {
      if (test_verbose > 1)
        printf ("info: UDP server %d: incoming query:"
                " %zd bytes, %s/%u/%u, tnxid=0x%02x%02x\n",
                server_index, length, qinfo.qname, qinfo.qclass, qinfo.qtype,
                query[0], query[1]);
      else
        printf ("info: UDP server %d: incoming query:"
                " %zd bytes, %s/%u/%u\n",
                server_index, length, qinfo.qname, qinfo.qclass, qinfo.qtype);
    }

  struct resolv_response_context ctx =
    {
      .query_buffer = query,
      .query_length = length,
      .server_index = server_index,
      .tcp = false,
      .edns = qinfo.edns,
    };
  struct resolv_response_builder *b = response_builder_allocate (query, length);
  obj->config.response_callback
    (&ctx, b, qinfo.qname, qinfo.qclass, qinfo.qtype);

  if (b->drop)
    {
      if (test_verbose)
        printf ("info: UDP server %d: dropping response to %s/%u/%u\n",
                server_index, qinfo.qname, qinfo.qclass, qinfo.qtype);
    }
  else
    {
      if (test_verbose)
        {
          if (b->offset >= 12)
            printf ("info: UDP server %d: sending response:"
                    " %zu bytes, RCODE %d (for %s/%u/%u)\n",
                    server_index, b->offset, b->buffer[3] & 0x0f,
                    qinfo.qname, qinfo.qclass, qinfo.qtype);
          else
            printf ("info: UDP server %d: sending response: %zu bytes"
                    " (for %s/%u/%u)\n",
                    server_index, b->offset,
                    qinfo.qname, qinfo.qclass, qinfo.qtype);
          if (b->truncate_bytes > 0)
            printf ("info:    truncated by %u bytes\n", b->truncate_bytes);
        }
      size_t to_send = b->offset;
      if (to_send < b->truncate_bytes)
        to_send = 0;
      else
        to_send -= b->truncate_bytes;

      /* Ignore most errors here because the other end may have closed
         the socket. */
      if (sendto (obj->servers[server_index].socket_udp,
                  b->buffer, to_send, 0,
                  (struct sockaddr *) &peer, peerlen) < 0)
        TEST_VERIFY_EXIT (errno != EBADF);
    }
  response_builder_free (b);
  return true;
}

/* UDP thread_callback function.  Variant for one thread per
   server.  */
static void
server_thread_udp (struct resolv_test *obj, int server_index)
{
  while (server_thread_udp_process_one (obj, server_index))
    ;
}

/* Single-threaded UDP processing function, for the single_thread_udp
   case.  */
static void *
server_thread_udp_single (void *closure)
{
  struct resolv_test *obj = closure;

  struct pollfd fds[resolv_max_test_servers];
  for (int server_index = 0; server_index < resolv_max_test_servers;
       ++server_index)
    if (obj->config.servers[server_index].disable_udp)
      fds[server_index] = (struct pollfd) {.fd = -1};
    else
      {
        fds[server_index] = (struct pollfd)
          {
            .fd = obj->servers[server_index].socket_udp,
            .events = POLLIN
          };

        /* Make the socket non-blocking.  */
        int flags = fcntl (obj->servers[server_index].socket_udp, F_GETFL, 0);
        if (flags < 0)
          FAIL_EXIT1 ("fcntl (F_GETFL): %m");
        flags |= O_NONBLOCK;
        if (fcntl (obj->servers[server_index].socket_udp, F_SETFL, flags) < 0)
          FAIL_EXIT1 ("fcntl (F_SETFL): %m");
      }

  while (true)
    {
      xpoll (fds, resolv_max_test_servers, -1);
      for (int server_index = 0; server_index < resolv_max_test_servers;
           ++server_index)
        if (fds[server_index].revents != 0)
          {
            if (!server_thread_udp_process_one (obj, server_index))
              goto out;
            fds[server_index].revents = 0;
          }
    }

 out:
  return NULL;
}

/* Start the single UDP handler thread (for the single_thread_udp
   case).  */
static void
start_server_thread_udp_single (struct resolv_test *obj)
{
  obj->thread_udp_single
    = xpthread_create (NULL, server_thread_udp_single, obj);
}

/* Data describing a TCP client connect.  */
struct tcp_thread_closure
{
  struct resolv_test *obj;
  int server_index;
  int client_socket;
};

/* Read a complete DNS query packet.  If EOF_OK, an immediate
   end-of-file condition is acceptable.  */
static bool
read_fully (int fd, void *buf, size_t len, bool eof_ok)
{
  const void *const end = buf + len;
  while (buf < end)
    {
      ssize_t ret = read (fd, buf, end - buf);
      if (ret == 0)
        {
          if (!eof_ok)
            {
              support_record_failure ();
              printf ("error: unexpected EOF on TCP connection\n");
            }
          return false;
        }
      else if (ret < 0)
        {
          if (!eof_ok || errno != ECONNRESET)
            {
              support_record_failure ();
              printf ("error: TCP read: %m\n");
            }
          return false;
        }
      buf += ret;
      eof_ok = false;
    }
  return true;
}

/* Write an array of iovecs.  Terminate the process on failure.  */
static void
writev_fully (int fd, struct iovec *buffers, size_t count)
{
  while (count > 0)
    {
      /* Skip zero-length write requests.  */
      if (buffers->iov_len == 0)
        {
          ++buffers;
          --count;
          continue;
        }
      /* Try to rewrite the remaing buffers.  */
      ssize_t ret = writev (fd, buffers, count);
      if (ret < 0)
        FAIL_EXIT1 ("writev: %m");
      if (ret == 0)
        FAIL_EXIT1 ("writev: invalid return value zero");
      /* Find the buffers that were successfully written.  */
      while (ret > 0)
        {
          if (count == 0)
            FAIL_EXIT1 ("internal writev consistency failure");
          /* Current buffer was partially written.  */
          if (buffers->iov_len > (size_t) ret)
            {
              buffers->iov_base += ret;
              buffers->iov_len -= ret;
              ret = 0;
            }
          else
            {
              ret -= buffers->iov_len;
              buffers->iov_len = 0;
              ++buffers;
              --count;
            }
        }
    }
}

/* Thread callback for handling a single established TCP connection to
   a client.  */
static void *
server_thread_tcp_client (void *arg)
{
  struct tcp_thread_closure *closure = arg;

  while (true)
    {
      /* Read packet length.  */
      uint16_t query_length;
      if (!read_fully (closure->client_socket,
                       &query_length, sizeof (query_length), true))
        break;
      query_length = ntohs (query_length);

      /* Read the packet.  */
      unsigned char *query_buffer = xmalloc (query_length);
      read_fully (closure->client_socket, query_buffer, query_length, false);

      struct query_info qinfo;
      parse_query (&qinfo, query_buffer, query_length);
      if (test_verbose > 0)
        {
          if (test_verbose > 1)
            printf ("info: UDP server %d: incoming query:"
                    " %d bytes, %s/%u/%u, tnxid=0x%02x%02x\n",
                    closure->server_index, query_length,
                    qinfo.qname, qinfo.qclass, qinfo.qtype,
                    query_buffer[0], query_buffer[1]);
          else
            printf ("info: TCP server %d: incoming query:"
                    " %u bytes, %s/%u/%u\n",
                    closure->server_index, query_length,
                    qinfo.qname, qinfo.qclass, qinfo.qtype);
        }

      struct resolv_response_context ctx =
        {
          .query_buffer = query_buffer,
          .query_length = query_length,
          .server_index = closure->server_index,
          .tcp = true,
          .edns = qinfo.edns,
        };
      struct resolv_response_builder *b = response_builder_allocate
        (query_buffer, query_length);
      closure->obj->config.response_callback
        (&ctx, b, qinfo.qname, qinfo.qclass, qinfo.qtype);

      if (b->drop)
        {
          if (test_verbose)
            printf ("info: TCP server %d: dropping response to %s/%u/%u\n",
                    closure->server_index,
                    qinfo.qname, qinfo.qclass, qinfo.qtype);
        }
      else
        {
          if (test_verbose)
            printf ("info: TCP server %d: sending response: %zu bytes"
                    " (for %s/%u/%u)\n",
                    closure->server_index, b->offset,
                    qinfo.qname, qinfo.qclass, qinfo.qtype);
          uint16_t length = htons (b->offset);
          size_t to_send = b->offset;
          if (to_send < b->truncate_bytes)
            to_send = 0;
          else
            to_send -= b->truncate_bytes;
          struct iovec buffers[2] =
            {
              {&length, sizeof (length)},
              {b->buffer, to_send}
            };
          writev_fully (closure->client_socket, buffers, 2);
        }
      bool close_flag = b->close;
      response_builder_free (b);
      free (query_buffer);
      if (close_flag)
        break;
    }

  xclose (closure->client_socket);
  free (closure);
  return NULL;
}

/* thread_callback for the TCP case.  Accept connections and create a
   new thread for each client.  */
static void
server_thread_tcp (struct resolv_test *obj, int server_index)
{
  while (true)
    {
      /* Get the client conenction.  */
      int client_socket = xaccept
        (obj->servers[server_index].socket_tcp, NULL, NULL);

      /* Check for termination.  */
      xpthread_mutex_lock (&obj->lock);
      if (obj->termination_requested)
        {
          xpthread_mutex_unlock (&obj->lock);
          xclose (client_socket);
          break;
        }
      xpthread_mutex_unlock (&obj->lock);

      /* Spawn a new thread for handling this connection.  */
      struct tcp_thread_closure *closure = xmalloc (sizeof (*closure));
      *closure = (struct tcp_thread_closure)
        {
          .obj = obj,
          .server_index = server_index,
          .client_socket = client_socket,
        };

      pthread_t thr
        = xpthread_create (NULL, server_thread_tcp_client, closure);
      /* TODO: We should keep track of this thread so that we can
         block in resolv_test_end until it has exited.  */
      xpthread_detach (thr);
    }
}

/* Create UDP and TCP server sockets.  */
static void
make_server_sockets (struct resolv_test_server *server)
{
  while (true)
    {
      server->socket_udp = xsocket (AF_INET, SOCK_DGRAM, IPPROTO_UDP);
      server->socket_tcp = xsocket (AF_INET, SOCK_STREAM, IPPROTO_TCP);

      /* Pick the address for the UDP socket.  */
      server->address = (struct sockaddr_in)
        {
          .sin_family = AF_INET,
          .sin_addr = {.s_addr = htonl (INADDR_LOOPBACK)}
        };
      xbind (server->socket_udp,
             (struct sockaddr *)&server->address, sizeof (server->address));

      /* Retrieve the address. */
      socklen_t addrlen = sizeof (server->address);
      xgetsockname (server->socket_udp,
                    (struct sockaddr *)&server->address, &addrlen);

      /* Bind the TCP socket to the same address.  */
      {
        int on = 1;
        xsetsockopt (server->socket_tcp, SOL_SOCKET, SO_REUSEADDR,
                     &on, sizeof (on));
      }
      if (bind (server->socket_tcp,
                (struct sockaddr *)&server->address,
                sizeof (server->address)) != 0)
        {
          /* Port collision.  The UDP bind succeeded, but the TCP BIND
             failed.  We assume here that the kernel will pick the
             next local UDP address randomly.  */
          if (errno == EADDRINUSE)
            {
              xclose (server->socket_udp);
              xclose (server->socket_tcp);
              continue;
            }
          FAIL_EXIT1 ("TCP bind: %m");
        }
      xlisten (server->socket_tcp, 5);
      break;
    }
}

/* Like make_server_sockets, but the caller supplies the address to
   use.  */
static void
make_server_sockets_for_address (struct resolv_test_server *server,
                                 const struct sockaddr *addr)
{
  server->socket_udp = xsocket (AF_INET, SOCK_DGRAM, IPPROTO_UDP);
  server->socket_tcp = xsocket (AF_INET, SOCK_STREAM, IPPROTO_TCP);

  if (addr->sa_family == AF_INET)
    server->address = *(const struct sockaddr_in *) addr;
  else
    /* We cannot store the server address in the socket.  This should
       not matter if disable_redirect is used.  */
    server->address = (struct sockaddr_in) { .sin_family = 0, };

  xbind (server->socket_udp,
         (struct sockaddr *)&server->address, sizeof (server->address));
  xbind (server->socket_tcp,
         (struct sockaddr *)&server->address, sizeof (server->address));
  xlisten (server->socket_tcp, 5);
}

/* One-time initialization of NSS.  */
static void
resolv_redirect_once (void)
{
  /* Only use nss_dns.  */
  __nss_configure_lookup ("hosts", "dns");
  __nss_configure_lookup ("networks", "dns");
  /* Enter a network namespace for isolation and firewall state
     cleanup.  The tests will still work if these steps fail, but they
     may be less reliable.  */
  support_become_root ();
  support_enter_network_namespace ();
}
pthread_once_t resolv_redirect_once_var = PTHREAD_ONCE_INIT;

void
resolv_test_init (void)
{
  /* Perform one-time initialization of NSS.  */
  xpthread_once (&resolv_redirect_once_var, resolv_redirect_once);
}

/* Copy the search path from CONFIG.search to the _res object.  */
static void
set_search_path (struct resolv_redirect_config config)
{
  memset (_res.defdname, 0, sizeof (_res.defdname));
  memset (_res.dnsrch, 0, sizeof (_res.dnsrch));

  char *current = _res.defdname;
  char *end = current + sizeof (_res.defdname);

  for (unsigned int i = 0;
       i < sizeof (config.search) / sizeof (config.search[0]); ++i)
    {
      if (config.search[i] == NULL)
        continue;

      size_t length = strlen (config.search[i]) + 1;
      size_t remaining = end - current;
      TEST_VERIFY_EXIT (length <= remaining);
      memcpy (current, config.search[i], length);
      _res.dnsrch[i] = current;
      current += length;
    }
}

struct resolv_test *
resolv_test_start (struct resolv_redirect_config config)
{
  /* Apply configuration defaults.  */
  if (config.nscount == 0)
    config.nscount = resolv_max_test_servers;

  struct resolv_test *obj = xmalloc (sizeof (*obj));
  *obj = (struct resolv_test) {
    .config = config,
    .lock = PTHREAD_MUTEX_INITIALIZER,
  };

  if (!config.disable_redirect)
    resolv_test_init ();

  /* Create all the servers, to reserve the necessary ports.  */
  for (int server_index = 0; server_index < config.nscount; ++server_index)
    if (config.disable_redirect && config.server_address_overrides != NULL)
      make_server_sockets_for_address
        (obj->servers + server_index,
         config.server_address_overrides[server_index]);
    else
      make_server_sockets (obj->servers + server_index);

  /* Start server threads.  Disable the server ports, as
     requested.  */
  for (int server_index = 0; server_index < config.nscount; ++server_index)
    {
      struct resolv_test_server *server = obj->servers + server_index;
      if (config.servers[server_index].disable_udp)
        {
          xclose (server->socket_udp);
          server->socket_udp = -1;
        }
      else if (!config.single_thread_udp)
        server->thread_udp = start_server_thread (obj, server_index,
                                                  server_thread_udp);
      if (config.servers[server_index].disable_tcp)
        {
          xclose (server->socket_tcp);
          server->socket_tcp = -1;
        }
      else
        server->thread_tcp = start_server_thread (obj, server_index,
                                                  server_thread_tcp);
    }
  if (config.single_thread_udp)
    start_server_thread_udp_single (obj);

  if (config.disable_redirect)
    return obj;

  int timeout = 1;

  /* Initialize libresolv.  */
  TEST_VERIFY_EXIT (res_init () == 0);

  /* Disable IPv6 name server addresses.  The code below only
     overrides the IPv4 addresses.  */
  __res_iclose (&_res, true);
  _res._u._ext.nscount = 0;

  /* Redirect queries to the server socket.  */
  if (test_verbose)
    {
      printf ("info: old timeout value: %d\n", _res.retrans);
      printf ("info: old retry attempt value: %d\n", _res.retry);
      printf ("info: old _res.options: 0x%lx\n", _res.options);
      printf ("info: old _res.nscount value: %d\n", _res.nscount);
      printf ("info: old _res.ndots value: %d\n", _res.ndots);
    }
  _res.retrans = timeout;
  _res.retry = 4;
  _res.nscount = config.nscount;
  _res.options = RES_INIT | RES_RECURSE | RES_DEFNAMES | RES_DNSRCH;
  _res.ndots = 1;
  if (test_verbose)
    {
      printf ("info: new timeout value: %d\n", _res.retrans);
      printf ("info: new retry attempt value: %d\n", _res.retry);
      printf ("info: new _res.options: 0x%lx\n", _res.options);
      printf ("info: new _res.nscount value: %d\n", _res.nscount);
      printf ("info: new _res.ndots value: %d\n", _res.ndots);
    }
  for (int server_index = 0; server_index < config.nscount; ++server_index)
    {
      TEST_VERIFY_EXIT (obj->servers[server_index].address.sin_port != 0);
      _res.nsaddr_list[server_index] = obj->servers[server_index].address;
      if (test_verbose)
        {
          char buf[256];
          TEST_VERIFY_EXIT
            (inet_ntop (AF_INET, &obj->servers[server_index].address.sin_addr,
                        buf, sizeof (buf)) != NULL);
          printf ("info: server %d: %s/%u\n",
                  server_index, buf,
                  htons (obj->servers[server_index].address.sin_port));
        }
    }

  set_search_path (config);

  return obj;
}

void
resolv_test_end (struct resolv_test *obj)
{
  res_close ();

  xpthread_mutex_lock (&obj->lock);
  obj->termination_requested = true;
  xpthread_mutex_unlock (&obj->lock);

  /* Send trigger packets to unblock the server threads.  */
  for (int server_index = 0; server_index < obj->config.nscount;
       ++server_index)
    {
      if (!obj->config.servers[server_index].disable_udp)
        {
          int sock = xsocket (AF_INET, SOCK_DGRAM, IPPROTO_UDP);
          xsendto (sock, "", 1, 0,
                   (struct sockaddr *) &obj->servers[server_index].address,
                   sizeof (obj->servers[server_index].address));
          xclose (sock);
        }
      if (!obj->config.servers[server_index].disable_tcp)
        {
          int sock = xsocket (AF_INET, SOCK_STREAM, IPPROTO_TCP);
          xconnect (sock,
                    (struct sockaddr *) &obj->servers[server_index].address,
                    sizeof (obj->servers[server_index].address));
          xclose (sock);
        }
    }

  if (obj->config.single_thread_udp)
    xpthread_join (obj->thread_udp_single);

  /* Wait for the server threads to terminate.  */
  for (int server_index = 0; server_index < obj->config.nscount;
       ++server_index)
    {
      if (!obj->config.servers[server_index].disable_udp)
        {
          if (!obj->config.single_thread_udp)
            xpthread_join (obj->servers[server_index].thread_udp);
          xclose (obj->servers[server_index].socket_udp);
        }
      if (!obj->config.servers[server_index].disable_tcp)
        {
          xpthread_join (obj->servers[server_index].thread_tcp);
          xclose (obj->servers[server_index].socket_tcp);
        }
    }

  free (obj);
}