summaryrefslogtreecommitdiff
path: root/src/resolve/resolved-dns-cache.c
blob: ba937107b6e7a7106e2e11ffa1fbee85c6fb6457 (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
/***
  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 <net/if.h>

#include "af-list.h"
#include "alloc-util.h"
#include "dns-domain.h"
#include "resolved-dns-answer.h"
#include "resolved-dns-cache.h"
#include "resolved-dns-packet.h"
#include "string-util.h"

/* Never cache more than 4K entries. RFC 1536, Section 5 suggests to
 * leave DNS caches unbounded, but that's crazy. */
#define CACHE_MAX 4096

/* We never keep any item longer than 2h in our cache */
#define CACHE_TTL_MAX_USEC (2 * USEC_PER_HOUR)

typedef enum DnsCacheItemType DnsCacheItemType;
typedef struct DnsCacheItem DnsCacheItem;

enum DnsCacheItemType {
        DNS_CACHE_POSITIVE,
        DNS_CACHE_NODATA,
        DNS_CACHE_NXDOMAIN,
};

struct DnsCacheItem {
        DnsCacheItemType type;
        DnsResourceKey *key;
        DnsResourceRecord *rr;

        usec_t until;
        bool authenticated:1;
        bool shared_owner:1;

        int ifindex;
        int owner_family;
        union in_addr_union owner_address;

        unsigned prioq_idx;
        LIST_FIELDS(DnsCacheItem, by_key);
};

static void dns_cache_item_free(DnsCacheItem *i) {
        if (!i)
                return;

        dns_resource_record_unref(i->rr);
        dns_resource_key_unref(i->key);
        free(i);
}

DEFINE_TRIVIAL_CLEANUP_FUNC(DnsCacheItem*, dns_cache_item_free);

static void dns_cache_item_unlink_and_free(DnsCache *c, DnsCacheItem *i) {
        DnsCacheItem *first;

        assert(c);

        if (!i)
                return;

        first = hashmap_get(c->by_key, i->key);
        LIST_REMOVE(by_key, first, i);

        if (first)
                assert_se(hashmap_replace(c->by_key, first->key, first) >= 0);
        else
                hashmap_remove(c->by_key, i->key);

        prioq_remove(c->by_expiry, i, &i->prioq_idx);

        dns_cache_item_free(i);
}

static bool dns_cache_remove_by_rr(DnsCache *c, DnsResourceRecord *rr) {
        DnsCacheItem *first, *i;
        int r;

        first = hashmap_get(c->by_key, rr->key);
        LIST_FOREACH(by_key, i, first) {
                r = dns_resource_record_equal(i->rr, rr);
                if (r < 0)
                        return r;
                if (r > 0) {
                        dns_cache_item_unlink_and_free(c, i);
                        return true;
                }
        }

        return false;
}

static bool dns_cache_remove_by_key(DnsCache *c, DnsResourceKey *key) {
        DnsCacheItem *first, *i, *n;

        assert(c);
        assert(key);

        first = hashmap_remove(c->by_key, key);
        if (!first)
                return false;

        LIST_FOREACH_SAFE(by_key, i, n, first) {
                prioq_remove(c->by_expiry, i, &i->prioq_idx);
                dns_cache_item_free(i);
        }

        return true;
}

void dns_cache_flush(DnsCache *c) {
        DnsResourceKey *key;

        assert(c);

        while ((key = hashmap_first_key(c->by_key)))
                dns_cache_remove_by_key(c, key);

        assert(hashmap_size(c->by_key) == 0);
        assert(prioq_size(c->by_expiry) == 0);

        c->by_key = hashmap_free(c->by_key);
        c->by_expiry = prioq_free(c->by_expiry);
}

static void dns_cache_make_space(DnsCache *c, unsigned add) {
        assert(c);

        if (add <= 0)
                return;

        /* Makes space for n new entries. Note that we actually allow
         * the cache to grow beyond CACHE_MAX, but only when we shall
         * add more RRs to the cache than CACHE_MAX at once. In that
         * case the cache will be emptied completely otherwise. */

        for (;;) {
                _cleanup_(dns_resource_key_unrefp) DnsResourceKey *key = NULL;
                DnsCacheItem *i;

                if (prioq_size(c->by_expiry) <= 0)
                        break;

                if (prioq_size(c->by_expiry) + add < CACHE_MAX)
                        break;

                i = prioq_peek(c->by_expiry);
                assert(i);

                /* Take an extra reference to the key so that it
                 * doesn't go away in the middle of the remove call */
                key = dns_resource_key_ref(i->key);
                dns_cache_remove_by_key(c, key);
        }
}

void dns_cache_prune(DnsCache *c) {
        usec_t t = 0;

        assert(c);

        /* Remove all entries that are past their TTL */

        for (;;) {
                DnsCacheItem *i;
                char key_str[DNS_RESOURCE_KEY_STRING_MAX];

                i = prioq_peek(c->by_expiry);
                if (!i)
                        break;

                if (t <= 0)
                        t = now(clock_boottime_or_monotonic());

                if (i->until > t)
                        break;

                /* Depending whether this is an mDNS shared entry
                 * either remove only this one RR or the whole RRset */
                log_debug("Removing %scache entry for %s (expired "USEC_FMT"s ago)",
                          i->shared_owner ? "shared " : "",
                          dns_resource_key_to_string(i->key, key_str, sizeof key_str),
                          (t - i->until) / USEC_PER_SEC);

                if (i->shared_owner)
                        dns_cache_item_unlink_and_free(c, i);
                else {
                        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *key = NULL;

                        /* Take an extra reference to the key so that it
                         * doesn't go away in the middle of the remove call */
                        key = dns_resource_key_ref(i->key);
                        dns_cache_remove_by_key(c, key);
                }
        }
}

static int dns_cache_item_prioq_compare_func(const void *a, const void *b) {
        const DnsCacheItem *x = a, *y = b;

        if (x->until < y->until)
                return -1;
        if (x->until > y->until)
                return 1;
        return 0;
}

static int dns_cache_init(DnsCache *c) {
        int r;

        assert(c);

        r = prioq_ensure_allocated(&c->by_expiry, dns_cache_item_prioq_compare_func);
        if (r < 0)
                return r;

        r = hashmap_ensure_allocated(&c->by_key, &dns_resource_key_hash_ops);
        if (r < 0)
                return r;

        return r;
}

static int dns_cache_link_item(DnsCache *c, DnsCacheItem *i) {
        DnsCacheItem *first;
        int r;

        assert(c);
        assert(i);

        r = prioq_put(c->by_expiry, i, &i->prioq_idx);
        if (r < 0)
                return r;

        first = hashmap_get(c->by_key, i->key);
        if (first) {
                _cleanup_(dns_resource_key_unrefp) DnsResourceKey *k = NULL;

                /* Keep a reference to the original key, while we manipulate the list. */
                k = dns_resource_key_ref(first->key);

                /* Now, try to reduce the number of keys we keep */
                dns_resource_key_reduce(&first->key, &i->key);

                if (first->rr)
                        dns_resource_key_reduce(&first->rr->key, &i->key);
                if (i->rr)
                        dns_resource_key_reduce(&i->rr->key, &i->key);

                LIST_PREPEND(by_key, first, i);
                assert_se(hashmap_replace(c->by_key, first->key, first) >= 0);
        } else {
                r = hashmap_put(c->by_key, i->key, i);
                if (r < 0) {
                        prioq_remove(c->by_expiry, i, &i->prioq_idx);
                        return r;
                }
        }

        return 0;
}

static DnsCacheItem* dns_cache_get(DnsCache *c, DnsResourceRecord *rr) {
        DnsCacheItem *i;

        assert(c);
        assert(rr);

        LIST_FOREACH(by_key, i, hashmap_get(c->by_key, rr->key))
                if (i->rr && dns_resource_record_equal(i->rr, rr) > 0)
                        return i;

        return NULL;
}

static usec_t calculate_until(DnsResourceRecord *rr, uint32_t nsec_ttl, usec_t timestamp, bool use_soa_minimum) {
        uint32_t ttl;
        usec_t u;

        assert(rr);

        ttl = MIN(rr->ttl, nsec_ttl);
        if (rr->key->type == DNS_TYPE_SOA && use_soa_minimum) {
                /* If this is a SOA RR, and it is requested, clamp to
                 * the SOA's minimum field. This is used when we do
                 * negative caching, to determine the TTL for the
                 * negative caching entry.  See RFC 2308, Section
                 * 5. */

                if (ttl > rr->soa.minimum)
                        ttl = rr->soa.minimum;
        }

        u = ttl * USEC_PER_SEC;
        if (u > CACHE_TTL_MAX_USEC)
                u = CACHE_TTL_MAX_USEC;

        if (rr->expiry != USEC_INFINITY) {
                usec_t left;

                /* Make use of the DNSSEC RRSIG expiry info, if we
                 * have it */

                left = LESS_BY(rr->expiry, now(CLOCK_REALTIME));
                if (u > left)
                        u = left;
        }

        return timestamp + u;
}

static void dns_cache_item_update_positive(
                DnsCache *c,
                DnsCacheItem *i,
                DnsResourceRecord *rr,
                bool authenticated,
                bool shared_owner,
                usec_t timestamp,
                int ifindex,
                int owner_family,
                const union in_addr_union *owner_address) {

        assert(c);
        assert(i);
        assert(rr);
        assert(owner_address);

        i->type = DNS_CACHE_POSITIVE;

        if (!i->by_key_prev)
                /* We are the first item in the list, we need to
                 * update the key used in the hashmap */

                assert_se(hashmap_replace(c->by_key, rr->key, i) >= 0);

        dns_resource_record_ref(rr);
        dns_resource_record_unref(i->rr);
        i->rr = rr;

        dns_resource_key_unref(i->key);
        i->key = dns_resource_key_ref(rr->key);

        i->until = calculate_until(rr, (uint32_t) -1, timestamp, false);
        i->authenticated = authenticated;
        i->shared_owner = shared_owner;

        i->ifindex = ifindex;

        i->owner_family = owner_family;
        i->owner_address = *owner_address;

        prioq_reshuffle(c->by_expiry, i, &i->prioq_idx);
}

static int dns_cache_put_positive(
                DnsCache *c,
                DnsResourceRecord *rr,
                bool authenticated,
                bool shared_owner,
                usec_t timestamp,
                int ifindex,
                int owner_family,
                const union in_addr_union *owner_address) {

        _cleanup_(dns_cache_item_freep) DnsCacheItem *i = NULL;
        DnsCacheItem *existing;
        char key_str[DNS_RESOURCE_KEY_STRING_MAX], ifname[IF_NAMESIZE];
        int r, k;

        assert(c);
        assert(rr);
        assert(owner_address);

        /* Never cache pseudo RRs */
        if (dns_class_is_pseudo(rr->key->class))
                return 0;
        if (dns_type_is_pseudo(rr->key->type))
                return 0;

        /* New TTL is 0? Delete this specific entry... */
        if (rr->ttl <= 0) {
                k = dns_cache_remove_by_rr(c, rr);
                log_debug("%s: %s",
                          k > 0 ? "Removed zero TTL entry from cache" : "Not caching zero TTL cache entry",
                          dns_resource_key_to_string(rr->key, key_str, sizeof key_str));
                return 0;
        }

        /* Entry exists already? Update TTL, timestamp and owner*/
        existing = dns_cache_get(c, rr);
        if (existing) {
                dns_cache_item_update_positive(
                                c,
                                existing,
                                rr,
                                authenticated,
                                shared_owner,
                                timestamp,
                                ifindex,
                                owner_family,
                                owner_address);
                return 0;
        }

        /* Otherwise, add the new RR */
        r = dns_cache_init(c);
        if (r < 0)
                return r;

        dns_cache_make_space(c, 1);

        i = new0(DnsCacheItem, 1);
        if (!i)
                return -ENOMEM;

        i->type = DNS_CACHE_POSITIVE;
        i->key = dns_resource_key_ref(rr->key);
        i->rr = dns_resource_record_ref(rr);
        i->until = calculate_until(rr, (uint32_t) -1, timestamp, false);
        i->authenticated = authenticated;
        i->shared_owner = shared_owner;
        i->ifindex = ifindex;
        i->owner_family = owner_family;
        i->owner_address = *owner_address;
        i->prioq_idx = PRIOQ_IDX_NULL;

        r = dns_cache_link_item(c, i);
        if (r < 0)
                return r;

        if (log_get_max_level() >= LOG_DEBUG) {
                _cleanup_free_ char *t = NULL;

                (void) in_addr_to_string(i->owner_family, &i->owner_address, &t);

                log_debug("Added positive %s%s cache entry for %s "USEC_FMT"s on %s/%s/%s",
                          i->authenticated ? "authenticated" : "unauthenticated",
                          i->shared_owner ? " shared" : "",
                          dns_resource_key_to_string(i->key, key_str, sizeof key_str),
                          (i->until - timestamp) / USEC_PER_SEC,
                          i->ifindex == 0 ? "*" : strna(if_indextoname(i->ifindex, ifname)),
                          af_to_name_short(i->owner_family),
                          strna(t));
        }

        i = NULL;
        return 0;
}

static int dns_cache_put_negative(
                DnsCache *c,
                DnsResourceKey *key,
                int rcode,
                bool authenticated,
                uint32_t nsec_ttl,
                usec_t timestamp,
                DnsResourceRecord *soa,
                int owner_family,
                const union in_addr_union *owner_address) {

        _cleanup_(dns_cache_item_freep) DnsCacheItem *i = NULL;
        char key_str[DNS_RESOURCE_KEY_STRING_MAX];
        int r;

        assert(c);
        assert(key);
        assert(soa);
        assert(owner_address);

        /* Never cache pseudo RR keys. DNS_TYPE_ANY is particularly
         * important to filter out as we use this as a pseudo-type for
         * NXDOMAIN entries */
        if (dns_class_is_pseudo(key->class))
                return 0;
        if (dns_type_is_pseudo(key->type))
                return 0;

        if (nsec_ttl <= 0 || soa->soa.minimum <= 0 || soa->ttl <= 0) {
                log_debug("Not caching negative entry with zero SOA/NSEC/NSEC3 TTL: %s",
                          dns_resource_key_to_string(key, key_str, sizeof key_str));
                return 0;
        }

        if (!IN_SET(rcode, DNS_RCODE_SUCCESS, DNS_RCODE_NXDOMAIN))
                return 0;

        r = dns_cache_init(c);
        if (r < 0)
                return r;

        dns_cache_make_space(c, 1);

        i = new0(DnsCacheItem, 1);
        if (!i)
                return -ENOMEM;

        i->type = rcode == DNS_RCODE_SUCCESS ? DNS_CACHE_NODATA : DNS_CACHE_NXDOMAIN;
        i->until = calculate_until(soa, nsec_ttl, timestamp, true);
        i->authenticated = authenticated;
        i->owner_family = owner_family;
        i->owner_address = *owner_address;
        i->prioq_idx = PRIOQ_IDX_NULL;

        if (i->type == DNS_CACHE_NXDOMAIN) {
                /* NXDOMAIN entries should apply equally to all types, so we use ANY as
                 * a pseudo type for this purpose here. */
                i->key = dns_resource_key_new(key->class, DNS_TYPE_ANY, dns_resource_key_name(key));
                if (!i->key)
                        return -ENOMEM;

                /* Make sure to remove any previous entry for this
                 * specific ANY key. (For non-ANY keys the cache data
                 * is already cleared by the caller.) Note that we
                 * don't bother removing positive or NODATA cache
                 * items in this case, because it would either be slow
                 * or require explicit indexing by name */
                dns_cache_remove_by_key(c, key);
        } else
                i->key = dns_resource_key_ref(key);

        r = dns_cache_link_item(c, i);
        if (r < 0)
                return r;

        log_debug("Added %s cache entry for %s "USEC_FMT"s",
                  i->type == DNS_CACHE_NODATA ? "NODATA" : "NXDOMAIN",
                  dns_resource_key_to_string(i->key, key_str, sizeof key_str),
                  (i->until - timestamp) / USEC_PER_SEC);

        i = NULL;
        return 0;
}

static void dns_cache_remove_previous(
                DnsCache *c,
                DnsResourceKey *key,
                DnsAnswer *answer) {

        DnsResourceRecord *rr;
        DnsAnswerFlags flags;

        assert(c);

        /* First, if we were passed a key (i.e. on LLMNR/DNS, but
         * not on mDNS), delete all matching old RRs, so that we only
         * keep complete by_key in place. */
        if (key)
                dns_cache_remove_by_key(c, key);

        /* Second, flush all entries matching the answer, unless this
         * is an RR that is explicitly marked to be "shared" between
         * peers (i.e. mDNS RRs without the flush-cache bit set). */
        DNS_ANSWER_FOREACH_FLAGS(rr, flags, answer) {
                if ((flags & DNS_ANSWER_CACHEABLE) == 0)
                        continue;

                if (flags & DNS_ANSWER_SHARED_OWNER)
                        continue;

                dns_cache_remove_by_key(c, rr->key);
        }
}

static bool rr_eligible(DnsResourceRecord *rr) {
        assert(rr);

        /* When we see an NSEC/NSEC3 RR, we'll only cache it if it is from the lower zone, not the upper zone, since
         * that's where the interesting bits are (with exception of DS RRs). Of course, this way we cannot derive DS
         * existence from any cached NSEC/NSEC3, but that should be fine. */

        switch (rr->key->type) {

        case DNS_TYPE_NSEC:
                return !bitmap_isset(rr->nsec.types, DNS_TYPE_NS) ||
                        bitmap_isset(rr->nsec.types, DNS_TYPE_SOA);

        case DNS_TYPE_NSEC3:
                return !bitmap_isset(rr->nsec3.types, DNS_TYPE_NS) ||
                        bitmap_isset(rr->nsec3.types, DNS_TYPE_SOA);

        default:
                return true;
        }
}

int dns_cache_put(
                DnsCache *c,
                DnsResourceKey *key,
                int rcode,
                DnsAnswer *answer,
                bool authenticated,
                uint32_t nsec_ttl,
                usec_t timestamp,
                int owner_family,
                const union in_addr_union *owner_address) {

        DnsResourceRecord *soa = NULL, *rr;
        DnsAnswerFlags flags;
        unsigned cache_keys;
        int r, ifindex;

        assert(c);
        assert(owner_address);

        dns_cache_remove_previous(c, key, answer);

        /* We only care for positive replies and NXDOMAINs, on all
         * other replies we will simply flush the respective entries,
         * and that's it */
        if (!IN_SET(rcode, DNS_RCODE_SUCCESS, DNS_RCODE_NXDOMAIN))
                return 0;

        if (dns_answer_size(answer) <= 0) {
                char key_str[DNS_RESOURCE_KEY_STRING_MAX];

                log_debug("Not caching negative entry without a SOA record: %s",
                          dns_resource_key_to_string(key, key_str, sizeof key_str));
                return 0;
        }

        cache_keys = dns_answer_size(answer);
        if (key)
                cache_keys++;

        /* Make some space for our new entries */
        dns_cache_make_space(c, cache_keys);

        if (timestamp <= 0)
                timestamp = now(clock_boottime_or_monotonic());

        /* Second, add in positive entries for all contained RRs */
        DNS_ANSWER_FOREACH_FULL(rr, ifindex, flags, answer) {
                if ((flags & DNS_ANSWER_CACHEABLE) == 0)
                        continue;

                r = rr_eligible(rr);
                if (r < 0)
                        return r;
                if (r == 0)
                        continue;

                r = dns_cache_put_positive(
                                c,
                                rr,
                                flags & DNS_ANSWER_AUTHENTICATED,
                                flags & DNS_ANSWER_SHARED_OWNER,
                                timestamp,
                                ifindex,
                                owner_family, owner_address);
                if (r < 0)
                        goto fail;
        }

        if (!key) /* mDNS doesn't know negative caching, really */
                return 0;

        /* Third, add in negative entries if the key has no RR */
        r = dns_answer_match_key(answer, key, NULL);
        if (r < 0)
                goto fail;
        if (r > 0)
                return 0;

        /* But not if it has a matching CNAME/DNAME (the negative
         * caching will be done on the canonical name, not on the
         * alias) */
        r = dns_answer_find_cname_or_dname(answer, key, NULL, NULL);
        if (r < 0)
                goto fail;
        if (r > 0)
                return 0;

        /* See https://tools.ietf.org/html/rfc2308, which say that a
         * matching SOA record in the packet is used to to enable
         * negative caching. */
        r = dns_answer_find_soa(answer, key, &soa, &flags);
        if (r < 0)
                goto fail;
        if (r == 0)
                return 0;

        /* Refuse using the SOA data if it is unsigned, but the key is
         * signed */
        if (authenticated && (flags & DNS_ANSWER_AUTHENTICATED) == 0)
                return 0;

        r = dns_cache_put_negative(
                        c,
                        key,
                        rcode,
                        authenticated,
                        nsec_ttl,
                        timestamp,
                        soa,
                        owner_family, owner_address);
        if (r < 0)
                goto fail;

        return 0;

fail:
        /* Adding all RRs failed. Let's clean up what we already
         * added, just in case */

        if (key)
                dns_cache_remove_by_key(c, key);

        DNS_ANSWER_FOREACH_FLAGS(rr, flags, answer) {
                if ((flags & DNS_ANSWER_CACHEABLE) == 0)
                        continue;

                dns_cache_remove_by_key(c, rr->key);
        }

        return r;
}

static DnsCacheItem *dns_cache_get_by_key_follow_cname_dname_nsec(DnsCache *c, DnsResourceKey *k) {
        DnsCacheItem *i;
        const char *n;
        int r;

        assert(c);
        assert(k);

        /* If we hit some OOM error, or suchlike, we don't care too
         * much, after all this is just a cache */

        i = hashmap_get(c->by_key, k);
        if (i)
                return i;

        n = dns_resource_key_name(k);

        /* Check if we have an NXDOMAIN cache item for the name, notice that we use
         * the pseudo-type ANY for NXDOMAIN cache items. */
        i = hashmap_get(c->by_key, &DNS_RESOURCE_KEY_CONST(k->class, DNS_TYPE_ANY, n));
        if (i && i->type == DNS_CACHE_NXDOMAIN)
                return i;

        if (dns_type_may_redirect(k->type)) {
                /* Check if we have a CNAME record instead */
                i = hashmap_get(c->by_key, &DNS_RESOURCE_KEY_CONST(k->class, DNS_TYPE_CNAME, n));
                if (i)
                        return i;

                /* OK, let's look for cached DNAME records. */
                for (;;) {
                        if (isempty(n))
                                return NULL;

                        i = hashmap_get(c->by_key, &DNS_RESOURCE_KEY_CONST(k->class, DNS_TYPE_DNAME, n));
                        if (i)
                                return i;

                        /* Jump one label ahead */
                        r = dns_name_parent(&n);
                        if (r <= 0)
                                return NULL;
                }
        }

        if (k->type != DNS_TYPE_NSEC) {
                /* Check if we have an NSEC record instead for the name. */
                i = hashmap_get(c->by_key, &DNS_RESOURCE_KEY_CONST(k->class, DNS_TYPE_NSEC, n));
                if (i)
                        return i;
        }

        return NULL;
}

int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, int *rcode, DnsAnswer **ret, bool *authenticated) {
        _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
        char key_str[DNS_RESOURCE_KEY_STRING_MAX];
        unsigned n = 0;
        int r;
        bool nxdomain = false;
        DnsCacheItem *j, *first, *nsec = NULL;
        bool have_authenticated = false, have_non_authenticated = false;

        assert(c);
        assert(key);
        assert(rcode);
        assert(ret);
        assert(authenticated);

        if (key->type == DNS_TYPE_ANY || key->class == DNS_CLASS_ANY) {
                /* If we have ANY lookups we don't use the cache, so
                 * that the caller refreshes via the network. */

                log_debug("Ignoring cache for ANY lookup: %s",
                          dns_resource_key_to_string(key, key_str, sizeof key_str));

                c->n_miss++;

                *ret = NULL;
                *rcode = DNS_RCODE_SUCCESS;
                return 0;
        }

        first = dns_cache_get_by_key_follow_cname_dname_nsec(c, key);
        if (!first) {
                /* If one question cannot be answered we need to refresh */

                log_debug("Cache miss for %s",
                          dns_resource_key_to_string(key, key_str, sizeof key_str));

                c->n_miss++;

                *ret = NULL;
                *rcode = DNS_RCODE_SUCCESS;
                return 0;
        }

        LIST_FOREACH(by_key, j, first) {
                if (j->rr) {
                        if (j->rr->key->type == DNS_TYPE_NSEC)
                                nsec = j;

                        n++;
                } else if (j->type == DNS_CACHE_NXDOMAIN)
                        nxdomain = true;

                if (j->authenticated)
                        have_authenticated = true;
                else
                        have_non_authenticated = true;
        }

        if (nsec && !IN_SET(key->type, DNS_TYPE_NSEC, DNS_TYPE_DS)) {
                /* Note that we won't derive information for DS RRs from an NSEC, because we only cache NSEC RRs from
                 * the lower-zone of a zone cut, but the DS RRs are on the upper zone. */

                log_debug("NSEC NODATA cache hit for %s",
                          dns_resource_key_to_string(key, key_str, sizeof key_str));

                /* We only found an NSEC record that matches our name.
                 * If it says the type doesn't exist report
                 * NODATA. Otherwise report a cache miss. */

                *ret = NULL;
                *rcode = DNS_RCODE_SUCCESS;
                *authenticated = nsec->authenticated;

                if (!bitmap_isset(nsec->rr->nsec.types, key->type) &&
                    !bitmap_isset(nsec->rr->nsec.types, DNS_TYPE_CNAME) &&
                    !bitmap_isset(nsec->rr->nsec.types, DNS_TYPE_DNAME)) {
                        c->n_hit++;
                        return 1;
                }

                c->n_miss++;
                return 0;
        }

        log_debug("%s cache hit for %s",
                  n > 0    ? "Positive" :
                  nxdomain ? "NXDOMAIN" : "NODATA",
                  dns_resource_key_to_string(key, key_str, sizeof key_str));

        if (n <= 0) {
                c->n_hit++;

                *ret = NULL;
                *rcode = nxdomain ? DNS_RCODE_NXDOMAIN : DNS_RCODE_SUCCESS;
                *authenticated = have_authenticated && !have_non_authenticated;
                return 1;
        }

        answer = dns_answer_new(n);
        if (!answer)
                return -ENOMEM;

        LIST_FOREACH(by_key, j, first) {
                if (!j->rr)
                        continue;

                r = dns_answer_add(answer, j->rr, j->ifindex, j->authenticated ? DNS_ANSWER_AUTHENTICATED : 0);
                if (r < 0)
                        return r;
        }

        c->n_hit++;

        *ret = answer;
        *rcode = DNS_RCODE_SUCCESS;
        *authenticated = have_authenticated && !have_non_authenticated;
        answer = NULL;

        return n;
}

int dns_cache_check_conflicts(DnsCache *cache, DnsResourceRecord *rr, int owner_family, const union in_addr_union *owner_address) {
        DnsCacheItem *i, *first;
        bool same_owner = true;

        assert(cache);
        assert(rr);

        dns_cache_prune(cache);

        /* See if there's a cache entry for the same key. If there
         * isn't there's no conflict */
        first = hashmap_get(cache->by_key, rr->key);
        if (!first)
                return 0;

        /* See if the RR key is owned by the same owner, if so, there
         * isn't a conflict either */
        LIST_FOREACH(by_key, i, first) {
                if (i->owner_family != owner_family ||
                    !in_addr_equal(owner_family, &i->owner_address, owner_address)) {
                        same_owner = false;
                        break;
                }
        }
        if (same_owner)
                return 0;

        /* See if there's the exact same RR in the cache. If yes, then
         * there's no conflict. */
        if (dns_cache_get(cache, rr))
                return 0;

        /* There's a conflict */
        return 1;
}

int dns_cache_export_shared_to_packet(DnsCache *cache, DnsPacket *p) {
        unsigned ancount = 0;
        Iterator iterator;
        DnsCacheItem *i;
        int r;

        assert(cache);
        assert(p);

        HASHMAP_FOREACH(i, cache->by_key, iterator) {
                DnsCacheItem *j;

                LIST_FOREACH(by_key, j, i) {
                        if (!j->rr)
                                continue;

                        if (!j->shared_owner)
                                continue;

                        r = dns_packet_append_rr(p, j->rr, NULL, NULL);
                        if (r == -EMSGSIZE && p->protocol == DNS_PROTOCOL_MDNS) {
                                /* For mDNS, if we're unable to stuff all known answers into the given packet,
                                 * allocate a new one, push the RR into that one and link it to the current one.
                                 */

                                DNS_PACKET_HEADER(p)->ancount = htobe16(ancount);
                                ancount = 0;

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

                                /* continue with new packet */
                                p = p->more;
                                r = dns_packet_append_rr(p, j->rr, NULL, NULL);
                        }

                        if (r < 0)
                                return r;

                        ancount++;
                }
        }

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

        return 0;
}

void dns_cache_dump(DnsCache *cache, FILE *f) {
        Iterator iterator;
        DnsCacheItem *i;

        if (!cache)
                return;

        if (!f)
                f = stdout;

        HASHMAP_FOREACH(i, cache->by_key, iterator) {
                DnsCacheItem *j;

                LIST_FOREACH(by_key, j, i) {

                        fputc('\t', f);

                        if (j->rr) {
                                const char *t;
                                t = dns_resource_record_to_string(j->rr);
                                if (!t) {
                                        log_oom();
                                        continue;
                                }

                                fputs(t, f);
                                fputc('\n', f);
                        } else {
                                char key_str[DNS_RESOURCE_KEY_STRING_MAX];

                                fputs(dns_resource_key_to_string(j->key, key_str, sizeof key_str), f);
                                fputs(" -- ", f);
                                fputs(j->type == DNS_CACHE_NODATA ? "NODATA" : "NXDOMAIN", f);
                                fputc('\n', f);
                        }
                }
        }
}

bool dns_cache_is_empty(DnsCache *cache) {
        if (!cache)
                return true;

        return hashmap_isempty(cache->by_key);
}

unsigned dns_cache_size(DnsCache *cache) {
        if (!cache)
                return 0;

        return hashmap_size(cache->by_key);
}