Adding upstream version 255.4.upstream/255.4

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 862 insertions, 0 deletions

diff --git a/src/resolve/resolved-dns-answer.c b/src/resolve/resolved-dns-answer.c
new file mode 100644
index 0000000..bf023a7
--- /dev/null
+++ b/src/resolve/resolved-dns-answer.c
@@ -0,0 +1,862 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <stdio.h>
+
+#include "alloc-util.h"
+#include "dns-domain.h"
+#include "random-util.h"
+#include "resolved-dns-answer.h"
+#include "resolved-dns-dnssec.h"
+#include "string-util.h"
+
+static DnsAnswerItem *dns_answer_item_free(DnsAnswerItem *item) {
+        if (!item)
+                return NULL;
+
+        dns_resource_record_unref(item->rr);
+        dns_resource_record_unref(item->rrsig);
+
+        return mfree(item);
+}
+
+DEFINE_PRIVATE_TRIVIAL_REF_UNREF_FUNC(DnsAnswerItem, dns_answer_item, dns_answer_item_free);
+DEFINE_TRIVIAL_CLEANUP_FUNC(DnsAnswerItem*, dns_answer_item_unref);
+
+static void dns_answer_item_hash_func(const DnsAnswerItem *a, struct siphash *state) {
+        assert(a);
+        assert(state);
+
+        siphash24_compress(&a->ifindex, sizeof(a->ifindex), state);
+
+        dns_resource_record_hash_func(a->rr, state);
+}
+
+static int dns_answer_item_compare_func(const DnsAnswerItem *a, const DnsAnswerItem *b) {
+        int r;
+
+        assert(a);
+        assert(b);
+
+        r = CMP(a->ifindex, b->ifindex);
+        if (r != 0)
+                return r;
+
+        return dns_resource_record_compare_func(a->rr, b->rr);
+}
+
+DEFINE_PRIVATE_HASH_OPS_WITH_KEY_DESTRUCTOR(
+        dns_answer_item_hash_ops,
+        DnsAnswerItem,
+        dns_answer_item_hash_func,
+        dns_answer_item_compare_func,
+        dns_answer_item_unref);
+
+static int dns_answer_reserve_internal(DnsAnswer *a, size_t n) {
+        size_t m;
+
+        assert(a);
+        assert(a->items);
+
+        m = ordered_set_size(a->items);
+        assert(m <= UINT16_MAX); /* We can only place 64K RRs in an answer at max */
+
+        n = saturate_add(m, n, UINT16_MAX);
+
+        /* Higher multipliers give slightly higher efficiency through hash collisions, but the gains
+         * quickly drop off after 2. */
+        return ordered_set_reserve(a->items, n * 2);
+}
+
+DnsAnswer *dns_answer_new(size_t n) {
+        _cleanup_ordered_set_free_ OrderedSet *s = NULL;
+        _cleanup_(dns_answer_unrefp) DnsAnswer *a = NULL;
+
+        if (n > UINT16_MAX)
+                n = UINT16_MAX;
+
+        s = ordered_set_new(&dns_answer_item_hash_ops);
+        if (!s)
+                return NULL;
+
+        a = new(DnsAnswer, 1);
+        if (!a)
+                return NULL;
+
+        *a = (DnsAnswer) {
+                .n_ref = 1,
+                .items = TAKE_PTR(s),
+        };
+
+        if (dns_answer_reserve_internal(a, n) < 0)
+                return NULL;
+
+        return TAKE_PTR(a);
+}
+
+static DnsAnswer *dns_answer_free(DnsAnswer *a) {
+        assert(a);
+
+        ordered_set_free(a->items);
+        return mfree(a);
+}
+
+DEFINE_TRIVIAL_REF_UNREF_FUNC(DnsAnswer, dns_answer, dns_answer_free);
+
+static int dns_answer_add_raw(
+                DnsAnswer *a,
+                DnsResourceRecord *rr,
+                int ifindex,
+                DnsAnswerFlags flags,
+                DnsResourceRecord *rrsig) {
+
+        _cleanup_(dns_answer_item_unrefp) DnsAnswerItem *item = NULL;
+        int r;
+
+        assert(rr);
+
+        if (!a)
+                return -ENOSPC;
+
+        if (dns_answer_size(a) >= UINT16_MAX)
+                return -ENOSPC;
+
+        item = new(DnsAnswerItem, 1);
+        if (!item)
+                return -ENOMEM;
+
+        *item = (DnsAnswerItem) {
+                .n_ref = 1,
+                .rr = dns_resource_record_ref(rr),
+                .ifindex = ifindex,
+                .flags = flags,
+                .rrsig = dns_resource_record_ref(rrsig),
+        };
+
+        r = ordered_set_put(a->items, item);
+        if (r < 0)
+                return r;
+
+        TAKE_PTR(item);
+        return 1;
+}
+
+static int dns_answer_add_raw_all(DnsAnswer *a, DnsAnswer *source) {
+        DnsAnswerItem *item;
+        int r;
+
+        DNS_ANSWER_FOREACH_ITEM(item, source) {
+                r = dns_answer_add_raw(
+                                a,
+                                item->rr,
+                                item->ifindex,
+                                item->flags,
+                                item->rrsig);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
+int dns_answer_add(
+                DnsAnswer *a,
+                DnsResourceRecord *rr,
+                int ifindex,
+                DnsAnswerFlags flags,
+                DnsResourceRecord *rrsig) {
+
+        DnsAnswerItem tmp, *exist;
+
+        assert(rr);
+
+        if (!a)
+                return -ENOSPC;
+        if (a->n_ref > 1)
+                return -EBUSY;
+
+        tmp = (DnsAnswerItem) {
+                .rr = rr,
+                .ifindex = ifindex,
+        };
+
+        exist = ordered_set_get(a->items, &tmp);
+        if (exist) {
+                /* There's already an RR of the same RRset in place! Let's see if the TTLs more or
+                 * less match. RFC 2181, Section 5.2 suggests clients should reject RRsets
+                 * containing RRs with differing TTLs. We are more tolerant of this situation except
+                 * if one RR has a zero TTL and the other a nonzero TTL. In mDNS, zero TTLs are
+                 * special, so we must error in that case. */
+                if ((rr->ttl == 0) != (exist->rr->ttl == 0)) {
+                        if ((exist->flags | flags) & DNS_ANSWER_REFUSE_TTL_NO_MATCH)
+                                return log_debug_errno(
+                                                SYNTHETIC_ERRNO(EINVAL),
+                                                "Refusing to merge RRs with zero TTL and non-zero TTL: %s vs. %s",
+                                                dns_resource_record_to_string(rr),
+                                                dns_resource_record_to_string(exist->rr));
+
+                        log_debug("Merging RRs with zero TTL and non-zero TTL (not RFC 2181/5.2 compliant): %s vs. %s",
+                                  dns_resource_record_to_string(rr),
+                                  dns_resource_record_to_string(exist->rr));
+                }
+
+                /* Entry already exists, keep the entry with the higher TTL. */
+                if (rr->ttl > exist->rr->ttl) {
+                        DNS_RR_REPLACE(exist->rr, dns_resource_record_ref(rr));
+
+                        /* Update RRSIG and RR at the same time */
+                        if (rrsig)
+                                DNS_RR_REPLACE(exist->rrsig, dns_resource_record_ref(rrsig));
+                }
+
+                exist->flags |= flags;
+
+                if (rr->key->type == DNS_TYPE_RRSIG) {
+                        /* If the rr is RRSIG, then move the rr to the end. */
+                        assert_se(ordered_set_remove(a->items, exist) == exist);
+                        assert_se(ordered_set_put(a->items, exist) == 1);
+                }
+                return 0;
+        }
+
+        return dns_answer_add_raw(a, rr, ifindex, flags, rrsig);
+}
+
+static int dns_answer_add_all(DnsAnswer *a, DnsAnswer *b) {
+        DnsAnswerItem *item;
+        int r;
+
+        DNS_ANSWER_FOREACH_ITEM(item, b) {
+                r = dns_answer_add(a, item->rr, item->ifindex, item->flags, item->rrsig);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
+int dns_answer_add_extend(
+                DnsAnswer **a,
+                DnsResourceRecord *rr,
+                int ifindex,
+                DnsAnswerFlags flags,
+                DnsResourceRecord *rrsig) {
+
+        int r;
+
+        assert(a);
+        assert(rr);
+
+        r = dns_answer_reserve_or_clone(a, 1);
+        if (r < 0)
+                return r;
+
+        return dns_answer_add(*a, rr, ifindex, flags, rrsig);
+}
+
+int dns_answer_add_soa(DnsAnswer *a, const char *name, uint32_t ttl, int ifindex) {
+        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *soa = NULL;
+
+        soa = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_SOA, name);
+        if (!soa)
+                return -ENOMEM;
+
+        soa->ttl = ttl;
+
+        soa->soa.mname = strdup(name);
+        if (!soa->soa.mname)
+                return -ENOMEM;
+
+        soa->soa.rname = strjoin("root.", name);
+        if (!soa->soa.rname)
+                return -ENOMEM;
+
+        soa->soa.serial = 1;
+        soa->soa.refresh = 1;
+        soa->soa.retry = 1;
+        soa->soa.expire = 1;
+        soa->soa.minimum = ttl;
+
+        return dns_answer_add(a, soa, ifindex, DNS_ANSWER_AUTHENTICATED, NULL);
+}
+
+int dns_answer_match_key(DnsAnswer *a, const DnsResourceKey *key, DnsAnswerFlags *ret_flags) {
+        DnsAnswerFlags flags = 0, i_flags;
+        DnsResourceRecord *i;
+        bool found = false;
+        int r;
+
+        assert(key);
+
+        DNS_ANSWER_FOREACH_FLAGS(i, i_flags, a) {
+                r = dns_resource_key_match_rr(key, i, NULL);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        continue;
+
+                if (!ret_flags)
+                        return 1;
+
+                if (found)
+                        flags &= i_flags;
+                else {
+                        flags = i_flags;
+                        found = true;
+                }
+        }
+
+        if (ret_flags)
+                *ret_flags = flags;
+
+        return found;
+}
+
+bool dns_answer_contains_nsec_or_nsec3(DnsAnswer *a) {
+        DnsResourceRecord *i;
+
+        DNS_ANSWER_FOREACH(i, a)
+                if (IN_SET(i->key->type, DNS_TYPE_NSEC, DNS_TYPE_NSEC3))
+                        return true;
+
+        return false;
+}
+
+int dns_answer_contains_zone_nsec3(DnsAnswer *answer, const char *zone) {
+        DnsResourceRecord *rr;
+        int r;
+
+        /* Checks whether the specified answer contains at least one NSEC3 RR in the specified zone */
+
+        DNS_ANSWER_FOREACH(rr, answer) {
+                const char *p;
+
+                if (rr->key->type != DNS_TYPE_NSEC3)
+                        continue;
+
+                p = dns_resource_key_name(rr->key);
+                r = dns_name_parent(&p);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        continue;
+
+                r = dns_name_equal(p, zone);
+                if (r != 0)
+                        return r;
+        }
+
+        return false;
+}
+
+bool dns_answer_contains(DnsAnswer *answer, DnsResourceRecord *rr) {
+        DnsResourceRecord *i;
+
+        DNS_ANSWER_FOREACH(i, answer)
+                if (dns_resource_record_equal(i, rr))
+                        return true;
+
+        return false;
+}
+
+int dns_answer_find_soa(
+                DnsAnswer *a,
+                const DnsResourceKey *key,
+                DnsResourceRecord **ret,
+                DnsAnswerFlags *ret_flags) {
+
+        DnsResourceRecord *rr, *soa = NULL;
+        DnsAnswerFlags rr_flags, soa_flags = 0;
+        int r;
+
+        assert(key);
+
+        /* For a SOA record we can never find a matching SOA record */
+        if (key->type == DNS_TYPE_SOA)
+                goto not_found;
+
+        DNS_ANSWER_FOREACH_FLAGS(rr, rr_flags, a) {
+                r = dns_resource_key_match_soa(key, rr->key);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+
+                        if (soa) {
+                                r = dns_name_endswith(dns_resource_key_name(rr->key), dns_resource_key_name(soa->key));
+                                if (r < 0)
+                                        return r;
+                                if (r > 0)
+                                        continue;
+                        }
+
+                        soa = rr;
+                        soa_flags = rr_flags;
+                }
+        }
+
+        if (!soa)
+                goto not_found;
+
+        if (ret)
+                *ret = soa;
+        if (ret_flags)
+                *ret_flags = soa_flags;
+
+        return 1;
+
+not_found:
+        if (ret)
+                *ret = NULL;
+        if (ret_flags)
+                *ret_flags = 0;
+
+        return 0;
+}
+
+int dns_answer_find_cname_or_dname(
+                DnsAnswer *a,
+                const DnsResourceKey *key,
+                DnsResourceRecord **ret,
+                DnsAnswerFlags *ret_flags) {
+
+        DnsResourceRecord *rr;
+        DnsAnswerFlags rr_flags;
+        int r;
+
+        assert(key);
+
+        /* For a {C,D}NAME record we can never find a matching {C,D}NAME record */
+        if (!dns_type_may_redirect(key->type))
+                return 0;
+
+        DNS_ANSWER_FOREACH_FLAGS(rr, rr_flags, a) {
+                r = dns_resource_key_match_cname_or_dname(key, rr->key, NULL);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        if (ret)
+                                *ret = rr;
+                        if (ret_flags)
+                                *ret_flags = rr_flags;
+                        return 1;
+                }
+        }
+
+        if (ret)
+                *ret = NULL;
+        if (ret_flags)
+                *ret_flags = 0;
+
+        return 0;
+}
+
+int dns_answer_merge(DnsAnswer *a, DnsAnswer *b, DnsAnswer **ret) {
+        _cleanup_(dns_answer_unrefp) DnsAnswer *k = NULL;
+        int r;
+
+        assert(ret);
+
+        if (a == b) {
+                *ret = dns_answer_ref(a);
+                return 0;
+        }
+
+        if (dns_answer_size(a) <= 0) {
+                *ret = dns_answer_ref(b);
+                return 0;
+        }
+
+        if (dns_answer_size(b) <= 0) {
+                *ret = dns_answer_ref(a);
+                return 0;
+        }
+
+        k = dns_answer_new(dns_answer_size(a) + dns_answer_size(b));
+        if (!k)
+                return -ENOMEM;
+
+        r = dns_answer_add_raw_all(k, a);
+        if (r < 0)
+                return r;
+
+        r = dns_answer_add_all(k, b);
+        if (r < 0)
+                return r;
+
+        *ret = TAKE_PTR(k);
+
+        return 0;
+}
+
+int dns_answer_extend(DnsAnswer **a, DnsAnswer *b) {
+        DnsAnswer *merged;
+        int r;
+
+        assert(a);
+
+        r = dns_answer_merge(*a, b, &merged);
+        if (r < 0)
+                return r;
+
+        DNS_ANSWER_REPLACE(*a, merged);
+        return 0;
+}
+
+int dns_answer_remove_by_key(DnsAnswer **a, const DnsResourceKey *key) {
+        DnsAnswerItem *item;
+        bool found = false;
+        int r;
+
+        assert(a);
+        assert(key);
+
+        /* Remove all entries matching the specified key from *a */
+
+        DNS_ANSWER_FOREACH_ITEM(item, *a) {
+                r = dns_resource_key_equal(item->rr->key, key);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        dns_answer_item_unref(ordered_set_remove((*a)->items, item));
+                        found = true;
+                }
+        }
+
+        if (!found)
+                return 0;
+
+        if (dns_answer_isempty(*a))
+                *a = dns_answer_unref(*a); /* Return NULL for the empty answer */
+
+        return 1;
+}
+
+int dns_answer_remove_by_rr(DnsAnswer **a, DnsResourceRecord *rr) {
+        _unused_ _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr_ref = dns_resource_record_ref(rr);
+        DnsAnswerItem *item;
+        bool found = false;
+        int r;
+
+        assert(a);
+        assert(rr);
+
+        /* Remove all entries matching the specified RR from *a */
+
+        DNS_ANSWER_FOREACH_ITEM(item, *a) {
+                r = dns_resource_record_equal(item->rr, rr);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        dns_answer_item_unref(ordered_set_remove((*a)->items, item));
+                        found = true;
+                }
+        }
+
+        if (!found)
+                return 0;
+
+        if (dns_answer_isempty(*a))
+                *a = dns_answer_unref(*a); /* Return NULL for the empty answer */
+
+        return 1;
+}
+
+int dns_answer_remove_by_answer_keys(DnsAnswer **a, DnsAnswer *b) {
+        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *prev = NULL;
+        DnsAnswerItem *item;
+        int r;
+
+        /* Removes all items from '*a' that have a matching key in 'b' */
+
+        DNS_ANSWER_FOREACH_ITEM(item, b) {
+
+                if (prev && dns_resource_key_equal(item->rr->key, prev)) /* Skip this one, we already looked at it */
+                        continue;
+
+                r = dns_answer_remove_by_key(a, item->rr->key);
+                if (r < 0)
+                        return r;
+                if (!*a)
+                        return 0; /* a is already empty. */
+
+                /* Let's remember this entry's RR key, to optimize the loop a bit: if we have an RRset with
+                 * more than one item then we don't need to remove the key multiple times */
+                DNS_RESOURCE_KEY_REPLACE(prev, dns_resource_key_ref(item->rr->key));
+        }
+
+        return 0;
+}
+
+int dns_answer_copy_by_key(
+                DnsAnswer **a,
+                DnsAnswer *source,
+                const DnsResourceKey *key,
+                DnsAnswerFlags or_flags,
+                DnsResourceRecord *rrsig) {
+
+        DnsAnswerItem *item;
+        int r;
+
+        assert(a);
+        assert(key);
+
+        /* Copy all RRs matching the specified key from source into *a */
+
+        DNS_ANSWER_FOREACH_ITEM(item, source) {
+
+                r = dns_resource_key_equal(item->rr->key, key);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        continue;
+
+                r = dns_answer_add_extend(a, item->rr, item->ifindex, item->flags|or_flags, rrsig ?: item->rrsig);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
+int dns_answer_move_by_key(
+                DnsAnswer **to,
+                DnsAnswer **from,
+                const DnsResourceKey *key,
+                DnsAnswerFlags or_flags,
+                DnsResourceRecord *rrsig) {
+
+        int r;
+
+        assert(to);
+        assert(from);
+        assert(key);
+
+        r = dns_answer_copy_by_key(to, *from, key, or_flags, rrsig);
+        if (r < 0)
+                return r;
+
+        return dns_answer_remove_by_key(from, key);
+}
+
+void dns_answer_order_by_scope(DnsAnswer *a, bool prefer_link_local) {
+        _cleanup_free_ DnsAnswerItem **items = NULL;
+        DnsAnswerItem **p, *item;
+        size_t n;
+
+        n = dns_answer_size(a);
+        if (n <= 1)
+                return;
+
+        /* RFC 4795, Section 2.6 suggests we should order entries
+         * depending on whether the sender is a link-local address. */
+
+        p = items = new(DnsAnswerItem*, n);
+        if (!items)
+                return (void) log_oom();
+
+        /* Order preferred address records and other records to the beginning of the array */
+        DNS_ANSWER_FOREACH_ITEM(item, a)
+                if (dns_resource_record_is_link_local_address(item->rr) == prefer_link_local)
+                        *p++ = dns_answer_item_ref(item);
+
+        /* Order address records that are not preferred to the end of the array */
+        DNS_ANSWER_FOREACH_ITEM(item, a)
+                if (dns_resource_record_is_link_local_address(item->rr) != prefer_link_local)
+                        *p++ = dns_answer_item_ref(item);
+
+
+        assert((size_t) (p - items) == n);
+
+        ordered_set_clear(a->items);
+        for (size_t i = 0; i < n; i++)
+                assert_se(ordered_set_put(a->items, items[i]) >= 0);
+}
+
+int dns_answer_reserve(DnsAnswer **a, size_t n_free) {
+        assert(a);
+
+        if (n_free <= 0)
+                return 0;
+
+        if (!*a) {
+                DnsAnswer *n;
+
+                n = dns_answer_new(n_free);
+                if (!n)
+                        return -ENOMEM;
+
+                *a = n;
+                return 0;
+        }
+
+        if ((*a)->n_ref > 1)
+                return -EBUSY;
+
+        return dns_answer_reserve_internal(*a, n_free);
+}
+
+int dns_answer_reserve_or_clone(DnsAnswer **a, size_t n_free) {
+        _cleanup_(dns_answer_unrefp) DnsAnswer *n = NULL;
+        size_t ns;
+        int r;
+
+        assert(a);
+
+        r = dns_answer_reserve(a, n_free);
+        if (r != -EBUSY)
+                return r;
+
+        ns = dns_answer_size(*a);
+        assert(ns <= UINT16_MAX); /* Maximum number of RRs we can stick into a DNS packet section */
+
+        ns = saturate_add(ns, n_free, UINT16_MAX);
+
+        n = dns_answer_new(ns);
+        if (!n)
+                return -ENOMEM;
+
+        r = dns_answer_add_raw_all(n, *a);
+        if (r < 0)
+                return r;
+
+        DNS_ANSWER_REPLACE(*a, TAKE_PTR(n));
+        return 0;
+}
+
+/*
+ * This function is not used in the code base, but is useful when debugging. Do not delete.
+ */
+void dns_answer_dump(DnsAnswer *answer, FILE *f) {
+        DnsAnswerItem *item;
+
+        if (!f)
+                f = stdout;
+
+        DNS_ANSWER_FOREACH_ITEM(item, answer) {
+                const char *t;
+
+                fputc('\t', f);
+
+                t = dns_resource_record_to_string(item->rr);
+                if (!t) {
+                        log_oom();
+                        continue;
+                }
+
+                fputs(t, f);
+                fputs("\t;", f);
+                fprintf(f, " ttl=%" PRIu32, item->rr->ttl);
+
+                if (item->ifindex != 0)
+                        fprintf(f, " ifindex=%i", item->ifindex);
+                if (item->rrsig)
+                        fputs(" rrsig", f);
+                if (item->flags & DNS_ANSWER_AUTHENTICATED)
+                        fputs(" authenticated", f);
+                if (item->flags & DNS_ANSWER_CACHEABLE)
+                        fputs(" cacheable", f);
+                if (item->flags & DNS_ANSWER_SHARED_OWNER)
+                        fputs(" shared-owner", f);
+                if (item->flags & DNS_ANSWER_CACHE_FLUSH)
+                        fputs(" cache-flush", f);
+                if (item->flags & DNS_ANSWER_GOODBYE)
+                        fputs(" goodbye", f);
+                if (item->flags & DNS_ANSWER_SECTION_ANSWER)
+                        fputs(" section-answer", f);
+                if (item->flags & DNS_ANSWER_SECTION_AUTHORITY)
+                        fputs(" section-authority", f);
+                if (item->flags & DNS_ANSWER_SECTION_ADDITIONAL)
+                        fputs(" section-additional", f);
+
+                fputc('\n', f);
+        }
+}
+
+int dns_answer_has_dname_for_cname(DnsAnswer *a, DnsResourceRecord *cname) {
+        DnsResourceRecord *rr;
+        int r;
+
+        assert(cname);
+
+        /* Checks whether the answer contains a DNAME record that indicates that the specified CNAME record is
+         * synthesized from it */
+
+        if (cname->key->type != DNS_TYPE_CNAME)
+                return 0;
+
+        DNS_ANSWER_FOREACH(rr, a) {
+                _cleanup_free_ char *n = NULL;
+
+                if (rr->key->type != DNS_TYPE_DNAME)
+                        continue;
+                if (rr->key->class != cname->key->class)
+                        continue;
+
+                r = dns_name_change_suffix(cname->cname.name, rr->dname.name, dns_resource_key_name(rr->key), &n);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        continue;
+
+                r = dns_name_equal(n, dns_resource_key_name(cname->key));
+                if (r < 0)
+                        return r;
+                if (r > 0)
+                        return 1;
+        }
+
+        return 0;
+}
+
+void dns_answer_randomize(DnsAnswer *a) {
+        _cleanup_free_ DnsAnswerItem **items = NULL;
+        DnsAnswerItem **p, *item;
+        size_t n;
+
+        /* Permutes the answer list randomly (Knuth shuffle) */
+
+        n = dns_answer_size(a);
+        if (n <= 1)
+                return;
+
+        p = items = new(DnsAnswerItem*, n);
+        if (!items)
+                return (void) log_oom();
+
+        DNS_ANSWER_FOREACH_ITEM(item, a)
+                *p++ = dns_answer_item_ref(item);
+
+        assert((size_t) (p - items) == n);
+
+        for (size_t i = 0; i < n; i++) {
+                size_t k;
+
+                k = random_u64_range(n);
+                if (k == i)
+                        continue;
+
+                SWAP_TWO(items[i], items[k]);
+        }
+
+        ordered_set_clear(a->items);
+        for (size_t i = 0; i < n; i++)
+                assert_se(ordered_set_put(a->items, items[i]) >= 0);
+}
+
+uint32_t dns_answer_min_ttl(DnsAnswer *a) {
+        uint32_t ttl = UINT32_MAX;
+        DnsResourceRecord *rr;
+
+        /* Return the smallest TTL of all RRs in this answer */
+
+        DNS_ANSWER_FOREACH(rr, a) {
+                /* Don't consider OPT (where the TTL field is used for other purposes than an actual TTL) */
+
+                if (dns_type_is_pseudo(rr->key->type) ||
+                    dns_class_is_pseudo(rr->key->class))
+                        continue;
+
+                ttl = MIN(ttl, rr->ttl);
+        }
+
+        return ttl;
+}