Adding upstream version 247.3.upstream/247.3upstream

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

1 files changed, 1041 insertions, 0 deletions

diff --git a/src/resolve/resolved-dns-query.c b/src/resolve/resolved-dns-query.c
new file mode 100644
index 0000000..8ee4fd8
--- /dev/null
+++ b/src/resolve/resolved-dns-query.c
@@ -0,0 +1,1041 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include "alloc-util.h"
+#include "dns-domain.h"
+#include "dns-type.h"
+#include "hostname-util.h"
+#include "local-addresses.h"
+#include "resolved-dns-query.h"
+#include "resolved-dns-synthesize.h"
+#include "resolved-etc-hosts.h"
+#include "string-util.h"
+
+#define CNAME_MAX 8
+#define QUERIES_MAX 2048
+#define AUXILIARY_QUERIES_MAX 64
+
+static int dns_query_candidate_new(DnsQueryCandidate **ret, DnsQuery *q, DnsScope *s) {
+        DnsQueryCandidate *c;
+
+        assert(ret);
+        assert(q);
+        assert(s);
+
+        c = new(DnsQueryCandidate, 1);
+        if (!c)
+                return -ENOMEM;
+
+        *c = (DnsQueryCandidate) {
+                .n_ref = 1,
+                .query = q,
+                .scope = s,
+        };
+
+        LIST_PREPEND(candidates_by_query, q->candidates, c);
+        LIST_PREPEND(candidates_by_scope, s->query_candidates, c);
+
+        *ret = c;
+        return 0;
+}
+
+static void dns_query_candidate_stop(DnsQueryCandidate *c) {
+        DnsTransaction *t;
+
+        assert(c);
+
+        while ((t = set_steal_first(c->transactions))) {
+                set_remove(t->notify_query_candidates, c);
+                set_remove(t->notify_query_candidates_done, c);
+                dns_transaction_gc(t);
+        }
+}
+
+static DnsQueryCandidate* dns_query_candidate_free(DnsQueryCandidate *c) {
+        if (!c)
+                return NULL;
+
+        dns_query_candidate_stop(c);
+
+        set_free(c->transactions);
+        dns_search_domain_unref(c->search_domain);
+
+        if (c->query)
+                LIST_REMOVE(candidates_by_query, c->query->candidates, c);
+
+        if (c->scope)
+                LIST_REMOVE(candidates_by_scope, c->scope->query_candidates, c);
+
+        return mfree(c);
+}
+
+DEFINE_PUBLIC_TRIVIAL_REF_UNREF_FUNC(DnsQueryCandidate, dns_query_candidate, dns_query_candidate_free);
+
+static int dns_query_candidate_next_search_domain(DnsQueryCandidate *c) {
+        DnsSearchDomain *next;
+
+        assert(c);
+
+        if (c->search_domain && c->search_domain->linked)
+                next = c->search_domain->domains_next;
+        else
+                next = dns_scope_get_search_domains(c->scope);
+
+        for (;;) {
+                if (!next) /* We hit the end of the list */
+                        return 0;
+
+                if (!next->route_only)
+                        break;
+
+                /* Skip over route-only domains */
+                next = next->domains_next;
+        }
+
+        dns_search_domain_unref(c->search_domain);
+        c->search_domain = dns_search_domain_ref(next);
+
+        return 1;
+}
+
+static int dns_query_candidate_add_transaction(DnsQueryCandidate *c, DnsResourceKey *key) {
+        _cleanup_(dns_transaction_gcp) DnsTransaction *t = NULL;
+        int r;
+
+        assert(c);
+        assert(key);
+
+        t = dns_scope_find_transaction(c->scope, key, true);
+        if (!t) {
+                r = dns_transaction_new(&t, c->scope, key);
+                if (r < 0)
+                        return r;
+        } else if (set_contains(c->transactions, t))
+                return 0;
+
+        r = set_ensure_allocated(&t->notify_query_candidates_done, NULL);
+        if (r < 0)
+                return r;
+
+        r = set_ensure_put(&t->notify_query_candidates, NULL, c);
+        if (r < 0)
+                return r;
+
+        r = set_ensure_put(&c->transactions, NULL, t);
+        if (r < 0) {
+                (void) set_remove(t->notify_query_candidates, c);
+                return r;
+        }
+
+        t->clamp_ttl = c->query->clamp_ttl;
+        TAKE_PTR(t);
+        return 1;
+}
+
+static int dns_query_candidate_go(DnsQueryCandidate *c) {
+        _cleanup_(dns_query_candidate_unrefp) DnsQueryCandidate *keep_c = NULL;
+        DnsTransaction *t;
+        int r;
+        unsigned n = 0;
+
+        assert(c);
+
+        /* Let's keep a reference to the query while we're operating */
+        keep_c = dns_query_candidate_ref(c);
+
+        /* Start the transactions that are not started yet */
+        SET_FOREACH(t, c->transactions) {
+                if (t->state != DNS_TRANSACTION_NULL)
+                        continue;
+
+                r = dns_transaction_go(t);
+                if (r < 0)
+                        return r;
+
+                n++;
+        }
+
+        /* If there was nothing to start, then let's proceed immediately */
+        if (n == 0)
+                dns_query_candidate_notify(c);
+
+        return 0;
+}
+
+static DnsTransactionState dns_query_candidate_state(DnsQueryCandidate *c) {
+        DnsTransactionState state = DNS_TRANSACTION_NO_SERVERS;
+        DnsTransaction *t;
+
+        assert(c);
+
+        if (c->error_code != 0)
+                return DNS_TRANSACTION_ERRNO;
+
+        SET_FOREACH(t, c->transactions) {
+
+                switch (t->state) {
+
+                case DNS_TRANSACTION_NULL:
+                        /* If there's a NULL transaction pending, then
+                         * this means not all transactions where
+                         * started yet, and we were called from within
+                         * the stackframe that is supposed to start
+                         * remaining transactions. In this case,
+                         * simply claim the candidate is pending. */
+
+                case DNS_TRANSACTION_PENDING:
+                case DNS_TRANSACTION_VALIDATING:
+                        /* If there's one transaction currently in
+                         * VALIDATING state, then this means there's
+                         * also one in PENDING state, hence we can
+                         * return PENDING immediately. */
+                        return DNS_TRANSACTION_PENDING;
+
+                case DNS_TRANSACTION_SUCCESS:
+                        state = t->state;
+                        break;
+
+                default:
+                        if (state != DNS_TRANSACTION_SUCCESS)
+                                state = t->state;
+
+                        break;
+                }
+        }
+
+        return state;
+}
+
+static int dns_query_candidate_setup_transactions(DnsQueryCandidate *c) {
+        DnsQuestion *question;
+        DnsResourceKey *key;
+        int n = 0, r;
+
+        assert(c);
+
+        dns_query_candidate_stop(c);
+
+        question = dns_query_question_for_protocol(c->query, c->scope->protocol);
+
+        /* Create one transaction per question key */
+        DNS_QUESTION_FOREACH(key, question) {
+                _cleanup_(dns_resource_key_unrefp) DnsResourceKey *new_key = NULL;
+                DnsResourceKey *qkey;
+
+                if (c->search_domain) {
+                        r = dns_resource_key_new_append_suffix(&new_key, key, c->search_domain->name);
+                        if (r < 0)
+                                goto fail;
+
+                        qkey = new_key;
+                } else
+                        qkey = key;
+
+                if (!dns_scope_good_key(c->scope, qkey))
+                        continue;
+
+                r = dns_query_candidate_add_transaction(c, qkey);
+                if (r < 0)
+                        goto fail;
+
+                n++;
+        }
+
+        return n;
+
+fail:
+        dns_query_candidate_stop(c);
+        return r;
+}
+
+void dns_query_candidate_notify(DnsQueryCandidate *c) {
+        DnsTransactionState state;
+        int r;
+
+        assert(c);
+
+        state = dns_query_candidate_state(c);
+
+        if (DNS_TRANSACTION_IS_LIVE(state))
+                return;
+
+        if (state != DNS_TRANSACTION_SUCCESS && c->search_domain) {
+
+                r = dns_query_candidate_next_search_domain(c);
+                if (r < 0)
+                        goto fail;
+
+                if (r > 0) {
+                        /* OK, there's another search domain to try, let's do so. */
+
+                        r = dns_query_candidate_setup_transactions(c);
+                        if (r < 0)
+                                goto fail;
+
+                        if (r > 0) {
+                                /* New transactions where queued. Start them and wait */
+
+                                r = dns_query_candidate_go(c);
+                                if (r < 0)
+                                        goto fail;
+
+                                return;
+                        }
+                }
+
+        }
+
+        dns_query_ready(c->query);
+        return;
+
+fail:
+        c->error_code = log_warning_errno(r, "Failed to follow search domains: %m");
+        dns_query_ready(c->query);
+}
+
+static void dns_query_stop(DnsQuery *q) {
+        DnsQueryCandidate *c;
+
+        assert(q);
+
+        q->timeout_event_source = sd_event_source_unref(q->timeout_event_source);
+
+        LIST_FOREACH(candidates_by_query, c, q->candidates)
+                dns_query_candidate_stop(c);
+}
+
+static void dns_query_unref_candidates(DnsQuery *q) {
+        assert(q);
+
+        while (q->candidates)
+                dns_query_candidate_unref(q->candidates);
+}
+
+static void dns_query_reset_answer(DnsQuery *q) {
+        assert(q);
+
+        q->answer = dns_answer_unref(q->answer);
+        q->answer_rcode = 0;
+        q->answer_dnssec_result = _DNSSEC_RESULT_INVALID;
+        q->answer_errno = 0;
+        q->answer_authenticated = false;
+        q->answer_protocol = _DNS_PROTOCOL_INVALID;
+        q->answer_family = AF_UNSPEC;
+        q->answer_search_domain = dns_search_domain_unref(q->answer_search_domain);
+}
+
+DnsQuery *dns_query_free(DnsQuery *q) {
+        if (!q)
+                return NULL;
+
+        while (q->auxiliary_queries)
+                dns_query_free(q->auxiliary_queries);
+
+        if (q->auxiliary_for) {
+                assert(q->auxiliary_for->n_auxiliary_queries > 0);
+                q->auxiliary_for->n_auxiliary_queries--;
+                LIST_REMOVE(auxiliary_queries, q->auxiliary_for->auxiliary_queries, q);
+        }
+
+        dns_query_unref_candidates(q);
+
+        dns_question_unref(q->question_idna);
+        dns_question_unref(q->question_utf8);
+
+        dns_query_reset_answer(q);
+
+        sd_bus_message_unref(q->bus_request);
+        sd_bus_track_unref(q->bus_track);
+
+        if (q->varlink_request) {
+                varlink_set_userdata(q->varlink_request, NULL);
+                varlink_unref(q->varlink_request);
+        }
+
+        dns_packet_unref(q->request_dns_packet);
+        dns_packet_unref(q->reply_dns_packet);
+
+        if (q->request_dns_stream) {
+                /* Detach the stream from our query, in case something else keeps a reference to it. */
+                (void) set_remove(q->request_dns_stream->queries, q);
+                q->request_dns_stream = dns_stream_unref(q->request_dns_stream);
+        }
+
+        free(q->request_address_string);
+
+        if (q->manager) {
+                LIST_REMOVE(queries, q->manager->dns_queries, q);
+                q->manager->n_dns_queries--;
+        }
+
+        return mfree(q);
+}
+
+int dns_query_new(
+                Manager *m,
+                DnsQuery **ret,
+                DnsQuestion *question_utf8,
+                DnsQuestion *question_idna,
+                int ifindex,
+                uint64_t flags) {
+
+        _cleanup_(dns_query_freep) DnsQuery *q = NULL;
+        DnsResourceKey *key;
+        bool good = false;
+        int r;
+        char key_str[DNS_RESOURCE_KEY_STRING_MAX];
+
+        assert(m);
+
+        if (dns_question_size(question_utf8) > 0) {
+                r = dns_question_is_valid_for_query(question_utf8);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        return -EINVAL;
+
+                good = true;
+        }
+
+        /* If the IDNA and UTF8 questions are the same, merge their references */
+        r = dns_question_is_equal(question_idna, question_utf8);
+        if (r < 0)
+                return r;
+        if (r > 0)
+                question_idna = question_utf8;
+        else {
+                if (dns_question_size(question_idna) > 0) {
+                        r = dns_question_is_valid_for_query(question_idna);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                return -EINVAL;
+
+                        good = true;
+                }
+        }
+
+        if (!good) /* don't allow empty queries */
+                return -EINVAL;
+
+        if (m->n_dns_queries >= QUERIES_MAX)
+                return -EBUSY;
+
+        q = new(DnsQuery, 1);
+        if (!q)
+                return -ENOMEM;
+
+        *q = (DnsQuery) {
+                .question_utf8 = dns_question_ref(question_utf8),
+                .question_idna = dns_question_ref(question_idna),
+                .ifindex = ifindex,
+                .flags = flags,
+                .answer_dnssec_result = _DNSSEC_RESULT_INVALID,
+                .answer_protocol = _DNS_PROTOCOL_INVALID,
+                .answer_family = AF_UNSPEC,
+        };
+
+        /* First dump UTF8  question */
+        DNS_QUESTION_FOREACH(key, question_utf8)
+                log_debug("Looking up RR for %s.",
+                          dns_resource_key_to_string(key, key_str, sizeof key_str));
+
+        /* And then dump the IDNA question, but only what hasn't been dumped already through the UTF8 question. */
+        DNS_QUESTION_FOREACH(key, question_idna) {
+                r = dns_question_contains(question_utf8, key);
+                if (r < 0)
+                        return r;
+                if (r > 0)
+                        continue;
+
+                log_debug("Looking up IDNA RR for %s.",
+                          dns_resource_key_to_string(key, key_str, sizeof key_str));
+        }
+
+        LIST_PREPEND(queries, m->dns_queries, q);
+        m->n_dns_queries++;
+        q->manager = m;
+
+        if (ret)
+                *ret = q;
+        q = NULL;
+
+        return 0;
+}
+
+int dns_query_make_auxiliary(DnsQuery *q, DnsQuery *auxiliary_for) {
+        assert(q);
+        assert(auxiliary_for);
+
+        /* Ensure that the query is not auxiliary yet, and
+         * nothing else is auxiliary to it either */
+        assert(!q->auxiliary_for);
+        assert(!q->auxiliary_queries);
+
+        /* Ensure that the unit we shall be made auxiliary for isn't
+         * auxiliary itself */
+        assert(!auxiliary_for->auxiliary_for);
+
+        if (auxiliary_for->n_auxiliary_queries >= AUXILIARY_QUERIES_MAX)
+                return -EAGAIN;
+
+        LIST_PREPEND(auxiliary_queries, auxiliary_for->auxiliary_queries, q);
+        q->auxiliary_for = auxiliary_for;
+
+        auxiliary_for->n_auxiliary_queries++;
+        return 0;
+}
+
+void dns_query_complete(DnsQuery *q, DnsTransactionState state) {
+        assert(q);
+        assert(!DNS_TRANSACTION_IS_LIVE(state));
+        assert(DNS_TRANSACTION_IS_LIVE(q->state));
+
+        /* Note that this call might invalidate the query. Callers should hence not attempt to access the
+         * query or transaction after calling this function. */
+
+        q->state = state;
+
+        dns_query_stop(q);
+        if (q->complete)
+                q->complete(q);
+}
+
+static int on_query_timeout(sd_event_source *s, usec_t usec, void *userdata) {
+        DnsQuery *q = userdata;
+
+        assert(s);
+        assert(q);
+
+        dns_query_complete(q, DNS_TRANSACTION_TIMEOUT);
+        return 0;
+}
+
+static int dns_query_add_candidate(DnsQuery *q, DnsScope *s) {
+        _cleanup_(dns_query_candidate_unrefp) DnsQueryCandidate *c = NULL;
+        int r;
+
+        assert(q);
+        assert(s);
+
+        r = dns_query_candidate_new(&c, q, s);
+        if (r < 0)
+                return r;
+
+        /* If this a single-label domain on DNS, we might append a suitable search domain first. */
+        if (!FLAGS_SET(q->flags, SD_RESOLVED_NO_SEARCH) &&
+            dns_scope_name_wants_search_domain(s, dns_question_first_name(q->question_idna))) {
+                /* OK, we want a search domain now. Let's find one for this scope */
+
+                r = dns_query_candidate_next_search_domain(c);
+                if (r < 0)
+                        return r;
+        }
+
+        r = dns_query_candidate_setup_transactions(c);
+        if (r < 0)
+                return r;
+
+        TAKE_PTR(c);
+        return 0;
+}
+
+static int dns_query_synthesize_reply(DnsQuery *q, DnsTransactionState *state) {
+        _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
+        int r;
+
+        assert(q);
+        assert(state);
+
+        /* Tries to synthesize localhost RR replies (and others) where appropriate. Note that this is done *after* the
+         * the normal lookup finished. The data from the network hence takes precedence over the data we
+         * synthesize. (But note that many scopes refuse to resolve certain domain names) */
+
+        if (!IN_SET(*state,
+                    DNS_TRANSACTION_RCODE_FAILURE,
+                    DNS_TRANSACTION_NO_SERVERS,
+                    DNS_TRANSACTION_TIMEOUT,
+                    DNS_TRANSACTION_ATTEMPTS_MAX_REACHED,
+                    DNS_TRANSACTION_NETWORK_DOWN,
+                    DNS_TRANSACTION_NOT_FOUND))
+                return 0;
+
+        r = dns_synthesize_answer(
+                        q->manager,
+                        q->question_utf8,
+                        q->ifindex,
+                        &answer);
+        if (r == -ENXIO) {
+                /* If we get ENXIO this tells us to generate NXDOMAIN unconditionally. */
+
+                dns_query_reset_answer(q);
+                q->answer_rcode = DNS_RCODE_NXDOMAIN;
+                q->answer_protocol = dns_synthesize_protocol(q->flags);
+                q->answer_family = dns_synthesize_family(q->flags);
+                q->answer_authenticated = true;
+                *state = DNS_TRANSACTION_RCODE_FAILURE;
+
+                return 0;
+        }
+        if (r <= 0)
+                return r;
+
+        dns_query_reset_answer(q);
+
+        q->answer = TAKE_PTR(answer);
+        q->answer_rcode = DNS_RCODE_SUCCESS;
+        q->answer_protocol = dns_synthesize_protocol(q->flags);
+        q->answer_family = dns_synthesize_family(q->flags);
+        q->answer_authenticated = true;
+
+        *state = DNS_TRANSACTION_SUCCESS;
+
+        return 1;
+}
+
+static int dns_query_try_etc_hosts(DnsQuery *q) {
+        _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
+        int r;
+
+        assert(q);
+
+        /* Looks in /etc/hosts for matching entries. Note that this is done *before* the normal lookup is
+         * done. The data from /etc/hosts hence takes precedence over the network. */
+
+        r = manager_etc_hosts_lookup(
+                        q->manager,
+                        q->question_utf8,
+                        &answer);
+        if (r <= 0)
+                return r;
+
+        dns_query_reset_answer(q);
+
+        q->answer = TAKE_PTR(answer);
+        q->answer_rcode = DNS_RCODE_SUCCESS;
+        q->answer_protocol = dns_synthesize_protocol(q->flags);
+        q->answer_family = dns_synthesize_family(q->flags);
+        q->answer_authenticated = true;
+
+        return 1;
+}
+
+int dns_query_go(DnsQuery *q) {
+        DnsScopeMatch found = DNS_SCOPE_NO;
+        DnsScope *s, *first = NULL;
+        DnsQueryCandidate *c;
+        int r;
+
+        assert(q);
+
+        if (q->state != DNS_TRANSACTION_NULL)
+                return 0;
+
+        r = dns_query_try_etc_hosts(q);
+        if (r < 0)
+                return r;
+        if (r > 0) {
+                dns_query_complete(q, DNS_TRANSACTION_SUCCESS);
+                return 1;
+        }
+
+        LIST_FOREACH(scopes, s, q->manager->dns_scopes) {
+                DnsScopeMatch match;
+                const char *name;
+
+                name = dns_question_first_name(dns_query_question_for_protocol(q, s->protocol));
+                if (!name)
+                        continue;
+
+                match = dns_scope_good_domain(s, q->ifindex, q->flags, name);
+                if (match < 0) {
+                        log_debug("Couldn't check if '%s' matches against scope, ignoring.", name);
+                        continue;
+                }
+
+                if (match > found) { /* Does this match better? If so, remember how well it matched, and the first one
+                                      * that matches this well */
+                        found = match;
+                        first = s;
+                }
+        }
+
+        if (found == DNS_SCOPE_NO) {
+                DnsTransactionState state = DNS_TRANSACTION_NO_SERVERS;
+
+                r = dns_query_synthesize_reply(q, &state);
+                if (r < 0)
+                        return r;
+
+                dns_query_complete(q, state);
+                return 1;
+        }
+
+        r = dns_query_add_candidate(q, first);
+        if (r < 0)
+                goto fail;
+
+        LIST_FOREACH(scopes, s, first->scopes_next) {
+                DnsScopeMatch match;
+                const char *name;
+
+                name = dns_question_first_name(dns_query_question_for_protocol(q, s->protocol));
+                if (!name)
+                        continue;
+
+                match = dns_scope_good_domain(s, q->ifindex, q->flags, name);
+                if (match < 0) {
+                        log_debug("Couldn't check if '%s' matches against scope, ignoring.", name);
+                        continue;
+                }
+
+                if (match < found)
+                        continue;
+
+                r = dns_query_add_candidate(q, s);
+                if (r < 0)
+                        goto fail;
+        }
+
+        dns_query_reset_answer(q);
+
+        r = sd_event_add_time_relative(
+                        q->manager->event,
+                        &q->timeout_event_source,
+                        clock_boottime_or_monotonic(),
+                        SD_RESOLVED_QUERY_TIMEOUT_USEC,
+                        0, on_query_timeout, q);
+        if (r < 0)
+                goto fail;
+
+        (void) sd_event_source_set_description(q->timeout_event_source, "query-timeout");
+
+        q->state = DNS_TRANSACTION_PENDING;
+        q->block_ready++;
+
+        /* Start the transactions */
+        LIST_FOREACH(candidates_by_query, c, q->candidates) {
+                r = dns_query_candidate_go(c);
+                if (r < 0) {
+                        q->block_ready--;
+                        goto fail;
+                }
+        }
+
+        q->block_ready--;
+        dns_query_ready(q);
+
+        return 1;
+
+fail:
+        dns_query_stop(q);
+        return r;
+}
+
+static void dns_query_accept(DnsQuery *q, DnsQueryCandidate *c) {
+        DnsTransactionState state = DNS_TRANSACTION_NO_SERVERS;
+        bool has_authenticated = false, has_non_authenticated = false;
+        DnssecResult dnssec_result_authenticated = _DNSSEC_RESULT_INVALID, dnssec_result_non_authenticated = _DNSSEC_RESULT_INVALID;
+        DnsTransaction *t;
+        int r;
+
+        assert(q);
+
+        if (!c) {
+                r = dns_query_synthesize_reply(q, &state);
+                if (r < 0)
+                        goto fail;
+
+                dns_query_complete(q, state);
+                return;
+        }
+
+        if (c->error_code != 0) {
+                /* If the candidate had an error condition of its own, start with that. */
+                state = DNS_TRANSACTION_ERRNO;
+                q->answer = dns_answer_unref(q->answer);
+                q->answer_rcode = 0;
+                q->answer_dnssec_result = _DNSSEC_RESULT_INVALID;
+                q->answer_authenticated = false;
+                q->answer_errno = c->error_code;
+        }
+
+        SET_FOREACH(t, c->transactions) {
+
+                switch (t->state) {
+
+                case DNS_TRANSACTION_SUCCESS: {
+                        /* We found a successfully reply, merge it into the answer */
+                        r = dns_answer_extend(&q->answer, t->answer);
+                        if (r < 0)
+                                goto fail;
+
+                        q->answer_rcode = t->answer_rcode;
+                        q->answer_errno = 0;
+
+                        if (t->answer_authenticated) {
+                                has_authenticated = true;
+                                dnssec_result_authenticated = t->answer_dnssec_result;
+                        } else {
+                                has_non_authenticated = true;
+                                dnssec_result_non_authenticated = t->answer_dnssec_result;
+                        }
+
+                        state = DNS_TRANSACTION_SUCCESS;
+                        break;
+                }
+
+                case DNS_TRANSACTION_NULL:
+                case DNS_TRANSACTION_PENDING:
+                case DNS_TRANSACTION_VALIDATING:
+                case DNS_TRANSACTION_ABORTED:
+                        /* Ignore transactions that didn't complete */
+                        continue;
+
+                default:
+                        /* Any kind of failure? Store the data away, if there's nothing stored yet. */
+                        if (state == DNS_TRANSACTION_SUCCESS)
+                                continue;
+
+                        /* If there's already an authenticated negative reply stored, then prefer that over any unauthenticated one */
+                        if (q->answer_authenticated && !t->answer_authenticated)
+                                continue;
+
+                        q->answer = dns_answer_unref(q->answer);
+                        q->answer_rcode = t->answer_rcode;
+                        q->answer_dnssec_result = t->answer_dnssec_result;
+                        q->answer_authenticated = t->answer_authenticated;
+                        q->answer_errno = t->answer_errno;
+
+                        state = t->state;
+                        break;
+                }
+        }
+
+        if (state == DNS_TRANSACTION_SUCCESS) {
+                q->answer_authenticated = has_authenticated && !has_non_authenticated;
+                q->answer_dnssec_result = q->answer_authenticated ? dnssec_result_authenticated : dnssec_result_non_authenticated;
+        }
+
+        q->answer_protocol = c->scope->protocol;
+        q->answer_family = c->scope->family;
+
+        dns_search_domain_unref(q->answer_search_domain);
+        q->answer_search_domain = dns_search_domain_ref(c->search_domain);
+
+        r = dns_query_synthesize_reply(q, &state);
+        if (r < 0)
+                goto fail;
+
+        dns_query_complete(q, state);
+        return;
+
+fail:
+        q->answer_errno = -r;
+        dns_query_complete(q, DNS_TRANSACTION_ERRNO);
+}
+
+void dns_query_ready(DnsQuery *q) {
+
+        DnsQueryCandidate *bad = NULL, *c;
+        bool pending = false;
+
+        assert(q);
+        assert(DNS_TRANSACTION_IS_LIVE(q->state));
+
+        /* Note that this call might invalidate the query. Callers
+         * should hence not attempt to access the query or transaction
+         * after calling this function, unless the block_ready
+         * counter was explicitly bumped before doing so. */
+
+        if (q->block_ready > 0)
+                return;
+
+        LIST_FOREACH(candidates_by_query, c, q->candidates) {
+                DnsTransactionState state;
+
+                state = dns_query_candidate_state(c);
+                switch (state) {
+
+                case DNS_TRANSACTION_SUCCESS:
+                        /* One of the candidates is successful,
+                         * let's use it, and copy its data out */
+                        dns_query_accept(q, c);
+                        return;
+
+                case DNS_TRANSACTION_NULL:
+                case DNS_TRANSACTION_PENDING:
+                case DNS_TRANSACTION_VALIDATING:
+                        /* One of the candidates is still going on,
+                         * let's maybe wait for it */
+                        pending = true;
+                        break;
+
+                default:
+                        /* Any kind of failure */
+                        bad = c;
+                        break;
+                }
+        }
+
+        if (pending)
+                return;
+
+        dns_query_accept(q, bad);
+}
+
+static int dns_query_cname_redirect(DnsQuery *q, const DnsResourceRecord *cname) {
+        _cleanup_(dns_question_unrefp) DnsQuestion *nq_idna = NULL, *nq_utf8 = NULL;
+        int r, k;
+
+        assert(q);
+
+        q->n_cname_redirects++;
+        if (q->n_cname_redirects > CNAME_MAX)
+                return -ELOOP;
+
+        r = dns_question_cname_redirect(q->question_idna, cname, &nq_idna);
+        if (r < 0)
+                return r;
+        else if (r > 0)
+                log_debug("Following CNAME/DNAME %s → %s.", dns_question_first_name(q->question_idna), dns_question_first_name(nq_idna));
+
+        k = dns_question_is_equal(q->question_idna, q->question_utf8);
+        if (k < 0)
+                return r;
+        if (k > 0) {
+                /* Same question? Shortcut new question generation */
+                nq_utf8 = dns_question_ref(nq_idna);
+                k = r;
+        } else {
+                k = dns_question_cname_redirect(q->question_utf8, cname, &nq_utf8);
+                if (k < 0)
+                        return k;
+                else if (k > 0)
+                        log_debug("Following UTF8 CNAME/DNAME %s → %s.", dns_question_first_name(q->question_utf8), dns_question_first_name(nq_utf8));
+        }
+
+        if (r == 0 && k == 0) /* No actual cname happened? */
+                return -ELOOP;
+
+        if (q->answer_protocol == DNS_PROTOCOL_DNS)
+                /* Don't permit CNAME redirects from unicast DNS to LLMNR or MulticastDNS, so that global resources
+                 * cannot invade the local namespace. The opposite way we permit: local names may redirect to global
+                 * ones. */
+                q->flags &= ~(SD_RESOLVED_LLMNR|SD_RESOLVED_MDNS); /* mask away the local protocols */
+
+        /* Turn off searching for the new name */
+        q->flags |= SD_RESOLVED_NO_SEARCH;
+
+        dns_question_unref(q->question_idna);
+        q->question_idna = TAKE_PTR(nq_idna);
+
+        dns_question_unref(q->question_utf8);
+        q->question_utf8 = TAKE_PTR(nq_utf8);
+
+        dns_query_unref_candidates(q);
+        dns_query_reset_answer(q);
+
+        q->state = DNS_TRANSACTION_NULL;
+
+        return 0;
+}
+
+int dns_query_process_cname(DnsQuery *q) {
+        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *cname = NULL;
+        DnsQuestion *question;
+        DnsResourceRecord *rr;
+        int r;
+
+        assert(q);
+
+        if (!IN_SET(q->state, DNS_TRANSACTION_SUCCESS, DNS_TRANSACTION_NULL))
+                return DNS_QUERY_NOMATCH;
+
+        question = dns_query_question_for_protocol(q, q->answer_protocol);
+
+        DNS_ANSWER_FOREACH(rr, q->answer) {
+                r = dns_question_matches_rr(question, rr, DNS_SEARCH_DOMAIN_NAME(q->answer_search_domain));
+                if (r < 0)
+                        return r;
+                if (r > 0)
+                        return DNS_QUERY_MATCH; /* The answer matches directly, no need to follow cnames */
+
+                r = dns_question_matches_cname_or_dname(question, rr, DNS_SEARCH_DOMAIN_NAME(q->answer_search_domain));
+                if (r < 0)
+                        return r;
+                if (r > 0 && !cname)
+                        cname = dns_resource_record_ref(rr);
+        }
+
+        if (!cname)
+                return DNS_QUERY_NOMATCH; /* No match and no cname to follow */
+
+        if (q->flags & SD_RESOLVED_NO_CNAME)
+                return -ELOOP;
+
+        if (!q->answer_authenticated)
+                q->previous_redirect_unauthenticated = true;
+
+        /* OK, let's actually follow the CNAME */
+        r = dns_query_cname_redirect(q, cname);
+        if (r < 0)
+                return r;
+
+        /* Let's see if the answer can already answer the new
+         * redirected question */
+        r = dns_query_process_cname(q);
+        if (r != DNS_QUERY_NOMATCH)
+                return r;
+
+        /* OK, it cannot, let's begin with the new query */
+        r = dns_query_go(q);
+        if (r < 0)
+                return r;
+
+        return DNS_QUERY_RESTARTED; /* We restarted the query for a new cname */
+}
+
+DnsQuestion* dns_query_question_for_protocol(DnsQuery *q, DnsProtocol protocol) {
+        assert(q);
+
+        switch (protocol) {
+
+        case DNS_PROTOCOL_DNS:
+                return q->question_idna;
+
+        case DNS_PROTOCOL_MDNS:
+        case DNS_PROTOCOL_LLMNR:
+                return q->question_utf8;
+
+        default:
+                return NULL;
+        }
+}
+
+const char *dns_query_string(DnsQuery *q) {
+        const char *name;
+        int r;
+
+        /* Returns a somewhat useful human-readable lookup key string for this query */
+
+        if (q->request_address_string)
+                return q->request_address_string;
+
+        if (q->request_address_valid) {
+                r = in_addr_to_string(q->request_family, &q->request_address, &q->request_address_string);
+                if (r >= 0)
+                        return q->request_address_string;
+        }
+
+        name = dns_question_first_name(q->question_utf8);
+        if (name)
+                return name;
+
+        return dns_question_first_name(q->question_idna);
+}
+
+bool dns_query_fully_authenticated(DnsQuery *q) {
+        assert(q);
+
+        return q->answer_authenticated && !q->previous_redirect_unauthenticated;
+}