Adding upstream version 241.upstream/241upstream

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

1 files changed, 3277 insertions, 0 deletions

diff --git a/src/resolve/resolved-dns-transaction.c b/src/resolve/resolved-dns-transaction.c
new file mode 100644
index 0000000..4a2d2cc
--- /dev/null
+++ b/src/resolve/resolved-dns-transaction.c
@@ -0,0 +1,3277 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include "sd-messages.h"
+
+#include "af-list.h"
+#include "alloc-util.h"
+#include "dns-domain.h"
+#include "errno-list.h"
+#include "fd-util.h"
+#include "random-util.h"
+#include "resolved-dns-cache.h"
+#include "resolved-dns-transaction.h"
+#include "resolved-llmnr.h"
+#if ENABLE_DNS_OVER_TLS
+#include "resolved-dnstls.h"
+#endif
+#include "string-table.h"
+
+#define TRANSACTIONS_MAX 4096
+#define TRANSACTION_TCP_TIMEOUT_USEC (10U*USEC_PER_SEC)
+
+/* After how much time to repeat classic DNS requests */
+#define DNS_TIMEOUT_USEC (SD_RESOLVED_QUERY_TIMEOUT_USEC / DNS_TRANSACTION_ATTEMPTS_MAX)
+
+static void dns_transaction_reset_answer(DnsTransaction *t) {
+        assert(t);
+
+        t->received = dns_packet_unref(t->received);
+        t->answer = dns_answer_unref(t->answer);
+        t->answer_rcode = 0;
+        t->answer_dnssec_result = _DNSSEC_RESULT_INVALID;
+        t->answer_source = _DNS_TRANSACTION_SOURCE_INVALID;
+        t->answer_authenticated = false;
+        t->answer_nsec_ttl = (uint32_t) -1;
+        t->answer_errno = 0;
+}
+
+static void dns_transaction_flush_dnssec_transactions(DnsTransaction *t) {
+        DnsTransaction *z;
+
+        assert(t);
+
+        while ((z = set_steal_first(t->dnssec_transactions))) {
+                set_remove(z->notify_transactions, t);
+                set_remove(z->notify_transactions_done, t);
+                dns_transaction_gc(z);
+        }
+}
+
+static void dns_transaction_close_connection(DnsTransaction *t) {
+        assert(t);
+
+        if (t->stream) {
+                /* Let's detach the stream from our transaction, in case something else keeps a reference to it. */
+                LIST_REMOVE(transactions_by_stream, t->stream->transactions, t);
+
+                /* Remove packet in case it's still in the queue */
+                dns_packet_unref(ordered_set_remove(t->stream->write_queue, t->sent));
+
+                t->stream = dns_stream_unref(t->stream);
+        }
+
+        t->dns_udp_event_source = sd_event_source_unref(t->dns_udp_event_source);
+        t->dns_udp_fd = safe_close(t->dns_udp_fd);
+}
+
+static void dns_transaction_stop_timeout(DnsTransaction *t) {
+        assert(t);
+
+        t->timeout_event_source = sd_event_source_unref(t->timeout_event_source);
+}
+
+DnsTransaction* dns_transaction_free(DnsTransaction *t) {
+        DnsQueryCandidate *c;
+        DnsZoneItem *i;
+        DnsTransaction *z;
+
+        if (!t)
+                return NULL;
+
+        log_debug("Freeing transaction %" PRIu16 ".", t->id);
+
+        dns_transaction_close_connection(t);
+        dns_transaction_stop_timeout(t);
+
+        dns_packet_unref(t->sent);
+        dns_transaction_reset_answer(t);
+
+        dns_server_unref(t->server);
+
+        if (t->scope) {
+                hashmap_remove_value(t->scope->transactions_by_key, t->key, t);
+                LIST_REMOVE(transactions_by_scope, t->scope->transactions, t);
+
+                if (t->id != 0)
+                        hashmap_remove(t->scope->manager->dns_transactions, UINT_TO_PTR(t->id));
+        }
+
+        while ((c = set_steal_first(t->notify_query_candidates)))
+                set_remove(c->transactions, t);
+        set_free(t->notify_query_candidates);
+
+        while ((c = set_steal_first(t->notify_query_candidates_done)))
+                set_remove(c->transactions, t);
+        set_free(t->notify_query_candidates_done);
+
+        while ((i = set_steal_first(t->notify_zone_items)))
+                i->probe_transaction = NULL;
+        set_free(t->notify_zone_items);
+
+        while ((i = set_steal_first(t->notify_zone_items_done)))
+                i->probe_transaction = NULL;
+        set_free(t->notify_zone_items_done);
+
+        while ((z = set_steal_first(t->notify_transactions)))
+                set_remove(z->dnssec_transactions, t);
+        set_free(t->notify_transactions);
+
+        while ((z = set_steal_first(t->notify_transactions_done)))
+                set_remove(z->dnssec_transactions, t);
+        set_free(t->notify_transactions_done);
+
+        dns_transaction_flush_dnssec_transactions(t);
+        set_free(t->dnssec_transactions);
+
+        dns_answer_unref(t->validated_keys);
+        dns_resource_key_unref(t->key);
+
+        return mfree(t);
+}
+
+DEFINE_TRIVIAL_CLEANUP_FUNC(DnsTransaction*, dns_transaction_free);
+
+bool dns_transaction_gc(DnsTransaction *t) {
+        assert(t);
+
+        if (t->block_gc > 0)
+                return true;
+
+        if (set_isempty(t->notify_query_candidates) &&
+            set_isempty(t->notify_query_candidates_done) &&
+            set_isempty(t->notify_zone_items) &&
+            set_isempty(t->notify_zone_items_done) &&
+            set_isempty(t->notify_transactions) &&
+            set_isempty(t->notify_transactions_done)) {
+                dns_transaction_free(t);
+                return false;
+        }
+
+        return true;
+}
+
+static uint16_t pick_new_id(Manager *m) {
+        uint16_t new_id;
+
+        /* Find a fresh, unused transaction id. Note that this loop is bounded because there's a limit on the number of
+         * transactions, and it's much lower than the space of IDs. */
+
+        assert_cc(TRANSACTIONS_MAX < 0xFFFF);
+
+        do
+                random_bytes(&new_id, sizeof(new_id));
+        while (new_id == 0 ||
+               hashmap_get(m->dns_transactions, UINT_TO_PTR(new_id)));
+
+        return new_id;
+}
+
+int dns_transaction_new(DnsTransaction **ret, DnsScope *s, DnsResourceKey *key) {
+        _cleanup_(dns_transaction_freep) DnsTransaction *t = NULL;
+        int r;
+
+        assert(ret);
+        assert(s);
+        assert(key);
+
+        /* Don't allow looking up invalid or pseudo RRs */
+        if (!dns_type_is_valid_query(key->type))
+                return -EINVAL;
+        if (dns_type_is_obsolete(key->type))
+                return -EOPNOTSUPP;
+
+        /* We only support the IN class */
+        if (!IN_SET(key->class, DNS_CLASS_IN, DNS_CLASS_ANY))
+                return -EOPNOTSUPP;
+
+        if (hashmap_size(s->manager->dns_transactions) >= TRANSACTIONS_MAX)
+                return -EBUSY;
+
+        r = hashmap_ensure_allocated(&s->manager->dns_transactions, NULL);
+        if (r < 0)
+                return r;
+
+        r = hashmap_ensure_allocated(&s->transactions_by_key, &dns_resource_key_hash_ops);
+        if (r < 0)
+                return r;
+
+        t = new0(DnsTransaction, 1);
+        if (!t)
+                return -ENOMEM;
+
+        t->dns_udp_fd = -1;
+        t->answer_source = _DNS_TRANSACTION_SOURCE_INVALID;
+        t->answer_dnssec_result = _DNSSEC_RESULT_INVALID;
+        t->answer_nsec_ttl = (uint32_t) -1;
+        t->key = dns_resource_key_ref(key);
+        t->current_feature_level = _DNS_SERVER_FEATURE_LEVEL_INVALID;
+        t->clamp_feature_level = _DNS_SERVER_FEATURE_LEVEL_INVALID;
+
+        t->id = pick_new_id(s->manager);
+
+        r = hashmap_put(s->manager->dns_transactions, UINT_TO_PTR(t->id), t);
+        if (r < 0) {
+                t->id = 0;
+                return r;
+        }
+
+        r = hashmap_replace(s->transactions_by_key, t->key, t);
+        if (r < 0) {
+                hashmap_remove(s->manager->dns_transactions, UINT_TO_PTR(t->id));
+                return r;
+        }
+
+        LIST_PREPEND(transactions_by_scope, s->transactions, t);
+        t->scope = s;
+
+        s->manager->n_transactions_total++;
+
+        if (ret)
+                *ret = t;
+
+        t = NULL;
+
+        return 0;
+}
+
+static void dns_transaction_shuffle_id(DnsTransaction *t) {
+        uint16_t new_id;
+        assert(t);
+
+        /* Pick a new ID for this transaction. */
+
+        new_id = pick_new_id(t->scope->manager);
+        assert_se(hashmap_remove_and_put(t->scope->manager->dns_transactions, UINT_TO_PTR(t->id), UINT_TO_PTR(new_id), t) >= 0);
+
+        log_debug("Transaction %" PRIu16 " is now %" PRIu16 ".", t->id, new_id);
+        t->id = new_id;
+
+        /* Make sure we generate a new packet with the new ID */
+        t->sent = dns_packet_unref(t->sent);
+}
+
+static void dns_transaction_tentative(DnsTransaction *t, DnsPacket *p) {
+        _cleanup_free_ char *pretty = NULL;
+        char key_str[DNS_RESOURCE_KEY_STRING_MAX];
+        DnsZoneItem *z;
+
+        assert(t);
+        assert(p);
+
+        if (manager_our_packet(t->scope->manager, p) != 0)
+                return;
+
+        (void) in_addr_to_string(p->family, &p->sender, &pretty);
+
+        log_debug("Transaction %" PRIu16 " for <%s> on scope %s on %s/%s got tentative packet from %s.",
+                  t->id,
+                  dns_resource_key_to_string(t->key, key_str, sizeof key_str),
+                  dns_protocol_to_string(t->scope->protocol),
+                  t->scope->link ? t->scope->link->name : "*",
+                  af_to_name_short(t->scope->family),
+                  strnull(pretty));
+
+        /* RFC 4795, Section 4.1 says that the peer with the
+         * lexicographically smaller IP address loses */
+        if (memcmp(&p->sender, &p->destination, FAMILY_ADDRESS_SIZE(p->family)) >= 0) {
+                log_debug("Peer has lexicographically larger IP address and thus lost in the conflict.");
+                return;
+        }
+
+        log_debug("We have the lexicographically larger IP address and thus lost in the conflict.");
+
+        t->block_gc++;
+
+        while ((z = set_first(t->notify_zone_items))) {
+                /* First, make sure the zone item drops the reference
+                 * to us */
+                dns_zone_item_probe_stop(z);
+
+                /* Secondly, report this as conflict, so that we might
+                 * look for a different hostname */
+                dns_zone_item_conflict(z);
+        }
+        t->block_gc--;
+
+        dns_transaction_gc(t);
+}
+
+void dns_transaction_complete(DnsTransaction *t, DnsTransactionState state) {
+        DnsQueryCandidate *c;
+        DnsZoneItem *z;
+        DnsTransaction *d;
+        const char *st;
+        char key_str[DNS_RESOURCE_KEY_STRING_MAX];
+
+        assert(t);
+        assert(!DNS_TRANSACTION_IS_LIVE(state));
+
+        if (state == DNS_TRANSACTION_DNSSEC_FAILED) {
+                dns_resource_key_to_string(t->key, key_str, sizeof key_str);
+
+                log_struct(LOG_NOTICE,
+                           "MESSAGE_ID=" SD_MESSAGE_DNSSEC_FAILURE_STR,
+                           LOG_MESSAGE("DNSSEC validation failed for question %s: %s", key_str, dnssec_result_to_string(t->answer_dnssec_result)),
+                           "DNS_TRANSACTION=%" PRIu16, t->id,
+                           "DNS_QUESTION=%s", key_str,
+                           "DNSSEC_RESULT=%s", dnssec_result_to_string(t->answer_dnssec_result),
+                           "DNS_SERVER=%s", dns_server_string(t->server),
+                           "DNS_SERVER_FEATURE_LEVEL=%s", dns_server_feature_level_to_string(t->server->possible_feature_level));
+        }
+
+        /* Note that this call might invalidate the query. Callers
+         * should hence not attempt to access the query or transaction
+         * after calling this function. */
+
+        if (state == DNS_TRANSACTION_ERRNO)
+                st = errno_to_name(t->answer_errno);
+        else
+                st = dns_transaction_state_to_string(state);
+
+        log_debug("Transaction %" PRIu16 " for <%s> on scope %s on %s/%s now complete with <%s> from %s (%s).",
+                  t->id,
+                  dns_resource_key_to_string(t->key, key_str, sizeof key_str),
+                  dns_protocol_to_string(t->scope->protocol),
+                  t->scope->link ? t->scope->link->name : "*",
+                  af_to_name_short(t->scope->family),
+                  st,
+                  t->answer_source < 0 ? "none" : dns_transaction_source_to_string(t->answer_source),
+                  t->answer_authenticated ? "authenticated" : "unsigned");
+
+        t->state = state;
+
+        dns_transaction_close_connection(t);
+        dns_transaction_stop_timeout(t);
+
+        /* Notify all queries that are interested, but make sure the
+         * transaction isn't freed while we are still looking at it */
+        t->block_gc++;
+
+        SET_FOREACH_MOVE(c, t->notify_query_candidates_done, t->notify_query_candidates)
+                dns_query_candidate_notify(c);
+        SWAP_TWO(t->notify_query_candidates, t->notify_query_candidates_done);
+
+        SET_FOREACH_MOVE(z, t->notify_zone_items_done, t->notify_zone_items)
+                dns_zone_item_notify(z);
+        SWAP_TWO(t->notify_zone_items, t->notify_zone_items_done);
+        if (t->probing && t->state == DNS_TRANSACTION_ATTEMPTS_MAX_REACHED)
+                (void) dns_scope_announce(t->scope, false);
+
+        SET_FOREACH_MOVE(d, t->notify_transactions_done, t->notify_transactions)
+                dns_transaction_notify(d, t);
+        SWAP_TWO(t->notify_transactions, t->notify_transactions_done);
+
+        t->block_gc--;
+        dns_transaction_gc(t);
+}
+
+static int dns_transaction_pick_server(DnsTransaction *t) {
+        DnsServer *server;
+
+        assert(t);
+        assert(t->scope->protocol == DNS_PROTOCOL_DNS);
+
+        /* Pick a DNS server and a feature level for it. */
+
+        server = dns_scope_get_dns_server(t->scope);
+        if (!server)
+                return -ESRCH;
+
+        /* If we changed the server invalidate the feature level clamping, as the new server might have completely
+         * different properties. */
+        if (server != t->server)
+                t->clamp_feature_level = _DNS_SERVER_FEATURE_LEVEL_INVALID;
+
+        t->current_feature_level = dns_server_possible_feature_level(server);
+
+        /* Clamp the feature level if that is requested. */
+        if (t->clamp_feature_level != _DNS_SERVER_FEATURE_LEVEL_INVALID &&
+            t->current_feature_level > t->clamp_feature_level)
+                t->current_feature_level = t->clamp_feature_level;
+
+        log_debug("Using feature level %s for transaction %u.", dns_server_feature_level_to_string(t->current_feature_level), t->id);
+
+        if (server == t->server)
+                return 0;
+
+        dns_server_unref(t->server);
+        t->server = dns_server_ref(server);
+
+        t->n_picked_servers ++;
+
+        log_debug("Using DNS server %s for transaction %u.", dns_server_string(t->server), t->id);
+
+        return 1;
+}
+
+static void dns_transaction_retry(DnsTransaction *t, bool next_server) {
+        int r;
+
+        assert(t);
+
+        log_debug("Retrying transaction %" PRIu16 ".", t->id);
+
+        /* Before we try again, switch to a new server. */
+        if (next_server)
+                dns_scope_next_dns_server(t->scope);
+
+        r = dns_transaction_go(t);
+        if (r < 0) {
+                t->answer_errno = -r;
+                dns_transaction_complete(t, DNS_TRANSACTION_ERRNO);
+        }
+}
+
+static int dns_transaction_maybe_restart(DnsTransaction *t) {
+        int r;
+
+        assert(t);
+
+        /* Returns > 0 if the transaction was restarted, 0 if not */
+
+        if (!t->server)
+                return 0;
+
+        if (t->current_feature_level <= dns_server_possible_feature_level(t->server))
+                return 0;
+
+        /* The server's current feature level is lower than when we sent the original query. We learnt something from
+           the response or possibly an auxiliary DNSSEC response that we didn't know before.  We take that as reason to
+           restart the whole transaction. This is a good idea to deal with servers that respond rubbish if we include
+           OPT RR or DO bit. One of these cases is documented here, for example:
+           https://open.nlnetlabs.nl/pipermail/dnssec-trigger/2014-November/000376.html */
+
+        log_debug("Server feature level is now lower than when we began our transaction. Restarting with new ID.");
+        dns_transaction_shuffle_id(t);
+
+        r = dns_transaction_go(t);
+        if (r < 0)
+                return r;
+
+        return 1;
+}
+
+static void on_transaction_stream_error(DnsTransaction *t, int error) {
+        assert(t);
+
+        dns_transaction_close_connection(t);
+
+        if (ERRNO_IS_DISCONNECT(error)) {
+                if (t->scope->protocol == DNS_PROTOCOL_LLMNR) {
+                        /* If the LLMNR/TCP connection failed, the host doesn't support LLMNR, and we cannot answer the
+                         * question on this scope. */
+                        dns_transaction_complete(t, DNS_TRANSACTION_NOT_FOUND);
+                        return;
+                }
+
+                dns_transaction_retry(t, true);
+                return;
+        }
+        if (error != 0) {
+                t->answer_errno = error;
+                dns_transaction_complete(t, DNS_TRANSACTION_ERRNO);
+        }
+}
+
+static int dns_transaction_on_stream_packet(DnsTransaction *t, DnsPacket *p) {
+        assert(t);
+        assert(p);
+
+        dns_transaction_close_connection(t);
+
+        if (dns_packet_validate_reply(p) <= 0) {
+                log_debug("Invalid TCP reply packet.");
+                dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
+                return 0;
+        }
+
+        dns_scope_check_conflicts(t->scope, p);
+
+        t->block_gc++;
+        dns_transaction_process_reply(t, p);
+        t->block_gc--;
+
+        /* If the response wasn't useful, then complete the transition
+         * now. After all, we are the worst feature set now with TCP
+         * sockets, and there's really no point in retrying. */
+        if (t->state == DNS_TRANSACTION_PENDING)
+                dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
+        else
+                dns_transaction_gc(t);
+
+        return 0;
+}
+
+static int on_stream_complete(DnsStream *s, int error) {
+        assert(s);
+
+        if (ERRNO_IS_DISCONNECT(error) && s->protocol != DNS_PROTOCOL_LLMNR) {
+                log_debug_errno(error, "Connection failure for DNS TCP stream: %m");
+
+                if (s->transactions) {
+                        DnsTransaction *t;
+
+                        t = s->transactions;
+                        dns_server_packet_lost(t->server, IPPROTO_TCP, t->current_feature_level);
+                }
+        }
+
+        if (error != 0) {
+                DnsTransaction *t, *n;
+
+                LIST_FOREACH_SAFE(transactions_by_stream, t, n, s->transactions)
+                        on_transaction_stream_error(t, error);
+        }
+
+        return 0;
+}
+
+static int on_stream_packet(DnsStream *s) {
+        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
+        DnsTransaction *t;
+
+        assert(s);
+
+        /* Take ownership of packet to be able to receive new packets */
+        p = dns_stream_take_read_packet(s);
+        assert(p);
+
+        t = hashmap_get(s->manager->dns_transactions, UINT_TO_PTR(DNS_PACKET_ID(p)));
+        if (t)
+                return dns_transaction_on_stream_packet(t, p);
+
+        /* Ignore incorrect transaction id as transaction can have been canceled */
+        if (dns_packet_validate_reply(p) <= 0) {
+                log_debug("Invalid TCP reply packet.");
+                on_stream_complete(s, 0);
+        }
+
+        return 0;
+}
+
+static uint16_t dns_port_for_feature_level(DnsServerFeatureLevel level) {
+        return DNS_SERVER_FEATURE_LEVEL_IS_TLS(level) ? 853 : 53;
+}
+
+static int dns_transaction_emit_tcp(DnsTransaction *t) {
+        _cleanup_close_ int fd = -1;
+        _cleanup_(dns_stream_unrefp) DnsStream *s = NULL;
+        union sockaddr_union sa;
+        int r;
+
+        assert(t);
+
+        dns_transaction_close_connection(t);
+
+        switch (t->scope->protocol) {
+
+        case DNS_PROTOCOL_DNS:
+                r = dns_transaction_pick_server(t);
+                if (r < 0)
+                        return r;
+
+                if (!dns_server_dnssec_supported(t->server) && dns_type_is_dnssec(t->key->type))
+                        return -EOPNOTSUPP;
+
+                r = dns_server_adjust_opt(t->server, t->sent, t->current_feature_level);
+                if (r < 0)
+                        return r;
+
+                if (t->server->stream && (DNS_SERVER_FEATURE_LEVEL_IS_TLS(t->current_feature_level) == t->server->stream->encrypted))
+                        s = dns_stream_ref(t->server->stream);
+                else
+                        fd = dns_scope_socket_tcp(t->scope, AF_UNSPEC, NULL, t->server, dns_port_for_feature_level(t->current_feature_level), &sa);
+
+                break;
+
+        case DNS_PROTOCOL_LLMNR:
+                /* When we already received a reply to this (but it was truncated), send to its sender address */
+                if (t->received)
+                        fd = dns_scope_socket_tcp(t->scope, t->received->family, &t->received->sender, NULL, t->received->sender_port, &sa);
+                else {
+                        union in_addr_union address;
+                        int family = AF_UNSPEC;
+
+                        /* Otherwise, try to talk to the owner of a
+                         * the IP address, in case this is a reverse
+                         * PTR lookup */
+
+                        r = dns_name_address(dns_resource_key_name(t->key), &family, &address);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                return -EINVAL;
+                        if (family != t->scope->family)
+                                return -ESRCH;
+
+                        fd = dns_scope_socket_tcp(t->scope, family, &address, NULL, LLMNR_PORT, &sa);
+                }
+
+                break;
+
+        default:
+                return -EAFNOSUPPORT;
+        }
+
+        if (!s) {
+                if (fd < 0)
+                        return fd;
+
+                r = dns_stream_new(t->scope->manager, &s, t->scope->protocol, fd, &sa);
+                if (r < 0)
+                        return r;
+
+                fd = -1;
+
+#if ENABLE_DNS_OVER_TLS
+                if (t->scope->protocol == DNS_PROTOCOL_DNS &&
+                    DNS_SERVER_FEATURE_LEVEL_IS_TLS(t->current_feature_level)) {
+
+                        assert(t->server);
+                        r = dnstls_stream_connect_tls(s, t->server);
+                        if (r < 0)
+                                return r;
+                }
+#endif
+
+                if (t->server) {
+                        dns_server_unref_stream(t->server);
+                        t->server->stream = dns_stream_ref(s);
+                        s->server = dns_server_ref(t->server);
+                }
+
+                s->complete = on_stream_complete;
+                s->on_packet = on_stream_packet;
+
+                /* The interface index is difficult to determine if we are
+                 * connecting to the local host, hence fill this in right away
+                 * instead of determining it from the socket */
+                s->ifindex = dns_scope_ifindex(t->scope);
+        }
+
+        t->stream = TAKE_PTR(s);
+        LIST_PREPEND(transactions_by_stream, t->stream->transactions, t);
+
+        r = dns_stream_write_packet(t->stream, t->sent);
+        if (r < 0) {
+                dns_transaction_close_connection(t);
+                return r;
+        }
+
+        dns_transaction_reset_answer(t);
+
+        t->tried_stream = true;
+
+        return 0;
+}
+
+static void dns_transaction_cache_answer(DnsTransaction *t) {
+        assert(t);
+
+        /* For mDNS we cache whenever we get the packet, rather than
+         * in each transaction. */
+        if (!IN_SET(t->scope->protocol, DNS_PROTOCOL_DNS, DNS_PROTOCOL_LLMNR))
+                return;
+
+        /* Caching disabled? */
+        if (!t->scope->manager->enable_cache)
+                return;
+
+        /* We never cache if this packet is from the local host, under
+         * the assumption that a locally running DNS server would
+         * cache this anyway, and probably knows better when to flush
+         * the cache then we could. */
+        if (!DNS_PACKET_SHALL_CACHE(t->received))
+                return;
+
+        dns_cache_put(&t->scope->cache,
+                      t->key,
+                      t->answer_rcode,
+                      t->answer,
+                      t->answer_authenticated,
+                      t->answer_nsec_ttl,
+                      0,
+                      t->received->family,
+                      &t->received->sender);
+}
+
+static bool dns_transaction_dnssec_is_live(DnsTransaction *t) {
+        DnsTransaction *dt;
+        Iterator i;
+
+        assert(t);
+
+        SET_FOREACH(dt, t->dnssec_transactions, i)
+                if (DNS_TRANSACTION_IS_LIVE(dt->state))
+                        return true;
+
+        return false;
+}
+
+static int dns_transaction_dnssec_ready(DnsTransaction *t) {
+        DnsTransaction *dt;
+        Iterator i;
+
+        assert(t);
+
+        /* Checks whether the auxiliary DNSSEC transactions of our transaction have completed, or are still
+         * ongoing. Returns 0, if we aren't ready for the DNSSEC validation, positive if we are. */
+
+        SET_FOREACH(dt, t->dnssec_transactions, i) {
+
+                switch (dt->state) {
+
+                case DNS_TRANSACTION_NULL:
+                case DNS_TRANSACTION_PENDING:
+                case DNS_TRANSACTION_VALIDATING:
+                        /* Still ongoing */
+                        return 0;
+
+                case DNS_TRANSACTION_RCODE_FAILURE:
+                        if (!IN_SET(dt->answer_rcode, DNS_RCODE_NXDOMAIN, DNS_RCODE_SERVFAIL)) {
+                                log_debug("Auxiliary DNSSEC RR query failed with rcode=%s.", dns_rcode_to_string(dt->answer_rcode));
+                                goto fail;
+                        }
+
+                        /* Fall-through: NXDOMAIN/SERVFAIL is good enough for us. This is because some DNS servers
+                         * erronously return NXDOMAIN/SERVFAIL for empty non-terminals (Akamai...) or missing DS
+                         * records (Facebook), and we need to handle that nicely, when asking for parent SOA or similar
+                         * RRs to make unsigned proofs. */
+
+                case DNS_TRANSACTION_SUCCESS:
+                        /* All good. */
+                        break;
+
+                case DNS_TRANSACTION_DNSSEC_FAILED:
+                        /* We handle DNSSEC failures different from other errors, as we care about the DNSSEC
+                         * validationr result */
+
+                        log_debug("Auxiliary DNSSEC RR query failed validation: %s", dnssec_result_to_string(dt->answer_dnssec_result));
+                        t->answer_dnssec_result = dt->answer_dnssec_result; /* Copy error code over */
+                        dns_transaction_complete(t, DNS_TRANSACTION_DNSSEC_FAILED);
+                        return 0;
+
+                default:
+                        log_debug("Auxiliary DNSSEC RR query failed with %s", dns_transaction_state_to_string(dt->state));
+                        goto fail;
+                }
+        }
+
+        /* All is ready, we can go and validate */
+        return 1;
+
+fail:
+        t->answer_dnssec_result = DNSSEC_FAILED_AUXILIARY;
+        dns_transaction_complete(t, DNS_TRANSACTION_DNSSEC_FAILED);
+        return 0;
+}
+
+static void dns_transaction_process_dnssec(DnsTransaction *t) {
+        int r;
+
+        assert(t);
+
+        /* Are there ongoing DNSSEC transactions? If so, let's wait for them. */
+        r = dns_transaction_dnssec_ready(t);
+        if (r < 0)
+                goto fail;
+        if (r == 0) /* We aren't ready yet (or one of our auxiliary transactions failed, and we shouldn't validate now */
+                return;
+
+        /* See if we learnt things from the additional DNSSEC transactions, that we didn't know before, and better
+         * restart the lookup immediately. */
+        r = dns_transaction_maybe_restart(t);
+        if (r < 0)
+                goto fail;
+        if (r > 0) /* Transaction got restarted... */
+                return;
+
+        /* All our auxiliary DNSSEC transactions are complete now. Try
+         * to validate our RRset now. */
+        r = dns_transaction_validate_dnssec(t);
+        if (r == -EBADMSG) {
+                dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
+                return;
+        }
+        if (r < 0)
+                goto fail;
+
+        if (t->answer_dnssec_result == DNSSEC_INCOMPATIBLE_SERVER &&
+            t->scope->dnssec_mode == DNSSEC_YES) {
+
+                /*  We are not in automatic downgrade mode, and the server is bad. Let's try a different server, maybe
+                 *  that works. */
+
+                if (t->n_picked_servers < dns_scope_get_n_dns_servers(t->scope)) {
+                        /* We tried fewer servers on this transaction than we know, let's try another one then */
+                        dns_transaction_retry(t, true);
+                        return;
+                }
+
+                /* OK, let's give up, apparently all servers we tried didn't work. */
+                dns_transaction_complete(t, DNS_TRANSACTION_DNSSEC_FAILED);
+                return;
+        }
+
+        if (!IN_SET(t->answer_dnssec_result,
+                    _DNSSEC_RESULT_INVALID,        /* No DNSSEC validation enabled */
+                    DNSSEC_VALIDATED,              /* Answer is signed and validated successfully */
+                    DNSSEC_UNSIGNED,               /* Answer is right-fully unsigned */
+                    DNSSEC_INCOMPATIBLE_SERVER)) { /* Server does not do DNSSEC (Yay, we are downgrade attack vulnerable!) */
+                dns_transaction_complete(t, DNS_TRANSACTION_DNSSEC_FAILED);
+                return;
+        }
+
+        if (t->answer_dnssec_result == DNSSEC_INCOMPATIBLE_SERVER)
+                dns_server_warn_downgrade(t->server);
+
+        dns_transaction_cache_answer(t);
+
+        if (t->answer_rcode == DNS_RCODE_SUCCESS)
+                dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
+        else
+                dns_transaction_complete(t, DNS_TRANSACTION_RCODE_FAILURE);
+
+        return;
+
+fail:
+        t->answer_errno = -r;
+        dns_transaction_complete(t, DNS_TRANSACTION_ERRNO);
+}
+
+static int dns_transaction_has_positive_answer(DnsTransaction *t, DnsAnswerFlags *flags) {
+        int r;
+
+        assert(t);
+
+        /* Checks whether the answer is positive, i.e. either a direct
+         * answer to the question, or a CNAME/DNAME for it */
+
+        r = dns_answer_match_key(t->answer, t->key, flags);
+        if (r != 0)
+                return r;
+
+        r = dns_answer_find_cname_or_dname(t->answer, t->key, NULL, flags);
+        if (r != 0)
+                return r;
+
+        return false;
+}
+
+static int dns_transaction_fix_rcode(DnsTransaction *t) {
+        int r;
+
+        assert(t);
+
+        /* Fix up the RCODE to SUCCESS if we get at least one matching RR in a response. Note that this contradicts the
+         * DNS RFCs a bit. Specifically, RFC 6604 Section 3 clarifies that the RCODE shall say something about a
+         * CNAME/DNAME chain element coming after the last chain element contained in the message, and not the first
+         * one included. However, it also indicates that not all DNS servers implement this correctly. Moreover, when
+         * using DNSSEC we usually only can prove the first element of a CNAME/DNAME chain anyway, hence let's settle
+         * on always processing the RCODE as referring to the immediate look-up we do, i.e. the first element of a
+         * CNAME/DNAME chain. This way, we uniformly handle CNAME/DNAME chains, regardless if the DNS server
+         * incorrectly implements RCODE, whether DNSSEC is in use, or whether the DNS server only supplied us with an
+         * incomplete CNAME/DNAME chain.
+         *
+         * Or in other words: if we get at least one positive reply in a message we patch NXDOMAIN to become SUCCESS,
+         * and then rely on the CNAME chasing logic to figure out that there's actually a CNAME error with a new
+         * lookup. */
+
+        if (t->answer_rcode != DNS_RCODE_NXDOMAIN)
+                return 0;
+
+        r = dns_transaction_has_positive_answer(t, NULL);
+        if (r <= 0)
+                return r;
+
+        t->answer_rcode = DNS_RCODE_SUCCESS;
+        return 0;
+}
+
+void dns_transaction_process_reply(DnsTransaction *t, DnsPacket *p) {
+        usec_t ts;
+        int r;
+
+        assert(t);
+        assert(p);
+        assert(t->scope);
+        assert(t->scope->manager);
+
+        if (t->state != DNS_TRANSACTION_PENDING)
+                return;
+
+        /* Note that this call might invalidate the query. Callers
+         * should hence not attempt to access the query or transaction
+         * after calling this function. */
+
+        log_debug("Processing incoming packet on transaction %" PRIu16" (rcode=%s).",
+                  t->id, dns_rcode_to_string(DNS_PACKET_RCODE(p)));
+
+        switch (t->scope->protocol) {
+
+        case DNS_PROTOCOL_LLMNR:
+                /* For LLMNR we will not accept any packets from other interfaces */
+
+                if (p->ifindex != dns_scope_ifindex(t->scope))
+                        return;
+
+                if (p->family != t->scope->family)
+                        return;
+
+                /* Tentative packets are not full responses but still
+                 * useful for identifying uniqueness conflicts during
+                 * probing. */
+                if (DNS_PACKET_LLMNR_T(p)) {
+                        dns_transaction_tentative(t, p);
+                        return;
+                }
+
+                break;
+
+        case DNS_PROTOCOL_MDNS:
+                /* For mDNS we will not accept any packets from other interfaces */
+
+                if (p->ifindex != dns_scope_ifindex(t->scope))
+                        return;
+
+                if (p->family != t->scope->family)
+                        return;
+
+                break;
+
+        case DNS_PROTOCOL_DNS:
+                /* Note that we do not need to verify the
+                 * addresses/port numbers of incoming traffic, as we
+                 * invoked connect() on our UDP socket in which case
+                 * the kernel already does the needed verification for
+                 * us. */
+                break;
+
+        default:
+                assert_not_reached("Invalid DNS protocol.");
+        }
+
+        if (t->received != p) {
+                dns_packet_unref(t->received);
+                t->received = dns_packet_ref(p);
+        }
+
+        t->answer_source = DNS_TRANSACTION_NETWORK;
+
+        if (p->ipproto == IPPROTO_TCP) {
+                if (DNS_PACKET_TC(p)) {
+                        /* Truncated via TCP? Somebody must be fucking with us */
+                        dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
+                        return;
+                }
+
+                if (DNS_PACKET_ID(p) != t->id) {
+                        /* Not the reply to our query? Somebody must be fucking with us */
+                        dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
+                        return;
+                }
+        }
+
+        assert_se(sd_event_now(t->scope->manager->event, clock_boottime_or_monotonic(), &ts) >= 0);
+
+        switch (t->scope->protocol) {
+
+        case DNS_PROTOCOL_DNS:
+                assert(t->server);
+
+                if (IN_SET(DNS_PACKET_RCODE(p), DNS_RCODE_FORMERR, DNS_RCODE_SERVFAIL, DNS_RCODE_NOTIMP)) {
+
+                        /* Request failed, immediately try again with reduced features */
+
+                        if (t->current_feature_level <= DNS_SERVER_FEATURE_LEVEL_UDP) {
+
+                                /* This was already at UDP feature level? If so, it doesn't make sense to downgrade
+                                 * this transaction anymore, but let's see if it might make sense to send the request
+                                 * to a different DNS server instead. If not let's process the response, and accept the
+                                 * rcode. Note that we don't retry on TCP, since that's a suitable way to mitigate
+                                 * packet loss, but is not going to give us better rcodes should we actually have
+                                 * managed to get them already at UDP level. */
+
+                                if (t->n_picked_servers < dns_scope_get_n_dns_servers(t->scope)) {
+                                        /* We tried fewer servers on this transaction than we know, let's try another one then */
+                                        dns_transaction_retry(t, true);
+                                        return;
+                                }
+
+                                /* Give up, accept the rcode */
+                                log_debug("Server returned error: %s", dns_rcode_to_string(DNS_PACKET_RCODE(p)));
+                                break;
+                        }
+
+                        /* Reduce this feature level by one and try again. */
+                        switch (t->current_feature_level) {
+                        case DNS_SERVER_FEATURE_LEVEL_TLS_DO:
+                                t->clamp_feature_level = DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN;
+                                break;
+                        case DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN + 1:
+                                /* Skip plain TLS when TLS is not supported */
+                                t->clamp_feature_level = DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN - 1;
+                                break;
+                        default:
+                                t->clamp_feature_level = t->current_feature_level - 1;
+                        }
+
+                        log_debug("Server returned error %s, retrying transaction with reduced feature level %s.",
+                                  dns_rcode_to_string(DNS_PACKET_RCODE(p)),
+                                  dns_server_feature_level_to_string(t->clamp_feature_level));
+
+                        dns_transaction_retry(t, false /* use the same server */);
+                        return;
+                }
+
+                if (DNS_PACKET_RCODE(p) == DNS_RCODE_REFUSED) {
+                        /* This server refused our request? If so, try again, use a different server */
+                        log_debug("Server returned REFUSED, switching servers, and retrying.");
+                        dns_transaction_retry(t, true /* pick a new server */);
+                        return;
+                }
+
+                if (DNS_PACKET_TC(p))
+                        dns_server_packet_truncated(t->server, t->current_feature_level);
+
+                break;
+
+        case DNS_PROTOCOL_LLMNR:
+        case DNS_PROTOCOL_MDNS:
+                dns_scope_packet_received(t->scope, ts - t->start_usec);
+                break;
+
+        default:
+                assert_not_reached("Invalid DNS protocol.");
+        }
+
+        if (DNS_PACKET_TC(p)) {
+
+                /* Truncated packets for mDNS are not allowed. Give up immediately. */
+                if (t->scope->protocol == DNS_PROTOCOL_MDNS) {
+                        dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
+                        return;
+                }
+
+                log_debug("Reply truncated, retrying via TCP.");
+
+                /* Response was truncated, let's try again with good old TCP */
+                r = dns_transaction_emit_tcp(t);
+                if (r == -ESRCH) {
+                        /* No servers found? Damn! */
+                        dns_transaction_complete(t, DNS_TRANSACTION_NO_SERVERS);
+                        return;
+                }
+                if (r == -EOPNOTSUPP) {
+                        /* Tried to ask for DNSSEC RRs, on a server that doesn't do DNSSEC  */
+                        dns_transaction_complete(t, DNS_TRANSACTION_RR_TYPE_UNSUPPORTED);
+                        return;
+                }
+                if (r < 0) {
+                        /* On LLMNR, if we cannot connect to the host,
+                         * we immediately give up */
+                        if (t->scope->protocol != DNS_PROTOCOL_DNS)
+                                goto fail;
+
+                        /* On DNS, couldn't send? Try immediately again, with a new server */
+                        dns_transaction_retry(t, true);
+                }
+
+                return;
+        }
+
+        /* After the superficial checks, actually parse the message. */
+        r = dns_packet_extract(p);
+        if (r < 0) {
+                dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
+                return;
+        }
+
+        if (t->server) {
+                /* Report that we successfully received a valid packet with a good rcode after we initially got a bad
+                 * rcode and subsequently downgraded the protocol */
+
+                if (IN_SET(DNS_PACKET_RCODE(p), DNS_RCODE_SUCCESS, DNS_RCODE_NXDOMAIN) &&
+                    t->clamp_feature_level != _DNS_SERVER_FEATURE_LEVEL_INVALID)
+                        dns_server_packet_rcode_downgrade(t->server, t->clamp_feature_level);
+
+                /* Report that the OPT RR was missing */
+                if (!p->opt)
+                        dns_server_packet_bad_opt(t->server, t->current_feature_level);
+
+                /* Report that we successfully received a packet */
+                dns_server_packet_received(t->server, p->ipproto, t->current_feature_level, p->size);
+        }
+
+        /* See if we know things we didn't know before that indicate we better restart the lookup immediately. */
+        r = dns_transaction_maybe_restart(t);
+        if (r < 0)
+                goto fail;
+        if (r > 0) /* Transaction got restarted... */
+                return;
+
+        if (IN_SET(t->scope->protocol, DNS_PROTOCOL_DNS, DNS_PROTOCOL_LLMNR, DNS_PROTOCOL_MDNS)) {
+
+                /* When dealing with protocols other than mDNS only consider responses with
+                 * equivalent query section to the request. For mDNS this check doesn't make
+                 * sense, because the section 6 of RFC6762 states that "Multicast DNS responses MUST NOT
+                 * contain any questions in the Question Section". */
+                if (t->scope->protocol != DNS_PROTOCOL_MDNS) {
+                        r = dns_packet_is_reply_for(p, t->key);
+                        if (r < 0)
+                                goto fail;
+                        if (r == 0) {
+                                dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
+                                return;
+                        }
+                }
+
+                /* Install the answer as answer to the transaction */
+                dns_answer_unref(t->answer);
+                t->answer = dns_answer_ref(p->answer);
+                t->answer_rcode = DNS_PACKET_RCODE(p);
+                t->answer_dnssec_result = _DNSSEC_RESULT_INVALID;
+                t->answer_authenticated = false;
+
+                r = dns_transaction_fix_rcode(t);
+                if (r < 0)
+                        goto fail;
+
+                /* Block GC while starting requests for additional DNSSEC RRs */
+                t->block_gc++;
+                r = dns_transaction_request_dnssec_keys(t);
+                t->block_gc--;
+
+                /* Maybe the transaction is ready for GC'ing now? If so, free it and return. */
+                if (!dns_transaction_gc(t))
+                        return;
+
+                /* Requesting additional keys might have resulted in
+                 * this transaction to fail, since the auxiliary
+                 * request failed for some reason. If so, we are not
+                 * in pending state anymore, and we should exit
+                 * quickly. */
+                if (t->state != DNS_TRANSACTION_PENDING)
+                        return;
+                if (r < 0)
+                        goto fail;
+                if (r > 0) {
+                        /* There are DNSSEC transactions pending now. Update the state accordingly. */
+                        t->state = DNS_TRANSACTION_VALIDATING;
+                        dns_transaction_close_connection(t);
+                        dns_transaction_stop_timeout(t);
+                        return;
+                }
+        }
+
+        dns_transaction_process_dnssec(t);
+        return;
+
+fail:
+        t->answer_errno = -r;
+        dns_transaction_complete(t, DNS_TRANSACTION_ERRNO);
+}
+
+static int on_dns_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
+        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
+        DnsTransaction *t = userdata;
+        int r;
+
+        assert(t);
+        assert(t->scope);
+
+        r = manager_recv(t->scope->manager, fd, DNS_PROTOCOL_DNS, &p);
+        if (ERRNO_IS_DISCONNECT(-r)) {
+                usec_t usec;
+
+                /* UDP connection failure get reported via ICMP and then are possible delivered to us on the next
+                 * recvmsg(). Treat this like a lost packet. */
+
+                log_debug_errno(r, "Connection failure for DNS UDP packet: %m");
+                assert_se(sd_event_now(t->scope->manager->event, clock_boottime_or_monotonic(), &usec) >= 0);
+                dns_server_packet_lost(t->server, IPPROTO_UDP, t->current_feature_level);
+
+                dns_transaction_retry(t, true);
+                return 0;
+        }
+        if (r < 0) {
+                dns_transaction_complete(t, DNS_TRANSACTION_ERRNO);
+                t->answer_errno = -r;
+                return 0;
+        }
+
+        r = dns_packet_validate_reply(p);
+        if (r < 0) {
+                log_debug_errno(r, "Received invalid DNS packet as response, ignoring: %m");
+                return 0;
+        }
+        if (r == 0) {
+                log_debug("Received inappropriate DNS packet as response, ignoring.");
+                return 0;
+        }
+
+        if (DNS_PACKET_ID(p) != t->id) {
+                log_debug("Received packet with incorrect transaction ID, ignoring.");
+                return 0;
+        }
+
+        dns_transaction_process_reply(t, p);
+        return 0;
+}
+
+static int dns_transaction_emit_udp(DnsTransaction *t) {
+        int r;
+
+        assert(t);
+
+        if (t->scope->protocol == DNS_PROTOCOL_DNS) {
+
+                r = dns_transaction_pick_server(t);
+                if (r < 0)
+                        return r;
+
+                if (t->current_feature_level < DNS_SERVER_FEATURE_LEVEL_UDP || DNS_SERVER_FEATURE_LEVEL_IS_TLS(t->current_feature_level))
+                        return -EAGAIN; /* Sorry, can't do UDP, try TCP! */
+
+                if (!dns_server_dnssec_supported(t->server) && dns_type_is_dnssec(t->key->type))
+                        return -EOPNOTSUPP;
+
+                if (r > 0 || t->dns_udp_fd < 0) { /* Server changed, or no connection yet. */
+                        int fd;
+
+                        dns_transaction_close_connection(t);
+
+                        fd = dns_scope_socket_udp(t->scope, t->server, 53);
+                        if (fd < 0)
+                                return fd;
+
+                        r = sd_event_add_io(t->scope->manager->event, &t->dns_udp_event_source, fd, EPOLLIN, on_dns_packet, t);
+                        if (r < 0) {
+                                safe_close(fd);
+                                return r;
+                        }
+
+                        (void) sd_event_source_set_description(t->dns_udp_event_source, "dns-transaction-udp");
+                        t->dns_udp_fd = fd;
+                }
+
+                r = dns_server_adjust_opt(t->server, t->sent, t->current_feature_level);
+                if (r < 0)
+                        return r;
+        } else
+                dns_transaction_close_connection(t);
+
+        r = dns_scope_emit_udp(t->scope, t->dns_udp_fd, t->sent);
+        if (r < 0)
+                return r;
+
+        dns_transaction_reset_answer(t);
+
+        return 0;
+}
+
+static int on_transaction_timeout(sd_event_source *s, usec_t usec, void *userdata) {
+        DnsTransaction *t = userdata;
+
+        assert(s);
+        assert(t);
+
+        if (!t->initial_jitter_scheduled || t->initial_jitter_elapsed) {
+                /* Timeout reached? Increase the timeout for the server used */
+                switch (t->scope->protocol) {
+
+                case DNS_PROTOCOL_DNS:
+                        assert(t->server);
+                        dns_server_packet_lost(t->server, t->stream ? IPPROTO_TCP : IPPROTO_UDP, t->current_feature_level);
+                        break;
+
+                case DNS_PROTOCOL_LLMNR:
+                case DNS_PROTOCOL_MDNS:
+                        dns_scope_packet_lost(t->scope, usec - t->start_usec);
+                        break;
+
+                default:
+                        assert_not_reached("Invalid DNS protocol.");
+                }
+
+                if (t->initial_jitter_scheduled)
+                        t->initial_jitter_elapsed = true;
+        }
+
+        log_debug("Timeout reached on transaction %" PRIu16 ".", t->id);
+
+        dns_transaction_retry(t, true);
+        return 0;
+}
+
+static usec_t transaction_get_resend_timeout(DnsTransaction *t) {
+        assert(t);
+        assert(t->scope);
+
+        switch (t->scope->protocol) {
+
+        case DNS_PROTOCOL_DNS:
+
+                /* When we do TCP, grant a much longer timeout, as in this case there's no need for us to quickly
+                 * resend, as the kernel does that anyway for us, and we really don't want to interrupt it in that
+                 * needlessly. */
+                if (t->stream)
+                        return TRANSACTION_TCP_TIMEOUT_USEC;
+
+                return DNS_TIMEOUT_USEC;
+
+        case DNS_PROTOCOL_MDNS:
+                assert(t->n_attempts > 0);
+                if (t->probing)
+                        return MDNS_PROBING_INTERVAL_USEC;
+                else
+                        return (1 << (t->n_attempts - 1)) * USEC_PER_SEC;
+
+        case DNS_PROTOCOL_LLMNR:
+                return t->scope->resend_timeout;
+
+        default:
+                assert_not_reached("Invalid DNS protocol.");
+        }
+}
+
+static int dns_transaction_prepare(DnsTransaction *t, usec_t ts) {
+        int r;
+
+        assert(t);
+
+        dns_transaction_stop_timeout(t);
+
+        if (!dns_scope_network_good(t->scope)) {
+                dns_transaction_complete(t, DNS_TRANSACTION_NETWORK_DOWN);
+                return 0;
+        }
+
+        if (t->n_attempts >= TRANSACTION_ATTEMPTS_MAX(t->scope->protocol)) {
+                dns_transaction_complete(t, DNS_TRANSACTION_ATTEMPTS_MAX_REACHED);
+                return 0;
+        }
+
+        if (t->scope->protocol == DNS_PROTOCOL_LLMNR && t->tried_stream) {
+                /* If we already tried via a stream, then we don't
+                 * retry on LLMNR. See RFC 4795, Section 2.7. */
+                dns_transaction_complete(t, DNS_TRANSACTION_ATTEMPTS_MAX_REACHED);
+                return 0;
+        }
+
+        t->n_attempts++;
+        t->start_usec = ts;
+
+        dns_transaction_reset_answer(t);
+        dns_transaction_flush_dnssec_transactions(t);
+
+        /* Check the trust anchor. Do so only on classic DNS, since DNSSEC does not apply otherwise. */
+        if (t->scope->protocol == DNS_PROTOCOL_DNS) {
+                r = dns_trust_anchor_lookup_positive(&t->scope->manager->trust_anchor, t->key, &t->answer);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        t->answer_rcode = DNS_RCODE_SUCCESS;
+                        t->answer_source = DNS_TRANSACTION_TRUST_ANCHOR;
+                        t->answer_authenticated = true;
+                        dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
+                        return 0;
+                }
+
+                if (dns_name_is_root(dns_resource_key_name(t->key)) &&
+                    t->key->type == DNS_TYPE_DS) {
+
+                        /* Hmm, this is a request for the root DS? A
+                         * DS RR doesn't exist in the root zone, and
+                         * if our trust anchor didn't know it either,
+                         * this means we cannot do any DNSSEC logic
+                         * anymore. */
+
+                        if (t->scope->dnssec_mode == DNSSEC_ALLOW_DOWNGRADE) {
+                                /* We are in downgrade mode. In this
+                                 * case, synthesize an unsigned empty
+                                 * response, so that the any lookup
+                                 * depending on this one can continue
+                                 * assuming there was no DS, and hence
+                                 * the root zone was unsigned. */
+
+                                t->answer_rcode = DNS_RCODE_SUCCESS;
+                                t->answer_source = DNS_TRANSACTION_TRUST_ANCHOR;
+                                t->answer_authenticated = false;
+                                dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
+                        } else
+                                /* If we are not in downgrade mode,
+                                 * then fail the lookup, because we
+                                 * cannot reasonably answer it. There
+                                 * might be DS RRs, but we don't know
+                                 * them, and the DNS server won't tell
+                                 * them to us (and even if it would,
+                                 * we couldn't validate and trust them. */
+                                dns_transaction_complete(t, DNS_TRANSACTION_NO_TRUST_ANCHOR);
+
+                        return 0;
+                }
+        }
+
+        /* Check the zone, but only if this transaction is not used
+         * for probing or verifying a zone item. */
+        if (set_isempty(t->notify_zone_items)) {
+
+                r = dns_zone_lookup(&t->scope->zone, t->key, dns_scope_ifindex(t->scope), &t->answer, NULL, NULL);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        t->answer_rcode = DNS_RCODE_SUCCESS;
+                        t->answer_source = DNS_TRANSACTION_ZONE;
+                        t->answer_authenticated = true;
+                        dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
+                        return 0;
+                }
+        }
+
+        /* Check the cache, but only if this transaction is not used
+         * for probing or verifying a zone item. */
+        if (set_isempty(t->notify_zone_items)) {
+
+                /* Before trying the cache, let's make sure we figured out a
+                 * server to use. Should this cause a change of server this
+                 * might flush the cache. */
+                (void) dns_scope_get_dns_server(t->scope);
+
+                /* Let's then prune all outdated entries */
+                dns_cache_prune(&t->scope->cache);
+
+                r = dns_cache_lookup(&t->scope->cache, t->key, t->clamp_ttl, &t->answer_rcode, &t->answer, &t->answer_authenticated);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        t->answer_source = DNS_TRANSACTION_CACHE;
+                        if (t->answer_rcode == DNS_RCODE_SUCCESS)
+                                dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
+                        else
+                                dns_transaction_complete(t, DNS_TRANSACTION_RCODE_FAILURE);
+                        return 0;
+                }
+        }
+
+        return 1;
+}
+
+static int dns_transaction_make_packet_mdns(DnsTransaction *t) {
+
+        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
+        bool add_known_answers = false;
+        DnsTransaction *other;
+        Iterator i;
+        DnsResourceKey *tkey;
+        _cleanup_set_free_ Set *keys = NULL;
+        unsigned qdcount;
+        unsigned nscount = 0;
+        usec_t ts;
+        int r;
+
+        assert(t);
+        assert(t->scope->protocol == DNS_PROTOCOL_MDNS);
+
+        /* Discard any previously prepared packet, so we can start over and coalesce again */
+        t->sent = dns_packet_unref(t->sent);
+
+        r = dns_packet_new_query(&p, t->scope->protocol, 0, false);
+        if (r < 0)
+                return r;
+
+        r = dns_packet_append_key(p, t->key, 0, NULL);
+        if (r < 0)
+                return r;
+
+        qdcount = 1;
+
+        if (dns_key_is_shared(t->key))
+                add_known_answers = true;
+
+        if (t->key->type == DNS_TYPE_ANY) {
+                r = set_ensure_allocated(&keys, &dns_resource_key_hash_ops);
+                if (r < 0)
+                        return r;
+
+                r = set_put(keys, t->key);
+                if (r < 0)
+                        return r;
+        }
+
+        /*
+         * For mDNS, we want to coalesce as many open queries in pending transactions into one single
+         * query packet on the wire as possible. To achieve that, we iterate through all pending transactions
+         * in our current scope, and see whether their timing contraints allow them to be sent.
+         */
+
+        assert_se(sd_event_now(t->scope->manager->event, clock_boottime_or_monotonic(), &ts) >= 0);
+
+        LIST_FOREACH(transactions_by_scope, other, t->scope->transactions) {
+
+                /* Skip ourselves */
+                if (other == t)
+                        continue;
+
+                if (other->state != DNS_TRANSACTION_PENDING)
+                        continue;
+
+                if (other->next_attempt_after > ts)
+                        continue;
+
+                if (qdcount >= UINT16_MAX)
+                        break;
+
+                r = dns_packet_append_key(p, other->key, 0, NULL);
+
+                /*
+                 * If we can't stuff more questions into the packet, just give up.
+                 * One of the 'other' transactions will fire later and take care of the rest.
+                 */
+                if (r == -EMSGSIZE)
+                        break;
+
+                if (r < 0)
+                        return r;
+
+                r = dns_transaction_prepare(other, ts);
+                if (r <= 0)
+                        continue;
+
+                ts += transaction_get_resend_timeout(other);
+
+                r = sd_event_add_time(
+                                other->scope->manager->event,
+                                &other->timeout_event_source,
+                                clock_boottime_or_monotonic(),
+                                ts, 0,
+                                on_transaction_timeout, other);
+                if (r < 0)
+                        return r;
+
+                (void) sd_event_source_set_description(other->timeout_event_source, "dns-transaction-timeout");
+
+                other->state = DNS_TRANSACTION_PENDING;
+                other->next_attempt_after = ts;
+
+                qdcount++;
+
+                if (dns_key_is_shared(other->key))
+                        add_known_answers = true;
+
+                if (other->key->type == DNS_TYPE_ANY) {
+                        r = set_ensure_allocated(&keys, &dns_resource_key_hash_ops);
+                        if (r < 0)
+                                return r;
+
+                        r = set_put(keys, other->key);
+                        if (r < 0)
+                                return r;
+                }
+        }
+
+        DNS_PACKET_HEADER(p)->qdcount = htobe16(qdcount);
+
+        /* Append known answer section if we're asking for any shared record */
+        if (add_known_answers) {
+                r = dns_cache_export_shared_to_packet(&t->scope->cache, p);
+                if (r < 0)
+                        return r;
+        }
+
+        SET_FOREACH(tkey, keys, i) {
+                _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
+                bool tentative;
+
+                r = dns_zone_lookup(&t->scope->zone, tkey, t->scope->link->ifindex, &answer, NULL, &tentative);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_append_answer(p, answer);
+                if (r < 0)
+                        return r;
+
+                nscount += dns_answer_size(answer);
+        }
+        DNS_PACKET_HEADER(p)->nscount = htobe16(nscount);
+
+        t->sent = TAKE_PTR(p);
+
+        return 0;
+}
+
+static int dns_transaction_make_packet(DnsTransaction *t) {
+        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
+        int r;
+
+        assert(t);
+
+        if (t->scope->protocol == DNS_PROTOCOL_MDNS)
+                return dns_transaction_make_packet_mdns(t);
+
+        if (t->sent)
+                return 0;
+
+        r = dns_packet_new_query(&p, t->scope->protocol, 0, t->scope->dnssec_mode != DNSSEC_NO);
+        if (r < 0)
+                return r;
+
+        r = dns_packet_append_key(p, t->key, 0, NULL);
+        if (r < 0)
+                return r;
+
+        DNS_PACKET_HEADER(p)->qdcount = htobe16(1);
+        DNS_PACKET_HEADER(p)->id = t->id;
+
+        t->sent = TAKE_PTR(p);
+
+        return 0;
+}
+
+int dns_transaction_go(DnsTransaction *t) {
+        usec_t ts;
+        int r;
+        char key_str[DNS_RESOURCE_KEY_STRING_MAX];
+
+        assert(t);
+
+        /* Returns > 0 if the transaction is now pending, returns 0 if could be processed immediately and has finished
+         * now. */
+
+        assert_se(sd_event_now(t->scope->manager->event, clock_boottime_or_monotonic(), &ts) >= 0);
+
+        r = dns_transaction_prepare(t, ts);
+        if (r <= 0)
+                return r;
+
+        log_debug("Transaction %" PRIu16 " for <%s> scope %s on %s/%s.",
+                  t->id,
+                  dns_resource_key_to_string(t->key, key_str, sizeof key_str),
+                  dns_protocol_to_string(t->scope->protocol),
+                  t->scope->link ? t->scope->link->name : "*",
+                  af_to_name_short(t->scope->family));
+
+        if (!t->initial_jitter_scheduled &&
+            IN_SET(t->scope->protocol, DNS_PROTOCOL_LLMNR, DNS_PROTOCOL_MDNS)) {
+                usec_t jitter, accuracy;
+
+                /* RFC 4795 Section 2.7 suggests all queries should be
+                 * delayed by a random time from 0 to JITTER_INTERVAL. */
+
+                t->initial_jitter_scheduled = true;
+
+                random_bytes(&jitter, sizeof(jitter));
+
+                switch (t->scope->protocol) {
+
+                case DNS_PROTOCOL_LLMNR:
+                        jitter %= LLMNR_JITTER_INTERVAL_USEC;
+                        accuracy = LLMNR_JITTER_INTERVAL_USEC;
+                        break;
+
+                case DNS_PROTOCOL_MDNS:
+                        jitter %= MDNS_JITTER_RANGE_USEC;
+                        jitter += MDNS_JITTER_MIN_USEC;
+                        accuracy = MDNS_JITTER_RANGE_USEC;
+                        break;
+                default:
+                        assert_not_reached("bad protocol");
+                }
+
+                r = sd_event_add_time(
+                                t->scope->manager->event,
+                                &t->timeout_event_source,
+                                clock_boottime_or_monotonic(),
+                                ts + jitter, accuracy,
+                                on_transaction_timeout, t);
+                if (r < 0)
+                        return r;
+
+                (void) sd_event_source_set_description(t->timeout_event_source, "dns-transaction-timeout");
+
+                t->n_attempts = 0;
+                t->next_attempt_after = ts;
+                t->state = DNS_TRANSACTION_PENDING;
+
+                log_debug("Delaying %s transaction for " USEC_FMT "us.", dns_protocol_to_string(t->scope->protocol), jitter);
+                return 0;
+        }
+
+        /* Otherwise, we need to ask the network */
+        r = dns_transaction_make_packet(t);
+        if (r < 0)
+                return r;
+
+        if (t->scope->protocol == DNS_PROTOCOL_LLMNR &&
+            (dns_name_endswith(dns_resource_key_name(t->key), "in-addr.arpa") > 0 ||
+             dns_name_endswith(dns_resource_key_name(t->key), "ip6.arpa") > 0)) {
+
+                /* RFC 4795, Section 2.4. says reverse lookups shall
+                 * always be made via TCP on LLMNR */
+                r = dns_transaction_emit_tcp(t);
+        } else {
+                /* Try via UDP, and if that fails due to large size or lack of
+                 * support try via TCP */
+                r = dns_transaction_emit_udp(t);
+                if (r == -EMSGSIZE)
+                        log_debug("Sending query via TCP since it is too large.");
+                else if (r == -EAGAIN)
+                        log_debug("Sending query via TCP since UDP isn't supported.");
+                if (IN_SET(r, -EMSGSIZE, -EAGAIN))
+                        r = dns_transaction_emit_tcp(t);
+        }
+
+        if (r == -ESRCH) {
+                /* No servers to send this to? */
+                dns_transaction_complete(t, DNS_TRANSACTION_NO_SERVERS);
+                return 0;
+        }
+        if (r == -EOPNOTSUPP) {
+                /* Tried to ask for DNSSEC RRs, on a server that doesn't do DNSSEC  */
+                dns_transaction_complete(t, DNS_TRANSACTION_RR_TYPE_UNSUPPORTED);
+                return 0;
+        }
+        if (t->scope->protocol == DNS_PROTOCOL_LLMNR && ERRNO_IS_DISCONNECT(-r)) {
+                /* On LLMNR, if we cannot connect to a host via TCP when doing reverse lookups. This means we cannot
+                 * answer this request with this protocol. */
+                dns_transaction_complete(t, DNS_TRANSACTION_NOT_FOUND);
+                return 0;
+        }
+        if (r < 0) {
+                if (t->scope->protocol != DNS_PROTOCOL_DNS)
+                        return r;
+
+                /* Couldn't send? Try immediately again, with a new server */
+                dns_scope_next_dns_server(t->scope);
+
+                return dns_transaction_go(t);
+        }
+
+        ts += transaction_get_resend_timeout(t);
+
+        r = sd_event_add_time(
+                        t->scope->manager->event,
+                        &t->timeout_event_source,
+                        clock_boottime_or_monotonic(),
+                        ts, 0,
+                        on_transaction_timeout, t);
+        if (r < 0)
+                return r;
+
+        (void) sd_event_source_set_description(t->timeout_event_source, "dns-transaction-timeout");
+
+        t->state = DNS_TRANSACTION_PENDING;
+        t->next_attempt_after = ts;
+
+        return 1;
+}
+
+static int dns_transaction_find_cyclic(DnsTransaction *t, DnsTransaction *aux) {
+        DnsTransaction *n;
+        Iterator i;
+        int r;
+
+        assert(t);
+        assert(aux);
+
+        /* Try to find cyclic dependencies between transaction objects */
+
+        if (t == aux)
+                return 1;
+
+        SET_FOREACH(n, aux->dnssec_transactions, i) {
+                r = dns_transaction_find_cyclic(t, n);
+                if (r != 0)
+                        return r;
+        }
+
+        return 0;
+}
+
+static int dns_transaction_add_dnssec_transaction(DnsTransaction *t, DnsResourceKey *key, DnsTransaction **ret) {
+        DnsTransaction *aux;
+        int r;
+
+        assert(t);
+        assert(ret);
+        assert(key);
+
+        aux = dns_scope_find_transaction(t->scope, key, true);
+        if (!aux) {
+                r = dns_transaction_new(&aux, t->scope, key);
+                if (r < 0)
+                        return r;
+        } else {
+                if (set_contains(t->dnssec_transactions, aux)) {
+                        *ret = aux;
+                        return 0;
+                }
+
+                r = dns_transaction_find_cyclic(t, aux);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        char s[DNS_RESOURCE_KEY_STRING_MAX], saux[DNS_RESOURCE_KEY_STRING_MAX];
+
+                        return log_debug_errno(SYNTHETIC_ERRNO(ELOOP),
+                                               "Potential cyclic dependency, refusing to add transaction %" PRIu16 " (%s) as dependency for %" PRIu16 " (%s).",
+                                               aux->id,
+                                               dns_resource_key_to_string(t->key, s, sizeof s),
+                                               t->id,
+                                               dns_resource_key_to_string(aux->key, saux, sizeof saux));
+                }
+        }
+
+        r = set_ensure_allocated(&t->dnssec_transactions, NULL);
+        if (r < 0)
+                goto gc;
+
+        r = set_ensure_allocated(&aux->notify_transactions, NULL);
+        if (r < 0)
+                goto gc;
+
+        r = set_ensure_allocated(&aux->notify_transactions_done, NULL);
+        if (r < 0)
+                goto gc;
+
+        r = set_put(t->dnssec_transactions, aux);
+        if (r < 0)
+                goto gc;
+
+        r = set_put(aux->notify_transactions, t);
+        if (r < 0) {
+                (void) set_remove(t->dnssec_transactions, aux);
+                goto gc;
+        }
+
+        *ret = aux;
+        return 1;
+
+gc:
+        dns_transaction_gc(aux);
+        return r;
+}
+
+static int dns_transaction_request_dnssec_rr(DnsTransaction *t, DnsResourceKey *key) {
+        _cleanup_(dns_answer_unrefp) DnsAnswer *a = NULL;
+        DnsTransaction *aux;
+        int r;
+
+        assert(t);
+        assert(key);
+
+        /* Try to get the data from the trust anchor */
+        r = dns_trust_anchor_lookup_positive(&t->scope->manager->trust_anchor, key, &a);
+        if (r < 0)
+                return r;
+        if (r > 0) {
+                r = dns_answer_extend(&t->validated_keys, a);
+                if (r < 0)
+                        return r;
+
+                return 0;
+        }
+
+        /* This didn't work, ask for it via the network/cache then. */
+        r = dns_transaction_add_dnssec_transaction(t, key, &aux);
+        if (r == -ELOOP) /* This would result in a cyclic dependency */
+                return 0;
+        if (r < 0)
+                return r;
+
+        if (aux->state == DNS_TRANSACTION_NULL) {
+                r = dns_transaction_go(aux);
+                if (r < 0)
+                        return r;
+        }
+
+        return 1;
+}
+
+static int dns_transaction_negative_trust_anchor_lookup(DnsTransaction *t, const char *name) {
+        int r;
+
+        assert(t);
+
+        /* Check whether the specified name is in the NTA
+         * database, either in the global one, or the link-local
+         * one. */
+
+        r = dns_trust_anchor_lookup_negative(&t->scope->manager->trust_anchor, name);
+        if (r != 0)
+                return r;
+
+        if (!t->scope->link)
+                return 0;
+
+        return set_contains(t->scope->link->dnssec_negative_trust_anchors, name);
+}
+
+static int dns_transaction_has_unsigned_negative_answer(DnsTransaction *t) {
+        int r;
+
+        assert(t);
+
+        /* Checks whether the answer is negative, and lacks NSEC/NSEC3
+         * RRs to prove it */
+
+        r = dns_transaction_has_positive_answer(t, NULL);
+        if (r < 0)
+                return r;
+        if (r > 0)
+                return false;
+
+        /* Is this key explicitly listed as a negative trust anchor?
+         * If so, it's nothing we need to care about */
+        r = dns_transaction_negative_trust_anchor_lookup(t, dns_resource_key_name(t->key));
+        if (r < 0)
+                return r;
+        if (r > 0)
+                return false;
+
+        /* The answer does not contain any RRs that match to the
+         * question. If so, let's see if there are any NSEC/NSEC3 RRs
+         * included. If not, the answer is unsigned. */
+
+        r = dns_answer_contains_nsec_or_nsec3(t->answer);
+        if (r < 0)
+                return r;
+        if (r > 0)
+                return false;
+
+        return true;
+}
+
+static int dns_transaction_is_primary_response(DnsTransaction *t, DnsResourceRecord *rr) {
+        int r;
+
+        assert(t);
+        assert(rr);
+
+        /* Check if the specified RR is the "primary" response,
+         * i.e. either matches the question precisely or is a
+         * CNAME/DNAME for it. */
+
+        r = dns_resource_key_match_rr(t->key, rr, NULL);
+        if (r != 0)
+                return r;
+
+        return dns_resource_key_match_cname_or_dname(t->key, rr->key, NULL);
+}
+
+static bool dns_transaction_dnssec_supported(DnsTransaction *t) {
+        assert(t);
+
+        /* Checks whether our transaction's DNS server is assumed to be compatible with DNSSEC. Returns false as soon
+         * as we changed our mind about a server, and now believe it is incompatible with DNSSEC. */
+
+        if (t->scope->protocol != DNS_PROTOCOL_DNS)
+                return false;
+
+        /* If we have picked no server, then we are working from the cache or some other source, and DNSSEC might well
+         * be supported, hence return true. */
+        if (!t->server)
+                return true;
+
+        /* Note that we do not check the feature level actually used for the transaction but instead the feature level
+         * the server is known to support currently, as the transaction feature level might be lower than what the
+         * server actually supports, since we might have downgraded this transaction's feature level because we got a
+         * SERVFAIL earlier and wanted to check whether downgrading fixes it. */
+
+        return dns_server_dnssec_supported(t->server);
+}
+
+static bool dns_transaction_dnssec_supported_full(DnsTransaction *t) {
+        DnsTransaction *dt;
+        Iterator i;
+
+        assert(t);
+
+        /* Checks whether our transaction our any of the auxiliary transactions couldn't do DNSSEC. */
+
+        if (!dns_transaction_dnssec_supported(t))
+                return false;
+
+        SET_FOREACH(dt, t->dnssec_transactions, i)
+                if (!dns_transaction_dnssec_supported(dt))
+                        return false;
+
+        return true;
+}
+
+int dns_transaction_request_dnssec_keys(DnsTransaction *t) {
+        DnsResourceRecord *rr;
+
+        int r;
+
+        assert(t);
+
+        /*
+         * Retrieve all auxiliary RRs for the answer we got, so that
+         * we can verify signatures or prove that RRs are rightfully
+         * unsigned. Specifically:
+         *
+         * - For RRSIG we get the matching DNSKEY
+         * - For DNSKEY we get the matching DS
+         * - For unsigned SOA/NS we get the matching DS
+         * - For unsigned CNAME/DNAME/DS we get the parent SOA RR
+         * - For other unsigned RRs we get the matching SOA RR
+         * - For SOA/NS queries with no matching response RR, and no NSEC/NSEC3, the DS RR
+         * - For DS queries with no matching response RRs, and no NSEC/NSEC3, the parent's SOA RR
+         * - For other queries with no matching response RRs, and no NSEC/NSEC3, the SOA RR
+         */
+
+        if (t->scope->dnssec_mode == DNSSEC_NO)
+                return 0;
+        if (t->answer_source != DNS_TRANSACTION_NETWORK)
+                return 0; /* We only need to validate stuff from the network */
+        if (!dns_transaction_dnssec_supported(t))
+                return 0; /* If we can't do DNSSEC anyway there's no point in geting the auxiliary RRs */
+
+        DNS_ANSWER_FOREACH(rr, t->answer) {
+
+                if (dns_type_is_pseudo(rr->key->type))
+                        continue;
+
+                /* If this RR is in the negative trust anchor, we don't need to validate it. */
+                r = dns_transaction_negative_trust_anchor_lookup(t, dns_resource_key_name(rr->key));
+                if (r < 0)
+                        return r;
+                if (r > 0)
+                        continue;
+
+                switch (rr->key->type) {
+
+                case DNS_TYPE_RRSIG: {
+                        /* For each RRSIG we request the matching DNSKEY */
+                        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *dnskey = NULL;
+
+                        /* If this RRSIG is about a DNSKEY RR and the
+                         * signer is the same as the owner, then we
+                         * already have the DNSKEY, and we don't have
+                         * to look for more. */
+                        if (rr->rrsig.type_covered == DNS_TYPE_DNSKEY) {
+                                r = dns_name_equal(rr->rrsig.signer, dns_resource_key_name(rr->key));
+                                if (r < 0)
+                                        return r;
+                                if (r > 0)
+                                        continue;
+                        }
+
+                        /* If the signer is not a parent of our
+                         * original query, then this is about an
+                         * auxiliary RRset, but not anything we asked
+                         * for. In this case we aren't interested,
+                         * because we don't want to request additional
+                         * RRs for stuff we didn't really ask for, and
+                         * also to avoid request loops, where
+                         * additional RRs from one transaction result
+                         * in another transaction whose additonal RRs
+                         * point back to the original transaction, and
+                         * we deadlock. */
+                        r = dns_name_endswith(dns_resource_key_name(t->key), rr->rrsig.signer);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                continue;
+
+                        dnskey = dns_resource_key_new(rr->key->class, DNS_TYPE_DNSKEY, rr->rrsig.signer);
+                        if (!dnskey)
+                                return -ENOMEM;
+
+                        log_debug("Requesting DNSKEY to validate transaction %" PRIu16" (%s, RRSIG with key tag: %" PRIu16 ").",
+                                  t->id, dns_resource_key_name(rr->key), rr->rrsig.key_tag);
+                        r = dns_transaction_request_dnssec_rr(t, dnskey);
+                        if (r < 0)
+                                return r;
+                        break;
+                }
+
+                case DNS_TYPE_DNSKEY: {
+                        /* For each DNSKEY we request the matching DS */
+                        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *ds = NULL;
+
+                        /* If the DNSKEY we are looking at is not for
+                         * zone we are interested in, nor any of its
+                         * parents, we aren't interested, and don't
+                         * request it. After all, we don't want to end
+                         * up in request loops, and want to keep
+                         * additional traffic down. */
+
+                        r = dns_name_endswith(dns_resource_key_name(t->key), dns_resource_key_name(rr->key));
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                continue;
+
+                        ds = dns_resource_key_new(rr->key->class, DNS_TYPE_DS, dns_resource_key_name(rr->key));
+                        if (!ds)
+                                return -ENOMEM;
+
+                        log_debug("Requesting DS to validate transaction %" PRIu16" (%s, DNSKEY with key tag: %" PRIu16 ").",
+                                  t->id, dns_resource_key_name(rr->key), dnssec_keytag(rr, false));
+                        r = dns_transaction_request_dnssec_rr(t, ds);
+                        if (r < 0)
+                                return r;
+
+                        break;
+                }
+
+                case DNS_TYPE_SOA:
+                case DNS_TYPE_NS: {
+                        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *ds = NULL;
+
+                        /* For an unsigned SOA or NS, try to acquire
+                         * the matching DS RR, as we are at a zone cut
+                         * then, and whether a DS exists tells us
+                         * whether the zone is signed. Do so only if
+                         * this RR matches our original question,
+                         * however. */
+
+                        r = dns_resource_key_match_rr(t->key, rr, NULL);
+                        if (r < 0)
+                                return r;
+                        if (r == 0) {
+                                /* Hmm, so this SOA RR doesn't match our original question. In this case, maybe this is
+                                 * a negative reply, and we need the a SOA RR's TTL in order to cache a negative entry?
+                                 * If so, we need to validate it, too. */
+
+                                r = dns_answer_match_key(t->answer, t->key, NULL);
+                                if (r < 0)
+                                        return r;
+                                if (r > 0) /* positive reply, we won't need the SOA and hence don't need to validate
+                                            * it. */
+                                        continue;
+
+                                /* Only bother with this if the SOA/NS RR we are looking at is actually a parent of
+                                 * what we are looking for, otherwise there's no value in it for us. */
+                                r = dns_name_endswith(dns_resource_key_name(t->key), dns_resource_key_name(rr->key));
+                                if (r < 0)
+                                        return r;
+                                if (r == 0)
+                                        continue;
+                        }
+
+                        r = dnssec_has_rrsig(t->answer, rr->key);
+                        if (r < 0)
+                                return r;
+                        if (r > 0)
+                                continue;
+
+                        ds = dns_resource_key_new(rr->key->class, DNS_TYPE_DS, dns_resource_key_name(rr->key));
+                        if (!ds)
+                                return -ENOMEM;
+
+                        log_debug("Requesting DS to validate transaction %" PRIu16 " (%s, unsigned SOA/NS RRset).",
+                                  t->id, dns_resource_key_name(rr->key));
+                        r = dns_transaction_request_dnssec_rr(t, ds);
+                        if (r < 0)
+                                return r;
+
+                        break;
+                }
+
+                case DNS_TYPE_DS:
+                case DNS_TYPE_CNAME:
+                case DNS_TYPE_DNAME: {
+                        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *soa = NULL;
+                        const char *name;
+
+                        /* CNAMEs and DNAMEs cannot be located at a
+                         * zone apex, hence ask for the parent SOA for
+                         * unsigned CNAME/DNAME RRs, maybe that's the
+                         * apex. But do all that only if this is
+                         * actually a response to our original
+                         * question.
+                         *
+                         * Similar for DS RRs, which are signed when
+                         * the parent SOA is signed. */
+
+                        r = dns_transaction_is_primary_response(t, rr);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                continue;
+
+                        r = dnssec_has_rrsig(t->answer, rr->key);
+                        if (r < 0)
+                                return r;
+                        if (r > 0)
+                                continue;
+
+                        r = dns_answer_has_dname_for_cname(t->answer, rr);
+                        if (r < 0)
+                                return r;
+                        if (r > 0)
+                                continue;
+
+                        name = dns_resource_key_name(rr->key);
+                        r = dns_name_parent(&name);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                continue;
+
+                        soa = dns_resource_key_new(rr->key->class, DNS_TYPE_SOA, name);
+                        if (!soa)
+                                return -ENOMEM;
+
+                        log_debug("Requesting parent SOA to validate transaction %" PRIu16 " (%s, unsigned CNAME/DNAME/DS RRset).",
+                                  t->id, dns_resource_key_name(rr->key));
+                        r = dns_transaction_request_dnssec_rr(t, soa);
+                        if (r < 0)
+                                return r;
+
+                        break;
+                }
+
+                default: {
+                        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *soa = NULL;
+
+                        /* For other unsigned RRsets (including
+                         * NSEC/NSEC3!), look for proof the zone is
+                         * unsigned, by requesting the SOA RR of the
+                         * zone. However, do so only if they are
+                         * directly relevant to our original
+                         * question. */
+
+                        r = dns_transaction_is_primary_response(t, rr);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                continue;
+
+                        r = dnssec_has_rrsig(t->answer, rr->key);
+                        if (r < 0)
+                                return r;
+                        if (r > 0)
+                                continue;
+
+                        soa = dns_resource_key_new(rr->key->class, DNS_TYPE_SOA, dns_resource_key_name(rr->key));
+                        if (!soa)
+                                return -ENOMEM;
+
+                        log_debug("Requesting SOA to validate transaction %" PRIu16 " (%s, unsigned non-SOA/NS RRset <%s>).",
+                                  t->id, dns_resource_key_name(rr->key), dns_resource_record_to_string(rr));
+                        r = dns_transaction_request_dnssec_rr(t, soa);
+                        if (r < 0)
+                                return r;
+                        break;
+                }}
+        }
+
+        /* Above, we requested everything necessary to validate what
+         * we got. Now, let's request what we need to validate what we
+         * didn't get... */
+
+        r = dns_transaction_has_unsigned_negative_answer(t);
+        if (r < 0)
+                return r;
+        if (r > 0) {
+                const char *name;
+                uint16_t type = 0;
+
+                name = dns_resource_key_name(t->key);
+
+                /* If this was a SOA or NS request, then check if there's a DS RR for the same domain. Note that this
+                 * could also be used as indication that we are not at a zone apex, but in real world setups there are
+                 * too many broken DNS servers (Hello, incapdns.net!) where non-terminal zones return NXDOMAIN even
+                 * though they have further children. If this was a DS request, then it's signed when the parent zone
+                 * is signed, hence ask the parent SOA in that case. If this was any other RR then ask for the SOA RR,
+                 * to see if that is signed. */
+
+                if (t->key->type == DNS_TYPE_DS) {
+                        r = dns_name_parent(&name);
+                        if (r > 0) {
+                                type = DNS_TYPE_SOA;
+                                log_debug("Requesting parent SOA (→ %s) to validate transaction %" PRIu16 " (%s, unsigned empty DS response).",
+                                          name, t->id, dns_resource_key_name(t->key));
+                        } else
+                                name = NULL;
+
+                } else if (IN_SET(t->key->type, DNS_TYPE_SOA, DNS_TYPE_NS)) {
+
+                        type = DNS_TYPE_DS;
+                        log_debug("Requesting DS (→ %s) to validate transaction %" PRIu16 " (%s, unsigned empty SOA/NS response).",
+                                  name, t->id, name);
+
+                } else {
+                        type = DNS_TYPE_SOA;
+                        log_debug("Requesting SOA (→ %s) to validate transaction %" PRIu16 " (%s, unsigned empty non-SOA/NS/DS response).",
+                                  name, t->id, name);
+                }
+
+                if (name) {
+                        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *soa = NULL;
+
+                        soa = dns_resource_key_new(t->key->class, type, name);
+                        if (!soa)
+                                return -ENOMEM;
+
+                        r = dns_transaction_request_dnssec_rr(t, soa);
+                        if (r < 0)
+                                return r;
+                }
+        }
+
+        return dns_transaction_dnssec_is_live(t);
+}
+
+void dns_transaction_notify(DnsTransaction *t, DnsTransaction *source) {
+        assert(t);
+        assert(source);
+
+        /* Invoked whenever any of our auxiliary DNSSEC transactions completed its work. If the state is still PENDING,
+           we are still in the loop that adds further DNSSEC transactions, hence don't check if we are ready yet. If
+           the state is VALIDATING however, we should check if we are complete now. */
+
+        if (t->state == DNS_TRANSACTION_VALIDATING)
+                dns_transaction_process_dnssec(t);
+}
+
+static int dns_transaction_validate_dnskey_by_ds(DnsTransaction *t) {
+        DnsResourceRecord *rr;
+        int ifindex, r;
+
+        assert(t);
+
+        /* Add all DNSKEY RRs from the answer that are validated by DS
+         * RRs from the list of validated keys to the list of
+         * validated keys. */
+
+        DNS_ANSWER_FOREACH_IFINDEX(rr, ifindex, t->answer) {
+
+                r = dnssec_verify_dnskey_by_ds_search(rr, t->validated_keys);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        continue;
+
+                /* If so, the DNSKEY is validated too. */
+                r = dns_answer_add_extend(&t->validated_keys, rr, ifindex, DNS_ANSWER_AUTHENTICATED);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
+static int dns_transaction_requires_rrsig(DnsTransaction *t, DnsResourceRecord *rr) {
+        int r;
+
+        assert(t);
+        assert(rr);
+
+        /* Checks if the RR we are looking for must be signed with an
+         * RRSIG. This is used for positive responses. */
+
+        if (t->scope->dnssec_mode == DNSSEC_NO)
+                return false;
+
+        if (dns_type_is_pseudo(rr->key->type))
+                return -EINVAL;
+
+        r = dns_transaction_negative_trust_anchor_lookup(t, dns_resource_key_name(rr->key));
+        if (r < 0)
+                return r;
+        if (r > 0)
+                return false;
+
+        switch (rr->key->type) {
+
+        case DNS_TYPE_RRSIG:
+                /* RRSIGs are the signatures themselves, they need no signing. */
+                return false;
+
+        case DNS_TYPE_SOA:
+        case DNS_TYPE_NS: {
+                DnsTransaction *dt;
+                Iterator i;
+
+                /* For SOA or NS RRs we look for a matching DS transaction */
+
+                SET_FOREACH(dt, t->dnssec_transactions, i) {
+
+                        if (dt->key->class != rr->key->class)
+                                continue;
+                        if (dt->key->type != DNS_TYPE_DS)
+                                continue;
+
+                        r = dns_name_equal(dns_resource_key_name(dt->key), dns_resource_key_name(rr->key));
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                continue;
+
+                        /* We found a DS transactions for the SOA/NS
+                         * RRs we are looking at. If it discovered signed DS
+                         * RRs, then we need to be signed, too. */
+
+                        if (!dt->answer_authenticated)
+                                return false;
+
+                        return dns_answer_match_key(dt->answer, dt->key, NULL);
+                }
+
+                /* We found nothing that proves this is safe to leave
+                 * this unauthenticated, hence ask inist on
+                 * authentication. */
+                return true;
+        }
+
+        case DNS_TYPE_DS:
+        case DNS_TYPE_CNAME:
+        case DNS_TYPE_DNAME: {
+                const char *parent = NULL;
+                DnsTransaction *dt;
+                Iterator i;
+
+                /*
+                 * CNAME/DNAME RRs cannot be located at a zone apex, hence look directly for the parent SOA.
+                 *
+                 * DS RRs are signed if the parent is signed, hence also look at the parent SOA
+                 */
+
+                SET_FOREACH(dt, t->dnssec_transactions, i) {
+
+                        if (dt->key->class != rr->key->class)
+                                continue;
+                        if (dt->key->type != DNS_TYPE_SOA)
+                                continue;
+
+                        if (!parent) {
+                                parent = dns_resource_key_name(rr->key);
+                                r = dns_name_parent(&parent);
+                                if (r < 0)
+                                        return r;
+                                if (r == 0) {
+                                        if (rr->key->type == DNS_TYPE_DS)
+                                                return true;
+
+                                        /* A CNAME/DNAME without a parent? That's sooo weird. */
+                                        return log_debug_errno(SYNTHETIC_ERRNO(EBADMSG),
+                                                               "Transaction %" PRIu16 " claims CNAME/DNAME at root. Refusing.", t->id);
+                                }
+                        }
+
+                        r = dns_name_equal(dns_resource_key_name(dt->key), parent);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                continue;
+
+                        return t->answer_authenticated;
+                }
+
+                return true;
+        }
+
+        default: {
+                DnsTransaction *dt;
+                Iterator i;
+
+                /* Any other kind of RR (including DNSKEY/NSEC/NSEC3). Let's see if our SOA lookup was authenticated */
+
+                SET_FOREACH(dt, t->dnssec_transactions, i) {
+
+                        if (dt->key->class != rr->key->class)
+                                continue;
+                        if (dt->key->type != DNS_TYPE_SOA)
+                                continue;
+
+                        r = dns_name_equal(dns_resource_key_name(dt->key), dns_resource_key_name(rr->key));
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                continue;
+
+                        /* We found the transaction that was supposed to find
+                         * the SOA RR for us. It was successful, but found no
+                         * RR for us. This means we are not at a zone cut. In
+                         * this case, we require authentication if the SOA
+                         * lookup was authenticated too. */
+                        return t->answer_authenticated;
+                }
+
+                return true;
+        }}
+}
+
+static int dns_transaction_in_private_tld(DnsTransaction *t, const DnsResourceKey *key) {
+        DnsTransaction *dt;
+        const char *tld;
+        Iterator i;
+        int r;
+
+        /* If DNSSEC downgrade mode is on, checks whether the
+         * specified RR is one level below a TLD we have proven not to
+         * exist. In such a case we assume that this is a private
+         * domain, and permit it.
+         *
+         * This detects cases like the Fritz!Box router networks. Each
+         * Fritz!Box router serves a private "fritz.box" zone, in the
+         * non-existing TLD "box". Requests for the "fritz.box" domain
+         * are served by the router itself, while requests for the
+         * "box" domain will result in NXDOMAIN.
+         *
+         * Note that this logic is unable to detect cases where a
+         * router serves a private DNS zone directly under
+         * non-existing TLD. In such a case we cannot detect whether
+         * the TLD is supposed to exist or not, as all requests we
+         * make for it will be answered by the router's zone, and not
+         * by the root zone. */
+
+        assert(t);
+
+        if (t->scope->dnssec_mode != DNSSEC_ALLOW_DOWNGRADE)
+                return false; /* In strict DNSSEC mode what doesn't exist, doesn't exist */
+
+        tld = dns_resource_key_name(key);
+        r = dns_name_parent(&tld);
+        if (r < 0)
+                return r;
+        if (r == 0)
+                return false; /* Already the root domain */
+
+        if (!dns_name_is_single_label(tld))
+                return false;
+
+        SET_FOREACH(dt, t->dnssec_transactions, i) {
+
+                if (dt->key->class != key->class)
+                        continue;
+
+                r = dns_name_equal(dns_resource_key_name(dt->key), tld);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        continue;
+
+                /* We found an auxiliary lookup we did for the TLD. If
+                 * that returned with NXDOMAIN, we know the TLD didn't
+                 * exist, and hence this might be a private zone. */
+
+                return dt->answer_rcode == DNS_RCODE_NXDOMAIN;
+        }
+
+        return false;
+}
+
+static int dns_transaction_requires_nsec(DnsTransaction *t) {
+        char key_str[DNS_RESOURCE_KEY_STRING_MAX];
+        DnsTransaction *dt;
+        const char *name;
+        uint16_t type = 0;
+        Iterator i;
+        int r;
+
+        assert(t);
+
+        /* Checks if we need to insist on NSEC/NSEC3 RRs for proving
+         * this negative reply */
+
+        if (t->scope->dnssec_mode == DNSSEC_NO)
+                return false;
+
+        if (dns_type_is_pseudo(t->key->type))
+                return -EINVAL;
+
+        r = dns_transaction_negative_trust_anchor_lookup(t, dns_resource_key_name(t->key));
+        if (r < 0)
+                return r;
+        if (r > 0)
+                return false;
+
+        r = dns_transaction_in_private_tld(t, t->key);
+        if (r < 0)
+                return r;
+        if (r > 0) {
+                /* The lookup is from a TLD that is proven not to
+                 * exist, and we are in downgrade mode, hence ignore
+                 * that fact that we didn't get any NSEC RRs. */
+
+                log_info("Detected a negative query %s in a private DNS zone, permitting unsigned response.",
+                         dns_resource_key_to_string(t->key, key_str, sizeof key_str));
+                return false;
+        }
+
+        name = dns_resource_key_name(t->key);
+
+        if (t->key->type == DNS_TYPE_DS) {
+
+                /* We got a negative reply for this DS lookup? DS RRs are signed when their parent zone is signed,
+                 * hence check the parent SOA in this case. */
+
+                r = dns_name_parent(&name);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        return true;
+
+                type = DNS_TYPE_SOA;
+
+        } else if (IN_SET(t->key->type, DNS_TYPE_SOA, DNS_TYPE_NS))
+                /* We got a negative reply for this SOA/NS lookup? If so, check if there's a DS RR for this */
+                type = DNS_TYPE_DS;
+        else
+                /* For all other negative replies, check for the SOA lookup */
+                type = DNS_TYPE_SOA;
+
+        /* For all other RRs we check the SOA on the same level to see
+         * if it's signed. */
+
+        SET_FOREACH(dt, t->dnssec_transactions, i) {
+
+                if (dt->key->class != t->key->class)
+                        continue;
+                if (dt->key->type != type)
+                        continue;
+
+                r = dns_name_equal(dns_resource_key_name(dt->key), name);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        continue;
+
+                return dt->answer_authenticated;
+        }
+
+        /* If in doubt, require NSEC/NSEC3 */
+        return true;
+}
+
+static int dns_transaction_dnskey_authenticated(DnsTransaction *t, DnsResourceRecord *rr) {
+        DnsResourceRecord *rrsig;
+        bool found = false;
+        int r;
+
+        /* Checks whether any of the DNSKEYs used for the RRSIGs for
+         * the specified RRset is authenticated (i.e. has a matching
+         * DS RR). */
+
+        r = dns_transaction_negative_trust_anchor_lookup(t, dns_resource_key_name(rr->key));
+        if (r < 0)
+                return r;
+        if (r > 0)
+                return false;
+
+        DNS_ANSWER_FOREACH(rrsig, t->answer) {
+                DnsTransaction *dt;
+                Iterator i;
+
+                r = dnssec_key_match_rrsig(rr->key, rrsig);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        continue;
+
+                SET_FOREACH(dt, t->dnssec_transactions, i) {
+
+                        if (dt->key->class != rr->key->class)
+                                continue;
+
+                        if (dt->key->type == DNS_TYPE_DNSKEY) {
+
+                                r = dns_name_equal(dns_resource_key_name(dt->key), rrsig->rrsig.signer);
+                                if (r < 0)
+                                        return r;
+                                if (r == 0)
+                                        continue;
+
+                                /* OK, we found an auxiliary DNSKEY
+                                 * lookup. If that lookup is
+                                 * authenticated, report this. */
+
+                                if (dt->answer_authenticated)
+                                        return true;
+
+                                found = true;
+
+                        } else if (dt->key->type == DNS_TYPE_DS) {
+
+                                r = dns_name_equal(dns_resource_key_name(dt->key), rrsig->rrsig.signer);
+                                if (r < 0)
+                                        return r;
+                                if (r == 0)
+                                        continue;
+
+                                /* OK, we found an auxiliary DS
+                                 * lookup. If that lookup is
+                                 * authenticated and non-zero, we
+                                 * won! */
+
+                                if (!dt->answer_authenticated)
+                                        return false;
+
+                                return dns_answer_match_key(dt->answer, dt->key, NULL);
+                        }
+                }
+        }
+
+        return found ? false : -ENXIO;
+}
+
+static int dns_transaction_known_signed(DnsTransaction *t, DnsResourceRecord *rr) {
+        assert(t);
+        assert(rr);
+
+        /* We know that the root domain is signed, hence if it appears
+         * not to be signed, there's a problem with the DNS server */
+
+        return rr->key->class == DNS_CLASS_IN &&
+                dns_name_is_root(dns_resource_key_name(rr->key));
+}
+
+static int dns_transaction_check_revoked_trust_anchors(DnsTransaction *t) {
+        DnsResourceRecord *rr;
+        int r;
+
+        assert(t);
+
+        /* Maybe warn the user that we encountered a revoked DNSKEY
+         * for a key from our trust anchor. Note that we don't care
+         * whether the DNSKEY can be authenticated or not. It's
+         * sufficient if it is self-signed. */
+
+        DNS_ANSWER_FOREACH(rr, t->answer) {
+                r = dns_trust_anchor_check_revoked(&t->scope->manager->trust_anchor, rr, t->answer);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
+static int dns_transaction_invalidate_revoked_keys(DnsTransaction *t) {
+        bool changed;
+        int r;
+
+        assert(t);
+
+        /* Removes all DNSKEY/DS objects from t->validated_keys that
+         * our trust anchors database considers revoked. */
+
+        do {
+                DnsResourceRecord *rr;
+
+                changed = false;
+
+                DNS_ANSWER_FOREACH(rr, t->validated_keys) {
+                        r = dns_trust_anchor_is_revoked(&t->scope->manager->trust_anchor, rr);
+                        if (r < 0)
+                                return r;
+                        if (r > 0) {
+                                r = dns_answer_remove_by_rr(&t->validated_keys, rr);
+                                if (r < 0)
+                                        return r;
+
+                                assert(r > 0);
+                                changed = true;
+                                break;
+                        }
+                }
+        } while (changed);
+
+        return 0;
+}
+
+static int dns_transaction_copy_validated(DnsTransaction *t) {
+        DnsTransaction *dt;
+        Iterator i;
+        int r;
+
+        assert(t);
+
+        /* Copy all validated RRs from the auxiliary DNSSEC transactions into our set of validated RRs */
+
+        SET_FOREACH(dt, t->dnssec_transactions, i) {
+
+                if (DNS_TRANSACTION_IS_LIVE(dt->state))
+                        continue;
+
+                if (!dt->answer_authenticated)
+                        continue;
+
+                r = dns_answer_extend(&t->validated_keys, dt->answer);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
+typedef enum {
+        DNSSEC_PHASE_DNSKEY,   /* Phase #1, only validate DNSKEYs */
+        DNSSEC_PHASE_NSEC,     /* Phase #2, only validate NSEC+NSEC3 */
+        DNSSEC_PHASE_ALL,      /* Phase #3, validate everything else */
+} Phase;
+
+static int dnssec_validate_records(
+                DnsTransaction *t,
+                Phase phase,
+                bool *have_nsec,
+                DnsAnswer **validated) {
+
+        DnsResourceRecord *rr;
+        int r;
+
+        /* Returns negative on error, 0 if validation failed, 1 to restart validation, 2 when finished. */
+
+        DNS_ANSWER_FOREACH(rr, t->answer) {
+                DnsResourceRecord *rrsig = NULL;
+                DnssecResult result;
+
+                switch (rr->key->type) {
+                case DNS_TYPE_RRSIG:
+                        continue;
+
+                case DNS_TYPE_DNSKEY:
+                        /* We validate DNSKEYs only in the DNSKEY and ALL phases */
+                        if (phase == DNSSEC_PHASE_NSEC)
+                                continue;
+                        break;
+
+                case DNS_TYPE_NSEC:
+                case DNS_TYPE_NSEC3:
+                        *have_nsec = true;
+
+                        /* We validate NSEC/NSEC3 only in the NSEC and ALL phases */
+                        if (phase == DNSSEC_PHASE_DNSKEY)
+                                continue;
+                        break;
+
+                default:
+                        /* We validate all other RRs only in the ALL phases */
+                        if (phase != DNSSEC_PHASE_ALL)
+                                continue;
+                }
+
+                r = dnssec_verify_rrset_search(t->answer, rr->key, t->validated_keys, USEC_INFINITY, &result, &rrsig);
+                if (r < 0)
+                        return r;
+
+                log_debug("Looking at %s: %s", strna(dns_resource_record_to_string(rr)), dnssec_result_to_string(result));
+
+                if (result == DNSSEC_VALIDATED) {
+
+                        if (rr->key->type == DNS_TYPE_DNSKEY) {
+                                /* If we just validated a DNSKEY RRset, then let's add these keys to
+                                 * the set of validated keys for this transaction. */
+
+                                r = dns_answer_copy_by_key(&t->validated_keys, t->answer, rr->key, DNS_ANSWER_AUTHENTICATED);
+                                if (r < 0)
+                                        return r;
+
+                                /* Some of the DNSKEYs we just added might already have been revoked,
+                                 * remove them again in that case. */
+                                r = dns_transaction_invalidate_revoked_keys(t);
+                                if (r < 0)
+                                        return r;
+                        }
+
+                        /* Add the validated RRset to the new list of validated
+                         * RRsets, and remove it from the unvalidated RRsets.
+                         * We mark the RRset as authenticated and cacheable. */
+                        r = dns_answer_move_by_key(validated, &t->answer, rr->key, DNS_ANSWER_AUTHENTICATED|DNS_ANSWER_CACHEABLE);
+                        if (r < 0)
+                                return r;
+
+                        manager_dnssec_verdict(t->scope->manager, DNSSEC_SECURE, rr->key);
+
+                        /* Exit the loop, we dropped something from the answer, start from the beginning */
+                        return 1;
+                }
+
+                /* If we haven't read all DNSKEYs yet a negative result of the validation is irrelevant, as
+                 * there might be more DNSKEYs coming. Similar, if we haven't read all NSEC/NSEC3 RRs yet,
+                 * we cannot do positive wildcard proofs yet, as those require the NSEC/NSEC3 RRs. */
+                if (phase != DNSSEC_PHASE_ALL)
+                        continue;
+
+                if (result == DNSSEC_VALIDATED_WILDCARD) {
+                        bool authenticated = false;
+                        const char *source;
+
+                        /* This RRset validated, but as a wildcard. This means we need
+                         * to prove via NSEC/NSEC3 that no matching non-wildcard RR exists. */
+
+                        /* First step, determine the source of synthesis */
+                        r = dns_resource_record_source(rrsig, &source);
+                        if (r < 0)
+                                return r;
+
+                        r = dnssec_test_positive_wildcard(*validated,
+                                                          dns_resource_key_name(rr->key),
+                                                          source,
+                                                          rrsig->rrsig.signer,
+                                                          &authenticated);
+
+                        /* Unless the NSEC proof showed that the key really doesn't exist something is off. */
+                        if (r == 0)
+                                result = DNSSEC_INVALID;
+                        else {
+                                r = dns_answer_move_by_key(validated, &t->answer, rr->key,
+                                                           authenticated ? (DNS_ANSWER_AUTHENTICATED|DNS_ANSWER_CACHEABLE) : 0);
+                                if (r < 0)
+                                        return r;
+
+                                manager_dnssec_verdict(t->scope->manager, authenticated ? DNSSEC_SECURE : DNSSEC_INSECURE, rr->key);
+
+                                /* Exit the loop, we dropped something from the answer, start from the beginning */
+                                return 1;
+                        }
+                }
+
+                if (result == DNSSEC_NO_SIGNATURE) {
+                        r = dns_transaction_requires_rrsig(t, rr);
+                        if (r < 0)
+                                return r;
+                        if (r == 0) {
+                                /* Data does not require signing. In that case, just copy it over,
+                                 * but remember that this is by no means authenticated. */
+                                r = dns_answer_move_by_key(validated, &t->answer, rr->key, 0);
+                                if (r < 0)
+                                        return r;
+
+                                manager_dnssec_verdict(t->scope->manager, DNSSEC_INSECURE, rr->key);
+                                return 1;
+                        }
+
+                        r = dns_transaction_known_signed(t, rr);
+                        if (r < 0)
+                                return r;
+                        if (r > 0) {
+                                /* This is an RR we know has to be signed. If it isn't this means
+                                 * the server is not attaching RRSIGs, hence complain. */
+
+                                dns_server_packet_rrsig_missing(t->server, t->current_feature_level);
+
+                                if (t->scope->dnssec_mode == DNSSEC_ALLOW_DOWNGRADE) {
+
+                                        /* Downgrading is OK? If so, just consider the information unsigned */
+
+                                        r = dns_answer_move_by_key(validated, &t->answer, rr->key, 0);
+                                        if (r < 0)
+                                                return r;
+
+                                        manager_dnssec_verdict(t->scope->manager, DNSSEC_INSECURE, rr->key);
+                                        return 1;
+                                }
+
+                                /* Otherwise, fail */
+                                t->answer_dnssec_result = DNSSEC_INCOMPATIBLE_SERVER;
+                                return 0;
+                        }
+
+                        r = dns_transaction_in_private_tld(t, rr->key);
+                        if (r < 0)
+                                return r;
+                        if (r > 0) {
+                                char s[DNS_RESOURCE_KEY_STRING_MAX];
+
+                                /* The data is from a TLD that is proven not to exist, and we are in downgrade
+                                 * mode, hence ignore the fact that this was not signed. */
+
+                                log_info("Detected RRset %s is in a private DNS zone, permitting unsigned RRs.",
+                                         dns_resource_key_to_string(rr->key, s, sizeof s));
+
+                                r = dns_answer_move_by_key(validated, &t->answer, rr->key, 0);
+                                if (r < 0)
+                                        return r;
+
+                                manager_dnssec_verdict(t->scope->manager, DNSSEC_INSECURE, rr->key);
+                                return 1;
+                        }
+                }
+
+                if (IN_SET(result,
+                           DNSSEC_MISSING_KEY,
+                           DNSSEC_SIGNATURE_EXPIRED,
+                           DNSSEC_UNSUPPORTED_ALGORITHM)) {
+
+                        r = dns_transaction_dnskey_authenticated(t, rr);
+                        if (r < 0 && r != -ENXIO)
+                                return r;
+                        if (r == 0) {
+                                /* The DNSKEY transaction was not authenticated, this means there's
+                                 * no DS for this, which means it's OK if no keys are found for this signature. */
+
+                                r = dns_answer_move_by_key(validated, &t->answer, rr->key, 0);
+                                if (r < 0)
+                                        return r;
+
+                                manager_dnssec_verdict(t->scope->manager, DNSSEC_INSECURE, rr->key);
+                                return 1;
+                        }
+                }
+
+                r = dns_transaction_is_primary_response(t, rr);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        /* Look for a matching DNAME for this CNAME */
+                        r = dns_answer_has_dname_for_cname(t->answer, rr);
+                        if (r < 0)
+                                return r;
+                        if (r == 0) {
+                                /* Also look among the stuff we already validated */
+                                r = dns_answer_has_dname_for_cname(*validated, rr);
+                                if (r < 0)
+                                        return r;
+                        }
+
+                        if (r == 0) {
+                                if (IN_SET(result,
+                                           DNSSEC_INVALID,
+                                           DNSSEC_SIGNATURE_EXPIRED,
+                                           DNSSEC_NO_SIGNATURE))
+                                        manager_dnssec_verdict(t->scope->manager, DNSSEC_BOGUS, rr->key);
+                                else /* DNSSEC_MISSING_KEY or DNSSEC_UNSUPPORTED_ALGORITHM */
+                                        manager_dnssec_verdict(t->scope->manager, DNSSEC_INDETERMINATE, rr->key);
+
+                                /* This is a primary response to our question, and it failed validation.
+                                 * That's fatal. */
+                                t->answer_dnssec_result = result;
+                                return 0;
+                        }
+
+                        /* This is a primary response, but we do have a DNAME RR
+                         * in the RR that can replay this CNAME, hence rely on
+                         * that, and we can remove the CNAME in favour of it. */
+                }
+
+                /* This is just some auxiliary data. Just remove the RRset and continue. */
+                r = dns_answer_remove_by_key(&t->answer, rr->key);
+                if (r < 0)
+                        return r;
+
+                /* We dropped something from the answer, start from the beginning. */
+                return 1;
+        }
+
+        return 2; /* Finito. */
+}
+
+int dns_transaction_validate_dnssec(DnsTransaction *t) {
+        _cleanup_(dns_answer_unrefp) DnsAnswer *validated = NULL;
+        Phase phase;
+        DnsAnswerFlags flags;
+        int r;
+        char key_str[DNS_RESOURCE_KEY_STRING_MAX];
+
+        assert(t);
+
+        /* We have now collected all DS and DNSKEY RRs in
+         * t->validated_keys, let's see which RRs we can now
+         * authenticate with that. */
+
+        if (t->scope->dnssec_mode == DNSSEC_NO)
+                return 0;
+
+        /* Already validated */
+        if (t->answer_dnssec_result != _DNSSEC_RESULT_INVALID)
+                return 0;
+
+        /* Our own stuff needs no validation */
+        if (IN_SET(t->answer_source, DNS_TRANSACTION_ZONE, DNS_TRANSACTION_TRUST_ANCHOR)) {
+                t->answer_dnssec_result = DNSSEC_VALIDATED;
+                t->answer_authenticated = true;
+                return 0;
+        }
+
+        /* Cached stuff is not affected by validation. */
+        if (t->answer_source != DNS_TRANSACTION_NETWORK)
+                return 0;
+
+        if (!dns_transaction_dnssec_supported_full(t)) {
+                /* The server does not support DNSSEC, or doesn't augment responses with RRSIGs. */
+                t->answer_dnssec_result = DNSSEC_INCOMPATIBLE_SERVER;
+                log_debug("Not validating response for %" PRIu16 ", used server feature level does not support DNSSEC.", t->id);
+                return 0;
+        }
+
+        log_debug("Validating response from transaction %" PRIu16 " (%s).",
+                  t->id,
+                  dns_resource_key_to_string(t->key, key_str, sizeof key_str));
+
+        /* First, see if this response contains any revoked trust
+         * anchors we care about */
+        r = dns_transaction_check_revoked_trust_anchors(t);
+        if (r < 0)
+                return r;
+
+        /* Third, copy all RRs we acquired successfully from auxiliary RRs over. */
+        r = dns_transaction_copy_validated(t);
+        if (r < 0)
+                return r;
+
+        /* Second, see if there are DNSKEYs we already know a
+         * validated DS for. */
+        r = dns_transaction_validate_dnskey_by_ds(t);
+        if (r < 0)
+                return r;
+
+        /* Fourth, remove all DNSKEY and DS RRs again that our trust
+         * anchor says are revoked. After all we might have marked
+         * some keys revoked above, but they might still be lingering
+         * in our validated_keys list. */
+        r = dns_transaction_invalidate_revoked_keys(t);
+        if (r < 0)
+                return r;
+
+        phase = DNSSEC_PHASE_DNSKEY;
+        for (;;) {
+                bool have_nsec = false;
+
+                r = dnssec_validate_records(t, phase, &have_nsec, &validated);
+                if (r <= 0)
+                        return r;
+
+                /* Try again as long as we managed to achieve something */
+                if (r == 1)
+                        continue;
+
+                if (phase == DNSSEC_PHASE_DNSKEY && have_nsec) {
+                        /* OK, we processed all DNSKEYs, and there are NSEC/NSEC3 RRs, look at those now. */
+                        phase = DNSSEC_PHASE_NSEC;
+                        continue;
+                }
+
+                if (phase != DNSSEC_PHASE_ALL) {
+                        /* OK, we processed all DNSKEYs and NSEC/NSEC3 RRs, look at all the rest now.
+                         * Note that in this third phase we start to remove RRs we couldn't validate. */
+                        phase = DNSSEC_PHASE_ALL;
+                        continue;
+                }
+
+                /* We're done */
+                break;
+        }
+
+        dns_answer_unref(t->answer);
+        t->answer = TAKE_PTR(validated);
+
+        /* At this point the answer only contains validated
+         * RRsets. Now, let's see if it actually answers the question
+         * we asked. If so, great! If it doesn't, then see if
+         * NSEC/NSEC3 can prove this. */
+        r = dns_transaction_has_positive_answer(t, &flags);
+        if (r > 0) {
+                /* Yes, it answers the question! */
+
+                if (flags & DNS_ANSWER_AUTHENTICATED) {
+                        /* The answer is fully authenticated, yay. */
+                        t->answer_dnssec_result = DNSSEC_VALIDATED;
+                        t->answer_rcode = DNS_RCODE_SUCCESS;
+                        t->answer_authenticated = true;
+                } else {
+                        /* The answer is not fully authenticated. */
+                        t->answer_dnssec_result = DNSSEC_UNSIGNED;
+                        t->answer_authenticated = false;
+                }
+
+        } else if (r == 0) {
+                DnssecNsecResult nr;
+                bool authenticated = false;
+
+                /* Bummer! Let's check NSEC/NSEC3 */
+                r = dnssec_nsec_test(t->answer, t->key, &nr, &authenticated, &t->answer_nsec_ttl);
+                if (r < 0)
+                        return r;
+
+                switch (nr) {
+
+                case DNSSEC_NSEC_NXDOMAIN:
+                        /* NSEC proves the domain doesn't exist. Very good. */
+                        log_debug("Proved NXDOMAIN via NSEC/NSEC3 for transaction %u (%s)", t->id, key_str);
+                        t->answer_dnssec_result = DNSSEC_VALIDATED;
+                        t->answer_rcode = DNS_RCODE_NXDOMAIN;
+                        t->answer_authenticated = authenticated;
+
+                        manager_dnssec_verdict(t->scope->manager, authenticated ? DNSSEC_SECURE : DNSSEC_INSECURE, t->key);
+                        break;
+
+                case DNSSEC_NSEC_NODATA:
+                        /* NSEC proves that there's no data here, very good. */
+                        log_debug("Proved NODATA via NSEC/NSEC3 for transaction %u (%s)", t->id, key_str);
+                        t->answer_dnssec_result = DNSSEC_VALIDATED;
+                        t->answer_rcode = DNS_RCODE_SUCCESS;
+                        t->answer_authenticated = authenticated;
+
+                        manager_dnssec_verdict(t->scope->manager, authenticated ? DNSSEC_SECURE : DNSSEC_INSECURE, t->key);
+                        break;
+
+                case DNSSEC_NSEC_OPTOUT:
+                        /* NSEC3 says the data might not be signed */
+                        log_debug("Data is NSEC3 opt-out via NSEC/NSEC3 for transaction %u (%s)", t->id, key_str);
+                        t->answer_dnssec_result = DNSSEC_UNSIGNED;
+                        t->answer_authenticated = false;
+
+                        manager_dnssec_verdict(t->scope->manager, DNSSEC_INSECURE, t->key);
+                        break;
+
+                case DNSSEC_NSEC_NO_RR:
+                        /* No NSEC data? Bummer! */
+
+                        r = dns_transaction_requires_nsec(t);
+                        if (r < 0)
+                                return r;
+                        if (r > 0) {
+                                t->answer_dnssec_result = DNSSEC_NO_SIGNATURE;
+                                manager_dnssec_verdict(t->scope->manager, DNSSEC_BOGUS, t->key);
+                        } else {
+                                t->answer_dnssec_result = DNSSEC_UNSIGNED;
+                                t->answer_authenticated = false;
+                                manager_dnssec_verdict(t->scope->manager, DNSSEC_INSECURE, t->key);
+                        }
+
+                        break;
+
+                case DNSSEC_NSEC_UNSUPPORTED_ALGORITHM:
+                        /* We don't know the NSEC3 algorithm used? */
+                        t->answer_dnssec_result = DNSSEC_UNSUPPORTED_ALGORITHM;
+                        manager_dnssec_verdict(t->scope->manager, DNSSEC_INDETERMINATE, t->key);
+                        break;
+
+                case DNSSEC_NSEC_FOUND:
+                case DNSSEC_NSEC_CNAME:
+                        /* NSEC says it needs to be there, but we couldn't find it? Bummer! */
+                        t->answer_dnssec_result = DNSSEC_NSEC_MISMATCH;
+                        manager_dnssec_verdict(t->scope->manager, DNSSEC_BOGUS, t->key);
+                        break;
+
+                default:
+                        assert_not_reached("Unexpected NSEC result.");
+                }
+        }
+
+        return 1;
+}
+
+static const char* const dns_transaction_state_table[_DNS_TRANSACTION_STATE_MAX] = {
+        [DNS_TRANSACTION_NULL] = "null",
+        [DNS_TRANSACTION_PENDING] = "pending",
+        [DNS_TRANSACTION_VALIDATING] = "validating",
+        [DNS_TRANSACTION_RCODE_FAILURE] = "rcode-failure",
+        [DNS_TRANSACTION_SUCCESS] = "success",
+        [DNS_TRANSACTION_NO_SERVERS] = "no-servers",
+        [DNS_TRANSACTION_TIMEOUT] = "timeout",
+        [DNS_TRANSACTION_ATTEMPTS_MAX_REACHED] = "attempts-max-reached",
+        [DNS_TRANSACTION_INVALID_REPLY] = "invalid-reply",
+        [DNS_TRANSACTION_ERRNO] = "errno",
+        [DNS_TRANSACTION_ABORTED] = "aborted",
+        [DNS_TRANSACTION_DNSSEC_FAILED] = "dnssec-failed",
+        [DNS_TRANSACTION_NO_TRUST_ANCHOR] = "no-trust-anchor",
+        [DNS_TRANSACTION_RR_TYPE_UNSUPPORTED] = "rr-type-unsupported",
+        [DNS_TRANSACTION_NETWORK_DOWN] = "network-down",
+        [DNS_TRANSACTION_NOT_FOUND] = "not-found",
+};
+DEFINE_STRING_TABLE_LOOKUP(dns_transaction_state, DnsTransactionState);
+
+static const char* const dns_transaction_source_table[_DNS_TRANSACTION_SOURCE_MAX] = {
+        [DNS_TRANSACTION_NETWORK] = "network",
+        [DNS_TRANSACTION_CACHE] = "cache",
+        [DNS_TRANSACTION_ZONE] = "zone",
+        [DNS_TRANSACTION_TRUST_ANCHOR] = "trust-anchor",
+};
+DEFINE_STRING_TABLE_LOOKUP(dns_transaction_source, DnsTransactionSource);