src/resolve/resolved-dns-transaction.c - systemd-stable - Rivoreo Source Code Repositories

 /*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/

 /***
   This file is part of systemd.

   Copyright 2014 Lennart Poettering

   systemd is free software; you can redistribute it and/or modify it
   under the terms of the GNU Lesser General Public License as published by
   the Free Software Foundation; either version 2.1 of the License, or
   (at your option) any later version.

   systemd is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 ***/

 #include "af-list.h"

 #include "resolved-llmnr.h"
 #include "resolved-dns-transaction.h"
 #include "random-util.h"
 #include "dns-domain.h"

 DnsTransaction* dns_transaction_free(DnsTransaction *t) {
         DnsQuery *q;
         DnsZoneItem *i;

         if (!t)
                 return NULL;

         sd_event_source_unref(t->timeout_event_source);

         dns_packet_unref(t->sent);
         dns_packet_unref(t->received);
         dns_answer_unref(t->cached);

         sd_event_source_unref(t->dns_udp_event_source);
         safe_close(t->dns_udp_fd);

         dns_server_unref(t->server);
         dns_stream_free(t->stream);

         if (t->scope) {
                 hashmap_remove(t->scope->transactions, t->key);

                 if (t->id != 0)
                         hashmap_remove(t->scope->manager->dns_transactions, UINT_TO_PTR(t->id));
         }

         dns_resource_key_unref(t->key);

         while ((q = set_steal_first(t->queries)))
                 set_remove(q->transactions, t);
         set_free(t->queries);

         while ((i = set_steal_first(t->zone_items)))
                 i->probe_transaction = NULL;
         set_free(t->zone_items);

         free(t);
         return NULL;
 }

 DEFINE_TRIVIAL_CLEANUP_FUNC(DnsTransaction*, dns_transaction_free);

 void dns_transaction_gc(DnsTransaction *t) {
         assert(t);

         if (t->block_gc > 0)
                 return;

         if (set_isempty(t->queries) && set_isempty(t->zone_items))
                 dns_transaction_free(t);
 }

 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);

         r = hashmap_ensure_allocated(&s->manager->dns_transactions, NULL);
         if (r < 0)
                 return r;

         r = hashmap_ensure_allocated(&s->transactions, &dns_resource_key_hash_ops);
         if (r < 0)
                 return r;

         t = new0(DnsTransaction, 1);
         if (!t)
                 return -ENOMEM;

         t->dns_udp_fd = -1;
         t->key = dns_resource_key_ref(key);

         /* Find a fresh, unused transaction id */
         do
                 random_bytes(&t->id, sizeof(t->id));
         while (t->id == 0 ||
                hashmap_get(s->manager->dns_transactions, UINT_TO_PTR(t->id)));

         r = hashmap_put(s->manager->dns_transactions, UINT_TO_PTR(t->id), t);
         if (r < 0) {
                 t->id = 0;
                 return r;
         }

         r = hashmap_put(s->transactions, t->key, t);
         if (r < 0) {
                 hashmap_remove(s->manager->dns_transactions, UINT_TO_PTR(t->id));
                 return r;
         }

         t->scope = s;

         if (ret)
                 *ret = t;

         t = NULL;

         return 0;
 }

 static void dns_transaction_stop(DnsTransaction *t) {
         assert(t);

         t->timeout_event_source = sd_event_source_unref(t->timeout_event_source);
         t->stream = dns_stream_free(t->stream);
 }

 static void dns_transaction_tentative(DnsTransaction *t, DnsPacket *p) {
         _cleanup_free_ char *pretty = NULL;
         DnsZoneItem *z;

         assert(t);
         assert(p);

         if (manager_our_packet(t->scope->manager, p) != 0)
                 return;

         in_addr_to_string(p->family, &p->sender, &pretty);

         log_debug("Transaction on scope %s on %s/%s got tentative packet from %s",
                   dns_protocol_to_string(t->scope->protocol),
                   t->scope->link ? t->scope->link->name : "*",
                   t->scope->family == AF_UNSPEC ? "*" : af_to_name(t->scope->family),
                   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->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) {
         DnsQuery *q;
         DnsZoneItem *z;
         Iterator i;

         assert(t);
         assert(!IN_SET(state, DNS_TRANSACTION_NULL, DNS_TRANSACTION_PENDING));

         /* 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("Transaction on scope %s on %s/%s now complete with <%s>",
                   dns_protocol_to_string(t->scope->protocol),
                   t->scope->link ? t->scope->link->name : "*",
                   t->scope->family == AF_UNSPEC ? "*" : af_to_name(t->scope->family),
                   dns_transaction_state_to_string(state));

         t->state = state;

         dns_transaction_stop(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(q, t->queries, i)
                 dns_query_ready(q);
         SET_FOREACH(z, t->zone_items, i)
                 dns_zone_item_ready(z);
         t->block_gc--;

         dns_transaction_gc(t);
 }

 static int on_stream_complete(DnsStream *s, int error) {
         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
         DnsTransaction *t;

         assert(s);
         assert(s->transaction);

         /* Copy the data we care about out of the stream before we
          * destroy it. */
         t = s->transaction;
         p = dns_packet_ref(s->read_packet);

         t->stream = dns_stream_free(t->stream);

         if (error != 0) {
                 dns_transaction_complete(t, DNS_TRANSACTION_RESOURCES);
                 return 0;
         }

         if (dns_packet_validate_reply(p) <= 0) {
                 log_debug("Invalid LLMNR TCP 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 */
         if (t->state == DNS_TRANSACTION_PENDING)
                 dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);

         return 0;
 }

 static int dns_transaction_open_tcp(DnsTransaction *t) {
         DnsServer *server = NULL;
         _cleanup_close_ int fd = -1;
         int r;

         assert(t);

         if (t->stream)
                 return 0;

         switch (t->scope->protocol) {
         case DNS_PROTOCOL_DNS:
                 fd = dns_scope_tcp_socket(t->scope, AF_UNSPEC, NULL, 53, &server);
                 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_tcp_socket(t->scope, t->received->family, &t->received->sender, t->received->sender_port, NULL);
                 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_tcp_socket(t->scope, family, &address, LLMNR_PORT, NULL);
                 }

                 break;

         default:
                 return -EAFNOSUPPORT;
         }

         if (fd < 0)
                 return fd;

         r = dns_stream_new(t->scope->manager, &t->stream, t->scope->protocol, fd);
         if (r < 0)
                 return r;

         fd = -1;

         r = dns_stream_write_packet(t->stream, t->sent);
         if (r < 0) {
                 t->stream = dns_stream_free(t->stream);
                 return r;
         }

         dns_server_unref(t->server);
         t->server = dns_server_ref(server);
         t->received = dns_packet_unref(t->received);
         t->stream->complete = on_stream_complete;
         t->stream->transaction = t;

         /* 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 */
         if (t->scope->link)
                 t->stream->ifindex = t->scope->link->ifindex;

         return 0;
 }

 static void dns_transaction_next_dns_server(DnsTransaction *t) {
         assert(t);

         t->server = dns_server_unref(t->server);
         t->dns_udp_event_source = sd_event_source_unref(t->dns_udp_event_source);
         t->dns_udp_fd = safe_close(t->dns_udp_fd);

         dns_scope_next_dns_server(t->scope);
 }

 void dns_transaction_process_reply(DnsTransaction *t, DnsPacket *p) {
         usec_t ts;
         int r;

         assert(t);
         assert(p);
         assert(t->state == DNS_TRANSACTION_PENDING);
         assert(t->scope);
         assert(t->scope->manager);

         /* Note that this call might invalidate the query. Callers
          * should hence not attempt to access the query or transaction
          * after calling this function. */

         switch (t->scope->protocol) {
         case DNS_PROTOCOL_LLMNR:
                 assert(t->scope->link);

                 /* For LLMNR we will not accept any packets from other
                  * interfaces */

                 if (p->ifindex != t->scope->link->ifindex)
                         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_DNS:
                 break;

         default:
                 assert_not_reached("Invalid DNS protocol.");
         }

         if (t->received != p) {
                 dns_packet_unref(t->received);
                 t->received = dns_packet_ref(p);
         }

         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);

                 dns_server_packet_received(t->server, ts - t->start_usec);

                 break;
         case DNS_PROTOCOL_LLMNR:
         case DNS_PROTOCOL_MDNS:
                 dns_scope_packet_received(t->scope, ts - t->start_usec);

                 break;
         default:
                 break;
         }

         if (DNS_PACKET_TC(p)) {
                 /* Response was truncated, let's try again with good old TCP */
                 r = dns_transaction_open_tcp(t);
                 if (r == -ESRCH) {
                         /* No servers found? Damn! */
                         dns_transaction_complete(t, DNS_TRANSACTION_NO_SERVERS);
                         return;
                 }
                 if (r < 0) {
                         /* On LLMNR, if we cannot connect to the host,
                          * we immediately give up */
                         if (t->scope->protocol == DNS_PROTOCOL_LLMNR) {
                                 dns_transaction_complete(t, DNS_TRANSACTION_RESOURCES);
                                 return;
                         }

                         /* On DNS, couldn't send? Try immediately again, with a new server */
                         dns_transaction_next_dns_server(t);

                         r = dns_transaction_go(t);
                         if (r < 0) {
                                 dns_transaction_complete(t, DNS_TRANSACTION_RESOURCES);
                                 return;
                         }

                         return;
                 }
         }

         /* Parse and update the cache */
         r = dns_packet_extract(p);
         if (r < 0) {
                 dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
                 return;
         }

         /* Only consider responses with equivalent query section to the request */
         if (p->question->n_keys != 1 || dns_resource_key_equal(p->question->keys[0], t->key) <= 0) {
                 dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
                 return;
         }

         /* According to RFC 4795, section 2.9. only the RRs from the answer section shall be cached */
         dns_cache_put(&t->scope->cache, p->question, DNS_PACKET_RCODE(p), p->answer, DNS_PACKET_ANCOUNT(p), 0, p->family, &p->sender);

         if (DNS_PACKET_RCODE(p) == DNS_RCODE_SUCCESS)
                 dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
         else
                 dns_transaction_complete(t, DNS_TRANSACTION_FAILURE);
 }

 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 (r <= 0)
                 return r;

         if (dns_packet_validate_reply(p) > 0 &&
             DNS_PACKET_ID(p) == t->id)
                 dns_transaction_process_reply(t, p);
         else
                 log_debug("Invalid DNS packet.");

         return 0;
 }

 static int dns_transaction_emit(DnsTransaction *t) {
         int r;

         assert(t);

         if (t->scope->protocol == DNS_PROTOCOL_DNS && !t->server) {
                 DnsServer *server = NULL;
                 _cleanup_close_ int fd = -1;

                 fd = dns_scope_udp_dns_socket(t->scope, &server);
                 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)
                         return r;

                 t->dns_udp_fd = fd;
                 fd = -1;
                 t->server = dns_server_ref(server);
         }

         r = dns_scope_emit(t->scope, t->dns_udp_fd, t->sent);
         if (r < 0)
                 return r;

         return 0;
 }

 static int on_transaction_timeout(sd_event_source *s, usec_t usec, void *userdata) {
         DnsTransaction *t = userdata;
         int r;

         assert(s);
         assert(t);

         /* Timeout reached? Try again, with a new server */
         dns_transaction_next_dns_server(t);

         /* ... and possibly increased timeout */
         if (t->server)
                 dns_server_packet_lost(t->server, usec - t->start_usec);
         else
                 dns_scope_packet_lost(t->scope, usec - t->start_usec);

         r = dns_transaction_go(t);
         if (r < 0)
                 dns_transaction_complete(t, DNS_TRANSACTION_RESOURCES);

         return 0;
 }

 static int dns_transaction_make_packet(DnsTransaction *t) {
         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
         int r;

         assert(t);

         if (t->sent)
                 return 0;

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

         r = dns_scope_good_key(t->scope, t->key);
         if (r < 0)
                 return r;
         if (r == 0)
                 return -EDOM;

         r = dns_packet_append_key(p, t->key, NULL);
         if (r < 0)
                 return r;

         DNS_PACKET_HEADER(p)->qdcount = htobe16(1);
         DNS_PACKET_HEADER(p)->id = t->id;

         t->sent = p;
         p = NULL;

         return 0;
 }

 static usec_t transaction_get_resend_timeout(DnsTransaction *t) {
         assert(t);
         assert(t->scope);

         switch (t->scope->protocol) {
         case DNS_PROTOCOL_DNS:
                 assert(t->server);

                 return t->server->resend_timeout;
         case DNS_PROTOCOL_LLMNR:
         case DNS_PROTOCOL_MDNS:
                 return t->scope->resend_timeout;
         default:
                 assert_not_reached("Invalid DNS protocol.");
         }
 }

 int dns_transaction_go(DnsTransaction *t) {
         bool had_stream;
         usec_t ts;
         int r;

         assert(t);

         had_stream = !!t->stream;

         dns_transaction_stop(t);

         log_debug("Excercising transaction on scope %s on %s/%s",
                   dns_protocol_to_string(t->scope->protocol),
                   t->scope->link ? t->scope->link->name : "*",
                   t->scope->family == AF_UNSPEC ? "*" : af_to_name(t->scope->family));

         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 && had_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;
         }

         assert_se(sd_event_now(t->scope->manager->event, clock_boottime_or_monotonic(), &ts) >= 0);

         t->n_attempts++;
         t->start_usec = ts;
         t->received = dns_packet_unref(t->received);
         t->cached = dns_answer_unref(t->cached);
         t->cached_rcode = 0;

         /* Check the cache, but only if this transaction is not used
          * for probing or verifying a zone item. */
         if (set_isempty(t->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. */
                 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->cached_rcode, &t->cached);
                 if (r < 0)
                         return r;
                 if (r > 0) {
                         if (t->cached_rcode == DNS_RCODE_SUCCESS)
                                 dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
                         else
                                 dns_transaction_complete(t, DNS_TRANSACTION_FAILURE);
                         return 0;
                 }
         }

         if (t->scope->protocol == DNS_PROTOCOL_LLMNR && !t->initial_jitter) {
                 usec_t jitter;

                 /* RFC 4795 Section 2.7 suggests all queries should be
                  * delayed by a random time from 0 to JITTER_INTERVAL. */

                 t->initial_jitter = true;

                 random_bytes(&jitter, sizeof(jitter));
                 jitter %= LLMNR_JITTER_INTERVAL_USEC;

                 r = sd_event_add_time(
                                 t->scope->manager->event,
                                 &t->timeout_event_source,
                                 clock_boottime_or_monotonic(),
                                 ts + jitter,
                                 LLMNR_JITTER_INTERVAL_USEC,
                                 on_transaction_timeout, t);
                 if (r < 0)
                         return r;

                 t->n_attempts = 0;
                 t->state = DNS_TRANSACTION_PENDING;

                 log_debug("Delaying LLMNR transaction for " USEC_FMT "us.", jitter);
                 return 0;
         }

         /* Otherwise, we need to ask the network */
         r = dns_transaction_make_packet(t);
         if (r == -EDOM) {
                 /* Not the right request to make on this network?
                  * (i.e. an A request made on IPv6 or an AAAA request
                  * made on IPv4, on LLMNR or mDNS.) */
                 dns_transaction_complete(t, DNS_TRANSACTION_NO_SERVERS);
                 return 0;
         }
         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_open_tcp(t);
         } else {
                 /* Try via UDP, and if that fails due to large size try via TCP */
                 r = dns_transaction_emit(t);
                 if (r == -EMSGSIZE)
                         r = dns_transaction_open_tcp(t);
         }
         if (r == -ESRCH) {
                 /* No servers to send this to? */
                 dns_transaction_complete(t, DNS_TRANSACTION_NO_SERVERS);
                 return 0;
         } else if (r < 0) {
                 if (t->scope->protocol != DNS_PROTOCOL_DNS) {
                         dns_transaction_complete(t, DNS_TRANSACTION_RESOURCES);
                         return 0;
                 }

                 /* Couldn't send? Try immediately again, with a new server */
                 dns_transaction_next_dns_server(t);

                 return dns_transaction_go(t);
         }

         r = sd_event_add_time(
                         t->scope->manager->event,
                         &t->timeout_event_source,
                         clock_boottime_or_monotonic(),
                         ts + transaction_get_resend_timeout(t), 0,
                         on_transaction_timeout, t);
         if (r < 0)
                 return r;

         t->state = DNS_TRANSACTION_PENDING;
         return 1;
 }

 static const char* const dns_transaction_state_table[_DNS_TRANSACTION_STATE_MAX] = {
         [DNS_TRANSACTION_NULL] = "null",
         [DNS_TRANSACTION_PENDING] = "pending",
         [DNS_TRANSACTION_FAILURE] = "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_RESOURCES] = "resources",
         [DNS_TRANSACTION_ABORTED] = "aborted",
 };
 DEFINE_STRING_TABLE_LOOKUP(dns_transaction_state, DnsTransactionState);
	/-- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil --/

	/***
	This file is part of systemd.

	Copyright 2014 Lennart Poettering

	systemd is free software; you can redistribute it and/or modify it
	under the terms of the GNU Lesser General Public License as published by
	the Free Software Foundation; either version 2.1 of the License, or
	(at your option) any later version.

	systemd is distributed in the hope that it will be useful, but
	WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	Lesser General Public License for more details.

	You should have received a copy of the GNU Lesser General Public License
	along with systemd; If not, see <http://www.gnu.org/licenses/>.
	***/

	#include "af-list.h"

	#include "resolved-llmnr.h"
	#include "resolved-dns-transaction.h"
	#include "random-util.h"
	#include "dns-domain.h"

	DnsTransaction* dns_transaction_free(DnsTransaction *t) {
	DnsQuery *q;
	DnsZoneItem *i;

	if (!t)
	return NULL;

	sd_event_source_unref(t->timeout_event_source);

	dns_packet_unref(t->sent);
	dns_packet_unref(t->received);
	dns_answer_unref(t->cached);

	sd_event_source_unref(t->dns_udp_event_source);
	safe_close(t->dns_udp_fd);

	dns_server_unref(t->server);
	dns_stream_free(t->stream);

	if (t->scope) {
	hashmap_remove(t->scope->transactions, t->key);

	if (t->id != 0)
	hashmap_remove(t->scope->manager->dns_transactions, UINT_TO_PTR(t->id));
	}

	dns_resource_key_unref(t->key);

	while ((q = set_steal_first(t->queries)))
	set_remove(q->transactions, t);
	set_free(t->queries);

	while ((i = set_steal_first(t->zone_items)))
	i->probe_transaction = NULL;
	set_free(t->zone_items);

	free(t);
	return NULL;
	}

	DEFINE_TRIVIAL_CLEANUP_FUNC(DnsTransaction*, dns_transaction_free);

	void dns_transaction_gc(DnsTransaction *t) {
	assert(t);

	if (t->block_gc > 0)
	return;

	if (set_isempty(t->queries) && set_isempty(t->zone_items))
	dns_transaction_free(t);
	}

	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);

	r = hashmap_ensure_allocated(&s->manager->dns_transactions, NULL);
	if (r < 0)
	return r;

	r = hashmap_ensure_allocated(&s->transactions, &dns_resource_key_hash_ops);
	if (r < 0)
	return r;

	t = new0(DnsTransaction, 1);
	if (!t)
	return -ENOMEM;

	t->dns_udp_fd = -1;
	t->key = dns_resource_key_ref(key);

	/* Find a fresh, unused transaction id */
	do
	random_bytes(&t->id, sizeof(t->id));
	while (t->id == 0 \|\|
	hashmap_get(s->manager->dns_transactions, UINT_TO_PTR(t->id)));

	r = hashmap_put(s->manager->dns_transactions, UINT_TO_PTR(t->id), t);
	if (r < 0) {
	t->id = 0;
	return r;
	}

	r = hashmap_put(s->transactions, t->key, t);
	if (r < 0) {
	hashmap_remove(s->manager->dns_transactions, UINT_TO_PTR(t->id));
	return r;
	}

	t->scope = s;

	if (ret)
	*ret = t;

	t = NULL;

	return 0;
	}

	static void dns_transaction_stop(DnsTransaction *t) {
	assert(t);

	t->timeout_event_source = sd_event_source_unref(t->timeout_event_source);
	t->stream = dns_stream_free(t->stream);
	}

	static void dns_transaction_tentative(DnsTransaction t, DnsPacket p) {
	_cleanup_free_ char *pretty = NULL;
	DnsZoneItem *z;

	assert(t);
	assert(p);

	if (manager_our_packet(t->scope->manager, p) != 0)
	return;

	in_addr_to_string(p->family, &p->sender, &pretty);

	log_debug("Transaction on scope %s on %s/%s got tentative packet from %s",
	dns_protocol_to_string(t->scope->protocol),
	t->scope->link ? t->scope->link->name : "*",
	t->scope->family == AF_UNSPEC ? "*" : af_to_name(t->scope->family),
	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->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) {
	DnsQuery *q;
	DnsZoneItem *z;
	Iterator i;

	assert(t);
	assert(!IN_SET(state, DNS_TRANSACTION_NULL, DNS_TRANSACTION_PENDING));

	/* 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("Transaction on scope %s on %s/%s now complete with <%s>",
	dns_protocol_to_string(t->scope->protocol),
	t->scope->link ? t->scope->link->name : "*",
	t->scope->family == AF_UNSPEC ? "*" : af_to_name(t->scope->family),
	dns_transaction_state_to_string(state));

	t->state = state;

	dns_transaction_stop(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(q, t->queries, i)
	dns_query_ready(q);
	SET_FOREACH(z, t->zone_items, i)
	dns_zone_item_ready(z);
	t->block_gc--;

	dns_transaction_gc(t);
	}

	static int on_stream_complete(DnsStream *s, int error) {
	_cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
	DnsTransaction *t;

	assert(s);
	assert(s->transaction);

	/* Copy the data we care about out of the stream before we
	* destroy it. */
	t = s->transaction;
	p = dns_packet_ref(s->read_packet);

	t->stream = dns_stream_free(t->stream);

	if (error != 0) {
	dns_transaction_complete(t, DNS_TRANSACTION_RESOURCES);
	return 0;
	}

	if (dns_packet_validate_reply(p) <= 0) {
	log_debug("Invalid LLMNR TCP 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 */
	if (t->state == DNS_TRANSACTION_PENDING)
	dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);

	return 0;
	}

	static int dns_transaction_open_tcp(DnsTransaction *t) {
	DnsServer *server = NULL;
	_cleanup_close_ int fd = -1;
	int r;

	assert(t);

	if (t->stream)
	return 0;

	switch (t->scope->protocol) {
	case DNS_PROTOCOL_DNS:
	fd = dns_scope_tcp_socket(t->scope, AF_UNSPEC, NULL, 53, &server);
	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_tcp_socket(t->scope, t->received->family, &t->received->sender, t->received->sender_port, NULL);
	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_tcp_socket(t->scope, family, &address, LLMNR_PORT, NULL);
	}

	break;

	default:
	return -EAFNOSUPPORT;
	}

	if (fd < 0)
	return fd;

	r = dns_stream_new(t->scope->manager, &t->stream, t->scope->protocol, fd);
	if (r < 0)
	return r;

	fd = -1;

	r = dns_stream_write_packet(t->stream, t->sent);
	if (r < 0) {
	t->stream = dns_stream_free(t->stream);
	return r;
	}

	dns_server_unref(t->server);
	t->server = dns_server_ref(server);
	t->received = dns_packet_unref(t->received);
	t->stream->complete = on_stream_complete;
	t->stream->transaction = t;

	/* 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 */
	if (t->scope->link)
	t->stream->ifindex = t->scope->link->ifindex;

	return 0;
	}

	static void dns_transaction_next_dns_server(DnsTransaction *t) {
	assert(t);

	t->server = dns_server_unref(t->server);
	t->dns_udp_event_source = sd_event_source_unref(t->dns_udp_event_source);
	t->dns_udp_fd = safe_close(t->dns_udp_fd);

	dns_scope_next_dns_server(t->scope);
	}

	void dns_transaction_process_reply(DnsTransaction t, DnsPacket p) {
	usec_t ts;
	int r;

	assert(t);
	assert(p);
	assert(t->state == DNS_TRANSACTION_PENDING);
	assert(t->scope);
	assert(t->scope->manager);

	/* Note that this call might invalidate the query. Callers
	* should hence not attempt to access the query or transaction
	* after calling this function. */

	switch (t->scope->protocol) {
	case DNS_PROTOCOL_LLMNR:
	assert(t->scope->link);

	/* For LLMNR we will not accept any packets from other
	* interfaces */

	if (p->ifindex != t->scope->link->ifindex)
	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_DNS:
	break;

	default:
	assert_not_reached("Invalid DNS protocol.");
	}

	if (t->received != p) {
	dns_packet_unref(t->received);
	t->received = dns_packet_ref(p);
	}

	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);

	dns_server_packet_received(t->server, ts - t->start_usec);

	break;
	case DNS_PROTOCOL_LLMNR:
	case DNS_PROTOCOL_MDNS:
	dns_scope_packet_received(t->scope, ts - t->start_usec);

	break;
	default:
	break;
	}

	if (DNS_PACKET_TC(p)) {
	/* Response was truncated, let's try again with good old TCP */
	r = dns_transaction_open_tcp(t);
	if (r == -ESRCH) {
	/* No servers found? Damn! */
	dns_transaction_complete(t, DNS_TRANSACTION_NO_SERVERS);
	return;
	}
	if (r < 0) {
	/* On LLMNR, if we cannot connect to the host,
	* we immediately give up */
	if (t->scope->protocol == DNS_PROTOCOL_LLMNR) {
	dns_transaction_complete(t, DNS_TRANSACTION_RESOURCES);
	return;
	}

	/* On DNS, couldn't send? Try immediately again, with a new server */
	dns_transaction_next_dns_server(t);

	r = dns_transaction_go(t);
	if (r < 0) {
	dns_transaction_complete(t, DNS_TRANSACTION_RESOURCES);
	return;
	}

	return;
	}
	}

	/* Parse and update the cache */
	r = dns_packet_extract(p);
	if (r < 0) {
	dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
	return;
	}

	/* Only consider responses with equivalent query section to the request */
	if (p->question->n_keys != 1 \|\| dns_resource_key_equal(p->question->keys[0], t->key) <= 0) {
	dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
	return;
	}

	/* According to RFC 4795, section 2.9. only the RRs from the answer section shall be cached */
	dns_cache_put(&t->scope->cache, p->question, DNS_PACKET_RCODE(p), p->answer, DNS_PACKET_ANCOUNT(p), 0, p->family, &p->sender);

	if (DNS_PACKET_RCODE(p) == DNS_RCODE_SUCCESS)
	dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
	else
	dns_transaction_complete(t, DNS_TRANSACTION_FAILURE);
	}

	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 (r <= 0)
	return r;

	if (dns_packet_validate_reply(p) > 0 &&
	DNS_PACKET_ID(p) == t->id)
	dns_transaction_process_reply(t, p);
	else
	log_debug("Invalid DNS packet.");

	return 0;
	}

	static int dns_transaction_emit(DnsTransaction *t) {
	int r;

	assert(t);

	if (t->scope->protocol == DNS_PROTOCOL_DNS && !t->server) {
	DnsServer *server = NULL;
	_cleanup_close_ int fd = -1;

	fd = dns_scope_udp_dns_socket(t->scope, &server);
	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)
	return r;

	t->dns_udp_fd = fd;
	fd = -1;
	t->server = dns_server_ref(server);
	}

	r = dns_scope_emit(t->scope, t->dns_udp_fd, t->sent);
	if (r < 0)
	return r;

	return 0;
	}

	static int on_transaction_timeout(sd_event_source s, usec_t usec, void userdata) {
	DnsTransaction *t = userdata;
	int r;

	assert(s);
	assert(t);

	/* Timeout reached? Try again, with a new server */
	dns_transaction_next_dns_server(t);

	/* ... and possibly increased timeout */
	if (t->server)
	dns_server_packet_lost(t->server, usec - t->start_usec);
	else
	dns_scope_packet_lost(t->scope, usec - t->start_usec);

	r = dns_transaction_go(t);
	if (r < 0)
	dns_transaction_complete(t, DNS_TRANSACTION_RESOURCES);

	return 0;
	}

	static int dns_transaction_make_packet(DnsTransaction *t) {
	_cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
	int r;

	assert(t);

	if (t->sent)
	return 0;

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

	r = dns_scope_good_key(t->scope, t->key);
	if (r < 0)
	return r;
	if (r == 0)
	return -EDOM;

	r = dns_packet_append_key(p, t->key, NULL);
	if (r < 0)
	return r;

	DNS_PACKET_HEADER(p)->qdcount = htobe16(1);
	DNS_PACKET_HEADER(p)->id = t->id;

	t->sent = p;
	p = NULL;

	return 0;
	}

	static usec_t transaction_get_resend_timeout(DnsTransaction *t) {
	assert(t);
	assert(t->scope);

	switch (t->scope->protocol) {
	case DNS_PROTOCOL_DNS:
	assert(t->server);

	return t->server->resend_timeout;
	case DNS_PROTOCOL_LLMNR:
	case DNS_PROTOCOL_MDNS:
	return t->scope->resend_timeout;
	default:
	assert_not_reached("Invalid DNS protocol.");
	}
	}

	int dns_transaction_go(DnsTransaction *t) {
	bool had_stream;
	usec_t ts;
	int r;

	assert(t);

	had_stream = !!t->stream;

	dns_transaction_stop(t);

	log_debug("Excercising transaction on scope %s on %s/%s",
	dns_protocol_to_string(t->scope->protocol),
	t->scope->link ? t->scope->link->name : "*",
	t->scope->family == AF_UNSPEC ? "*" : af_to_name(t->scope->family));

	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 && had_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;
	}

	assert_se(sd_event_now(t->scope->manager->event, clock_boottime_or_monotonic(), &ts) >= 0);

	t->n_attempts++;
	t->start_usec = ts;
	t->received = dns_packet_unref(t->received);
	t->cached = dns_answer_unref(t->cached);
	t->cached_rcode = 0;

	/* Check the cache, but only if this transaction is not used
	* for probing or verifying a zone item. */
	if (set_isempty(t->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. */
	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->cached_rcode, &t->cached);
	if (r < 0)
	return r;
	if (r > 0) {
	if (t->cached_rcode == DNS_RCODE_SUCCESS)
	dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
	else
	dns_transaction_complete(t, DNS_TRANSACTION_FAILURE);
	return 0;
	}
	}

	if (t->scope->protocol == DNS_PROTOCOL_LLMNR && !t->initial_jitter) {
	usec_t jitter;

	/* RFC 4795 Section 2.7 suggests all queries should be
	* delayed by a random time from 0 to JITTER_INTERVAL. */

	t->initial_jitter = true;

	random_bytes(&jitter, sizeof(jitter));
	jitter %= LLMNR_JITTER_INTERVAL_USEC;

	r = sd_event_add_time(
	t->scope->manager->event,
	&t->timeout_event_source,
	clock_boottime_or_monotonic(),
	ts + jitter,
	LLMNR_JITTER_INTERVAL_USEC,
	on_transaction_timeout, t);
	if (r < 0)
	return r;

	t->n_attempts = 0;
	t->state = DNS_TRANSACTION_PENDING;

	log_debug("Delaying LLMNR transaction for " USEC_FMT "us.", jitter);
	return 0;
	}

	/* Otherwise, we need to ask the network */
	r = dns_transaction_make_packet(t);
	if (r == -EDOM) {
	/* Not the right request to make on this network?
	* (i.e. an A request made on IPv6 or an AAAA request
	* made on IPv4, on LLMNR or mDNS.) */
	dns_transaction_complete(t, DNS_TRANSACTION_NO_SERVERS);
	return 0;
	}
	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_open_tcp(t);
	} else {
	/* Try via UDP, and if that fails due to large size try via TCP */
	r = dns_transaction_emit(t);
	if (r == -EMSGSIZE)
	r = dns_transaction_open_tcp(t);
	}
	if (r == -ESRCH) {
	/* No servers to send this to? */
	dns_transaction_complete(t, DNS_TRANSACTION_NO_SERVERS);
	return 0;
	} else if (r < 0) {
	if (t->scope->protocol != DNS_PROTOCOL_DNS) {
	dns_transaction_complete(t, DNS_TRANSACTION_RESOURCES);
	return 0;
	}

	/* Couldn't send? Try immediately again, with a new server */
	dns_transaction_next_dns_server(t);

	return dns_transaction_go(t);
	}

	r = sd_event_add_time(
	t->scope->manager->event,
	&t->timeout_event_source,
	clock_boottime_or_monotonic(),
	ts + transaction_get_resend_timeout(t), 0,
	on_transaction_timeout, t);
	if (r < 0)
	return r;

	t->state = DNS_TRANSACTION_PENDING;
	return 1;
	}

	static const char* const dns_transaction_state_table[_DNS_TRANSACTION_STATE_MAX] = {
	[DNS_TRANSACTION_NULL] = "null",
	[DNS_TRANSACTION_PENDING] = "pending",
	[DNS_TRANSACTION_FAILURE] = "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_RESOURCES] = "resources",
	[DNS_TRANSACTION_ABORTED] = "aborted",
	};
	DEFINE_STRING_TABLE_LOOKUP(dns_transaction_state, DnsTransactionState);