| /* SPDX-License-Identifier: LGPL-2.1-or-later */ |
| |
| #include "sd-messages.h" |
| |
| #include "alloc-util.h" |
| #include "resolved-bus.h" |
| #include "resolved-dns-server.h" |
| #include "resolved-dns-stub.h" |
| #include "resolved-manager.h" |
| #include "resolved-resolv-conf.h" |
| #include "siphash24.h" |
| #include "string-table.h" |
| #include "string-util.h" |
| |
| /* The amount of time to wait before retrying with a full feature set */ |
| #define DNS_SERVER_FEATURE_GRACE_PERIOD_MAX_USEC (6 * USEC_PER_HOUR) |
| #define DNS_SERVER_FEATURE_GRACE_PERIOD_MIN_USEC (5 * USEC_PER_MINUTE) |
| |
| /* The number of times we will attempt a certain feature set before degrading */ |
| #define DNS_SERVER_FEATURE_RETRY_ATTEMPTS 3 |
| |
| int dns_server_new( |
| Manager *m, |
| DnsServer **ret, |
| DnsServerType type, |
| Link *l, |
| int family, |
| const union in_addr_union *in_addr, |
| uint16_t port, |
| int ifindex, |
| const char *server_name) { |
| |
| _cleanup_free_ char *name = NULL; |
| DnsServer *s; |
| |
| assert(m); |
| assert((type == DNS_SERVER_LINK) == !!l); |
| assert(in_addr); |
| |
| if (!IN_SET(family, AF_INET, AF_INET6)) |
| return -EAFNOSUPPORT; |
| |
| if (l) { |
| if (l->n_dns_servers >= LINK_DNS_SERVERS_MAX) |
| return -E2BIG; |
| } else { |
| if (m->n_dns_servers >= MANAGER_DNS_SERVERS_MAX) |
| return -E2BIG; |
| } |
| |
| if (!isempty(server_name)) { |
| name = strdup(server_name); |
| if (!name) |
| return -ENOMEM; |
| } |
| |
| s = new(DnsServer, 1); |
| if (!s) |
| return -ENOMEM; |
| |
| *s = (DnsServer) { |
| .n_ref = 1, |
| .manager = m, |
| .type = type, |
| .family = family, |
| .address = *in_addr, |
| .port = port, |
| .ifindex = ifindex, |
| .server_name = TAKE_PTR(name), |
| }; |
| |
| dns_server_reset_features(s); |
| |
| switch (type) { |
| |
| case DNS_SERVER_LINK: |
| s->link = l; |
| LIST_APPEND(servers, l->dns_servers, s); |
| l->n_dns_servers++; |
| break; |
| |
| case DNS_SERVER_SYSTEM: |
| LIST_APPEND(servers, m->dns_servers, s); |
| m->n_dns_servers++; |
| break; |
| |
| case DNS_SERVER_FALLBACK: |
| LIST_APPEND(servers, m->fallback_dns_servers, s); |
| m->n_dns_servers++; |
| break; |
| |
| default: |
| assert_not_reached(); |
| } |
| |
| s->linked = true; |
| |
| /* A new DNS server that isn't fallback is added and the one |
| * we used so far was a fallback one? Then let's try to pick |
| * the new one */ |
| if (type != DNS_SERVER_FALLBACK && |
| m->current_dns_server && |
| m->current_dns_server->type == DNS_SERVER_FALLBACK) |
| manager_set_dns_server(m, NULL); |
| |
| if (ret) |
| *ret = s; |
| |
| return 0; |
| } |
| |
| static DnsServer* dns_server_free(DnsServer *s) { |
| assert(s); |
| |
| dns_server_unref_stream(s); |
| |
| #if ENABLE_DNS_OVER_TLS |
| dnstls_server_free(s); |
| #endif |
| |
| free(s->server_string); |
| free(s->server_string_full); |
| free(s->server_name); |
| return mfree(s); |
| } |
| |
| DEFINE_TRIVIAL_REF_UNREF_FUNC(DnsServer, dns_server, dns_server_free); |
| |
| void dns_server_unlink(DnsServer *s) { |
| assert(s); |
| assert(s->manager); |
| |
| /* This removes the specified server from the linked list of |
| * servers, but any server might still stay around if it has |
| * refs, for example from an ongoing transaction. */ |
| |
| if (!s->linked) |
| return; |
| |
| switch (s->type) { |
| |
| case DNS_SERVER_LINK: |
| assert(s->link); |
| assert(s->link->n_dns_servers > 0); |
| LIST_REMOVE(servers, s->link->dns_servers, s); |
| s->link->n_dns_servers--; |
| break; |
| |
| case DNS_SERVER_SYSTEM: |
| assert(s->manager->n_dns_servers > 0); |
| LIST_REMOVE(servers, s->manager->dns_servers, s); |
| s->manager->n_dns_servers--; |
| break; |
| |
| case DNS_SERVER_FALLBACK: |
| assert(s->manager->n_dns_servers > 0); |
| LIST_REMOVE(servers, s->manager->fallback_dns_servers, s); |
| s->manager->n_dns_servers--; |
| break; |
| default: |
| assert_not_reached(); |
| } |
| |
| s->linked = false; |
| |
| if (s->link && s->link->current_dns_server == s) |
| link_set_dns_server(s->link, NULL); |
| |
| if (s->manager->current_dns_server == s) |
| manager_set_dns_server(s->manager, NULL); |
| |
| /* No need to keep a default stream around anymore */ |
| dns_server_unref_stream(s); |
| |
| dns_server_unref(s); |
| } |
| |
| void dns_server_move_back_and_unmark(DnsServer *s) { |
| DnsServer *tail; |
| |
| assert(s); |
| |
| if (!s->marked) |
| return; |
| |
| s->marked = false; |
| |
| if (!s->linked || !s->servers_next) |
| return; |
| |
| /* Move us to the end of the list, so that the order is |
| * strictly kept, if we are not at the end anyway. */ |
| |
| switch (s->type) { |
| |
| case DNS_SERVER_LINK: |
| assert(s->link); |
| tail = LIST_FIND_TAIL(servers, s); |
| LIST_REMOVE(servers, s->link->dns_servers, s); |
| LIST_INSERT_AFTER(servers, s->link->dns_servers, tail, s); |
| break; |
| |
| case DNS_SERVER_SYSTEM: |
| tail = LIST_FIND_TAIL(servers, s); |
| LIST_REMOVE(servers, s->manager->dns_servers, s); |
| LIST_INSERT_AFTER(servers, s->manager->dns_servers, tail, s); |
| break; |
| |
| case DNS_SERVER_FALLBACK: |
| tail = LIST_FIND_TAIL(servers, s); |
| LIST_REMOVE(servers, s->manager->fallback_dns_servers, s); |
| LIST_INSERT_AFTER(servers, s->manager->fallback_dns_servers, tail, s); |
| break; |
| |
| default: |
| assert_not_reached(); |
| } |
| } |
| |
| static void dns_server_verified(DnsServer *s, DnsServerFeatureLevel level) { |
| assert(s); |
| |
| if (s->verified_feature_level > level) |
| return; |
| |
| if (s->verified_feature_level != level) { |
| log_debug("Verified we get a response at feature level %s from DNS server %s.", |
| dns_server_feature_level_to_string(level), |
| strna(dns_server_string_full(s))); |
| s->verified_feature_level = level; |
| } |
| |
| assert_se(sd_event_now(s->manager->event, CLOCK_BOOTTIME, &s->verified_usec) >= 0); |
| } |
| |
| static void dns_server_reset_counters(DnsServer *s) { |
| assert(s); |
| |
| s->n_failed_udp = 0; |
| s->n_failed_tcp = 0; |
| s->n_failed_tls = 0; |
| s->packet_truncated = false; |
| s->packet_invalid = false; |
| s->verified_usec = 0; |
| |
| /* Note that we do not reset s->packet_bad_opt and s->packet_rrsig_missing here. We reset them only when the |
| * grace period ends, but not when lowering the possible feature level, as a lower level feature level should |
| * not make RRSIGs appear or OPT appear, but rather make them disappear. If the reappear anyway, then that's |
| * indication for a differently broken OPT/RRSIG implementation, and we really don't want to support that |
| * either. |
| * |
| * This is particularly important to deal with certain Belkin routers which break OPT for certain lookups (A), |
| * but pass traffic through for others (AAAA). If we detect the broken behaviour on one lookup we should not |
| * re-enable it for another, because we cannot validate things anyway, given that the RRSIG/OPT data will be |
| * incomplete. */ |
| } |
| |
| void dns_server_packet_received(DnsServer *s, int protocol, DnsServerFeatureLevel level, size_t fragsize) { |
| assert(s); |
| |
| if (protocol == IPPROTO_UDP) { |
| if (s->possible_feature_level == level) |
| s->n_failed_udp = 0; |
| } else if (protocol == IPPROTO_TCP) { |
| if (DNS_SERVER_FEATURE_LEVEL_IS_TLS(level)) { |
| if (s->possible_feature_level == level) |
| s->n_failed_tls = 0; |
| } else { |
| if (s->possible_feature_level == level) |
| s->n_failed_tcp = 0; |
| |
| /* Successful TCP connections are only useful to verify the TCP feature level. */ |
| level = DNS_SERVER_FEATURE_LEVEL_TCP; |
| } |
| } |
| |
| /* If the RRSIG data is missing, then we can only validate EDNS0 at max */ |
| if (s->packet_rrsig_missing && level >= DNS_SERVER_FEATURE_LEVEL_DO) |
| level = DNS_SERVER_FEATURE_LEVEL_IS_TLS(level) ? DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN : DNS_SERVER_FEATURE_LEVEL_EDNS0; |
| |
| /* If the OPT RR got lost, then we can only validate UDP at max */ |
| if (s->packet_bad_opt && level >= DNS_SERVER_FEATURE_LEVEL_EDNS0) |
| level = DNS_SERVER_FEATURE_LEVEL_EDNS0 - 1; |
| |
| dns_server_verified(s, level); |
| |
| /* Remember the size of the largest UDP packet fragment we received from a server, we know that we |
| * can always announce support for packets with at least this size. */ |
| if (protocol == IPPROTO_UDP && s->received_udp_fragment_max < fragsize) |
| s->received_udp_fragment_max = fragsize; |
| } |
| |
| void dns_server_packet_lost(DnsServer *s, int protocol, DnsServerFeatureLevel level) { |
| assert(s); |
| assert(s->manager); |
| |
| if (s->possible_feature_level != level) |
| return; |
| |
| if (protocol == IPPROTO_UDP) |
| s->n_failed_udp++; |
| else if (protocol == IPPROTO_TCP) { |
| if (DNS_SERVER_FEATURE_LEVEL_IS_TLS(level)) |
| s->n_failed_tls++; |
| else |
| s->n_failed_tcp++; |
| } |
| } |
| |
| void dns_server_packet_truncated(DnsServer *s, DnsServerFeatureLevel level) { |
| assert(s); |
| |
| /* Invoked whenever we get a packet with TC bit set. */ |
| |
| if (s->possible_feature_level != level) |
| return; |
| |
| s->packet_truncated = true; |
| } |
| |
| void dns_server_packet_rrsig_missing(DnsServer *s, DnsServerFeatureLevel level) { |
| assert(s); |
| |
| if (level < DNS_SERVER_FEATURE_LEVEL_DO) |
| return; |
| |
| /* If the RRSIG RRs are missing, we have to downgrade what we previously verified */ |
| if (s->verified_feature_level >= DNS_SERVER_FEATURE_LEVEL_DO) |
| s->verified_feature_level = DNS_SERVER_FEATURE_LEVEL_IS_TLS(level) ? DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN : DNS_SERVER_FEATURE_LEVEL_EDNS0; |
| |
| s->packet_rrsig_missing = true; |
| } |
| |
| void dns_server_packet_bad_opt(DnsServer *s, DnsServerFeatureLevel level) { |
| assert(s); |
| |
| if (level < DNS_SERVER_FEATURE_LEVEL_EDNS0) |
| return; |
| |
| /* If the OPT RR got lost, we have to downgrade what we previously verified */ |
| if (s->verified_feature_level >= DNS_SERVER_FEATURE_LEVEL_EDNS0) |
| s->verified_feature_level = DNS_SERVER_FEATURE_LEVEL_EDNS0-1; |
| |
| s->packet_bad_opt = true; |
| } |
| |
| void dns_server_packet_rcode_downgrade(DnsServer *s, DnsServerFeatureLevel level) { |
| assert(s); |
| |
| /* Invoked whenever we got a FORMERR, SERVFAIL or NOTIMP rcode from a server and downgrading the feature level |
| * for the transaction made it go away. In this case we immediately downgrade to the feature level that made |
| * things work. */ |
| |
| if (s->verified_feature_level > level) |
| s->verified_feature_level = level; |
| |
| if (s->possible_feature_level > level) { |
| s->possible_feature_level = level; |
| dns_server_reset_counters(s); |
| log_debug("Downgrading transaction feature level fixed an RCODE error, downgrading server %s too.", strna(dns_server_string_full(s))); |
| } |
| } |
| |
| void dns_server_packet_invalid(DnsServer *s, DnsServerFeatureLevel level) { |
| assert(s); |
| |
| /* Invoked whenever we got a packet we couldn't parse at all */ |
| |
| if (s->possible_feature_level != level) |
| return; |
| |
| s->packet_invalid = true; |
| } |
| |
| void dns_server_packet_do_off(DnsServer *s, DnsServerFeatureLevel level) { |
| assert(s); |
| |
| /* Invoked whenever the DO flag was not copied from our request to the response. */ |
| |
| if (s->possible_feature_level != level) |
| return; |
| |
| s->packet_do_off = true; |
| } |
| |
| void dns_server_packet_udp_fragmented(DnsServer *s, size_t fragsize) { |
| assert(s); |
| |
| /* Invoked whenever we got a fragmented UDP packet. Let's do two things: keep track of the largest |
| * fragment we ever received from the server, and remember this, so that we can use it to lower the |
| * advertised packet size in EDNS0 */ |
| |
| if (s->received_udp_fragment_max < fragsize) |
| s->received_udp_fragment_max = fragsize; |
| |
| s->packet_fragmented = true; |
| } |
| |
| static bool dns_server_grace_period_expired(DnsServer *s) { |
| usec_t ts; |
| |
| assert(s); |
| assert(s->manager); |
| |
| if (s->verified_usec == 0) |
| return false; |
| |
| assert_se(sd_event_now(s->manager->event, CLOCK_BOOTTIME, &ts) >= 0); |
| |
| if (s->verified_usec + s->features_grace_period_usec > ts) |
| return false; |
| |
| s->features_grace_period_usec = MIN(s->features_grace_period_usec * 2, DNS_SERVER_FEATURE_GRACE_PERIOD_MAX_USEC); |
| |
| return true; |
| } |
| |
| DnsServerFeatureLevel dns_server_possible_feature_level(DnsServer *s) { |
| DnsServerFeatureLevel best; |
| |
| assert(s); |
| |
| /* Determine the best feature level we care about. If DNSSEC mode is off there's no point in using anything |
| * better than EDNS0, hence don't even try. */ |
| if (dns_server_get_dnssec_mode(s) != DNSSEC_NO) |
| best = dns_server_get_dns_over_tls_mode(s) == DNS_OVER_TLS_NO ? |
| DNS_SERVER_FEATURE_LEVEL_DO : |
| DNS_SERVER_FEATURE_LEVEL_TLS_DO; |
| else |
| best = dns_server_get_dns_over_tls_mode(s) == DNS_OVER_TLS_NO ? |
| DNS_SERVER_FEATURE_LEVEL_EDNS0 : |
| DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN; |
| |
| /* Clamp the feature level the highest level we care about. The DNSSEC mode might have changed since the last |
| * time, hence let's downgrade if we are still at a higher level. */ |
| if (s->possible_feature_level > best) |
| s->possible_feature_level = best; |
| |
| if (s->possible_feature_level < best && dns_server_grace_period_expired(s)) { |
| |
| s->possible_feature_level = best; |
| |
| dns_server_reset_counters(s); |
| |
| s->packet_bad_opt = false; |
| s->packet_rrsig_missing = false; |
| |
| log_info("Grace period over, resuming full feature set (%s) for DNS server %s.", |
| dns_server_feature_level_to_string(s->possible_feature_level), |
| strna(dns_server_string_full(s))); |
| |
| dns_server_flush_cache(s); |
| |
| } else if (s->possible_feature_level <= s->verified_feature_level) |
| s->possible_feature_level = s->verified_feature_level; |
| else { |
| DnsServerFeatureLevel p = s->possible_feature_level; |
| int log_level = LOG_WARNING; |
| |
| if (s->n_failed_tcp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS && |
| s->possible_feature_level == DNS_SERVER_FEATURE_LEVEL_TCP) { |
| |
| /* We are at the TCP (lowest) level, and we tried a couple of TCP connections, and it didn't |
| * work. Upgrade back to UDP again. */ |
| log_debug("Reached maximum number of failed TCP connection attempts, trying UDP again..."); |
| s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_UDP; |
| |
| } else if (s->n_failed_tls > 0 && |
| DNS_SERVER_FEATURE_LEVEL_IS_TLS(s->possible_feature_level) && |
| dns_server_get_dns_over_tls_mode(s) != DNS_OVER_TLS_YES) { |
| |
| /* We tried to connect using DNS-over-TLS, and it didn't work. Downgrade to plaintext UDP |
| * if we don't require DNS-over-TLS */ |
| |
| log_debug("Server doesn't support DNS-over-TLS, downgrading protocol..."); |
| s->possible_feature_level--; |
| |
| } else if (s->packet_invalid && |
| s->possible_feature_level > DNS_SERVER_FEATURE_LEVEL_UDP && |
| s->possible_feature_level != DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN) { |
| |
| /* Downgrade from DO to EDNS0 + from EDNS0 to UDP, from TLS+DO to plain TLS. Or in |
| * other words, if we receive a packet we cannot parse jump to the next lower feature |
| * level that actually has an influence on the packet layout (and not just the |
| * transport). */ |
| |
| log_debug("Got invalid packet from server, downgrading protocol..."); |
| s->possible_feature_level = |
| s->possible_feature_level == DNS_SERVER_FEATURE_LEVEL_TLS_DO ? DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN : |
| DNS_SERVER_FEATURE_LEVEL_IS_DNSSEC(s->possible_feature_level) ? DNS_SERVER_FEATURE_LEVEL_EDNS0 : |
| DNS_SERVER_FEATURE_LEVEL_UDP; |
| |
| } else if (s->packet_bad_opt && |
| DNS_SERVER_FEATURE_LEVEL_IS_EDNS0(s->possible_feature_level) && |
| dns_server_get_dnssec_mode(s) != DNSSEC_YES && |
| dns_server_get_dns_over_tls_mode(s) != DNS_OVER_TLS_YES) { |
| |
| /* A reply to one of our EDNS0 queries didn't carry a valid OPT RR, then downgrade to |
| * below EDNS0 levels. After all, some servers generate different responses with and |
| * without OPT RR in the request. Example: |
| * |
| * https://open.nlnetlabs.nl/pipermail/dnssec-trigger/2014-November/000376.html |
| * |
| * If we are in strict DNSSEC or DoT mode, we don't do this kind of downgrade |
| * however, as both modes imply EDNS0 to work (DNSSEC strictly requires it, and DoT |
| * only in our implementation). */ |
| |
| log_debug("Server doesn't support EDNS(0) properly, downgrading feature level..."); |
| s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_UDP; |
| |
| /* Users often don't control the DNS server they use so let's not complain too loudly |
| * when we can't use EDNS because the DNS server doesn't support it. */ |
| log_level = LOG_NOTICE; |
| |
| } else if (s->packet_do_off && |
| DNS_SERVER_FEATURE_LEVEL_IS_DNSSEC(s->possible_feature_level) && |
| dns_server_get_dnssec_mode(s) != DNSSEC_YES) { |
| |
| /* The server didn't copy the DO bit from request to response, thus DNSSEC is not |
| * correctly implemented, let's downgrade if that's allowed. */ |
| |
| log_debug("Detected server didn't copy DO flag from request to response, downgrading feature level..."); |
| s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_IS_TLS(s->possible_feature_level) ? DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN : |
| DNS_SERVER_FEATURE_LEVEL_EDNS0; |
| |
| } else if (s->packet_rrsig_missing && |
| DNS_SERVER_FEATURE_LEVEL_IS_DNSSEC(s->possible_feature_level) && |
| dns_server_get_dnssec_mode(s) != DNSSEC_YES) { |
| |
| /* RRSIG data was missing on an EDNS0 packet with DO bit set. This means the server |
| * doesn't augment responses with DNSSEC RRs. If so, let's better not ask the server |
| * for it anymore, after all some servers generate different replies depending if an |
| * OPT RR is in the query or not. If we are in strict DNSSEC mode, don't allow such |
| * downgrades however, since a DNSSEC feature level is a requirement for strict |
| * DNSSEC mode. */ |
| |
| log_debug("Detected server responses lack RRSIG records, downgrading feature level..."); |
| s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_IS_TLS(s->possible_feature_level) ? DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN : |
| DNS_SERVER_FEATURE_LEVEL_EDNS0; |
| |
| } else if (s->n_failed_udp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS && |
| DNS_SERVER_FEATURE_LEVEL_IS_UDP(s->possible_feature_level) && |
| ((s->possible_feature_level != DNS_SERVER_FEATURE_LEVEL_DO) || dns_server_get_dnssec_mode(s) != DNSSEC_YES)) { |
| |
| /* We lost too many UDP packets in a row, and are on an UDP feature level. If the |
| * packets are lost, maybe the server cannot parse them, hence downgrading sounds |
| * like a good idea. We might downgrade all the way down to TCP this way. |
| * |
| * If strict DNSSEC mode is used we won't downgrade below DO level however, as packet loss |
| * might have many reasons, a broken DNSSEC implementation being only one reason. And if the |
| * user is strict on DNSSEC, then let's assume that DNSSEC is not the fault here. */ |
| |
| log_debug("Lost too many UDP packets, downgrading feature level..."); |
| if (s->possible_feature_level == DNS_SERVER_FEATURE_LEVEL_DO) /* skip over TLS_PLAIN */ |
| s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_EDNS0; |
| else |
| s->possible_feature_level--; |
| |
| } else if (s->n_failed_tcp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS && |
| s->packet_truncated && |
| s->possible_feature_level > DNS_SERVER_FEATURE_LEVEL_UDP && |
| DNS_SERVER_FEATURE_LEVEL_IS_UDP(s->possible_feature_level) && |
| (!DNS_SERVER_FEATURE_LEVEL_IS_DNSSEC(s->possible_feature_level) || dns_server_get_dnssec_mode(s) != DNSSEC_YES)) { |
| |
| /* We got too many TCP connection failures in a row, we had at least one truncated |
| * packet, and are on feature level above UDP. By downgrading things and getting rid |
| * of DNSSEC or EDNS0 data we hope to make the packet smaller, so that it still |
| * works via UDP given that TCP appears not to be a fallback. Note that if we are |
| * already at the lowest UDP level, we don't go further down, since that's TCP, and |
| * TCP failed too often after all. */ |
| |
| log_debug("Got too many failed TCP connection failures and truncated UDP packets, downgrading feature level..."); |
| |
| if (DNS_SERVER_FEATURE_LEVEL_IS_DNSSEC(s->possible_feature_level)) |
| s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_EDNS0; /* Go DNSSEC → EDNS0 */ |
| else |
| s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_UDP; /* Go EDNS0 → UDP */ |
| } |
| |
| if (p != s->possible_feature_level) { |
| |
| /* We changed the feature level, reset the counting */ |
| dns_server_reset_counters(s); |
| |
| log_full(log_level, "Using degraded feature set %s instead of %s for DNS server %s.", |
| dns_server_feature_level_to_string(s->possible_feature_level), |
| dns_server_feature_level_to_string(p), strna(dns_server_string_full(s))); |
| } |
| } |
| |
| return s->possible_feature_level; |
| } |
| |
| int dns_server_adjust_opt(DnsServer *server, DnsPacket *packet, DnsServerFeatureLevel level) { |
| size_t packet_size, udp_size; |
| bool edns_do; |
| int r; |
| |
| assert(server); |
| assert(packet); |
| assert(packet->protocol == DNS_PROTOCOL_DNS); |
| |
| /* Fix the OPT field in the packet to match our current feature level. */ |
| |
| r = dns_packet_truncate_opt(packet); |
| if (r < 0) |
| return r; |
| |
| if (level < DNS_SERVER_FEATURE_LEVEL_EDNS0) |
| return 0; |
| |
| edns_do = level >= DNS_SERVER_FEATURE_LEVEL_DO; |
| |
| udp_size = udp_header_size(server->family); |
| |
| if (in_addr_is_localhost(server->family, &server->address) > 0) |
| packet_size = 65536 - udp_size; /* force linux loopback MTU if localhost address */ |
| else { |
| /* Use the MTU pointing to the server, subtract the IP/UDP header size */ |
| packet_size = LESS_BY(dns_server_get_mtu(server), udp_size); |
| |
| /* On the Internet we want to avoid fragmentation for security reasons. If we saw |
| * fragmented packets, the above was too large, let's clamp it to the largest |
| * fragment we saw */ |
| if (server->packet_fragmented) |
| packet_size = MIN(server->received_udp_fragment_max, packet_size); |
| |
| /* Let's not pick ridiculously large sizes, i.e. not more than 4K. No one appears |
| * to ever use such large sized on the Internet IRL, hence let's not either. */ |
| packet_size = MIN(packet_size, 4096U); |
| } |
| |
| /* Strictly speaking we quite possibly can receive larger datagrams than the MTU (since the |
| * MTU is for egress, not for ingress), but more often than not the value is symmetric, and |
| * we want something that does the right thing in the majority of cases, and not just in the |
| * theoretical edge case. */ |
| |
| /* Safety clamp, never advertise less than 512 or more than 65535 */ |
| packet_size = CLAMP(packet_size, |
| DNS_PACKET_UNICAST_SIZE_MAX, |
| DNS_PACKET_SIZE_MAX); |
| |
| log_debug("Announcing packet size %zu in egress EDNS(0) packet.", packet_size); |
| |
| return dns_packet_append_opt(packet, packet_size, edns_do, /* include_rfc6975 = */ true, NULL, 0, NULL); |
| } |
| |
| int dns_server_ifindex(const DnsServer *s) { |
| assert(s); |
| |
| /* For loopback addresses, go via the loopback interface, regardless which interface this is linked |
| * to. */ |
| if (in_addr_is_localhost(s->family, &s->address)) |
| return LOOPBACK_IFINDEX; |
| |
| /* The link ifindex always takes precedence */ |
| if (s->link) |
| return s->link->ifindex; |
| |
| if (s->ifindex > 0) |
| return s->ifindex; |
| |
| return 0; |
| } |
| |
| uint16_t dns_server_port(const DnsServer *s) { |
| assert(s); |
| |
| if (s->port > 0) |
| return s->port; |
| |
| return 53; |
| } |
| |
| const char *dns_server_string(DnsServer *server) { |
| assert(server); |
| |
| if (!server->server_string) |
| (void) in_addr_ifindex_to_string(server->family, &server->address, dns_server_ifindex(server), &server->server_string); |
| |
| return server->server_string; |
| } |
| |
| const char *dns_server_string_full(DnsServer *server) { |
| assert(server); |
| |
| if (!server->server_string_full) |
| (void) in_addr_port_ifindex_name_to_string( |
| server->family, |
| &server->address, |
| server->port, |
| dns_server_ifindex(server), |
| server->server_name, |
| &server->server_string_full); |
| |
| return server->server_string_full; |
| } |
| |
| bool dns_server_dnssec_supported(DnsServer *server) { |
| assert(server); |
| |
| /* Returns whether the server supports DNSSEC according to what we know about it */ |
| |
| if (dns_server_get_dnssec_mode(server) == DNSSEC_YES) /* If strict DNSSEC mode is enabled, always assume DNSSEC mode is supported. */ |
| return true; |
| |
| if (!DNS_SERVER_FEATURE_LEVEL_IS_DNSSEC(server->possible_feature_level)) |
| return false; |
| |
| if (server->packet_bad_opt) |
| return false; |
| |
| if (server->packet_rrsig_missing) |
| return false; |
| |
| if (server->packet_do_off) |
| return false; |
| |
| /* DNSSEC servers need to support TCP properly (see RFC5966), if they don't, we assume DNSSEC is borked too */ |
| if (server->n_failed_tcp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS) |
| return false; |
| |
| return true; |
| } |
| |
| void dns_server_warn_downgrade(DnsServer *server) { |
| assert(server); |
| |
| if (server->warned_downgrade) |
| return; |
| |
| log_struct(LOG_NOTICE, |
| "MESSAGE_ID=" SD_MESSAGE_DNSSEC_DOWNGRADE_STR, |
| LOG_MESSAGE("Server %s does not support DNSSEC, downgrading to non-DNSSEC mode.", |
| strna(dns_server_string_full(server))), |
| "DNS_SERVER=%s", strna(dns_server_string_full(server)), |
| "DNS_SERVER_FEATURE_LEVEL=%s", dns_server_feature_level_to_string(server->possible_feature_level)); |
| |
| server->warned_downgrade = true; |
| } |
| |
| size_t dns_server_get_mtu(DnsServer *s) { |
| assert(s); |
| |
| if (s->link && s->link->mtu != 0) |
| return s->link->mtu; |
| |
| return manager_find_mtu(s->manager); |
| } |
| |
| static void dns_server_hash_func(const DnsServer *s, struct siphash *state) { |
| assert(s); |
| |
| siphash24_compress(&s->family, sizeof(s->family), state); |
| siphash24_compress(&s->address, FAMILY_ADDRESS_SIZE(s->family), state); |
| siphash24_compress(&s->port, sizeof(s->port), state); |
| siphash24_compress(&s->ifindex, sizeof(s->ifindex), state); |
| siphash24_compress_string(s->server_name, state); |
| } |
| |
| static int dns_server_compare_func(const DnsServer *x, const DnsServer *y) { |
| int r; |
| |
| r = CMP(x->family, y->family); |
| if (r != 0) |
| return r; |
| |
| r = memcmp(&x->address, &y->address, FAMILY_ADDRESS_SIZE(x->family)); |
| if (r != 0) |
| return r; |
| |
| r = CMP(x->port, y->port); |
| if (r != 0) |
| return r; |
| |
| r = CMP(x->ifindex, y->ifindex); |
| if (r != 0) |
| return r; |
| |
| return streq_ptr(x->server_name, y->server_name); |
| } |
| |
| DEFINE_HASH_OPS(dns_server_hash_ops, DnsServer, dns_server_hash_func, dns_server_compare_func); |
| |
| void dns_server_unlink_all(DnsServer *first) { |
| DnsServer *next; |
| |
| if (!first) |
| return; |
| |
| next = first->servers_next; |
| dns_server_unlink(first); |
| |
| dns_server_unlink_all(next); |
| } |
| |
| bool dns_server_unlink_marked(DnsServer *server) { |
| bool changed = false; |
| |
| while (server) { |
| DnsServer *next; |
| |
| next = server->servers_next; |
| |
| if (server->marked) { |
| dns_server_unlink(server); |
| changed = true; |
| } |
| |
| server = next; |
| } |
| |
| return changed; |
| } |
| |
| void dns_server_mark_all(DnsServer *server) { |
| while (server) { |
| server->marked = true; |
| server = server->servers_next; |
| } |
| } |
| |
| DnsServer *dns_server_find(DnsServer *first, int family, const union in_addr_union *in_addr, uint16_t port, int ifindex, const char *name) { |
| LIST_FOREACH(servers, s, first) |
| if (s->family == family && |
| in_addr_equal(family, &s->address, in_addr) > 0 && |
| s->port == port && |
| s->ifindex == ifindex && |
| streq_ptr(s->server_name, name)) |
| return s; |
| |
| return NULL; |
| } |
| |
| DnsServer *manager_get_first_dns_server(Manager *m, DnsServerType t) { |
| assert(m); |
| |
| switch (t) { |
| |
| case DNS_SERVER_SYSTEM: |
| return m->dns_servers; |
| |
| case DNS_SERVER_FALLBACK: |
| return m->fallback_dns_servers; |
| |
| default: |
| return NULL; |
| } |
| } |
| |
| DnsServer *manager_set_dns_server(Manager *m, DnsServer *s) { |
| assert(m); |
| |
| if (m->current_dns_server == s) |
| return s; |
| |
| /* Let's log about the server switch, at debug level. Except if we switch from a non-fallback server |
| * to a fallback server or back, since that is noteworthy and possibly a configuration issue */ |
| if (s) |
| log_full((s->type == DNS_SERVER_FALLBACK) != (m->current_dns_server && m->current_dns_server->type == DNS_SERVER_FALLBACK) ? LOG_NOTICE : LOG_DEBUG, |
| "Switching to %s DNS server %s.", dns_server_type_to_string(s->type), strna(dns_server_string_full(s))); |
| |
| dns_server_unref(m->current_dns_server); |
| m->current_dns_server = dns_server_ref(s); |
| |
| if (m->unicast_scope) |
| dns_cache_flush(&m->unicast_scope->cache); |
| |
| (void) manager_send_changed(m, "CurrentDNSServer"); |
| |
| return s; |
| } |
| |
| DnsServer *manager_get_dns_server(Manager *m) { |
| Link *l; |
| assert(m); |
| |
| /* Try to read updates resolv.conf */ |
| manager_read_resolv_conf(m); |
| |
| /* If no DNS server was chosen so far, pick the first one */ |
| if (!m->current_dns_server || |
| /* In case m->current_dns_server != m->dns_servers */ |
| manager_server_is_stub(m, m->current_dns_server)) |
| manager_set_dns_server(m, m->dns_servers); |
| |
| while (m->current_dns_server && |
| manager_server_is_stub(m, m->current_dns_server)) { |
| manager_next_dns_server(m, NULL); |
| if (m->current_dns_server == m->dns_servers) |
| manager_set_dns_server(m, NULL); |
| } |
| |
| if (!m->current_dns_server) { |
| bool found = false; |
| |
| /* No DNS servers configured, let's see if there are |
| * any on any links. If not, we use the fallback |
| * servers */ |
| |
| HASHMAP_FOREACH(l, m->links) |
| if (l->dns_servers) { |
| found = true; |
| break; |
| } |
| |
| if (!found) |
| manager_set_dns_server(m, m->fallback_dns_servers); |
| } |
| |
| return m->current_dns_server; |
| } |
| |
| void manager_next_dns_server(Manager *m, DnsServer *if_current) { |
| assert(m); |
| |
| /* If the DNS server is already a different one than the one specified in 'if_current' don't do anything */ |
| if (if_current && m->current_dns_server != if_current) |
| return; |
| |
| /* If there's currently no DNS server set, then the next manager_get_dns_server() will find one */ |
| if (!m->current_dns_server) |
| return; |
| |
| /* Change to the next one, but make sure to follow the linked list only if the server is still |
| * linked. */ |
| if (m->current_dns_server->linked && m->current_dns_server->servers_next) { |
| manager_set_dns_server(m, m->current_dns_server->servers_next); |
| return; |
| } |
| |
| /* If there was no next one, then start from the beginning of the list */ |
| if (m->current_dns_server->type == DNS_SERVER_FALLBACK) |
| manager_set_dns_server(m, m->fallback_dns_servers); |
| else |
| manager_set_dns_server(m, m->dns_servers); |
| } |
| |
| DnssecMode dns_server_get_dnssec_mode(DnsServer *s) { |
| assert(s); |
| |
| if (s->link) |
| return link_get_dnssec_mode(s->link); |
| |
| return manager_get_dnssec_mode(s->manager); |
| } |
| |
| DnsOverTlsMode dns_server_get_dns_over_tls_mode(DnsServer *s) { |
| assert(s); |
| |
| if (s->link) |
| return link_get_dns_over_tls_mode(s->link); |
| |
| return manager_get_dns_over_tls_mode(s->manager); |
| } |
| |
| void dns_server_flush_cache(DnsServer *s) { |
| DnsServer *current; |
| DnsScope *scope; |
| |
| assert(s); |
| |
| /* Flush the cache of the scope this server belongs to */ |
| |
| current = s->link ? s->link->current_dns_server : s->manager->current_dns_server; |
| if (current != s) |
| return; |
| |
| scope = s->link ? s->link->unicast_scope : s->manager->unicast_scope; |
| if (!scope) |
| return; |
| |
| dns_cache_flush(&scope->cache); |
| } |
| |
| void dns_server_reset_features(DnsServer *s) { |
| assert(s); |
| |
| s->verified_feature_level = _DNS_SERVER_FEATURE_LEVEL_INVALID; |
| s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_BEST; |
| |
| s->received_udp_fragment_max = DNS_PACKET_UNICAST_SIZE_MAX; |
| |
| s->packet_bad_opt = false; |
| s->packet_rrsig_missing = false; |
| s->packet_do_off = false; |
| |
| s->features_grace_period_usec = DNS_SERVER_FEATURE_GRACE_PERIOD_MIN_USEC; |
| |
| s->warned_downgrade = false; |
| |
| dns_server_reset_counters(s); |
| |
| /* Let's close the default stream, so that we reprobe with the new features */ |
| dns_server_unref_stream(s); |
| } |
| |
| void dns_server_reset_features_all(DnsServer *s) { |
| LIST_FOREACH(servers, i, s) |
| dns_server_reset_features(i); |
| } |
| |
| void dns_server_dump(DnsServer *s, FILE *f) { |
| assert(s); |
| |
| if (!f) |
| f = stdout; |
| |
| fputs("[Server ", f); |
| fputs(strna(dns_server_string_full(s)), f); |
| fputs(" type=", f); |
| fputs(dns_server_type_to_string(s->type), f); |
| |
| if (s->type == DNS_SERVER_LINK) { |
| assert(s->link); |
| |
| fputs(" interface=", f); |
| fputs(s->link->ifname, f); |
| } |
| |
| fputs("]\n", f); |
| |
| fputs("\tVerified feature level: ", f); |
| fputs(strna(dns_server_feature_level_to_string(s->verified_feature_level)), f); |
| fputc('\n', f); |
| |
| fputs("\tPossible feature level: ", f); |
| fputs(strna(dns_server_feature_level_to_string(s->possible_feature_level)), f); |
| fputc('\n', f); |
| |
| fputs("\tDNSSEC Mode: ", f); |
| fputs(strna(dnssec_mode_to_string(dns_server_get_dnssec_mode(s))), f); |
| fputc('\n', f); |
| |
| fputs("\tCan do DNSSEC: ", f); |
| fputs(yes_no(dns_server_dnssec_supported(s)), f); |
| fputc('\n', f); |
| |
| fprintf(f, |
| "\tMaximum UDP fragment size received: %zu\n" |
| "\tFailed UDP attempts: %u\n" |
| "\tFailed TCP attempts: %u\n" |
| "\tSeen truncated packet: %s\n" |
| "\tSeen OPT RR getting lost: %s\n" |
| "\tSeen RRSIG RR missing: %s\n" |
| "\tSeen invalid packet: %s\n" |
| "\tServer dropped DO flag: %s\n", |
| s->received_udp_fragment_max, |
| s->n_failed_udp, |
| s->n_failed_tcp, |
| yes_no(s->packet_truncated), |
| yes_no(s->packet_bad_opt), |
| yes_no(s->packet_rrsig_missing), |
| yes_no(s->packet_invalid), |
| yes_no(s->packet_do_off)); |
| } |
| |
| void dns_server_unref_stream(DnsServer *s) { |
| DnsStream *ref; |
| |
| assert(s); |
| |
| /* Detaches the default stream of this server. Some special care needs to be taken here, as that stream and |
| * this server reference each other. First, take the stream out of the server. It's destructor will check if it |
| * is registered with us, hence let's invalidate this separately, so that it is already unregistered. */ |
| ref = TAKE_PTR(s->stream); |
| |
| /* And then, unref it */ |
| dns_stream_unref(ref); |
| } |
| |
| DnsScope *dns_server_scope(DnsServer *s) { |
| assert(s); |
| assert((s->type == DNS_SERVER_LINK) == !!s->link); |
| |
| if (s->link) |
| return s->link->unicast_scope; |
| |
| return s->manager->unicast_scope; |
| } |
| |
| static const char* const dns_server_type_table[_DNS_SERVER_TYPE_MAX] = { |
| [DNS_SERVER_SYSTEM] = "system", |
| [DNS_SERVER_FALLBACK] = "fallback", |
| [DNS_SERVER_LINK] = "link", |
| }; |
| DEFINE_STRING_TABLE_LOOKUP(dns_server_type, DnsServerType); |
| |
| static const char* const dns_server_feature_level_table[_DNS_SERVER_FEATURE_LEVEL_MAX] = { |
| [DNS_SERVER_FEATURE_LEVEL_TCP] = "TCP", |
| [DNS_SERVER_FEATURE_LEVEL_UDP] = "UDP", |
| [DNS_SERVER_FEATURE_LEVEL_EDNS0] = "UDP+EDNS0", |
| [DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN] = "TLS+EDNS0", |
| [DNS_SERVER_FEATURE_LEVEL_DO] = "UDP+EDNS0+DO", |
| [DNS_SERVER_FEATURE_LEVEL_TLS_DO] = "TLS+EDNS0+DO", |
| }; |
| DEFINE_STRING_TABLE_LOOKUP(dns_server_feature_level, DnsServerFeatureLevel); |
