/* 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("Unknown server type"); } 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("Unknown server type"); } 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); LIST_FIND_TAIL(servers, s, tail); LIST_REMOVE(servers, s->link->dns_servers, s); LIST_INSERT_AFTER(servers, s->link->dns_servers, tail, s); break; case DNS_SERVER_SYSTEM: LIST_FIND_TAIL(servers, s, tail); LIST_REMOVE(servers, s->manager->dns_servers, s); LIST_INSERT_AFTER(servers, s->manager->dns_servers, tail, s); break; case DNS_SERVER_FALLBACK: LIST_FIND_TAIL(servers, s, tail); 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("Unknown server type"); } } 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_or_monotonic(), &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; /* Even if we successfully receive a reply to a request announcing support for large packets, that * does not mean we can necessarily receive large packets. */ if (level == DNS_SERVER_FEATURE_LEVEL_LARGE) level = DNS_SERVER_FEATURE_LEVEL_LARGE - 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_or_monotonic(), &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_LARGE : 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 a 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; 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; if (level == DNS_SERVER_FEATURE_LEVEL_LARGE) { size_t udp_size; /* In large mode, advertise the local MTU, in order to avoid fragmentation (for security * reasons) – except if we are talking to localhost (where the security considerations don't * matter). If we see fragmentation, lower the reported size to the largest fragment, to * avoid it. */ 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. */ } else /* In non-large mode, let's advertise the size of the largest fragment we ever managed to accept. */ packet_size = server->received_udp_fragment_max; /* 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); /* 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 *first) { DnsServer *next; bool changed; if (!first) return false; next = first->servers_next; if (first->marked) { changed = true; dns_server_unlink(first); } else changed = false; return changed || dns_server_unlink_marked(next); } void dns_server_mark_all(DnsServer *first) { if (!first) return; first->marked = true; dns_server_mark_all(first->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) { DnsServer *s; 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) manager_set_dns_server(m, m->dns_servers); 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) { DnsServer *i; 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_LARGE] = "UDP+EDNS0+DO+LARGE", [DNS_SERVER_FEATURE_LEVEL_TLS_DO] = "TLS+EDNS0+D0", }; DEFINE_STRING_TABLE_LOOKUP(dns_server_feature_level, DnsServerFeatureLevel);