diff options
Diffstat (limited to 'src/resolve/resolved-dns-server.c')
| -rw-r--r-- | src/resolve/resolved-dns-server.c | 325 |
1 files changed, 270 insertions, 55 deletions
diff --git a/src/resolve/resolved-dns-server.c b/src/resolve/resolved-dns-server.c index d565f99c09..5a86661807 100644 --- a/src/resolve/resolved-dns-server.c +++ b/src/resolve/resolved-dns-server.c @@ -68,8 +68,8 @@ int dns_server_new( s->n_ref = 1; s->manager = m; - s->verified_features = _DNS_SERVER_FEATURE_LEVEL_INVALID; - s->possible_features = DNS_SERVER_FEATURE_LEVEL_BEST; + s->verified_feature_level = _DNS_SERVER_FEATURE_LEVEL_INVALID; + s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_BEST; s->features_grace_period_usec = DNS_SERVER_FEATURE_GRACE_PERIOD_MIN_USEC; s->received_udp_packet_max = DNS_PACKET_UNICAST_SIZE_MAX; s->type = type; @@ -135,6 +135,7 @@ DnsServer* dns_server_unref(DnsServer *s) { if (s->n_ref > 0) return NULL; + free(s->server_string); free(s); return NULL; } @@ -224,43 +225,75 @@ void dns_server_move_back_and_unmark(DnsServer *s) { } } -void dns_server_packet_received(DnsServer *s, DnsServerFeatureLevel features, usec_t rtt, size_t size) { +static void dns_server_verified(DnsServer *s, DnsServerFeatureLevel level) { assert(s); - if (features == DNS_SERVER_FEATURE_LEVEL_LARGE) { - /* 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 (s->verified_features < DNS_SERVER_FEATURE_LEVEL_LARGE - 1) { - s->verified_features = DNS_SERVER_FEATURE_LEVEL_LARGE - 1; - assert_se(sd_event_now(s->manager->event, clock_boottime_or_monotonic(), &s->verified_usec) >= 0); - } - } else if (s->verified_features < features) { - s->verified_features = features; - assert_se(sd_event_now(s->manager->event, clock_boottime_or_monotonic(), &s->verified_usec) >= 0); + 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), + dns_server_string(s)); + s->verified_feature_level = level; } - if (s->possible_features == features) - s->n_failed_attempts = 0; + assert_se(sd_event_now(s->manager->event, clock_boottime_or_monotonic(), &s->verified_usec) >= 0); +} + +void dns_server_packet_received(DnsServer *s, int protocol, DnsServerFeatureLevel level, usec_t rtt, size_t size) { + assert(s); + + if (protocol == IPPROTO_UDP) { + if (s->possible_feature_level == level) + s->n_failed_udp = 0; + + /* 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_DO - 1; + + /* 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; + + } else if (protocol == IPPROTO_TCP) { + + 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; + } + + dns_server_verified(s, level); /* Remember the size of the largest UDP packet we received from a server, we know that we can always announce support for packets with at least this size. */ - if (s->received_udp_packet_max < size) + if (protocol == IPPROTO_UDP && s->received_udp_packet_max < size) s->received_udp_packet_max = size; if (s->max_rtt < rtt) { s->max_rtt = rtt; - s->resend_timeout = MIN(MAX(DNS_TIMEOUT_MIN_USEC, s->max_rtt * 2), DNS_TIMEOUT_MAX_USEC); + s->resend_timeout = CLAMP(s->max_rtt * 2, DNS_TIMEOUT_MIN_USEC, DNS_TIMEOUT_MAX_USEC); } } -void dns_server_packet_lost(DnsServer *s, DnsServerFeatureLevel features, usec_t usec) { +void dns_server_packet_lost(DnsServer *s, int protocol, DnsServerFeatureLevel level, usec_t usec) { assert(s); assert(s->manager); - if (s->possible_features == features) - s->n_failed_attempts ++; + if (s->possible_feature_level == level) { + if (protocol == IPPROTO_UDP) + s->n_failed_udp ++; + else if (protocol == IPPROTO_TCP) + s->n_failed_tcp ++; + } if (s->resend_timeout > usec) return; @@ -268,14 +301,52 @@ void dns_server_packet_lost(DnsServer *s, DnsServerFeatureLevel features, usec_t s->resend_timeout = MIN(s->resend_timeout * 2, DNS_TIMEOUT_MAX_USEC); } -void dns_server_packet_failed(DnsServer *s, DnsServerFeatureLevel features) { +void dns_server_packet_failed(DnsServer *s, DnsServerFeatureLevel level) { assert(s); - assert(s->manager); - if (s->possible_features != features) + /* Invoked whenever we get a FORMERR, SERVFAIL or NOTIMP rcode from a server. */ + + if (s->possible_feature_level != level) + return; + + s->packet_failed = true; +} + +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->n_failed_attempts = (unsigned) -1; + 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_DO-1; + + 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; } static bool dns_server_grace_period_expired(DnsServer *s) { @@ -297,35 +368,183 @@ static bool dns_server_grace_period_expired(DnsServer *s) { return true; } -DnsServerFeatureLevel dns_server_possible_features(DnsServer *s) { +static void dns_server_reset_counters(DnsServer *s) { + assert(s); + + s->n_failed_udp = 0; + s->n_failed_tcp = 0; + s->packet_failed = false; + s->packet_truncated = 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 + * reenable it for another, because we cannot validate things anyway, given that the RRSIG/OPT data will be + * incomplete. */ +} + +DnsServerFeatureLevel dns_server_possible_feature_level(DnsServer *s) { assert(s); - if (s->possible_features != DNS_SERVER_FEATURE_LEVEL_BEST && + if (s->possible_feature_level != DNS_SERVER_FEATURE_LEVEL_BEST && dns_server_grace_period_expired(s)) { - _cleanup_free_ char *ip = NULL; - - s->possible_features = DNS_SERVER_FEATURE_LEVEL_BEST; - s->n_failed_attempts = 0; - s->verified_usec = 0; - - in_addr_to_string(s->family, &s->address, &ip); - log_info("Grace period over, resuming full feature set for DNS server %s", strna(ip)); - } else if (s->possible_features <= s->verified_features) - s->possible_features = s->verified_features; - else if (s->n_failed_attempts >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS && - s->possible_features > DNS_SERVER_FEATURE_LEVEL_WORST) { - _cleanup_free_ char *ip = NULL; - - s->possible_features --; - s->n_failed_attempts = 0; - s->verified_usec = 0; - - in_addr_to_string(s->family, &s->address, &ip); - log_warning("Using degraded feature set (%s) for DNS server %s", - dns_server_feature_level_to_string(s->possible_features), strna(ip)); + + s->possible_feature_level = DNS_SERVER_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), + dns_server_string(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; + + 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->packet_bad_opt && + s->possible_feature_level >= DNS_SERVER_FEATURE_LEVEL_EDNS0) { + + /* A reply to one of our EDNS0 queries didn't carry a valid OPT RR, then downgrade to below + * EDNS0 levels. After all, some records generate different responses with and without OPT RR + * in the request. Example: + * https://open.nlnetlabs.nl/pipermail/dnssec-trigger/2014-November/000376.html */ + + log_debug("Server doesn't support EDNS(0) properly, downgrading feature level..."); + s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_UDP; + + } else if (s->packet_rrsig_missing && + s->possible_feature_level >= DNS_SERVER_FEATURE_LEVEL_DO) { + + /* 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. */ + + log_debug("Detected server responses lack RRSIG records, downgrading feature level..."); + s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_EDNS0; + + } else if (s->n_failed_udp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS && + s->possible_feature_level >= DNS_SERVER_FEATURE_LEVEL_UDP) { + + /* We lost too many UDP packets in a row, and are on a feature level of UDP or higher. 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. */ + + log_debug("Lost too many UDP packets, downgrading feature level..."); + s->possible_feature_level--; + + } else if (s->packet_failed && + s->possible_feature_level > DNS_SERVER_FEATURE_LEVEL_UDP) { + + /* We got a failure packet, and are at a feature level above UDP. Note that in this case we + * downgrade no further than UDP, under the assumption that a failure packet indicates an + * incompatible packet contents, but not a problem with the transport. */ + + log_debug("Got server failure, downgrading feature level..."); + 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) { + + /* We got too many TCP connection failures in a row, we had at least one truncated packet, and + * are on a 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..."); + s->possible_feature_level--; + } + + if (p != s->possible_feature_level) { + + /* We changed the feature level, reset the counting */ + dns_server_reset_counters(s); + + log_warning("Using degraded feature set (%s) for DNS server %s.", + dns_server_feature_level_to_string(s->possible_feature_level), + dns_server_string(s)); + } } - return s->possible_features; + 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) + packet_size = DNS_PACKET_UNICAST_SIZE_LARGE_MAX; + else + packet_size = server->received_udp_packet_max; + + return dns_packet_append_opt(packet, packet_size, edns_do, NULL); +} + +const char *dns_server_string(DnsServer *server) { + assert(server); + + if (!server->server_string) + (void) in_addr_to_string(server->family, &server->address, &server->server_string); + + return strna(server->server_string); +} + +bool dns_server_dnssec_supported(DnsServer *server) { + assert(server); + + /* Returns whether the server supports DNSSEC according to what we know about it */ + + if (server->possible_feature_level < DNS_SERVER_FEATURE_LEVEL_DO) + return false; + + if (server->packet_bad_opt) + return false; + + if (server->packet_rrsig_missing) + 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; } static void dns_server_hash_func(const void *p, struct siphash *state) { @@ -419,12 +638,8 @@ DnsServer *manager_set_dns_server(Manager *m, DnsServer *s) { if (m->current_dns_server == s) return s; - if (s) { - _cleanup_free_ char *ip = NULL; - - in_addr_to_string(s->family, &s->address, &ip); - log_info("Switching to system DNS server %s.", strna(ip)); - } + if (s) + log_info("Switching to system DNS server %s.", dns_server_string(s)); dns_server_unref(m->current_dns_server); m->current_dns_server = dns_server_ref(s); |