diff options
Diffstat (limited to 'src/resolve/resolved-dns-server.c')
-rw-r--r-- | src/resolve/resolved-dns-server.c | 631 |
1 files changed, 591 insertions, 40 deletions
diff --git a/src/resolve/resolved-dns-server.c b/src/resolve/resolved-dns-server.c index 2ff5b192df..5a86661807 100644 --- a/src/resolve/resolved-dns-server.c +++ b/src/resolve/resolved-dns-server.c @@ -19,14 +19,24 @@ along with systemd; If not, see <http://www.gnu.org/licenses/>. ***/ -#include "siphash24.h" - +#include "alloc-util.h" #include "resolved-dns-server.h" +#include "resolved-resolv-conf.h" +#include "siphash24.h" +#include "string-table.h" +#include "string-util.h" /* After how much time to repeat classic DNS requests */ #define DNS_TIMEOUT_MIN_USEC (500 * USEC_PER_MSEC) #define DNS_TIMEOUT_MAX_USEC (5 * USEC_PER_SEC) +/* 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, @@ -35,36 +45,61 @@ int dns_server_new( int family, const union in_addr_union *in_addr) { - DnsServer *s, *tail; + 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; + } + s = new0(DnsServer, 1); if (!s) return -ENOMEM; s->n_ref = 1; + s->manager = m; + 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; s->family = family; s->address = *in_addr; s->resend_timeout = DNS_TIMEOUT_MIN_USEC; - if (type == DNS_SERVER_LINK) { - LIST_FIND_TAIL(servers, l->dns_servers, tail); - LIST_INSERT_AFTER(servers, l->dns_servers, tail, s); + switch (type) { + + case DNS_SERVER_LINK: s->link = l; - } else if (type == DNS_SERVER_SYSTEM) { - LIST_FIND_TAIL(servers, m->dns_servers, tail); - LIST_INSERT_AFTER(servers, m->dns_servers, tail, s); - } else if (type == DNS_SERVER_FALLBACK) { - LIST_FIND_TAIL(servers, m->fallback_dns_servers, tail); - LIST_INSERT_AFTER(servers, m->fallback_dns_servers, tail, s); - } else + 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->manager = m; + 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 @@ -85,66 +120,440 @@ DnsServer* dns_server_ref(DnsServer *s) { return NULL; assert(s->n_ref > 0); - s->n_ref ++; return s; } -static DnsServer* dns_server_free(DnsServer *s) { +DnsServer* dns_server_unref(DnsServer *s) { if (!s) return NULL; + assert(s->n_ref > 0); + s->n_ref --; + + if (s->n_ref > 0) + return NULL; + + free(s->server_string); + free(s); + return NULL; +} + +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); + 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; + } + + s->linked = false; + if (s->link && s->link->current_dns_server == s) link_set_dns_server(s->link, NULL); - if (s->manager && s->manager->current_dns_server == s) + if (s->manager->current_dns_server == s) manager_set_dns_server(s->manager, NULL); - free(s); + dns_server_unref(s); +} - return NULL; +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"); + } } -DnsServer* dns_server_unref(DnsServer *s) { - if (!s) - return NULL; +static void dns_server_verified(DnsServer *s, DnsServerFeatureLevel level) { + assert(s); - assert(s->n_ref > 0); + if (s->verified_feature_level > level) + return; - if (s->n_ref == 1) - dns_server_free(s); - else - s->n_ref --; + 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; + } - return NULL; + assert_se(sd_event_now(s->manager->event, clock_boottime_or_monotonic(), &s->verified_usec) >= 0); } -void dns_server_packet_received(DnsServer *s, usec_t rtt) { +void dns_server_packet_received(DnsServer *s, int protocol, DnsServerFeatureLevel level, usec_t rtt, size_t size) { assert(s); - if (rtt > s->max_rtt) { + 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 (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, int protocol, DnsServerFeatureLevel level, usec_t usec) { + assert(s); + assert(s->manager); + + 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; + + s->resend_timeout = MIN(s->resend_timeout * 2, DNS_TIMEOUT_MAX_USEC); +} + +void dns_server_packet_failed(DnsServer *s, DnsServerFeatureLevel level) { + assert(s); + + /* 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->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_lost(DnsServer *s, usec_t usec) { +void dns_server_packet_bad_opt(DnsServer *s, DnsServerFeatureLevel level) { assert(s); - if (s->resend_timeout <= usec) - s->resend_timeout = MIN(s->resend_timeout * 2, DNS_TIMEOUT_MAX_USEC); + 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 unsigned long dns_server_hash_func(const void *p, const uint8_t hash_key[HASH_KEY_SIZE]) { +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; +} + +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_feature_level != DNS_SERVER_FEATURE_LEVEL_BEST && + dns_server_grace_period_expired(s)) { + + 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_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) { const DnsServer *s = p; - uint64_t u; - siphash24((uint8_t*) &u, &s->address, FAMILY_ADDRESS_SIZE(s->family), hash_key); - u = u * hash_key[0] + u + s->family; + assert(s); - return u; + siphash24_compress(&s->family, sizeof(s->family), state); + siphash24_compress(&s->address, FAMILY_ADDRESS_SIZE(s->family), state); } static int dns_server_compare_func(const void *a, const void *b) { @@ -162,3 +571,145 @@ const struct hash_ops dns_server_hash_ops = { .hash = dns_server_hash_func, .compare = 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); +} + +void dns_server_unlink_marked(DnsServer *first) { + DnsServer *next; + + if (!first) + return; + + next = first->servers_next; + + if (first->marked) + dns_server_unlink(first); + + 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) { + DnsServer *s; + + LIST_FOREACH(servers, s, first) + if (s->family == family && in_addr_equal(family, &s->address, in_addr) > 0) + 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; + + 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); + + if (m->unicast_scope) + dns_cache_flush(&m->unicast_scope->cache); + + 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 chose 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; + Iterator i; + + /* 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, i) + 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) { + assert(m); + + /* 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); +} + +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_DO] = "UDP+EDNS0+DO", + [DNS_SERVER_FEATURE_LEVEL_LARGE] = "UDP+EDNS0+DO+LARGE", +}; +DEFINE_STRING_TABLE_LOOKUP(dns_server_feature_level, DnsServerFeatureLevel); |