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-rw-r--r--src/resolve/resolved-dns-server.c1097
1 files changed, 1097 insertions, 0 deletions
diff --git a/src/resolve/resolved-dns-server.c b/src/resolve/resolved-dns-server.c
new file mode 100644
index 0000000..8ff513f
--- /dev/null
+++ b/src/resolve/resolved-dns-server.c
@@ -0,0 +1,1097 @@
+/* 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);
+ 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();
+ }
+}
+
+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);