1105 lines
41 KiB
C
1105 lines
41 KiB
C
/* SPDX-License-Identifier: LGPL-2.1-or-later */
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#include "sd-messages.h"
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#include "alloc-util.h"
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#include "resolved-bus.h"
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#include "resolved-dns-server.h"
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#include "resolved-dns-stub.h"
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#include "resolved-manager.h"
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#include "resolved-resolv-conf.h"
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#include "siphash24.h"
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#include "string-table.h"
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#include "string-util.h"
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/* The amount of time to wait before retrying with a full feature set */
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#define DNS_SERVER_FEATURE_GRACE_PERIOD_MAX_USEC (6 * USEC_PER_HOUR)
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#define DNS_SERVER_FEATURE_GRACE_PERIOD_MIN_USEC (5 * USEC_PER_MINUTE)
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/* The number of times we will attempt a certain feature set before degrading */
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#define DNS_SERVER_FEATURE_RETRY_ATTEMPTS 3
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int dns_server_new(
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Manager *m,
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DnsServer **ret,
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DnsServerType type,
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Link *l,
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int family,
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const union in_addr_union *in_addr,
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uint16_t port,
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int ifindex,
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const char *server_name) {
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_cleanup_free_ char *name = NULL;
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DnsServer *s;
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assert(m);
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assert((type == DNS_SERVER_LINK) == !!l);
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assert(in_addr);
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if (!IN_SET(family, AF_INET, AF_INET6))
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return -EAFNOSUPPORT;
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if (l) {
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if (l->n_dns_servers >= LINK_DNS_SERVERS_MAX)
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return -E2BIG;
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} else {
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if (m->n_dns_servers >= MANAGER_DNS_SERVERS_MAX)
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return -E2BIG;
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}
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if (!isempty(server_name)) {
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name = strdup(server_name);
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if (!name)
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return -ENOMEM;
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}
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s = new(DnsServer, 1);
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if (!s)
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return -ENOMEM;
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*s = (DnsServer) {
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.n_ref = 1,
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.manager = m,
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.type = type,
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.family = family,
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.address = *in_addr,
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.port = port,
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.ifindex = ifindex,
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.server_name = TAKE_PTR(name),
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};
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dns_server_reset_features(s);
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switch (type) {
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case DNS_SERVER_LINK:
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s->link = l;
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LIST_APPEND(servers, l->dns_servers, s);
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l->n_dns_servers++;
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break;
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case DNS_SERVER_SYSTEM:
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LIST_APPEND(servers, m->dns_servers, s);
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m->n_dns_servers++;
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break;
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case DNS_SERVER_FALLBACK:
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LIST_APPEND(servers, m->fallback_dns_servers, s);
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m->n_dns_servers++;
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break;
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default:
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assert_not_reached("Unknown server type");
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}
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s->linked = true;
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/* A new DNS server that isn't fallback is added and the one
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* we used so far was a fallback one? Then let's try to pick
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* the new one */
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if (type != DNS_SERVER_FALLBACK &&
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m->current_dns_server &&
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m->current_dns_server->type == DNS_SERVER_FALLBACK)
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manager_set_dns_server(m, NULL);
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if (ret)
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*ret = s;
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return 0;
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}
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static DnsServer* dns_server_free(DnsServer *s) {
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assert(s);
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dns_server_unref_stream(s);
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#if ENABLE_DNS_OVER_TLS
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dnstls_server_free(s);
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#endif
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free(s->server_string);
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free(s->server_string_full);
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free(s->server_name);
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return mfree(s);
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}
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DEFINE_TRIVIAL_REF_UNREF_FUNC(DnsServer, dns_server, dns_server_free);
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void dns_server_unlink(DnsServer *s) {
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assert(s);
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assert(s->manager);
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/* This removes the specified server from the linked list of
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* servers, but any server might still stay around if it has
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* refs, for example from an ongoing transaction. */
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if (!s->linked)
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return;
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switch (s->type) {
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case DNS_SERVER_LINK:
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assert(s->link);
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assert(s->link->n_dns_servers > 0);
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LIST_REMOVE(servers, s->link->dns_servers, s);
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s->link->n_dns_servers--;
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break;
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case DNS_SERVER_SYSTEM:
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assert(s->manager->n_dns_servers > 0);
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LIST_REMOVE(servers, s->manager->dns_servers, s);
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s->manager->n_dns_servers--;
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break;
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case DNS_SERVER_FALLBACK:
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assert(s->manager->n_dns_servers > 0);
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LIST_REMOVE(servers, s->manager->fallback_dns_servers, s);
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s->manager->n_dns_servers--;
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break;
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default:
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assert_not_reached("Unknown server type");
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}
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s->linked = false;
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if (s->link && s->link->current_dns_server == s)
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link_set_dns_server(s->link, NULL);
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if (s->manager->current_dns_server == s)
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manager_set_dns_server(s->manager, NULL);
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/* No need to keep a default stream around anymore */
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dns_server_unref_stream(s);
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dns_server_unref(s);
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}
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void dns_server_move_back_and_unmark(DnsServer *s) {
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DnsServer *tail;
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assert(s);
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if (!s->marked)
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return;
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s->marked = false;
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if (!s->linked || !s->servers_next)
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return;
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/* Move us to the end of the list, so that the order is
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* strictly kept, if we are not at the end anyway. */
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switch (s->type) {
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case DNS_SERVER_LINK:
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assert(s->link);
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LIST_FIND_TAIL(servers, s, tail);
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LIST_REMOVE(servers, s->link->dns_servers, s);
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LIST_INSERT_AFTER(servers, s->link->dns_servers, tail, s);
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break;
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case DNS_SERVER_SYSTEM:
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LIST_FIND_TAIL(servers, s, tail);
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LIST_REMOVE(servers, s->manager->dns_servers, s);
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LIST_INSERT_AFTER(servers, s->manager->dns_servers, tail, s);
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break;
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case DNS_SERVER_FALLBACK:
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LIST_FIND_TAIL(servers, s, tail);
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LIST_REMOVE(servers, s->manager->fallback_dns_servers, s);
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LIST_INSERT_AFTER(servers, s->manager->fallback_dns_servers, tail, s);
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break;
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default:
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assert_not_reached("Unknown server type");
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}
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}
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static void dns_server_verified(DnsServer *s, DnsServerFeatureLevel level) {
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assert(s);
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if (s->verified_feature_level > level)
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return;
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if (s->verified_feature_level != level) {
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log_debug("Verified we get a response at feature level %s from DNS server %s.",
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dns_server_feature_level_to_string(level),
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strna(dns_server_string_full(s)));
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s->verified_feature_level = level;
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}
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assert_se(sd_event_now(s->manager->event, clock_boottime_or_monotonic(), &s->verified_usec) >= 0);
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}
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static void dns_server_reset_counters(DnsServer *s) {
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assert(s);
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s->n_failed_udp = 0;
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s->n_failed_tcp = 0;
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s->n_failed_tls = 0;
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s->packet_truncated = false;
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s->packet_invalid = false;
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s->verified_usec = 0;
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/* Note that we do not reset s->packet_bad_opt and s->packet_rrsig_missing here. We reset them only when the
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* grace period ends, but not when lowering the possible feature level, as a lower level feature level should
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* not make RRSIGs appear or OPT appear, but rather make them disappear. If the reappear anyway, then that's
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* indication for a differently broken OPT/RRSIG implementation, and we really don't want to support that
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* either.
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*
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* This is particularly important to deal with certain Belkin routers which break OPT for certain lookups (A),
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* but pass traffic through for others (AAAA). If we detect the broken behaviour on one lookup we should not
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* re-enable it for another, because we cannot validate things anyway, given that the RRSIG/OPT data will be
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* incomplete. */
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}
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void dns_server_packet_received(DnsServer *s, int protocol, DnsServerFeatureLevel level, size_t fragsize) {
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assert(s);
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if (protocol == IPPROTO_UDP) {
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if (s->possible_feature_level == level)
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s->n_failed_udp = 0;
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} else if (protocol == IPPROTO_TCP) {
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if (DNS_SERVER_FEATURE_LEVEL_IS_TLS(level)) {
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if (s->possible_feature_level == level)
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s->n_failed_tls = 0;
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} else {
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if (s->possible_feature_level == level)
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s->n_failed_tcp = 0;
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/* Successful TCP connections are only useful to verify the TCP feature level. */
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level = DNS_SERVER_FEATURE_LEVEL_TCP;
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}
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}
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/* If the RRSIG data is missing, then we can only validate EDNS0 at max */
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if (s->packet_rrsig_missing && level >= DNS_SERVER_FEATURE_LEVEL_DO)
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level = DNS_SERVER_FEATURE_LEVEL_IS_TLS(level) ? DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN : DNS_SERVER_FEATURE_LEVEL_EDNS0;
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/* If the OPT RR got lost, then we can only validate UDP at max */
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if (s->packet_bad_opt && level >= DNS_SERVER_FEATURE_LEVEL_EDNS0)
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level = DNS_SERVER_FEATURE_LEVEL_EDNS0 - 1;
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/* Even if we successfully receive a reply to a request announcing support for large packets, that
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* does not mean we can necessarily receive large packets. */
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if (level == DNS_SERVER_FEATURE_LEVEL_LARGE)
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level = DNS_SERVER_FEATURE_LEVEL_LARGE - 1;
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dns_server_verified(s, level);
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/* Remember the size of the largest UDP packet fragment we received from a server, we know that we
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* can always announce support for packets with at least this size. */
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if (protocol == IPPROTO_UDP && s->received_udp_fragment_max < fragsize)
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s->received_udp_fragment_max = fragsize;
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}
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void dns_server_packet_lost(DnsServer *s, int protocol, DnsServerFeatureLevel level) {
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assert(s);
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assert(s->manager);
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if (s->possible_feature_level != level)
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return;
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if (protocol == IPPROTO_UDP)
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s->n_failed_udp++;
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else if (protocol == IPPROTO_TCP) {
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if (DNS_SERVER_FEATURE_LEVEL_IS_TLS(level))
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s->n_failed_tls++;
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else
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s->n_failed_tcp++;
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}
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}
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void dns_server_packet_truncated(DnsServer *s, DnsServerFeatureLevel level) {
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assert(s);
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/* Invoked whenever we get a packet with TC bit set. */
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if (s->possible_feature_level != level)
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return;
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s->packet_truncated = true;
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}
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void dns_server_packet_rrsig_missing(DnsServer *s, DnsServerFeatureLevel level) {
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assert(s);
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if (level < DNS_SERVER_FEATURE_LEVEL_DO)
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return;
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/* If the RRSIG RRs are missing, we have to downgrade what we previously verified */
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if (s->verified_feature_level >= DNS_SERVER_FEATURE_LEVEL_DO)
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s->verified_feature_level = DNS_SERVER_FEATURE_LEVEL_IS_TLS(level) ? DNS_SERVER_FEATURE_LEVEL_TLS_PLAIN : DNS_SERVER_FEATURE_LEVEL_EDNS0;
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s->packet_rrsig_missing = true;
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}
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void dns_server_packet_bad_opt(DnsServer *s, DnsServerFeatureLevel level) {
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assert(s);
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if (level < DNS_SERVER_FEATURE_LEVEL_EDNS0)
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return;
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/* If the OPT RR got lost, we have to downgrade what we previously verified */
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if (s->verified_feature_level >= DNS_SERVER_FEATURE_LEVEL_EDNS0)
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s->verified_feature_level = DNS_SERVER_FEATURE_LEVEL_EDNS0-1;
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s->packet_bad_opt = true;
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}
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void dns_server_packet_rcode_downgrade(DnsServer *s, DnsServerFeatureLevel level) {
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assert(s);
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/* Invoked whenever we got a FORMERR, SERVFAIL or NOTIMP rcode from a server and downgrading the feature level
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* for the transaction made it go away. In this case we immediately downgrade to the feature level that made
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* things work. */
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if (s->verified_feature_level > level)
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s->verified_feature_level = level;
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if (s->possible_feature_level > level) {
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s->possible_feature_level = level;
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dns_server_reset_counters(s);
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}
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log_debug("Downgrading transaction feature level fixed an RCODE error, downgrading server %s too.", strna(dns_server_string_full(s)));
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}
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void dns_server_packet_invalid(DnsServer *s, DnsServerFeatureLevel level) {
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assert(s);
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/* Invoked whenever we got a packet we couldn't parse at all */
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if (s->possible_feature_level != level)
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return;
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s->packet_invalid = true;
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}
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void dns_server_packet_do_off(DnsServer *s, DnsServerFeatureLevel level) {
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assert(s);
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/* Invoked whenever the DO flag was not copied from our request to the response. */
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if (s->possible_feature_level != level)
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return;
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s->packet_do_off = true;
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}
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void dns_server_packet_udp_fragmented(DnsServer *s, size_t fragsize) {
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assert(s);
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/* Invoked whenever we got a fragmented UDP packet. Let's do two things: keep track of the largest
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* fragment we ever received from the server, and remember this, so that we can use it to lower the
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* advertised packet size in EDNS0 */
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if (s->received_udp_fragment_max < fragsize)
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s->received_udp_fragment_max = fragsize;
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s->packet_fragmented = true;
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}
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static bool dns_server_grace_period_expired(DnsServer *s) {
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usec_t ts;
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assert(s);
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assert(s->manager);
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if (s->verified_usec == 0)
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return false;
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assert_se(sd_event_now(s->manager->event, clock_boottime_or_monotonic(), &ts) >= 0);
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if (s->verified_usec + s->features_grace_period_usec > ts)
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return false;
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s->features_grace_period_usec = MIN(s->features_grace_period_usec * 2, DNS_SERVER_FEATURE_GRACE_PERIOD_MAX_USEC);
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return true;
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}
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DnsServerFeatureLevel dns_server_possible_feature_level(DnsServer *s) {
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DnsServerFeatureLevel best;
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assert(s);
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/* Determine the best feature level we care about. If DNSSEC mode is off there's no point in using anything
|
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* better than EDNS0, hence don't even try. */
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if (dns_server_get_dnssec_mode(s) != DNSSEC_NO)
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best = dns_server_get_dns_over_tls_mode(s) == DNS_OVER_TLS_NO ?
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DNS_SERVER_FEATURE_LEVEL_LARGE :
|
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DNS_SERVER_FEATURE_LEVEL_TLS_DO;
|
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else
|
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best = dns_server_get_dns_over_tls_mode(s) == DNS_OVER_TLS_NO ?
|
||
DNS_SERVER_FEATURE_LEVEL_EDNS0 :
|
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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)
|
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s->possible_feature_level = best;
|
||
|
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if (s->possible_feature_level < best && dns_server_grace_period_expired(s)) {
|
||
|
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s->possible_feature_level = best;
|
||
|
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dns_server_reset_counters(s);
|
||
|
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s->packet_bad_opt = false;
|
||
s->packet_rrsig_missing = false;
|
||
|
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log_info("Grace period over, resuming full feature set (%s) for DNS server %s.",
|
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dns_server_feature_level_to_string(s->possible_feature_level),
|
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strna(dns_server_string_full(s)));
|
||
|
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dns_server_flush_cache(s);
|
||
|
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} else if (s->possible_feature_level <= s->verified_feature_level)
|
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s->possible_feature_level = s->verified_feature_level;
|
||
else {
|
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DnsServerFeatureLevel p = s->possible_feature_level;
|
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int log_level = LOG_WARNING;
|
||
|
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if (s->n_failed_tcp >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS &&
|
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s->possible_feature_level == DNS_SERVER_FEATURE_LEVEL_TCP) {
|
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|
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/* 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;
|
||
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 *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) {
|
||
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);
|