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Diffstat (limited to 'src/resolve/resolved-dns-server.c')
-rw-r--r--src/resolve/resolved-dns-server.c118
1 files changed, 112 insertions, 6 deletions
diff --git a/src/resolve/resolved-dns-server.c b/src/resolve/resolved-dns-server.c
index 0ebd22fe22..d565f99c09 100644
--- a/src/resolve/resolved-dns-server.c
+++ b/src/resolve/resolved-dns-server.c
@@ -23,12 +23,20 @@
#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,
@@ -60,6 +68,10 @@ int dns_server_new(
s->n_ref = 1;
s->manager = m;
+ s->verified_features = _DNS_SERVER_FEATURE_LEVEL_INVALID;
+ s->possible_features = DNS_SERVER_FEATURE_LEVEL_BEST;
+ s->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;
@@ -212,18 +224,43 @@ void dns_server_move_back_and_unmark(DnsServer *s) {
}
}
-void dns_server_packet_received(DnsServer *s, usec_t rtt) {
+void dns_server_packet_received(DnsServer *s, DnsServerFeatureLevel features, usec_t rtt, size_t size) {
assert(s);
- if (rtt <= s->max_rtt)
- return;
+ if (features == DNS_SERVER_FEATURE_LEVEL_LARGE) {
+ /* even if we successfully receive a reply to a request announcing
+ support for large packets, that does not mean we can necessarily
+ receive large packets. */
+ if (s->verified_features < DNS_SERVER_FEATURE_LEVEL_LARGE - 1) {
+ s->verified_features = DNS_SERVER_FEATURE_LEVEL_LARGE - 1;
+ assert_se(sd_event_now(s->manager->event, clock_boottime_or_monotonic(), &s->verified_usec) >= 0);
+ }
+ } else if (s->verified_features < features) {
+ s->verified_features = features;
+ assert_se(sd_event_now(s->manager->event, clock_boottime_or_monotonic(), &s->verified_usec) >= 0);
+ }
+
+ if (s->possible_features == features)
+ s->n_failed_attempts = 0;
+
+ /* Remember the size of the largest UDP packet we received from a server,
+ we know that we can always announce support for packets with at least
+ this size. */
+ if (s->received_udp_packet_max < size)
+ s->received_udp_packet_max = size;
- s->max_rtt = rtt;
- s->resend_timeout = MIN(MAX(DNS_TIMEOUT_MIN_USEC, s->max_rtt * 2), DNS_TIMEOUT_MAX_USEC);
+ 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);
+ }
}
-void dns_server_packet_lost(DnsServer *s, usec_t usec) {
+void dns_server_packet_lost(DnsServer *s, DnsServerFeatureLevel features, usec_t usec) {
assert(s);
+ assert(s->manager);
+
+ if (s->possible_features == features)
+ s->n_failed_attempts ++;
if (s->resend_timeout > usec)
return;
@@ -231,6 +268,66 @@ void dns_server_packet_lost(DnsServer *s, usec_t usec) {
s->resend_timeout = MIN(s->resend_timeout * 2, DNS_TIMEOUT_MAX_USEC);
}
+void dns_server_packet_failed(DnsServer *s, DnsServerFeatureLevel features) {
+ assert(s);
+ assert(s->manager);
+
+ if (s->possible_features != features)
+ return;
+
+ s->n_failed_attempts = (unsigned) -1;
+}
+
+static bool dns_server_grace_period_expired(DnsServer *s) {
+ usec_t ts;
+
+ assert(s);
+ assert(s->manager);
+
+ if (s->verified_usec == 0)
+ return false;
+
+ assert_se(sd_event_now(s->manager->event, clock_boottime_or_monotonic(), &ts) >= 0);
+
+ if (s->verified_usec + s->features_grace_period_usec > ts)
+ return false;
+
+ s->features_grace_period_usec = MIN(s->features_grace_period_usec * 2, DNS_SERVER_FEATURE_GRACE_PERIOD_MAX_USEC);
+
+ return true;
+}
+
+DnsServerFeatureLevel dns_server_possible_features(DnsServer *s) {
+ assert(s);
+
+ if (s->possible_features != DNS_SERVER_FEATURE_LEVEL_BEST &&
+ dns_server_grace_period_expired(s)) {
+ _cleanup_free_ char *ip = NULL;
+
+ s->possible_features = DNS_SERVER_FEATURE_LEVEL_BEST;
+ s->n_failed_attempts = 0;
+ s->verified_usec = 0;
+
+ in_addr_to_string(s->family, &s->address, &ip);
+ log_info("Grace period over, resuming full feature set for DNS server %s", strna(ip));
+ } else if (s->possible_features <= s->verified_features)
+ s->possible_features = s->verified_features;
+ else if (s->n_failed_attempts >= DNS_SERVER_FEATURE_RETRY_ATTEMPTS &&
+ s->possible_features > DNS_SERVER_FEATURE_LEVEL_WORST) {
+ _cleanup_free_ char *ip = NULL;
+
+ s->possible_features --;
+ s->n_failed_attempts = 0;
+ s->verified_usec = 0;
+
+ in_addr_to_string(s->family, &s->address, &ip);
+ log_warning("Using degraded feature set (%s) for DNS server %s",
+ dns_server_feature_level_to_string(s->possible_features), strna(ip));
+ }
+
+ return s->possible_features;
+}
+
static void dns_server_hash_func(const void *p, struct siphash *state) {
const DnsServer *s = p;
@@ -392,3 +489,12 @@ void manager_next_dns_server(Manager *m) {
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);