Merge pull request #5347 from poettering/local-nta

more resolved fixes

src/resolve/resolve-tool.c

@@ -38,7 +38,7 @@
 #include "strv.h"
 #include "terminal-util.h"
 
-#define DNS_CALL_TIMEOUT_USEC (45*USEC_PER_SEC)
+#define DNS_CALL_TIMEOUT_USEC (90*USEC_PER_SEC)
 
 static int arg_family = AF_UNSPEC;
 static int arg_ifindex = 0;

src/resolve/resolved-dns-cache.c

@@ -34,6 +34,10 @@
 /* We never keep any item longer than 2h in our cache */
 #define CACHE_TTL_MAX_USEC (2 * USEC_PER_HOUR)
 
+/* How long to cache strange rcodes, i.e. rcodes != SUCCESS and != NXDOMAIN (specifically: that's only SERVFAIL for
+ * now) */
+#define CACHE_TTL_STRANGE_RCODE_USEC (30 * USEC_PER_SEC)
+
 typedef enum DnsCacheItemType DnsCacheItemType;
 typedef struct DnsCacheItem DnsCacheItem;
 
@@ -41,12 +45,14 @@ enum DnsCacheItemType {
         DNS_CACHE_POSITIVE,
         DNS_CACHE_NODATA,
         DNS_CACHE_NXDOMAIN,
+        DNS_CACHE_RCODE,      /* "strange" RCODE (effective only SERVFAIL for now) */
 };
 
 struct DnsCacheItem {
         DnsCacheItemType type;
         DnsResourceKey *key;
         DnsResourceRecord *rr;
+        int rcode;
 
         usec_t until;
         bool authenticated:1;
@@ -60,6 +66,27 @@ struct DnsCacheItem {
         LIST_FIELDS(DnsCacheItem, by_key);
 };
 
+static const char *dns_cache_item_type_to_string(DnsCacheItem *item) {
+        assert(item);
+
+        switch (item->type) {
+
+        case DNS_CACHE_POSITIVE:
+                return "POSITIVE";
+
+        case DNS_CACHE_NODATA:
+                return "NODATA";
+
+        case DNS_CACHE_NXDOMAIN:
+                return "NXDOMAIN";
+
+        case DNS_CACHE_RCODE:
+                return dns_rcode_to_string(item->rcode);
+        }
+
+        return NULL;
+}
+
 static void dns_cache_item_free(DnsCacheItem *i) {
         if (!i)
                 return;
@@ -484,7 +511,6 @@ static int dns_cache_put_negative(
 
         assert(c);
         assert(key);
-        assert(soa);
         assert(owner_address);
 
         /* Never cache pseudo RR keys. DNS_TYPE_ANY is particularly
@@ -495,13 +521,17 @@ static int dns_cache_put_negative(
         if (dns_type_is_pseudo(key->type))
                 return 0;
 
-        if (nsec_ttl <= 0 || soa->soa.minimum <= 0 || soa->ttl <= 0) {
-                log_debug("Not caching negative entry with zero SOA/NSEC/NSEC3 TTL: %s",
-                          dns_resource_key_to_string(key, key_str, sizeof key_str));
-                return 0;
-        }
+        if (IN_SET(rcode, DNS_RCODE_SUCCESS, DNS_RCODE_NXDOMAIN)) {
+                if (!soa)
+                        return 0;
 
-        if (!IN_SET(rcode, DNS_RCODE_SUCCESS, DNS_RCODE_NXDOMAIN))
+                /* For negative replies, check if we have a TTL of a SOA */
+                if (nsec_ttl <= 0 || soa->soa.minimum <= 0 || soa->ttl <= 0) {
+                        log_debug("Not caching negative entry with zero SOA/NSEC/NSEC3 TTL: %s",
+                                  dns_resource_key_to_string(key, key_str, sizeof key_str));
+                        return 0;
+                }
+        } else if (rcode != DNS_RCODE_SERVFAIL)
                 return 0;
 
         r = dns_cache_init(c);
@@ -514,12 +544,17 @@ static int dns_cache_put_negative(
         if (!i)
                 return -ENOMEM;
 
-        i->type = rcode == DNS_RCODE_SUCCESS ? DNS_CACHE_NODATA : DNS_CACHE_NXDOMAIN;
-        i->until = calculate_until(soa, nsec_ttl, timestamp, true);
+        i->type =
+                rcode == DNS_RCODE_SUCCESS ? DNS_CACHE_NODATA :
+                rcode == DNS_RCODE_NXDOMAIN ? DNS_CACHE_NXDOMAIN : DNS_CACHE_RCODE;
+        i->until =
+                i->type == DNS_CACHE_RCODE ? timestamp + CACHE_TTL_STRANGE_RCODE_USEC :
+                calculate_until(soa, nsec_ttl, timestamp, true);
         i->authenticated = authenticated;
         i->owner_family = owner_family;
         i->owner_address = *owner_address;
         i->prioq_idx = PRIOQ_IDX_NULL;
+        i->rcode = rcode;
 
         if (i->type == DNS_CACHE_NXDOMAIN) {
                 /* NXDOMAIN entries should apply equally to all types, so we use ANY as
@@ -543,7 +578,7 @@ static int dns_cache_put_negative(
                 return r;
 
         log_debug("Added %s cache entry for %s "USEC_FMT"s",
-                  i->type == DNS_CACHE_NODATA ? "NODATA" : "NXDOMAIN",
+                  dns_cache_item_type_to_string(i),
                   dns_resource_key_to_string(i->key, key_str, sizeof key_str),
                   (i->until - timestamp) / USEC_PER_SEC);
 
@@ -615,6 +650,7 @@ int dns_cache_put(
                 const union in_addr_union *owner_address) {
 
         DnsResourceRecord *soa = NULL, *rr;
+        bool weird_rcode = false;
         DnsAnswerFlags flags;
         unsigned cache_keys;
         int r, ifindex;
@@ -624,18 +660,28 @@ int dns_cache_put(
 
         dns_cache_remove_previous(c, key, answer);
 
-        /* We only care for positive replies and NXDOMAINs, on all
-         * other replies we will simply flush the respective entries,
-         * and that's it */
-        if (!IN_SET(rcode, DNS_RCODE_SUCCESS, DNS_RCODE_NXDOMAIN))
-                return 0;
+        /* We only care for positive replies and NXDOMAINs, on all other replies we will simply flush the respective
+         * entries, and that's it. (Well, with one further exception: since some DNS zones (akamai!) return SERVFAIL
+         * consistently for some lookups, and forwarders tend to propagate that we'll cache that too, but only for a
+         * short time.) */
 
-        if (dns_answer_size(answer) <= 0) {
-                char key_str[DNS_RESOURCE_KEY_STRING_MAX];
+        if (IN_SET(rcode, DNS_RCODE_SUCCESS, DNS_RCODE_NXDOMAIN)) {
 
-                log_debug("Not caching negative entry without a SOA record: %s",
-                          dns_resource_key_to_string(key, key_str, sizeof key_str));
-                return 0;
+                if (dns_answer_size(answer) <= 0) {
+                        char key_str[DNS_RESOURCE_KEY_STRING_MAX];
+
+                        log_debug("Not caching negative entry without a SOA record: %s",
+                                  dns_resource_key_to_string(key, key_str, sizeof key_str));
+                        return 0;
+                }
+
+        } else {
+                /* Only cache SERVFAIL as "weird" rcode for now. We can add more later, should that turn out to be
+                 * beneficial. */
+                if (rcode != DNS_RCODE_SERVFAIL)
+                        return 0;
+
+                weird_rcode = true;
         }
 
         cache_keys = dns_answer_size(answer);
@@ -690,19 +736,20 @@ int dns_cache_put(
         if (r > 0)
                 return 0;
 
-        /* See https://tools.ietf.org/html/rfc2308, which say that a
-         * matching SOA record in the packet is used to enable
-         * negative caching. */
+        /* See https://tools.ietf.org/html/rfc2308, which say that a matching SOA record in the packet is used to
+         * enable negative caching. We apply one exception though: if we are about to cache a weird rcode we do so
+         * regardless of a SOA. */
         r = dns_answer_find_soa(answer, key, &soa, &flags);
         if (r < 0)
                 goto fail;
-        if (r == 0)
-                return 0;
-
-        /* Refuse using the SOA data if it is unsigned, but the key is
-         * signed */
-        if (authenticated && (flags & DNS_ANSWER_AUTHENTICATED) == 0)
+        if (r == 0 && !weird_rcode)
                 return 0;
+        if (r > 0) {
+                /* Refuse using the SOA data if it is unsigned, but the key is
+                 * signed */
+                if (authenticated && (flags & DNS_ANSWER_AUTHENTICATED) == 0)
+                        return 0;
+        }
 
         r = dns_cache_put_negative(
                         c,
@@ -799,6 +846,7 @@ int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, bool clamp_ttl, int *rcod
         DnsCacheItem *j, *first, *nsec = NULL;
         bool have_authenticated = false, have_non_authenticated = false;
         usec_t current;
+        int found_rcode = -1;
 
         assert(c);
         assert(key);
@@ -817,6 +865,8 @@ int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, bool clamp_ttl, int *rcod
 
                 *ret = NULL;
                 *rcode = DNS_RCODE_SUCCESS;
+                *authenticated = false;
+
                 return 0;
         }
 
@@ -831,6 +881,8 @@ int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, bool clamp_ttl, int *rcod
 
                 *ret = NULL;
                 *rcode = DNS_RCODE_SUCCESS;
+                *authenticated = false;
+
                 return 0;
         }
 
@@ -842,6 +894,8 @@ int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, bool clamp_ttl, int *rcod
                         n++;
                 } else if (j->type == DNS_CACHE_NXDOMAIN)
                         nxdomain = true;
+                else if (j->type == DNS_CACHE_RCODE)
+                        found_rcode = j->rcode;
 
                 if (j->authenticated)
                         have_authenticated = true;
@@ -849,6 +903,19 @@ int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, bool clamp_ttl, int *rcod
                         have_non_authenticated = true;
         }
 
+        if (found_rcode >= 0) {
+                log_debug("RCODE %s cache hit for %s",
+                          dns_rcode_to_string(found_rcode),
+                          dns_resource_key_to_string(key, key_str, sizeof(key_str)));
+
+                *ret = NULL;
+                *rcode = found_rcode;
+                *authenticated = false;
+
+                c->n_hit++;
+                return 1;
+        }
+
         if (nsec && !IN_SET(key->type, DNS_TYPE_NSEC, DNS_TYPE_DS)) {
                 /* Note that we won't derive information for DS RRs from an NSEC, because we only cache NSEC RRs from
                  * the lower-zone of a zone cut, but the DS RRs are on the upper zone. */
@@ -1042,7 +1109,7 @@ void dns_cache_dump(DnsCache *cache, FILE *f) {
 
                                 fputs(dns_resource_key_to_string(j->key, key_str, sizeof key_str), f);
                                 fputs(" -- ", f);
-                                fputs(j->type == DNS_CACHE_NODATA ? "NODATA" : "NXDOMAIN", f);
+                                fputs(dns_cache_item_type_to_string(j), f);
                                 fputc('\n', f);
                         }
                 }

src/resolve/resolved-dns-dnssec.c

@@ -1710,7 +1710,8 @@ static int dnssec_nsec_covers(DnsResourceRecord *rr, const char *name) {
 }
 
 static int dnssec_nsec_covers_wildcard(DnsResourceRecord *rr, const char *name) {
-        const char *common_suffix, *wc;
+        _cleanup_free_ char *wc = NULL;
+        const char *common_suffix;
         int r;
 
         assert(rr);
@@ -1734,7 +1735,10 @@ static int dnssec_nsec_covers_wildcard(DnsResourceRecord *rr, const char *name)
         if (r <= 0)
                 return r;
 
-        wc = strjoina("*.", common_suffix);
+        r = dns_name_concat("*", common_suffix, &wc);
+        if (r < 0)
+                return r;
+
         return dns_name_between(dns_resource_key_name(rr->key), wc, rr->nsec.next_domain_name);
 }
 

src/resolve/resolved-dns-query.c

@@ -28,7 +28,7 @@
 #include "string-util.h"
 
 /* How long to wait for the query in total */
-#define QUERY_TIMEOUT_USEC (30 * USEC_PER_SEC)
+#define QUERY_TIMEOUT_USEC (60 * USEC_PER_SEC)
 
 #define CNAME_MAX 8
 #define QUERIES_MAX 2048
@@ -811,6 +811,7 @@ static void dns_query_accept(DnsQuery *q, DnsQueryCandidate *c) {
                 q->answer = dns_answer_unref(q->answer);
                 q->answer_rcode = 0;
                 q->answer_dnssec_result = _DNSSEC_RESULT_INVALID;
+                q->answer_authenticated = false;
                 q->answer_errno = c->error_code;
         }
 
@@ -847,15 +848,18 @@ static void dns_query_accept(DnsQuery *q, DnsQueryCandidate *c) {
                         continue;
 
                 default:
-                        /* Any kind of failure? Store the data away,
-                         * if there's nothing stored yet. */
-
+                        /* Any kind of failure? Store the data away, if there's nothing stored yet. */
                         if (state == DNS_TRANSACTION_SUCCESS)
                                 continue;
 
+                        /* If there's already an authenticated negative reply stored, then prefer that over any unauthenticated one */
+                        if (q->answer_authenticated && !t->answer_authenticated)
+                                continue;
+
                         q->answer = dns_answer_unref(q->answer);
                         q->answer_rcode = t->answer_rcode;
                         q->answer_dnssec_result = t->answer_dnssec_result;
+                        q->answer_authenticated = t->answer_authenticated;
                         q->answer_errno = t->answer_errno;
 
                         state = t->state;

src/resolve/resolved-dns-server.c

@@ -28,7 +28,7 @@
 #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_MIN_USEC (750 * 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 */
@@ -399,12 +399,24 @@ static bool dns_server_grace_period_expired(DnsServer *s) {
 }
 
 DnsServerFeatureLevel dns_server_possible_feature_level(DnsServer *s) {
+        DnsServerFeatureLevel best;
+
         assert(s);
 
-        if (s->possible_feature_level != DNS_SERVER_FEATURE_LEVEL_BEST &&
-            dns_server_grace_period_expired(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. */
+        best = dns_server_get_dnssec_mode(s) == DNSSEC_NO ?
+                DNS_SERVER_FEATURE_LEVEL_EDNS0 :
+                DNS_SERVER_FEATURE_LEVEL_BEST;
 
-                s->possible_feature_level = DNS_SERVER_FEATURE_LEVEL_BEST;
+        /* 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);
 
@@ -415,6 +427,8 @@ DnsServerFeatureLevel dns_server_possible_feature_level(DnsServer *s) {
                          dns_server_feature_level_to_string(s->possible_feature_level),
                          dns_server_string(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 {
@@ -792,6 +806,25 @@ DnssecMode dns_server_get_dnssec_mode(DnsServer *s) {
         return manager_get_dnssec_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);
+}
+
 static const char* const dns_server_type_table[_DNS_SERVER_TYPE_MAX] = {
         [DNS_SERVER_SYSTEM] = "system",
         [DNS_SERVER_FALLBACK] = "fallback",

src/resolve/resolved-dns-server.h

@@ -149,3 +149,5 @@ DnssecMode dns_server_get_dnssec_mode(DnsServer *s);
 DEFINE_TRIVIAL_CLEANUP_FUNC(DnsServer*, dns_server_unref);
 
 extern const struct hash_ops dns_server_hash_ops;
+
+void dns_server_flush_cache(DnsServer *s);

src/resolve/resolved-dns-stub.c

@@ -94,9 +94,18 @@ static int dns_stub_finish_reply_packet(
 
         assert(p);
 
-        /* If the client didn't do EDNS, clamp the rcode to 4 bit */
-        if (!add_opt && rcode > 0xF)
-                rcode = DNS_RCODE_SERVFAIL;
+        if (!add_opt) {
+                /* If the client can't to EDNS0, don't do DO either */
+                edns0_do = false;
+
+                /* If the client didn't do EDNS, clamp the rcode to 4 bit */
+                if (rcode > 0xF)
+                        rcode = DNS_RCODE_SERVFAIL;
+        }
+
+        /* Don't set the AD bit unless DO is on, too */
+        if (!edns0_do)
+                ad = false;
 
         DNS_PACKET_HEADER(p)->id = id;
 
@@ -162,7 +171,7 @@ static int dns_stub_send(Manager *m, DnsStream *s, DnsPacket *p, DnsPacket *repl
         return 0;
 }
 
-static int dns_stub_send_failure(Manager *m, DnsStream *s, DnsPacket *p, int rcode) {
+static int dns_stub_send_failure(Manager *m, DnsStream *s, DnsPacket *p, int rcode, bool authenticated) {
         _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
         int r;
 
@@ -173,7 +182,7 @@ static int dns_stub_send_failure(Manager *m, DnsStream *s, DnsPacket *p, int rco
         if (r < 0)
                 return log_debug_errno(r, "Failed to make failure packet: %m");
 
-        r = dns_stub_finish_reply_packet(reply, DNS_PACKET_ID(p), rcode, !!p->opt, DNS_PACKET_DO(p), false);
+        r = dns_stub_finish_reply_packet(reply, DNS_PACKET_ID(p), rcode, !!p->opt, DNS_PACKET_DO(p), authenticated);
         if (r < 0)
                 return log_debug_errno(r, "Failed to build failure packet: %m");
 
@@ -198,7 +207,7 @@ static void dns_stub_query_complete(DnsQuery *q) {
 
                 r = dns_query_process_cname(q);
                 if (r == -ELOOP) {
-                        (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL);
+                        (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL, false);
                         break;
                 }
                 if (r < 0) {
@@ -214,7 +223,7 @@ static void dns_stub_query_complete(DnsQuery *q) {
                                 q->answer_rcode,
                                 !!q->request_dns_packet->opt,
                                 DNS_PACKET_DO(q->request_dns_packet),
-                                DNS_PACKET_DO(q->request_dns_packet) && dns_query_fully_authenticated(q));
+                                dns_query_fully_authenticated(q));
                 if (r < 0) {
                         log_debug_errno(r, "Failed to finish reply packet: %m");
                         break;
@@ -224,11 +233,11 @@ static void dns_stub_query_complete(DnsQuery *q) {
                 break;
 
         case DNS_TRANSACTION_RCODE_FAILURE:
-                (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, q->answer_rcode);
+                (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, q->answer_rcode, dns_query_fully_authenticated(q));
                 break;
 
         case DNS_TRANSACTION_NOT_FOUND:
-                (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_NXDOMAIN);
+                (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_NXDOMAIN, dns_query_fully_authenticated(q));
                 break;
 
         case DNS_TRANSACTION_TIMEOUT:
@@ -244,7 +253,7 @@ static void dns_stub_query_complete(DnsQuery *q) {
         case DNS_TRANSACTION_NO_TRUST_ANCHOR:
         case DNS_TRANSACTION_RR_TYPE_UNSUPPORTED:
         case DNS_TRANSACTION_NETWORK_DOWN:
-                (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL);
+                (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL, false);
                 break;
 
         case DNS_TRANSACTION_NULL:
@@ -291,52 +300,52 @@ static void dns_stub_process_query(Manager *m, DnsStream *s, DnsPacket *p) {
         if (in_addr_is_localhost(p->family, &p->sender) <= 0 ||
             in_addr_is_localhost(p->family, &p->destination) <= 0) {
                 log_error("Got packet on unexpected IP range, refusing.");
-                dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL);
+                dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
                 goto fail;
         }
 
         r = dns_packet_extract(p);
         if (r < 0) {
                 log_debug_errno(r, "Failed to extract resources from incoming packet, ignoring packet: %m");
-                dns_stub_send_failure(m, s, p, DNS_RCODE_FORMERR);
+                dns_stub_send_failure(m, s, p, DNS_RCODE_FORMERR, false);
                 goto fail;
         }
 
         if (!DNS_PACKET_VERSION_SUPPORTED(p)) {
                 log_debug("Got EDNS OPT field with unsupported version number.");
-                dns_stub_send_failure(m, s, p, DNS_RCODE_BADVERS);
+                dns_stub_send_failure(m, s, p, DNS_RCODE_BADVERS, false);
                 goto fail;
         }
 
         if (dns_type_is_obsolete(p->question->keys[0]->type)) {
                 log_debug("Got message with obsolete key type, refusing.");
-                dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP);
+                dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
                 goto fail;
         }
 
         if (dns_type_is_zone_transer(p->question->keys[0]->type)) {
                 log_debug("Got request for zone transfer, refusing.");
-                dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP);
+                dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
                 goto fail;
         }
 
         if (!DNS_PACKET_RD(p))  {
                 /* If the "rd" bit is off (i.e. recursion was not requested), then refuse operation */
                 log_debug("Got request with recursion disabled, refusing.");
-                dns_stub_send_failure(m, s, p, DNS_RCODE_REFUSED);
+                dns_stub_send_failure(m, s, p, DNS_RCODE_REFUSED, false);
                 goto fail;
         }
 
         if (DNS_PACKET_DO(p) && DNS_PACKET_CD(p)) {
                 log_debug("Got request with DNSSEC CD bit set, refusing.");
-                dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP);
+                dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
                 goto fail;
         }
 
         r = dns_query_new(m, &q, p->question, p->question, 0, SD_RESOLVED_PROTOCOLS_ALL|SD_RESOLVED_NO_SEARCH);
         if (r < 0) {
                 log_error_errno(r, "Failed to generate query object: %m");
-                dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL);
+                dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
                 goto fail;
         }
 
@@ -356,7 +365,7 @@ static void dns_stub_process_query(Manager *m, DnsStream *s, DnsPacket *p) {
         r = dns_query_go(q);
         if (r < 0) {
                 log_error_errno(r, "Failed to start query: %m");
-                dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL);
+                dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
                 goto fail;
         }
 

src/resolve/resolved-dns-transaction.c

@@ -31,6 +31,7 @@
 #include "string-table.h"
 
 #define TRANSACTIONS_MAX 4096
+#define TRANSACTION_TCP_TIMEOUT_USEC (10U*USEC_PER_SEC)
 
 static void dns_transaction_reset_answer(DnsTransaction *t) {
         assert(t);
@@ -832,7 +833,7 @@ void dns_transaction_process_reply(DnsTransaction *t, DnsPacket *p) {
          * should hence not attempt to access the query or transaction
          * after calling this function. */
 
-        log_debug("Processing incoming packet on transaction %" PRIu16".", t->id);
+        log_debug("Processing incoming packet on transaction %" PRIu16". (rcode=%s)", t->id, dns_rcode_to_string(DNS_PACKET_RCODE(p)));
 
         switch (t->scope->protocol) {
 
@@ -910,9 +911,13 @@ void dns_transaction_process_reply(DnsTransaction *t, DnsPacket *p) {
 
                         /* Request failed, immediately try again with reduced features */
 
-                        if (t->current_feature_level <= DNS_SERVER_FEATURE_LEVEL_WORST) {
-                                /* This was already at the lowest possible feature level? If so, we can't downgrade
-                                 * this transaction anymore, hence let's process the response, and accept the rcode. */
+                        if (t->current_feature_level <= DNS_SERVER_FEATURE_LEVEL_UDP) {
+                                /* This was already at UDP feature level? If so, it doesn't make sense to downgrade
+                                 * this transaction anymore, hence let's process the response, and accept the
+                                 * rcode. Note that we don't retry on TCP, since that's a suitable way to mitigate
+                                 * packet loss, but is not going to give us better rcodes should we actually have
+                                 * managed to get them already at UDP level. */
+
                                 log_debug("Server returned error: %s", dns_rcode_to_string(DNS_PACKET_RCODE(p)));
                                 break;
                         }
@@ -1135,7 +1140,7 @@ static int dns_transaction_emit_udp(DnsTransaction *t) {
                         return r;
 
                 if (t->current_feature_level < DNS_SERVER_FEATURE_LEVEL_UDP)
-                        return -EAGAIN;
+                        return -EAGAIN; /* Sorry, can't do UDP, try TCP! */
 
                 if (!dns_server_dnssec_supported(t->server) && dns_type_is_dnssec(t->key->type))
                         return -EOPNOTSUPP;
@@ -1212,9 +1217,17 @@ static usec_t transaction_get_resend_timeout(DnsTransaction *t) {
         assert(t);
         assert(t->scope);
 
+
         switch (t->scope->protocol) {
 
         case DNS_PROTOCOL_DNS:
+
+                /* When we do TCP, grant a much longer timeout, as in this case there's no need for us to quickly
+                 * resend, as the kernel does that anyway for us, and we really don't want to interrupt it in that
+                 * needlessly. */
+                if (t->stream)
+                        return TRANSACTION_TCP_TIMEOUT_USEC;
+
                 assert(t->server);
                 return t->server->resend_timeout;
 
@@ -1579,7 +1592,7 @@ int dns_transaction_go(DnsTransaction *t) {
                 r = dns_transaction_emit_udp(t);
                 if (r == -EMSGSIZE)
                         log_debug("Sending query via TCP since it is too large.");
-                if (r == -EAGAIN)
+                else if (r == -EAGAIN)
                         log_debug("Sending query via TCP since server doesn't support UDP.");
                 if (r == -EMSGSIZE || r == -EAGAIN)
                         r = dns_transaction_open_tcp(t);
@@ -1996,8 +2009,18 @@ int dns_transaction_request_dnssec_keys(DnsTransaction *t) {
                         r = dns_resource_key_match_rr(t->key, rr, NULL);
                         if (r < 0)
                                 return r;
-                        if (r == 0)
-                                continue;
+                        if (r == 0) {
+                                /* Hmm, so this SOA RR doesn't match our original question. In this case, maybe this is
+                                 * a negative reply, and we need the a SOA RR's TTL in order to cache a negative entry?
+                                 * If so, we need to validate it, too. */
+
+                                r = dns_answer_match_key(t->answer, t->key, NULL);
+                                if (r < 0)
+                                        return r;
+                                if (r > 0) /* positive reply, we won't need the SOA and hence don't need to validate
+                                            * it. */
+                                        continue;
+                        }
 
                         r = dnssec_has_rrsig(t->answer, rr->key);
                         if (r < 0)

src/resolve/resolved-dns-transaction.h

@@ -178,7 +178,7 @@ DnsTransactionSource dns_transaction_source_from_string(const char *s) _pure_;
 #define MDNS_PROBING_INTERVAL_USEC (250 * USEC_PER_MSEC)
 
 /* Maximum attempts to send DNS requests, across all DNS servers */
-#define DNS_TRANSACTION_ATTEMPTS_MAX 16
+#define DNS_TRANSACTION_ATTEMPTS_MAX 24
 
 /* Maximum attempts to send LLMNR requests, see RFC 4795 Section 2.7 */
 #define LLMNR_TRANSACTION_ATTEMPTS_MAX 3

src/resolve/resolved-dns-trust-anchor.c

@@ -547,10 +547,33 @@ int dns_trust_anchor_lookup_positive(DnsTrustAnchor *d, const DnsResourceKey *ke
 }
 
 int dns_trust_anchor_lookup_negative(DnsTrustAnchor *d, const char *name) {
+        int r;
+
         assert(d);
         assert(name);
 
-        return set_contains(d->negative_by_name, name);
+        for (;;) {
+                /* If the domain is listed as-is in the NTA database, then that counts */
+                if (set_contains(d->negative_by_name, name))
+                        return true;
+
+                /* If the domain isn't listed as NTA, but is listed as positive trust anchor, then that counts. See RFC
+                 * 7646, section 1.1 */
+                if (hashmap_contains(d->positive_by_key, &DNS_RESOURCE_KEY_CONST(DNS_CLASS_IN, DNS_TYPE_DS, name)))
+                        return false;
+
+                if (hashmap_contains(d->positive_by_key, &DNS_RESOURCE_KEY_CONST(DNS_CLASS_IN, DNS_TYPE_KEY, name)))
+                        return false;
+
+                /* And now, let's look at the parent, and check that too */
+                r = dns_name_parent(&name);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        break;
+        }
+
+        return false;
 }
 
 static int dns_trust_anchor_revoked_put(DnsTrustAnchor *d, DnsResourceRecord *rr) {