resolved: optionally allow single-label A/AAAA queries

Author: keszybz

src/resolve/resolved-dns-query.c

@@ -524,12 +524,12 @@ static int dns_query_add_candidate(DnsQuery *q, DnsScope *s) {
                 return r;
 
         /* If this a single-label domain on DNS, we might append a suitable search domain first. */
-        if ((q->flags & SD_RESOLVED_NO_SEARCH) == 0 &&
-            dns_scope_name_needs_search_domain(s, dns_question_first_name(q->question_idna))) {
-                /* OK, we need a search domain now. Let's find one for this scope */
+        if (!FLAGS_SET(q->flags, SD_RESOLVED_NO_SEARCH) &&
+            dns_scope_name_wants_search_domain(s, dns_question_first_name(q->question_idna))) {
+                /* OK, we want a search domain now. Let's find one for this scope */
 
                 r = dns_query_candidate_next_search_domain(c);
-                if (r <= 0) /* if there's no search domain, then we won't add any transaction. */
+                if (r < 0)
                         return r;
         }
 

src/resolve/resolved-dns-scope.c

@@ -619,7 +619,7 @@ DnsScopeMatch dns_scope_good_domain(
                      manager_is_own_hostname(s->manager, domain) <= 0))  /* never resolve the local hostname via LLMNR */
                         return DNS_SCOPE_YES_BASE + 1; /* Return +1, as we consider ourselves authoritative
                                                         * for single-label names, i.e. one label. This is
-                                                        * particular relevant as it means a "." route on some
+                                                        * particularly relevant as it means a "." route on some
                                                         * other scope won't pull all traffic away from
                                                         * us. (If people actually want to pull traffic away
                                                         * from us they should turn off LLMNR on the
@@ -651,20 +651,21 @@ bool dns_scope_good_key(DnsScope *s, const DnsResourceKey *key) {
 
         if (s->protocol == DNS_PROTOCOL_DNS) {
 
-                /* On classic DNS, looking up non-address RRs is always
-                 * fine. (Specifically, we want to permit looking up
-                 * DNSKEY and DS records on the root and top-level
-                 * domains.) */
+                /* On classic DNS, looking up non-address RRs is always fine. (Specifically, we want to
+                 * permit looking up DNSKEY and DS records on the root and top-level domains.) */
                 if (!dns_resource_key_is_address(key))
                         return true;
 
-                /* However, we refuse to look up A and AAAA RRs on the
-                 * root and single-label domains, under the assumption
-                 * that those should be resolved via LLMNR or search
-                 * path only, and should not be leaked onto the
-                 * internet. */
-                return !(dns_name_is_single_label(dns_resource_key_name(key)) ||
-                         dns_name_is_root(dns_resource_key_name(key)));
+                /* Unless explicitly overridden, we refuse to look up A and AAAA RRs on the root and
+                 * single-label domains, under the assumption that those should be resolved via LLMNR or
+                 * search path only, and should not be leaked onto the internet. */
+                const char* name = dns_resource_key_name(key);
+
+                if (!s->manager->resolve_unicast_single_label &&
+                    dns_name_is_single_label(name))
+                        return false;
+
+                return !dns_name_is_root(name);
         }
 
         /* On mDNS and LLMNR, send A and AAAA queries only on the
@@ -1169,7 +1170,7 @@ DnsSearchDomain *dns_scope_get_search_domains(DnsScope *s) {
         return s->manager->search_domains;
 }
 
-bool dns_scope_name_needs_search_domain(DnsScope *s, const char *name) {
+bool dns_scope_name_wants_search_domain(DnsScope *s, const char *name) {
         assert(s);
 
         if (s->protocol != DNS_PROTOCOL_DNS)

src/resolve/resolved-dns-scope.h

@@ -99,7 +99,7 @@ void dns_scope_dump(DnsScope *s, FILE *f);
 
 DnsSearchDomain *dns_scope_get_search_domains(DnsScope *s);
 
-bool dns_scope_name_needs_search_domain(DnsScope *s, const char *name);
+bool dns_scope_name_wants_search_domain(DnsScope *s, const char *name);
 
 bool dns_scope_network_good(DnsScope *s);
 

src/resolve/resolved-gperf.gperf

@@ -18,13 +18,14 @@ struct ConfigPerfItem;
 %struct-type
 %includes
 %%
-Resolve.DNS,             config_parse_dns_servers,            DNS_SERVER_SYSTEM,   0
-Resolve.FallbackDNS,     config_parse_dns_servers,            DNS_SERVER_FALLBACK, 0
-Resolve.Domains,         config_parse_search_domains,         0,                   0
-Resolve.LLMNR,           config_parse_resolve_support,        0,                   offsetof(Manager, llmnr_support)
-Resolve.MulticastDNS,    config_parse_resolve_support,        0,                   offsetof(Manager, mdns_support)
-Resolve.DNSSEC,          config_parse_dnssec_mode,            0,                   offsetof(Manager, dnssec_mode)
-Resolve.DNSOverTLS,      config_parse_dns_over_tls_mode,      0,                   offsetof(Manager, dns_over_tls_mode)
-Resolve.Cache,           config_parse_dns_cache_mode,         DNS_CACHE_MODE_YES,  offsetof(Manager, enable_cache)
-Resolve.DNSStubListener, config_parse_dns_stub_listener_mode, 0,                   offsetof(Manager, dns_stub_listener_mode)
-Resolve.ReadEtcHosts,    config_parse_bool,                   0,                   offsetof(Manager, read_etc_hosts)
+Resolve.DNS,                       config_parse_dns_servers,            DNS_SERVER_SYSTEM,   0
+Resolve.FallbackDNS,               config_parse_dns_servers,            DNS_SERVER_FALLBACK, 0
+Resolve.Domains,                   config_parse_search_domains,         0,                   0
+Resolve.LLMNR,                     config_parse_resolve_support,        0,                   offsetof(Manager, llmnr_support)
+Resolve.MulticastDNS,              config_parse_resolve_support,        0,                   offsetof(Manager, mdns_support)
+Resolve.DNSSEC,                    config_parse_dnssec_mode,            0,                   offsetof(Manager, dnssec_mode)
+Resolve.DNSOverTLS,                config_parse_dns_over_tls_mode,      0,                   offsetof(Manager, dns_over_tls_mode)
+Resolve.Cache,                     config_parse_dns_cache_mode,         DNS_CACHE_MODE_YES,  offsetof(Manager, enable_cache)
+Resolve.DNSStubListener,           config_parse_dns_stub_listener_mode, 0,                   offsetof(Manager, dns_stub_listener_mode)
+Resolve.ReadEtcHosts,              config_parse_bool,                   0,                   offsetof(Manager, read_etc_hosts)
+Resolve.ResolveUnicastSingleLabel, config_parse_bool,                   0,                   offsetof(Manager, resolve_unicast_single_label)

src/resolve/resolved-manager.h

@@ -72,6 +72,7 @@ struct Manager {
 
         bool need_builtin_fallbacks;
         bool read_resolv_conf;
+        bool resolve_unicast_single_label;
 
         struct stat resolv_conf_stat;
 

src/resolve/resolved.conf.in

@@ -22,3 +22,4 @@
 #Cache=yes
 #DNSStubListener=yes
 #ReadEtcHosts=yes
+#ResolveUnicastSingleLabel=no