Revert "resolved: filter out our own stub resolvers when parsing servers"

This reverts commit 0ad4efb14beea9148838a0d974821e3b98cafc47.

See
https://github.com/systemd/systemd/pull/20559#issuecomment-1028011030
for reasoning. Quoting:

> I think it should be OK to advertise extra stub listeners to local
> clients, but you prohibit this now. i.e. there are two different
> concepts here, and we shouldn't mix them up:
>
> 1. tracking configured dns servers and advertise them to local programs
> 2. actually using them ourselves
>
> I am pretty sure that our own stubs are OK for 1 but not OK for 2,
> hence we should filter at the time of use not at the time of parse.

1 files changed, 13 insertions, 15 deletions

diff --git a/src/resolve/resolved-conf.c b/src/resolve/resolved-conf.c
index 7873c363b3..930313b844 100644
--- a/src/resolve/resolved-conf.c
+++ b/src/resolve/resolved-conf.c
@@ -35,16 +35,15 @@ static int manager_add_dns_server_by_string(Manager *m, DnsServerType type, cons
         if (r < 0)
                 return r;
 
-        /* By default, the port number is determined by the transaction feature level.
+        /* Silently filter out 0.0.0.0, 127.0.0.53, 127.0.0.54 (our own stub DNS listener) */
+        if (!dns_server_address_valid(family, &address))
+                return 0;
+
+        /* By default, the port number is determined with the transaction feature level.
          * See dns_transaction_port() and dns_server_port(). */
         if (IN_SET(port, 53, 853))
                 port = 0;
 
-        /* Refuse 0.0.0.0, 127.0.0.53, 127.0.0.54 and the rest of our own stub DNS listeners. */
-        if (!dns_server_address_valid(family, &address) ||
-            manager_server_address_is_stub(m, family, &address, port ?: 53))
-                return -ELOOP;
-
         /* Filter out duplicates */
         s = dns_server_find(manager_get_first_dns_server(m, type), family, &address, port, ifindex, server_name);
         if (s) {
@@ -57,7 +56,7 @@ static int manager_add_dns_server_by_string(Manager *m, DnsServerType type, cons
         return dns_server_new(m, NULL, type, NULL, family, &address, port, ifindex, server_name);
 }
 
-int manager_parse_dns_server_string_and_warn(Manager *m, DnsServerType type, const char *string, bool ignore_self_quietly) {
+int manager_parse_dns_server_string_and_warn(Manager *m, DnsServerType type, const char *string) {
         int r;
 
         assert(m);
@@ -71,10 +70,7 @@ int manager_parse_dns_server_string_and_warn(Manager *m, DnsServerType type, con
                         return r;
 
                 r = manager_add_dns_server_by_string(m, type, word);
-                if (r == -ELOOP)
-                        log_full(ignore_self_quietly ? LOG_DEBUG : LOG_INFO,
-                                 "DNS server string '%s' points to our own listener, ignoring.", word);
-                else if (r < 0)
+                if (r < 0)
                         log_warning_errno(r, "Failed to add DNS server address '%s', ignoring: %m", word);
         }
 }
@@ -155,7 +151,7 @@ int config_parse_dns_servers(
                 dns_server_unlink_all(manager_get_first_dns_server(m, ltype));
         else {
                 /* Otherwise, add to the list */
-                r = manager_parse_dns_server_string_and_warn(m, ltype, rvalue, false);
+                r = manager_parse_dns_server_string_and_warn(m, ltype, rvalue);
                 if (r < 0) {
                         log_syntax(unit, LOG_WARNING, filename, line, r,
                                    "Failed to parse DNS server string '%s', ignoring.", rvalue);
@@ -163,7 +159,8 @@ int config_parse_dns_servers(
                 }
         }
 
-        /* If we have a manual setting, then we stop reading /etc/resolv.conf */
+        /* If we have a manual setting, then we stop reading
+         * /etc/resolv.conf */
         if (ltype == DNS_SERVER_SYSTEM)
                 m->read_resolv_conf = false;
         if (ltype == DNS_SERVER_FALLBACK)
@@ -205,7 +202,8 @@ int config_parse_search_domains(
                 }
         }
 
-        /* If we have a manual setting, then we stop reading /etc/resolv.conf */
+        /* If we have a manual setting, then we stop reading
+         * /etc/resolv.conf */
         m->read_resolv_conf = false;
 
         return 0;
@@ -487,7 +485,7 @@ int manager_parse_config_file(Manager *m) {
                 return r;
 
         if (m->need_builtin_fallbacks) {
-                r = manager_parse_dns_server_string_and_warn(m, DNS_SERVER_FALLBACK, DNS_SERVERS, false);
+                r = manager_parse_dns_server_string_and_warn(m, DNS_SERVER_FALLBACK, DNS_SERVERS);
                 if (r < 0)
                         return r;
         }