resolved: in dns stub always report "lo" as interface for "localhost"

Previously, we'd return the ifindex the user asked on, and if none was
specified "lo". Let's always return "lo".

This should be a better choice usually, since localhost addresses are
typically not reachable over arbitrary interfaces once SO_BINDTODEVICE
or so is used. Hence, let's report the interface that is always right
for these addresses.

1 files changed, 14 insertions, 29 deletions

diff --git a/src/resolve/resolved-dns-synthesize.c b/src/resolve/resolved-dns-synthesize.c
index b3442ad906..8e09ef20d5 100644
--- a/src/resolve/resolved-dns-synthesize.c
+++ b/src/resolve/resolved-dns-synthesize.c
@@ -7,20 +7,6 @@
 #include "missing_network.h"
 #include "resolved-dns-synthesize.h"
 
-int dns_synthesize_ifindex(int ifindex) {
-
-        /* When the caller asked for resolving on a specific
-         * interface, we synthesize the answer for that
-         * interface. However, if nothing specific was claimed and we
-         * only return localhost RRs, we synthesize the answer for
-         * localhost. */
-
-        if (ifindex > 0)
-                return ifindex;
-
-        return LOOPBACK_IFINDEX;
-}
-
 int dns_synthesize_family(uint64_t flags) {
 
         /* Picks an address family depending on set flags. This is
@@ -57,7 +43,7 @@ DnsProtocol dns_synthesize_protocol(uint64_t flags) {
         return DNS_PROTOCOL_DNS;
 }
 
-static int synthesize_localhost_rr(Manager *m, const DnsResourceKey *key, int ifindex, DnsAnswer **answer) {
+static int synthesize_localhost_rr(Manager *m, const DnsResourceKey *key, DnsAnswer **answer) {
         int r;
 
         assert(m);
@@ -77,7 +63,7 @@ static int synthesize_localhost_rr(Manager *m, const DnsResourceKey *key, int if
 
                 rr->a.in_addr.s_addr = htobe32(INADDR_LOOPBACK);
 
-                r = dns_answer_add(*answer, rr, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED, NULL);
+                r = dns_answer_add(*answer, rr, LOOPBACK_IFINDEX, DNS_ANSWER_AUTHENTICATED, NULL);
                 if (r < 0)
                         return r;
         }
@@ -91,7 +77,7 @@ static int synthesize_localhost_rr(Manager *m, const DnsResourceKey *key, int if
 
                 rr->aaaa.in6_addr = in6addr_loopback;
 
-                r = dns_answer_add(*answer, rr, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED, NULL);
+                r = dns_answer_add(*answer, rr, LOOPBACK_IFINDEX, DNS_ANSWER_AUTHENTICATED, NULL);
                 if (r < 0)
                         return r;
         }
@@ -113,7 +99,7 @@ static int answer_add_ptr(DnsAnswer **answer, const char *from, const char *to,
         return dns_answer_add(*answer, rr, ifindex, flags, NULL);
 }
 
-static int synthesize_localhost_ptr(Manager *m, const DnsResourceKey *key, int ifindex, DnsAnswer **answer) {
+static int synthesize_localhost_ptr(Manager *m, const DnsResourceKey *key, DnsAnswer **answer) {
         int r;
 
         assert(m);
@@ -125,7 +111,7 @@ static int synthesize_localhost_ptr(Manager *m, const DnsResourceKey *key, int i
                 if (r < 0)
                         return r;
 
-                r = answer_add_ptr(answer, dns_resource_key_name(key), "localhost", dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
+                r = answer_add_ptr(answer, dns_resource_key_name(key), "localhost", LOOPBACK_IFINDEX, DNS_ANSWER_AUTHENTICATED);
                 if (r < 0)
                         return r;
         }
@@ -225,20 +211,19 @@ static int synthesize_system_hostname_rr(Manager *m, const DnsResourceKey *key,
                 if (n == 0) {
                         struct local_address buffer[2];
 
-                        /* If we have no local addresses then use ::1
-                         * and 127.0.0.2 as local ones. */
+                        /* If we have no local addresses then use ::1 and 127.0.0.2 as local ones. */
 
                         if (IN_SET(af, AF_INET, AF_UNSPEC))
                                 buffer[n++] = (struct local_address) {
                                         .family = AF_INET,
-                                        .ifindex = dns_synthesize_ifindex(ifindex),
+                                        .ifindex = LOOPBACK_IFINDEX,
                                         .address.in.s_addr = htobe32(0x7F000002),
                                 };
 
                         if (IN_SET(af, AF_INET6, AF_UNSPEC) && socket_ipv6_is_enabled())
                                 buffer[n++] = (struct local_address) {
                                         .family = AF_INET6,
-                                        .ifindex = dns_synthesize_ifindex(ifindex),
+                                        .ifindex = LOOPBACK_IFINDEX,
                                         .address.in6 = in6addr_loopback,
                                 };
 
@@ -268,19 +253,19 @@ static int synthesize_system_hostname_ptr(Manager *m, int af, const union in_add
                 if (r < 0)
                         return r;
 
-                r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", m->full_hostname, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
+                r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", m->full_hostname, LOOPBACK_IFINDEX, DNS_ANSWER_AUTHENTICATED);
                 if (r < 0)
                         return r;
 
-                r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", m->llmnr_hostname, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
+                r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", m->llmnr_hostname, LOOPBACK_IFINDEX, DNS_ANSWER_AUTHENTICATED);
                 if (r < 0)
                         return r;
 
-                r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", m->mdns_hostname, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
+                r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", m->mdns_hostname, LOOPBACK_IFINDEX, DNS_ANSWER_AUTHENTICATED);
                 if (r < 0)
                         return r;
 
-                r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", "localhost", dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
+                r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", "localhost", LOOPBACK_IFINDEX, DNS_ANSWER_AUTHENTICATED);
                 if (r < 0)
                         return r;
 
@@ -405,7 +390,7 @@ int dns_synthesize_answer(
 
                 } else if (is_localhost(name)) {
 
-                        r = synthesize_localhost_rr(m, key, ifindex, &answer);
+                        r = synthesize_localhost_rr(m, key, &answer);
                         if (r < 0)
                                 return log_error_errno(r, "Failed to synthesize localhost RRs: %m");
 
@@ -440,7 +425,7 @@ int dns_synthesize_answer(
                 } else if ((dns_name_endswith(name, "127.in-addr.arpa") > 0 && dns_name_equal(name, "2.0.0.127.in-addr.arpa") == 0) ||
                            dns_name_equal(name, "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa") > 0) {
 
-                        r = synthesize_localhost_ptr(m, key, ifindex, &answer);
+                        r = synthesize_localhost_ptr(m, key, &answer);
                         if (r < 0)
                                 return log_error_errno(r, "Failed to synthesize localhost PTR RRs: %m");