resolved: correctly handle non-address RR types with /etc/hosts lookups (#4808)

Fix wrong condition test in manager_etc_hosts_lookup(), which caused it to
return an IPv4 answer when an IPv6 question was asked, and vice versa.
Also only return success if we actually found any A or AAAA record.

In systemd-resolved.service(8), point out that /etc/hosts mappings only
affect address-type lookups, not other types.

The test case currently disables DNSSEC in resolved, as there is a bug
where "-t MX" fails due to "DNSSEC validation failed" even after
"downgrading to non-DNSSEC mode". This should be dropped once that bug
gets fixed.

Fixes #4801

1 files changed, 3 insertions, 3 deletions

diff --git a/src/resolve/resolved-etc-hosts.c b/src/resolve/resolved-etc-hosts.c
index 40d650949d..0a284825a1 100644
--- a/src/resolve/resolved-etc-hosts.c
+++ b/src/resolve/resolved-etc-hosts.c
@@ -431,8 +431,8 @@ int manager_etc_hosts_lookup(Manager *m, DnsQuestion* q, DnsAnswer **answer) {
         for (i = 0; i < bn->n_items; i++) {
                 _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
 
-                if ((found_a && bn->items[i]->family != AF_INET) &&
-                    (found_aaaa && bn->items[i]->family != AF_INET6))
+                if ((!found_a && bn->items[i]->family == AF_INET) ||
+                    (!found_aaaa && bn->items[i]->family == AF_INET6))
                         continue;
 
                 r = dns_resource_record_new_address(&rr, bn->items[i]->family, &bn->items[i]->address, bn->name);
@@ -444,5 +444,5 @@ int manager_etc_hosts_lookup(Manager *m, DnsQuestion* q, DnsAnswer **answer) {
                         return r;
         }
 
-        return 1;
+        return found_a || found_aaaa;
 }