resolved: when answer A or AAAA questions, order responses by whether addresses are link-local or not

3 files changed, 34 insertions, 0 deletions

diff --git a/src/resolve/resolved-dns-answer.c b/src/resolve/resolved-dns-answer.c
index d907664527..93e51fc248 100644
--- a/src/resolve/resolved-dns-answer.c
+++ b/src/resolve/resolved-dns-answer.c
@@ -175,3 +175,34 @@ DnsAnswer *dns_answer_merge(DnsAnswer *a, DnsAnswer *b) {
 
         return k;
 }
+
+void dns_answer_order_by_scope(DnsAnswer *a, bool prefer_link_local) {
+        DnsResourceRecord **rrs;
+        unsigned i, start, end;
+        assert(a);
+
+        if (a->n_rrs <= 1)
+                return;
+
+        start = 0;
+        end = a->n_rrs-1;
+
+        /* RFC 4795, Section 2.6 suggests we should order entries
+         * depending on whether the sender is a link-local address. */
+
+        rrs = newa(DnsResourceRecord*, a->n_rrs);
+        for (i = 0; i < a->n_rrs; i++) {
+
+                if (a->rrs[i]->key->class == DNS_CLASS_IN &&
+                    ((a->rrs[i]->key->type == DNS_TYPE_A && in_addr_is_link_local(AF_INET, (union in_addr_union*) &a->rrs[i]->a.in_addr) != prefer_link_local) ||
+                     (a->rrs[i]->key->type == DNS_TYPE_AAAA && in_addr_is_link_local(AF_INET6, (union in_addr_union*) &a->rrs[i]->aaaa.in6_addr) != prefer_link_local)))
+                        /* Order address records that are are not preferred to the end of the array */
+                        rrs[end--] = a->rrs[i];
+                else
+                        /* Order all other records to the beginning of the array */
+                        rrs[start++] = a->rrs[i];
+        }
+
+        assert(start == end+1);
+        memcpy(a->rrs, rrs, sizeof(DnsResourceRecord*) * a->n_rrs);
+}
diff --git a/src/resolve/resolved-dns-answer.h b/src/resolve/resolved-dns-answer.h
index 135a421f29..268bb38537 100644
--- a/src/resolve/resolved-dns-answer.h
+++ b/src/resolve/resolved-dns-answer.h
@@ -42,5 +42,6 @@ int dns_answer_contains(DnsAnswer *a, DnsResourceKey *key);
 int dns_answer_find_soa(DnsAnswer *a, DnsResourceKey *key, DnsResourceRecord **ret);
 
 DnsAnswer *dns_answer_merge(DnsAnswer *a, DnsAnswer *b);
+void dns_answer_order_by_scope(DnsAnswer *a, bool prefer_link_local);
 
 DEFINE_TRIVIAL_CLEANUP_FUNC(DnsAnswer*, dns_answer_unref);
diff --git a/src/resolve/resolved-dns-scope.c b/src/resolve/resolved-dns-scope.c
index b975ac4092..b17de0c88f 100644
--- a/src/resolve/resolved-dns-scope.c
+++ b/src/resolve/resolved-dns-scope.c
@@ -483,6 +483,8 @@ void dns_scope_process_query(DnsScope *s, DnsStream *stream, DnsPacket *p) {
         if (r == 0)
                 return;
 
+        dns_answer_order_by_scope(answer, in_addr_is_link_local(p->family, &p->sender) > 0);
+
         r = dns_scope_make_reply_packet(s, DNS_PACKET_ID(p), DNS_RCODE_SUCCESS, p->question, answer, &reply);
         if (r < 0) {
                 log_debug("Failed to build reply packet: %s", strerror(-r));