resolved: rework synthesizing logic

With this change we'll now also generate synthesized RRs for the local
LLMNR hostname (first label of system hostname), the local mDNS hostname
(first label of system hostname suffixed with .local), the "gateway"
hostname and all the reverse PTRs. This hence takes over part of what
nss-myhostname already implemented.

Local hostnames resolve to the set of local IP addresses. Since the
addresses are possibly on different interfaces it is necessary to change
the internal DnsAnswer object to track per-RR interface indexes, and to
change the bus API to always return the interface per-address rather than
per-reply. This change also patches  the existing clients for resolved
accordingly (nss-resolve + systemd-resolve-host).

This also changes the routing logic for queries slightly: we now ensure
that the local hostname is never resolved via LLMNR, thus making it
trustable on the local system.

1 files changed, 14 insertions, 3 deletions

diff --git a/src/resolve/resolved-dns-answer.h b/src/resolve/resolved-dns-answer.h
index af3e462ed5..0757dd60d0 100644
--- a/src/resolve/resolved-dns-answer.h
+++ b/src/resolve/resolved-dns-answer.h
@@ -22,22 +22,31 @@
 ***/
 
 typedef struct DnsAnswer DnsAnswer;
+typedef struct DnsAnswerItem DnsAnswerItem;
 
 #include "resolved-dns-rr.h"
 
-/* A simple array of resource records */
+/* A simple array of resource records. We keep track of the
+ * originating ifindex for each RR where that makes sense, so that we
+ * can qualify A and AAAA RRs referring to a local link with the
+ * right ifindex. */
+
+struct DnsAnswerItem {
+        DnsResourceRecord *rr;
+        int ifindex;
+};
 
 struct DnsAnswer {
         unsigned n_ref;
         unsigned n_rrs, n_allocated;
-        DnsResourceRecord* rrs[0];
+        DnsAnswerItem items[0];
 };
 
 DnsAnswer *dns_answer_new(unsigned n);
 DnsAnswer *dns_answer_ref(DnsAnswer *a);
 DnsAnswer *dns_answer_unref(DnsAnswer *a);
 
-int dns_answer_add(DnsAnswer *a, DnsResourceRecord *rr);
+int dns_answer_add(DnsAnswer *a, DnsResourceRecord *rr, int ifindex);
 int dns_answer_add_soa(DnsAnswer *a, const char *name, uint32_t ttl);
 int dns_answer_contains(DnsAnswer *a, DnsResourceKey *key);
 int dns_answer_find_soa(DnsAnswer *a, DnsResourceKey *key, DnsResourceRecord **ret);
@@ -45,4 +54,6 @@ int dns_answer_find_soa(DnsAnswer *a, DnsResourceKey *key, DnsResourceRecord **r
 DnsAnswer *dns_answer_merge(DnsAnswer *a, DnsAnswer *b);
 void dns_answer_order_by_scope(DnsAnswer *a, bool prefer_link_local);
 
+int dns_answer_reserve(DnsAnswer **a, unsigned n_free);
+
 DEFINE_TRIVIAL_CLEANUP_FUNC(DnsAnswer*, dns_answer_unref);