resolved: chase DNSKEY/DS RRs when doing look-ups with DNSSEC enabled

This adds initial support for validating RRSIG/DNSKEY/DS chains when
doing lookups. Proof-of-non-existance, or proof-of-unsigned-zones is not
implemented yet.

With this change DnsTransaction objects will generate additional
DnsTransaction objects when looking for DNSKEY or DS RRs to validate an
RRSIG on a response. DnsTransaction objects are thus created for three
reasons now:

1) Because a user asked for something to be resolved, i.e. requested by
   a DnsQuery/DnsQueryCandidate object.
2) As result of LLMNR RR probing, requested by a DnsZoneItem.
3) Because another DnsTransaction requires the requested RRs for
   validation of its own response.

DnsTransactions are shared between all these users, and are GC
automatically as soon as all of these users don't need a specific
transaction anymore.

To unify the handling of these three reasons for existance for a
DnsTransaction, a new common naming is introduced: each DnsTransaction
now tracks its "owners" via a Set* object named "notify_xyz", containing
all owners to notify on completion.

A new DnsTransaction state is introduced called "VALIDATING" that is
entered after a response has been receieved which needs to be validated,
as long as we are still waiting for the DNSKEY/DS RRs from other
DnsTransactions.

This patch will request the DNSKEY/DS RRs bottom-up, and then validate
them top-down.

Caching of RRs is now only done after verification, so that the cache is
not poisoned with known invalid data.

The "DnsAnswer" object gained a substantial number of new calls, since
we need to add/remove RRs to it dynamically now.

1 files changed, 20 insertions, 5 deletions

diff --git a/src/resolve/resolved-dns-answer.h b/src/resolve/resolved-dns-answer.h
index 08c84c1cda..8d95131dbe 100644
--- a/src/resolve/resolved-dns-answer.h
+++ b/src/resolve/resolved-dns-answer.h
@@ -30,7 +30,9 @@ typedef struct DnsAnswerItem DnsAnswerItem;
 /* 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. */
+ * right ifindex.
+ *
+ * Note that we usually encode the empty answer as a simple NULL. */
 
 struct DnsAnswerItem {
         DnsResourceRecord *rr;
@@ -48,15 +50,28 @@ DnsAnswer *dns_answer_ref(DnsAnswer *a);
 DnsAnswer *dns_answer_unref(DnsAnswer *a);
 
 int dns_answer_add(DnsAnswer *a, DnsResourceRecord *rr, int ifindex);
+int dns_answer_add_extend(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_match_soa(DnsResourceKey *key, DnsResourceKey *soa);
-int dns_answer_find_soa(DnsAnswer *a, DnsResourceKey *key, DnsResourceRecord **ret);
 
-DnsAnswer *dns_answer_merge(DnsAnswer *a, DnsAnswer *b);
+int dns_answer_match_key(DnsAnswer *a, const DnsResourceKey *key);
+int dns_answer_contains_rr(DnsAnswer *a, DnsResourceRecord *rr);
+
+int dns_answer_find_soa(DnsAnswer *a, const DnsResourceKey *key, DnsResourceRecord **ret);
+
+int dns_answer_merge(DnsAnswer *a, DnsAnswer *b, DnsAnswer **ret);
+int dns_answer_extend(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);
+int dns_answer_reserve_or_clone(DnsAnswer **a, unsigned n_free);
+
+int dns_answer_remove_by_key(DnsAnswer **a, const DnsResourceKey *key);
+int dns_answer_copy_by_key(DnsAnswer **a, DnsAnswer *source, const DnsResourceKey *key);
+
+static inline unsigned dns_answer_size(DnsAnswer *a) {
+        return a ? a->n_rrs : 0;
+}
 
 DEFINE_TRIVIAL_CLEANUP_FUNC(DnsAnswer*, dns_answer_unref);