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, 3 insertions, 1 deletions

diff --git a/src/resolve/test-dnssec.c b/src/resolve/test-dnssec.c
index 0b2ffeeddd..a2118513f1 100644
--- a/src/resolve/test-dnssec.c
+++ b/src/resolve/test-dnssec.c
@@ -56,6 +56,7 @@ static void test_dnssec_verify_rrset(void) {
         _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *a = NULL, *rrsig = NULL, *dnskey = NULL;
         _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
         _cleanup_free_ char *x = NULL, *y = NULL, *z = NULL;
+        DnssecResult result;
 
         a = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_A, "nAsA.gov");
         assert_se(a);
@@ -106,7 +107,8 @@ static void test_dnssec_verify_rrset(void) {
         assert_se(dns_answer_add(answer, a, 0) >= 0);
 
         /* Validate the RR as it if was 2015-12-2 today */
-        assert_se(dnssec_verify_rrset(answer, a->key, rrsig, dnskey, 1449092754*USEC_PER_SEC) == DNSSEC_VERIFIED);
+        assert_se(dnssec_verify_rrset(answer, a->key, rrsig, dnskey, 1449092754*USEC_PER_SEC, &result) >= 0);
+        assert_se(result == DNSSEC_VALIDATED);
 }
 
 static void test_dnssec_verify_dns_key(void) {