resolved: add a simple trust anchor database as additional RR source

When doing DNSSEC lookups we need to know one or more DS or DNSKEY RRs
as trust anchors to validate lookups. With this change we add a
compiled-in trust anchor database, serving the root DS key as of today,
retrieved from:

https://data.iana.org/root-anchors/root-anchors.xml

The interface is kept generic, so that additional DS or DNSKEY RRs may
be served via the same interface, for example by provisioning them
locally in external files to support "islands" of security.

The trust anchor database becomes the fourth source of RRs we maintain,
besides, the network, the local cache, and the local zone.

1 files changed, 15 insertions, 1 deletions

diff --git a/src/resolve/resolved-dns-transaction.c b/src/resolve/resolved-dns-transaction.c
index 90133cb332..7bef4be2ad 100644
--- a/src/resolve/resolved-dns-transaction.c
+++ b/src/resolve/resolved-dns-transaction.c
@@ -675,7 +675,20 @@ int dns_transaction_go(DnsTransaction *t) {
         t->answer_rcode = 0;
         t->answer_source = _DNS_TRANSACTION_SOURCE_INVALID;
 
-        /* Check the zone, but obly if this transaction is not used
+        /* Check the trust anchor. Do so only on classic DNS, since DNSSEC does not apply otherwise. */
+        if (t->scope->protocol == DNS_PROTOCOL_DNS) {
+                r = dns_trust_anchor_lookup(&t->scope->manager->trust_anchor, t->key, &t->answer);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        t->answer_rcode = DNS_RCODE_SUCCESS;
+                        t->answer_source = DNS_TRANSACTION_TRUST_ANCHOR;
+                        dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
+                        return 0;
+                }
+        }
+
+        /* Check the zone, but only if this transaction is not used
          * for probing or verifying a zone item. */
         if (set_isempty(t->zone_items)) {
 
@@ -817,5 +830,6 @@ static const char* const dns_transaction_source_table[_DNS_TRANSACTION_SOURCE_MA
         [DNS_TRANSACTION_NETWORK] = "network",
         [DNS_TRANSACTION_CACHE] = "cache",
         [DNS_TRANSACTION_ZONE] = "zone",
+        [DNS_TRANSACTION_TRUST_ANCHOR] = "trust-anchor",
 };
 DEFINE_STRING_TABLE_LOOKUP(dns_transaction_source, DnsTransactionSource);