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.

Makefile.am

@@ -5184,6 +5184,8 @@ systemd_resolved_SOURCES = \
 	src/resolve/resolved-dns-stream.c \
 	src/resolve/resolved-dns-dnssec.h \
 	src/resolve/resolved-dns-dnssec.c \
+	src/resolve/resolved-dns-trust-anchor.h \
+	src/resolve/resolved-dns-trust-anchor.c \
 	src/resolve/dns-type.c \
 	src/resolve/dns-type.h
 

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);

src/resolve/resolved-dns-transaction.h

@@ -44,6 +44,7 @@ enum DnsTransactionSource {
         DNS_TRANSACTION_NETWORK,
         DNS_TRANSACTION_CACHE,
         DNS_TRANSACTION_ZONE,
+        DNS_TRANSACTION_TRUST_ANCHOR,
         _DNS_TRANSACTION_SOURCE_MAX,
         _DNS_TRANSACTION_SOURCE_INVALID = -1
 };

src/resolve/resolved-dns-trust-anchor.c

@@ -0,0 +1,101 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2015 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include "alloc-util.h"
+#include "resolved-dns-trust-anchor.h"
+
+/* The DS RR from https://data.iana.org/root-anchors/root-anchors.xml */
+static const uint8_t root_digest[] =
+        { 0x49, 0xAA, 0xC1, 0x1D, 0x7B, 0x6F, 0x64, 0x46, 0x70, 0x2E, 0x54, 0xA1, 0x60, 0x73, 0x71, 0x60,
+          0x7A, 0x1A, 0x41, 0x85, 0x52, 0x00, 0xFD, 0x2C, 0xE1, 0xCD, 0xDE, 0x32, 0xF2, 0x4E, 0x8F, 0xB5 };
+
+int dns_trust_anchor_load(DnsTrustAnchor *d) {
+        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
+        _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
+        int r;
+
+        assert(d);
+
+        r = hashmap_ensure_allocated(&d->by_key, &dns_resource_key_hash_ops);
+        if (r < 0)
+                return r;
+
+        if (hashmap_get(d->by_key, &DNS_RESOURCE_KEY_CONST(DNS_CLASS_IN, DNS_TYPE_DS, ".")))
+                return 0;
+
+        /* Add the RR from https://data.iana.org/root-anchors/root-anchors.xml */
+        rr = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_DS, "");
+        if (!rr)
+                return -ENOMEM;
+
+        rr->ds.key_tag = 19036;
+        rr->ds.algorithm = DNSSEC_ALGORITHM_RSASHA256;
+        rr->ds.digest_type = DNSSEC_DIGEST_SHA256;
+        rr->ds.digest_size = sizeof(root_digest);
+        rr->ds.digest = memdup(root_digest, rr->ds.digest_size);
+        if (!rr->ds.digest)
+                return  -ENOMEM;
+
+        answer = dns_answer_new(1);
+        if (!answer)
+                return -ENOMEM;
+
+        r = dns_answer_add(answer, rr, 0);
+        if (r < 0)
+                return r;
+
+        r = hashmap_put(d->by_key, rr->key, answer);
+        if (r < 0)
+                return r;
+
+        answer = NULL;
+        return 0;
+}
+
+void dns_trust_anchor_flush(DnsTrustAnchor *d) {
+        DnsAnswer *a;
+
+        assert(d);
+
+        while ((a = hashmap_steal_first(d->by_key)))
+                dns_answer_unref(a);
+
+        d->by_key = hashmap_free(d->by_key);
+}
+
+int dns_trust_anchor_lookup(DnsTrustAnchor *d, DnsResourceKey *key, DnsAnswer **ret) {
+        DnsAnswer *a;
+
+        assert(d);
+        assert(key);
+        assert(ret);
+
+        /* We only serve DS and DNSKEY RRs. */
+        if (!IN_SET(key->type, DNS_TYPE_DS, DNS_TYPE_DNSKEY))
+                return 0;
+
+        a = hashmap_get(d->by_key, key);
+        if (!a)
+                return 0;
+
+        *ret = dns_answer_ref(a);
+        return 1;
+}

src/resolve/resolved-dns-trust-anchor.h

@@ -0,0 +1,39 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+#pragma once
+
+/***
+  This file is part of systemd.
+
+  Copyright 2015 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+typedef struct DnsTrustAnchor DnsTrustAnchor;
+
+#include "hashmap.h"
+#include "resolved-dns-answer.h"
+#include "resolved-dns-rr.h"
+
+/* This contains a fixed database mapping domain names to DS or DNSKEY records. */
+
+struct DnsTrustAnchor {
+        Hashmap *by_key;
+};
+
+int dns_trust_anchor_load(DnsTrustAnchor *d);
+void dns_trust_anchor_flush(DnsTrustAnchor *d);
+
+int dns_trust_anchor_lookup(DnsTrustAnchor *d, DnsResourceKey* key, DnsAnswer **answer);

src/resolve/resolved-manager.c

@@ -478,6 +478,10 @@ int manager_new(Manager **ret) {
         m->read_resolv_conf = true;
         m->need_builtin_fallbacks = true;
 
+        r = dns_trust_anchor_load(&m->trust_anchor);
+        if (r < 0)
+                return r;
+
         r = sd_event_default(&m->event);
         if (r < 0)
                 return r;
@@ -572,6 +576,8 @@ Manager *manager_free(Manager *m) {
         free(m->llmnr_hostname);
         free(m->mdns_hostname);
 
+        dns_trust_anchor_flush(&m->trust_anchor);
+
         free(m);
 
         return NULL;

src/resolve/resolved-manager.h

@@ -44,6 +44,7 @@ enum Support {
 #include "resolved-dns-search-domain.h"
 #include "resolved-dns-server.h"
 #include "resolved-dns-stream.h"
+#include "resolved-dns-trust-anchor.h"
 #include "resolved-link.h"
 
 #define MANAGER_SEARCH_DOMAINS_MAX 32
@@ -85,6 +86,8 @@ struct Manager {
         bool read_resolv_conf:1;
         usec_t resolv_conf_mtime;
 
+        DnsTrustAnchor trust_anchor;
+
         LIST_HEAD(DnsScope, dns_scopes);
         DnsScope *unicast_scope;