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, 101 insertions, 0 deletions

diff --git a/src/resolve/resolved-dns-trust-anchor.c b/src/resolve/resolved-dns-trust-anchor.c
new file mode 100644
index 0000000000..e55bdaa1ed
--- /dev/null
+++ b/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;
+}