resolved: add a DNS client stub resolver

Let's turn resolved into a something truly useful: a fully asynchronous
DNS stub resolver that subscribes to network changes.

(More to come: caching, LLMNR, mDNS/DNS-SD, DNSSEC, IDN, NSS module)

1 files changed, 408 insertions, 0 deletions

diff --git a/src/resolve/resolved-dns-query.c b/src/resolve/resolved-dns-query.c
new file mode 100644
index 0000000000..a9880524e6
--- /dev/null
+++ b/src/resolve/resolved-dns-query.c
@@ -0,0 +1,408 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2014 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 "resolved-dns-query.h"
+#include "resolved-dns-domain.h"
+
+#define TRANSACTION_TIMEOUT_USEC (5 * USEC_PER_SEC)
+#define QUERY_TIMEOUT_USEC (30 * USEC_PER_SEC)
+#define ATTEMPTS_MAX 8
+
+DnsQueryTransaction* dns_query_transaction_free(DnsQueryTransaction *t) {
+        if (!t)
+                return NULL;
+
+        sd_event_source_unref(t->timeout_event_source);
+        dns_packet_unref(t->packet);
+
+        if (t->query) {
+                LIST_REMOVE(transactions_by_query, t->query->transactions, t);
+                hashmap_remove(t->query->manager->dns_query_transactions, UINT_TO_PTR(t->id));
+        }
+
+        if (t->scope)
+                LIST_REMOVE(transactions_by_scope, t->scope->transactions, t);
+
+        free(t);
+        return NULL;
+}
+
+DEFINE_TRIVIAL_CLEANUP_FUNC(DnsQueryTransaction*, dns_query_transaction_free);
+
+static int dns_query_transaction_new(DnsQuery *q, DnsQueryTransaction **ret, DnsScope *s) {
+        _cleanup_(dns_query_transaction_freep) DnsQueryTransaction *t = NULL;
+        int r;
+
+        assert(q);
+        assert(s);
+
+        r = hashmap_ensure_allocated(&q->manager->dns_query_transactions, NULL, NULL);
+        if (r < 0)
+                return r;
+
+        t = new0(DnsQueryTransaction, 1);
+        if (!t)
+                return -ENOMEM;
+
+        do
+                random_bytes(&t->id, sizeof(t->id));
+        while (t->id == 0 ||
+               hashmap_get(q->manager->dns_query_transactions, UINT_TO_PTR(t->id)));
+
+        r = hashmap_put(q->manager->dns_query_transactions, UINT_TO_PTR(t->id), t);
+        if (r < 0) {
+                t->id = 0;
+                return r;
+        }
+
+        LIST_PREPEND(transactions_by_query, q->transactions, t);
+        t->query = q;
+
+        LIST_PREPEND(transactions_by_scope, s->transactions, t);
+        t->scope = s;
+
+        if (ret)
+                *ret = t;
+
+        t = NULL;
+
+        return 0;
+}
+
+static void dns_query_transaction_set_state(DnsQueryTransaction *t, DnsQueryState state) {
+        assert(t);
+
+        if (t->state == state)
+                return;
+
+        t->state = state;
+
+        if (state != DNS_QUERY_SENT)
+                t->timeout_event_source = sd_event_source_unref(t->timeout_event_source);
+
+        dns_query_finish(t->query);
+}
+
+int dns_query_transaction_reply(DnsQueryTransaction *t, DnsPacket *p) {
+        assert(t);
+        assert(p);
+
+        t->packet = dns_packet_ref(p);
+
+        if (DNS_PACKET_RCODE(p) == DNS_RCODE_SUCCESS) {
+                if( be16toh(DNS_PACKET_HEADER(p)->ancount) > 0)
+                        dns_query_transaction_set_state(t, DNS_QUERY_SUCCESS);
+                else
+                        dns_query_transaction_set_state(t, DNS_QUERY_INVALID_REPLY);
+        } else
+                dns_query_transaction_set_state(t, DNS_QUERY_FAILURE);
+
+        return 0;
+}
+
+static int on_transaction_timeout(sd_event_source *s, usec_t usec, void *userdata) {
+        DnsQueryTransaction *t = userdata;
+        int r;
+
+        assert(s);
+        assert(t);
+
+        /* Timeout reached? Try again, with a new server */
+        dns_scope_next_dns_server(t->scope);
+
+        r = dns_query_transaction_start(t);
+        if (r < 0)
+                dns_query_transaction_set_state(t, DNS_QUERY_FAILURE);
+
+        return 0;
+}
+
+int dns_query_transaction_start(DnsQueryTransaction *t) {
+        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
+        unsigned n;
+        int r;
+
+        assert(t);
+
+        t->timeout_event_source = sd_event_source_unref(t->timeout_event_source);
+
+        if (t->n_attempts >= ATTEMPTS_MAX) {
+                dns_query_transaction_set_state(t, DNS_QUERY_ATTEMPTS_MAX);
+                return 0;
+        }
+
+        t->n_attempts++;
+
+        r = dns_packet_new_query(&p, 0);
+        if (r < 0)
+                return r;
+
+        for (n = 0; n < t->query->n_keys; n++) {
+                r = dns_packet_append_key(p, &t->query->keys[n], NULL);
+                if (r < 0)
+                        return r;
+        }
+
+        DNS_PACKET_HEADER(p)->qdcount = htobe16(t->query->n_keys);
+        DNS_PACKET_HEADER(p)->id = t->id;
+
+        r = dns_scope_send(t->scope, p);
+        if (r < 0) {
+                /* Couldn't send? Try immediately again, with a new server */
+                dns_scope_next_dns_server(t->scope);
+
+                return dns_query_transaction_start(t);
+        }
+
+        if (r > 0) {
+                int q;
+
+                q = sd_event_add_time(t->query->manager->event, &t->timeout_event_source, CLOCK_MONOTONIC, now(CLOCK_MONOTONIC) + TRANSACTION_TIMEOUT_USEC, 0, on_transaction_timeout, t);
+                if (q < 0)
+                        return q;
+
+                dns_query_transaction_set_state(t, DNS_QUERY_SENT);
+        } else
+                dns_query_transaction_set_state(t, DNS_QUERY_SKIPPED);
+
+        return r;
+}
+
+DnsQuery *dns_query_free(DnsQuery *q) {
+        unsigned n;
+
+        if (!q)
+                return NULL;
+
+        sd_bus_message_unref(q->request);
+        dns_packet_unref(q->packet);
+        sd_event_source_unref(q->timeout_event_source);
+
+        while (q->transactions)
+                dns_query_transaction_free(q->transactions);
+
+        if (q->manager)
+                LIST_REMOVE(queries, q->manager->dns_queries, q);
+
+        for (n = 0; n < q->n_keys; n++)
+                free(q->keys[n].name);
+        free(q->keys);
+        free(q);
+
+        return NULL;
+}
+
+int dns_query_new(Manager *m, DnsQuery **ret, DnsResourceKey *keys, unsigned n_keys) {
+        _cleanup_(dns_query_freep) DnsQuery *q = NULL;
+        DnsScope *s, *first = NULL;
+        DnsScopeMatch found = DNS_SCOPE_NO;
+        const char *name = NULL;
+        int n, r;
+
+        assert(m);
+
+        if (n_keys <= 0 || n_keys >= 65535)
+                return -EINVAL;
+
+        assert(keys);
+
+        q = new0(DnsQuery, 1);
+        if (!q)
+                return -ENOMEM;
+
+        q->keys = new(DnsResourceKey, n_keys);
+        if (!q->keys)
+                return -ENOMEM;
+
+        for (q->n_keys = 0; q->n_keys < n_keys; q->n_keys++) {
+                q->keys[q->n_keys].class = keys[q->n_keys].class;
+                q->keys[q->n_keys].type = keys[q->n_keys].type;
+                q->keys[q->n_keys].name = strdup(keys[q->n_keys].name);
+                if (!q->keys[q->n_keys].name)
+                        return -ENOMEM;
+
+                if (!name)
+                        name = q->keys[q->n_keys].name;
+                else if (!dns_name_equal(name, q->keys[q->n_keys].name))
+                        return -EINVAL;
+        }
+
+        LIST_PREPEND(queries, m->dns_queries, q);
+        q->manager = m;
+
+        LIST_FOREACH(scopes, s, m->dns_scopes) {
+                DnsScopeMatch match;
+
+                match = dns_scope_test(s, name);
+                if (match < 0)
+                        return match;
+
+                if (match == DNS_SCOPE_NO)
+                        continue;
+
+                found = match;
+
+                if (match == DNS_SCOPE_YES) {
+                        first = s;
+                        break;
+                } else {
+                        assert(match == DNS_SCOPE_MAYBE);
+
+                        if (!first)
+                                first = s;
+                }
+        }
+
+        if (found == DNS_SCOPE_NO)
+                return -ENETDOWN;
+
+        r = dns_query_transaction_new(q, NULL, first);
+        if (r < 0)
+                return r;
+
+        n = 1;
+        LIST_FOREACH(scopes, s, first->scopes_next) {
+                DnsScopeMatch match;
+
+                match = dns_scope_test(s, name);
+                if (match < 0)
+                        return match;
+
+                if (match != found)
+                        continue;
+
+                r = dns_query_transaction_new(q, NULL, s);
+                if (r < 0)
+                        return r;
+
+                n++;
+        }
+
+        if (ret)
+                *ret = q;
+        q = NULL;
+
+        return n;
+}
+
+static void dns_query_set_state(DnsQuery *q, DnsQueryState state) {
+        assert(q);
+
+        if (q->state == state)
+                return;
+
+        q->state = state;
+
+        if (state == DNS_QUERY_SENT)
+                return;
+
+        q->timeout_event_source = sd_event_source_unref(q->timeout_event_source);
+
+        while (q->transactions)
+                dns_query_transaction_free(q->transactions);
+
+        if (q->complete)
+                q->complete(q);
+}
+
+static int on_query_timeout(sd_event_source *s, usec_t usec, void *userdata) {
+        DnsQuery *q = userdata;
+
+        assert(s);
+        assert(q);
+
+        dns_query_set_state(q, DNS_QUERY_TIMEOUT);
+        return 0;
+}
+
+int dns_query_start(DnsQuery *q) {
+        DnsQueryTransaction *t;
+        int r;
+
+        assert(q);
+        assert(q->state == DNS_QUERY_NULL);
+
+        if (!q->transactions)
+                return -ENETDOWN;
+
+        r = sd_event_add_time(q->manager->event, &q->timeout_event_source, CLOCK_MONOTONIC, now(CLOCK_MONOTONIC) + QUERY_TIMEOUT_USEC, 0, on_query_timeout, q);
+        if (r < 0)
+                goto fail;
+
+        dns_query_set_state(q, DNS_QUERY_SENT);
+
+        LIST_FOREACH(transactions_by_query, t, q->transactions) {
+
+                r = dns_query_transaction_start(t);
+                if (r < 0)
+                        goto fail;
+
+                if (q->state != DNS_QUERY_SENT)
+                        break;
+        }
+
+        return 0;
+
+fail:
+        while (q->transactions)
+                dns_query_transaction_free(q->transactions);
+
+        return r;
+}
+
+void dns_query_finish(DnsQuery *q) {
+        DnsQueryTransaction *t;
+        DnsQueryState state = DNS_QUERY_SKIPPED;
+        uint16_t rcode = 0;
+
+        assert(q);
+
+        if (q->state != DNS_QUERY_SENT)
+                return;
+
+        LIST_FOREACH(transactions_by_query, t, q->transactions) {
+
+                /* One of the transactions is still going on, let's wait for it */
+                if (t->state == DNS_QUERY_SENT || t->state == DNS_QUERY_NULL)
+                        return;
+
+                /* One of the transactions is sucecssful, let's use it */
+                if (t->state == DNS_QUERY_SUCCESS) {
+                        q->packet = dns_packet_ref(t->packet);
+                        dns_query_set_state(q, DNS_QUERY_SUCCESS);
+                        return;
+                }
+
+                if (t->state == DNS_QUERY_FAILURE) {
+                        state = DNS_QUERY_FAILURE;
+
+                        if (rcode == 0 && t->packet)
+                                rcode = DNS_PACKET_RCODE(t->packet);
+
+                } else if (state == DNS_QUERY_SKIPPED && t->state != DNS_QUERY_SKIPPED)
+                        state = t->state;
+        }
+
+        if (state == DNS_QUERY_FAILURE)
+                q->rcode = rcode;
+
+        dns_query_set_state(q, state);
+}