summaryrefslogtreecommitdiff
path: root/src/resolve/resolved-dns-server.c
blob: 371594c710f576695b24286f4c4472c7709bbe7c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
/*-*- 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 "alloc-util.h"
#include "resolved-dns-server.h"
#include "resolved-resolv-conf.h"
#include "siphash24.h"
#include "string-util.h"

/* After how much time to repeat classic DNS requests */
#define DNS_TIMEOUT_MIN_USEC (500 * USEC_PER_MSEC)
#define DNS_TIMEOUT_MAX_USEC (5 * USEC_PER_SEC)

int dns_server_new(
                Manager *m,
                DnsServer **ret,
                DnsServerType type,
                Link *l,
                int family,
                const union in_addr_union *in_addr) {

        DnsServer *s, *tail;

        assert(m);
        assert((type == DNS_SERVER_LINK) == !!l);
        assert(in_addr);

        s = new0(DnsServer, 1);
        if (!s)
                return -ENOMEM;

        s->n_ref = 1;
        s->type = type;
        s->family = family;
        s->address = *in_addr;
        s->resend_timeout = DNS_TIMEOUT_MIN_USEC;

        if (type == DNS_SERVER_LINK) {
                LIST_FIND_TAIL(servers, l->dns_servers, tail);
                LIST_INSERT_AFTER(servers, l->dns_servers, tail, s);
                s->link = l;
        } else if (type == DNS_SERVER_SYSTEM) {
                LIST_FIND_TAIL(servers, m->dns_servers, tail);
                LIST_INSERT_AFTER(servers, m->dns_servers, tail, s);
        } else if (type == DNS_SERVER_FALLBACK) {
                LIST_FIND_TAIL(servers, m->fallback_dns_servers, tail);
                LIST_INSERT_AFTER(servers, m->fallback_dns_servers, tail, s);
        } else
                assert_not_reached("Unknown server type");

        s->manager = m;
        s->linked = true;

        /* A new DNS server that isn't fallback is added and the one
         * we used so far was a fallback one? Then let's try to pick
         * the new one */
        if (type != DNS_SERVER_FALLBACK &&
            m->current_dns_server &&
            m->current_dns_server->type == DNS_SERVER_FALLBACK)
                manager_set_dns_server(m, NULL);

        if (ret)
                *ret = s;

        return 0;
}

DnsServer* dns_server_ref(DnsServer *s)  {
        if (!s)
                return NULL;

        assert(s->n_ref > 0);
        s->n_ref ++;

        return s;
}

DnsServer* dns_server_unref(DnsServer *s)  {
        if (!s)
                return NULL;

        assert(s->n_ref > 0);
        s->n_ref --;

        if (s->n_ref > 0)
                return NULL;

        free(s);
        return NULL;
}

void dns_server_unlink(DnsServer *s) {
        assert(s);
        assert(s->manager);

        /* This removes the specified server from the linked list of
         * servers, but any server might still stay around if it has
         * refs, for example from an ongoing transaction. */

        if (!s->linked)
                return;

        switch (s->type) {

        case DNS_SERVER_LINK:
                assert(s->link);
                LIST_REMOVE(servers, s->link->dns_servers, s);
                break;

        case DNS_SERVER_SYSTEM:
                LIST_REMOVE(servers, s->manager->dns_servers, s);
                break;

        case DNS_SERVER_FALLBACK:
                LIST_REMOVE(servers, s->manager->fallback_dns_servers, s);
                break;
        }

        s->linked = false;

        if (s->link && s->link->current_dns_server == s)
                link_set_dns_server(s->link, NULL);

        if (s->manager->current_dns_server == s)
                manager_set_dns_server(s->manager, NULL);

        dns_server_unref(s);
}

void dns_server_packet_received(DnsServer *s, usec_t rtt) {
        assert(s);

        if (rtt <= s->max_rtt)
                return;

        s->max_rtt = rtt;
        s->resend_timeout = MIN(MAX(DNS_TIMEOUT_MIN_USEC, s->max_rtt * 2), DNS_TIMEOUT_MAX_USEC);
}

void dns_server_packet_lost(DnsServer *s, usec_t usec) {
        assert(s);

        if (s->resend_timeout > usec)
                return;

        s->resend_timeout = MIN(s->resend_timeout * 2, DNS_TIMEOUT_MAX_USEC);
}

static void dns_server_hash_func(const void *p, struct siphash *state) {
        const DnsServer *s = p;

        assert(s);

        siphash24_compress(&s->family, sizeof(s->family), state);
        siphash24_compress(&s->address, FAMILY_ADDRESS_SIZE(s->family), state);
}

static int dns_server_compare_func(const void *a, const void *b) {
        const DnsServer *x = a, *y = b;

        if (x->family < y->family)
                return -1;
        if (x->family > y->family)
                return 1;

        return memcmp(&x->address, &y->address, FAMILY_ADDRESS_SIZE(x->family));
}

const struct hash_ops dns_server_hash_ops = {
        .hash = dns_server_hash_func,
        .compare = dns_server_compare_func
};

DnsServer *manager_get_first_dns_server(Manager *m, DnsServerType t) {
        assert(m);

        switch (t) {

        case DNS_SERVER_SYSTEM:
                return m->dns_servers;

        case DNS_SERVER_FALLBACK:
                return m->fallback_dns_servers;

        default:
                return NULL;
        }
}

void manager_flush_dns_servers(Manager *m, DnsServerType type) {
        assert(m);

        for (;;) {
                DnsServer *first;

                first = manager_get_first_dns_server(m, type);
                if (!first)
                        break;

                dns_server_unlink(first);
        }
}

void manager_flush_marked_dns_servers(Manager *m, DnsServerType type) {
        DnsServer *first, *s, *next;

        assert(m);

        first = manager_get_first_dns_server(m, type);

        LIST_FOREACH_SAFE(servers, s, next, first) {
                if (!s->marked)
                        continue;

                dns_server_unlink(s);
        }
}

void manager_mark_dns_servers(Manager *m, DnsServerType type) {
        DnsServer *first, *s;

        assert(m);

        first = manager_get_first_dns_server(m, type);
        LIST_FOREACH(servers, s, first)
                s->marked = true;
}

DnsServer* manager_find_dns_server(Manager *m, DnsServerType type, int family, const union in_addr_union *in_addr) {
        DnsServer *first, *s;

        assert(m);
        assert(in_addr);

        first = manager_get_first_dns_server(m, type);

        LIST_FOREACH(servers, s, first)
                if (s->family == family && in_addr_equal(family, &s->address, in_addr) > 0)
                        return s;

        return NULL;
}

DnsServer *manager_set_dns_server(Manager *m, DnsServer *s) {
        assert(m);

        if (m->current_dns_server == s)
                return s;

        if (s) {
                _cleanup_free_ char *ip = NULL;

                in_addr_to_string(s->family, &s->address, &ip);
                log_info("Switching to system DNS server %s.", strna(ip));
        }

        dns_server_unref(m->current_dns_server);
        m->current_dns_server = dns_server_ref(s);

        if (m->unicast_scope)
                dns_cache_flush(&m->unicast_scope->cache);

        return s;
}

DnsServer *manager_get_dns_server(Manager *m) {
        Link *l;
        assert(m);

        /* Try to read updates resolv.conf */
        manager_read_resolv_conf(m);

        /* If no DNS server was chose so far, pick the first one */
        if (!m->current_dns_server)
                manager_set_dns_server(m, m->dns_servers);

        if (!m->current_dns_server) {
                bool found = false;
                Iterator i;

                /* No DNS servers configured, let's see if there are
                 * any on any links. If not, we use the fallback
                 * servers */

                HASHMAP_FOREACH(l, m->links, i)
                        if (l->dns_servers) {
                                found = true;
                                break;
                        }

                if (!found)
                        manager_set_dns_server(m, m->fallback_dns_servers);
        }

        return m->current_dns_server;
}

void manager_next_dns_server(Manager *m) {
        assert(m);

        /* If there's currently no DNS server set, then the next
         * manager_get_dns_server() will find one */
        if (!m->current_dns_server)
                return;

        /* Change to the next one, but make sure to follow the linked
         * list only if the server is still linked. */
        if (m->current_dns_server->linked && m->current_dns_server->servers_next) {
                manager_set_dns_server(m, m->current_dns_server->servers_next);
                return;
        }

        /* If there was no next one, then start from the beginning of
         * the list */
        if (m->current_dns_server->type == DNS_SERVER_FALLBACK)
                manager_set_dns_server(m, m->fallback_dns_servers);
        else
                manager_set_dns_server(m, m->dns_servers);
}