summaryrefslogtreecommitdiff
path: root/src/resolve/resolved-resolv-conf.c
blob: 5749aa1dc3e08832e832d66e085a50a552b2779e (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
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
/* SPDX-License-Identifier: LGPL-2.1-or-later */

#include <resolv.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#include "alloc-util.h"
#include "dns-domain.h"
#include "fd-util.h"
#include "fileio.h"
#include "fs-util.h"
#include "label.h"
#include "ordered-set.h"
#include "resolved-conf.h"
#include "resolved-dns-server.h"
#include "resolved-resolv-conf.h"
#include "stat-util.h"
#include "string-table.h"
#include "string-util.h"
#include "strv.h"
#include "tmpfile-util-label.h"

int manager_check_resolv_conf(const Manager *m) {
        struct stat st, own;

        assert(m);

        /* This warns only when our stub listener is disabled and /etc/resolv.conf is a symlink to
         * PRIVATE_STATIC_RESOLV_CONF. */

        if (m->dns_stub_listener_mode != DNS_STUB_LISTENER_NO)
                return 0;

        if (stat("/etc/resolv.conf", &st) < 0) {
                if (errno == ENOENT)
                        return 0;

                return log_warning_errno(errno, "Failed to stat /etc/resolv.conf: %m");
        }

        /* Is it symlinked to our own uplink file? */
        if (stat(PRIVATE_STATIC_RESOLV_CONF, &own) >= 0 &&
            stat_inode_same(&st, &own))
                return log_warning_errno(SYNTHETIC_ERRNO(EOPNOTSUPP),
                                         "DNSStubListener= is disabled, but /etc/resolv.conf is a symlink to "
                                         PRIVATE_STATIC_RESOLV_CONF " which expects DNSStubListener= to be enabled.");

        return 0;
}

static bool file_is_our_own(const struct stat *st) {
        assert(st);

        FOREACH_STRING(path,
                       PRIVATE_UPLINK_RESOLV_CONF,
                       PRIVATE_STUB_RESOLV_CONF,
                       PRIVATE_STATIC_RESOLV_CONF) {

                struct stat own;

                /* Is it symlinked to our own uplink file? */
                if (stat(path, &own) >= 0 &&
                    stat_inode_same(st, &own))
                        return true;
        }

        return false;
}

int manager_read_resolv_conf(Manager *m) {
        _cleanup_fclose_ FILE *f = NULL;
        struct stat st;
        unsigned n = 0;
        int r;

        assert(m);

        /* Reads the system /etc/resolv.conf, if it exists and is not
         * symlinked to our own resolv.conf instance */

        if (!m->read_resolv_conf)
                return 0;

        r = stat("/etc/resolv.conf", &st);
        if (r < 0) {
                if (errno == ENOENT)
                        return 0;

                r = log_warning_errno(errno, "Failed to stat /etc/resolv.conf: %m");
                goto clear;
        }

        /* Have we already seen the file? */
        if (stat_inode_unmodified(&st, &m->resolv_conf_stat))
                return 0;

        if (file_is_our_own(&st))
                return 0;

        f = fopen("/etc/resolv.conf", "re");
        if (!f) {
                if (errno == ENOENT)
                        return 0;

                r = log_warning_errno(errno, "Failed to open /etc/resolv.conf: %m");
                goto clear;
        }

        if (fstat(fileno(f), &st) < 0) {
                r = log_error_errno(errno, "Failed to stat open file: %m");
                goto clear;
        }

        if (file_is_our_own(&st))
                return 0;

        dns_server_mark_all(m->dns_servers);
        dns_search_domain_mark_all(m->search_domains);

        for (;;) {
                _cleanup_free_ char *line = NULL;
                const char *a;
                char *l;

                r = read_line(f, LONG_LINE_MAX, &line);
                if (r < 0) {
                        log_error_errno(r, "Failed to read /etc/resolv.conf: %m");
                        goto clear;
                }
                if (r == 0)
                        break;

                n++;

                l = strstrip(line);
                if (IN_SET(*l, '#', ';', 0))
                        continue;

                a = first_word(l, "nameserver");
                if (a) {
                        r = manager_parse_dns_server_string_and_warn(m, DNS_SERVER_SYSTEM, a);
                        if (r < 0)
                                log_warning_errno(r, "Failed to parse DNS server address '%s', ignoring.", a);

                        continue;
                }

                a = first_word(l, "domain");
                if (!a) /* We treat "domain" lines, and "search" lines as equivalent, and add both to our list. */
                        a = first_word(l, "search");
                if (a) {
                        r = manager_parse_search_domains_and_warn(m, a);
                        if (r < 0)
                                log_warning_errno(r, "Failed to parse search domain string '%s', ignoring.", a);

                        continue;
                }

                log_syntax(NULL, LOG_DEBUG, "/etc/resolv.conf", n, 0, "Ignoring resolv.conf line: %s", l);
        }

        m->resolv_conf_stat = st;

        /* Flush out all servers and search domains that are still
         * marked. Those are then ones that didn't appear in the new
         * /etc/resolv.conf */
        dns_server_unlink_marked(m->dns_servers);
        dns_search_domain_unlink_marked(m->search_domains);

        /* Whenever /etc/resolv.conf changes, start using the first
         * DNS server of it. This is useful to deal with broken
         * network managing implementations (like NetworkManager),
         * that when connecting to a VPN place both the VPN DNS
         * servers and the local ones in /etc/resolv.conf. Without
         * resetting the DNS server to use back to the first entry we
         * will continue to use the local one thus being unable to
         * resolve VPN domains. */
        manager_set_dns_server(m, m->dns_servers);

        /* Unconditionally flush the cache when /etc/resolv.conf is
         * modified, even if the data it contained was completely
         * identical to the previous version we used. We do this
         * because altering /etc/resolv.conf is typically done when
         * the network configuration changes, and that should be
         * enough to flush the global unicast DNS cache. */
        if (m->unicast_scope)
                dns_cache_flush(&m->unicast_scope->cache);

        /* If /etc/resolv.conf changed, make sure to forget everything we learned about the DNS servers. After all we
         * might now talk to a very different DNS server that just happens to have the same IP address as an old one
         * (think 192.168.1.1). */
        dns_server_reset_features_all(m->dns_servers);

        return 0;

clear:
        dns_server_unlink_all(m->dns_servers);
        dns_search_domain_unlink_all(m->search_domains);
        return r;
}

static void write_resolv_conf_server(DnsServer *s, FILE *f, unsigned *count) {
        DnsScope *scope;

        assert(s);
        assert(f);
        assert(count);

        if (!dns_server_string(s)) {
                log_warning("Out of memory, or invalid DNS address. Ignoring server.");
                return;
        }

        /* resolv.conf simply doesn't support any other ports than 53, hence there's nothing much we can
         * do — we have to suppress these entries */
        if (dns_server_port(s) != 53) {
                log_debug("DNS server %s with non-standard UDP port number, suppressing from generated resolv.conf.", dns_server_string(s));
                return;
        }

        /* Check if the scope this DNS server belongs to is suitable as 'default' route for lookups; resolv.conf does
         * not have a syntax to express that, so it must not appear as a global name server to avoid routing unrelated
         * domains to it (which is a privacy violation, will most probably fail anyway, and adds unnecessary load) */
        scope = dns_server_scope(s);
        if (scope && !dns_scope_is_default_route(scope)) {
                log_debug("Scope of DNS server %s has only route-only domains, not using as global name server", dns_server_string(s));
                return;
        }

        if (*count == MAXNS)
                fputs("# Too many DNS servers configured, the following entries may be ignored.\n", f);
        (*count)++;

        fprintf(f, "nameserver %s\n", dns_server_string(s));
}

static void write_resolv_conf_search(
                OrderedSet *domains,
                FILE *f) {
        char *domain;

        assert(domains);
        assert(f);

        fputs("search", f);

        ORDERED_SET_FOREACH(domain, domains) {
                fputc(' ', f);
                fputs(domain, f);
        }

        fputs("\n", f);
}

static int write_uplink_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *domains) {

        fputs("# This is "PRIVATE_UPLINK_RESOLV_CONF" managed by man:systemd-resolved(8).\n"
              "# Do not edit.\n"
              "#\n"
              "# This file might be symlinked as /etc/resolv.conf. If you're looking at\n"
              "# /etc/resolv.conf and seeing this text, you have followed the symlink.\n"
              "#\n"
              "# This is a dynamic resolv.conf file for connecting local clients directly to\n"
              "# all known uplink DNS servers. This file lists all configured search domains.\n"
              "#\n"
              "# Third party programs should typically not access this file directly, but only\n"
              "# through the symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a\n"
              "# different way, replace this symlink by a static file or a different symlink.\n"
              "#\n"
              "# See man:systemd-resolved.service(8) for details about the supported modes of\n"
              "# operation for /etc/resolv.conf.\n"
              "\n", f);

        if (ordered_set_isempty(dns))
                fputs("# No DNS servers known.\n", f);
        else {
                unsigned count = 0;
                DnsServer *s;

                ORDERED_SET_FOREACH(s, dns)
                        write_resolv_conf_server(s, f, &count);
        }

        if (ordered_set_isempty(domains))
                fputs("search .\n", f); /* Make sure that if the local hostname is chosen as fqdn this does not
                                         * imply a search domain */
        else
                write_resolv_conf_search(domains, f);

        return fflush_and_check(f);
}

static int write_stub_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *domains) {
        fputs("# This is "PRIVATE_STUB_RESOLV_CONF" managed by man:systemd-resolved(8).\n"
              "# Do not edit.\n"
              "#\n"
              "# This file might be symlinked as /etc/resolv.conf. If you're looking at\n"
              "# /etc/resolv.conf and seeing this text, you have followed the symlink.\n"
              "#\n"
              "# This is a dynamic resolv.conf file for connecting local clients to the\n"
              "# internal DNS stub resolver of systemd-resolved. This file lists all\n"
              "# configured search domains.\n"
              "#\n"
              "# Run \"resolvectl status\" to see details about the uplink DNS servers\n"
              "# currently in use.\n"
              "#\n"
              "# Third party programs should typically not access this file directly, but only\n"
              "# through the symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a\n"
              "# different way, replace this symlink by a static file or a different symlink.\n"
              "#\n"
              "# See man:systemd-resolved.service(8) for details about the supported modes of\n"
              "# operation for /etc/resolv.conf.\n"
              "\n"
              "nameserver 127.0.0.53\n"
              "options edns0 trust-ad\n", f);

        if (ordered_set_isempty(domains))
                fputs("search .\n", f); /* Make sure that if the local hostname is chosen as fqdn this does not
                                         * imply a search domain */
        else
                write_resolv_conf_search(domains, f);

        return fflush_and_check(f);
}

int manager_write_resolv_conf(Manager *m) {
        _cleanup_ordered_set_free_ OrderedSet *dns = NULL, *domains = NULL;
        _cleanup_(unlink_and_freep) char *temp_path_uplink = NULL, *temp_path_stub = NULL;
        _cleanup_fclose_ FILE *f_uplink = NULL, *f_stub = NULL;
        int r;

        assert(m);

        /* Read the system /etc/resolv.conf first */
        (void) manager_read_resolv_conf(m);

        /* Add the full list to a set, to filter out duplicates */
        r = manager_compile_dns_servers(m, &dns);
        if (r < 0)
                return log_warning_errno(r, "Failed to compile list of DNS servers, ignoring: %m");

        r = manager_compile_search_domains(m, &domains, false);
        if (r < 0)
                return log_warning_errno(r, "Failed to compile list of search domains, ignoring: %m");

        r = fopen_temporary_label(PRIVATE_UPLINK_RESOLV_CONF, PRIVATE_UPLINK_RESOLV_CONF, &f_uplink, &temp_path_uplink);
        if (r < 0)
                return log_warning_errno(r, "Failed to open new %s for writing, ignoring: %m", PRIVATE_UPLINK_RESOLV_CONF);

        (void) fchmod(fileno(f_uplink), 0644);

        r = write_uplink_resolv_conf_contents(f_uplink, dns, domains);
        if (r < 0)
                return log_warning_errno(r, "Failed to write new %s, ignoring: %m", PRIVATE_UPLINK_RESOLV_CONF);

        if (m->dns_stub_listener_mode != DNS_STUB_LISTENER_NO) {
                r = fopen_temporary_label(PRIVATE_STUB_RESOLV_CONF, PRIVATE_STUB_RESOLV_CONF, &f_stub, &temp_path_stub);
                if (r < 0)
                        return log_warning_errno(r, "Failed to open new %s for writing, ignoring: %m", PRIVATE_STUB_RESOLV_CONF);

                (void) fchmod(fileno(f_stub), 0644);

                r = write_stub_resolv_conf_contents(f_stub, dns, domains);
                if (r < 0)
                        return log_warning_errno(r, "Failed to write new %s, ignoring: %m", PRIVATE_STUB_RESOLV_CONF);

                r = conservative_rename(temp_path_stub, PRIVATE_STUB_RESOLV_CONF);
                if (r < 0)
                        log_warning_errno(r, "Failed to move new %s into place, ignoring: %m", PRIVATE_STUB_RESOLV_CONF);

                temp_path_stub = mfree(temp_path_stub); /* free the string explicitly, so that we don't unlink anymore */
        } else {
                r = symlink_atomic_label(basename(PRIVATE_UPLINK_RESOLV_CONF), PRIVATE_STUB_RESOLV_CONF);
                if (r < 0)
                        log_warning_errno(r, "Failed to symlink %s, ignoring: %m", PRIVATE_STUB_RESOLV_CONF);
        }

        r = conservative_rename(temp_path_uplink, PRIVATE_UPLINK_RESOLV_CONF);
        if (r < 0)
                log_warning_errno(r, "Failed to move new %s into place: %m", PRIVATE_UPLINK_RESOLV_CONF);

        temp_path_uplink = mfree(temp_path_uplink); /* free the string explicitly, so that we don't unlink anymore */
        return r;
}

int resolv_conf_mode(void) {
        static const char * const table[_RESOLV_CONF_MODE_MAX] = {
                [RESOLV_CONF_UPLINK] = PRIVATE_UPLINK_RESOLV_CONF,
                [RESOLV_CONF_STUB] = PRIVATE_STUB_RESOLV_CONF,
                [RESOLV_CONF_STATIC] = PRIVATE_STATIC_RESOLV_CONF,
        };

        struct stat system_st;

        if (stat("/etc/resolv.conf", &system_st) < 0) {
                if (errno == ENOENT)
                        return RESOLV_CONF_MISSING;

                return -errno;
        }

        for (ResolvConfMode m = 0; m < _RESOLV_CONF_MODE_MAX; m++) {
                struct stat our_st;

                if (!table[m])
                        continue;

                if (stat(table[m], &our_st) < 0) {
                        if (errno != ENOENT)
                                log_debug_errno(errno, "Failed to stat() %s, ignoring: %m", table[m]);

                        continue;
                }

                if (stat_inode_same(&system_st, &our_st))
                        return m;
        }

        return RESOLV_CONF_FOREIGN;
}

static const char* const resolv_conf_mode_table[_RESOLV_CONF_MODE_MAX] = {
        [RESOLV_CONF_UPLINK] = "uplink",
        [RESOLV_CONF_STUB] = "stub",
        [RESOLV_CONF_STATIC] = "static",
        [RESOLV_CONF_MISSING] = "missing",
        [RESOLV_CONF_FOREIGN] = "foreign",
};
DEFINE_STRING_TABLE_LOOKUP(resolv_conf_mode, ResolvConfMode);