[thirdparty/systemd.git] / src / resolve / resolved-resolv-conf.c

/***
  This file is part of systemd.

  Copyright 2014 Tom Gundersen <teg@jklm.no>

  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 <resolv.h>

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

int manager_read_resolv_conf(Manager *m) {
        _cleanup_fclose_ FILE *f = NULL;
        struct stat st, own;
        char line[LINE_MAX];
        usec_t t;
        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? */
        t = timespec_load(&st.st_mtim);
        if (t == m->resolv_conf_mtime)
                return 0;

        /* Is it symlinked to our own file? */
        if (stat(PRIVATE_RESOLV_CONF, &own) >= 0 &&
            st.st_dev == own.st_dev &&
            st.st_ino == own.st_ino)
                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;
        }

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

        FOREACH_LINE(line, f, r = -errno; goto clear) {
                const char *a;
                char *l;

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

        m->resolv_conf_mtime = t;

        /* 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) {
        assert(s);
        assert(f);
        assert(count);

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

        /* Check if the DNS server is limited to particular domains;
         * 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) */
        if (dns_server_limited_domains(s)) {
                log_debug("DNS server %s has route-only domains, not using as global name server", dns_server_string(s));
                return;
        }

        if (*count == MAXNS)
                fputs_unlocked("# 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) {
        unsigned length = 0, count = 0;
        Iterator i;
        char *domain;

        assert(domains);
        assert(f);

        fputs_unlocked("search", f);

        ORDERED_SET_FOREACH(domain, domains, i) {
                if (++count > MAXDNSRCH) {
                        fputs_unlocked("\n# Too many search domains configured, remaining ones ignored.", f);
                        break;
                }
                length += strlen(domain) + 1;
                if (length > 256) {
                        fputs_unlocked("\n# Total length of all search domains is too long, remaining ones ignored.", f);
                        break;
                }
                fputc_unlocked(' ', f);
                fputs_unlocked(domain, f);
        }

        fputs_unlocked("\n", f);
}

static int write_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *domains) {
        Iterator i;

        fputs_unlocked("# This file is managed by man:systemd-resolved(8). Do not edit.\n#\n"
                       "# This is a dynamic resolv.conf file for connecting local clients directly to\n"
                       "# all known DNS servers.\n#\n"
                       "# Third party programs must not access this file directly, but only through the\n"
                       "# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,\n"
                       "# 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_unlocked("# No DNS servers known.\n", f);
        else {
                unsigned count = 0;
                DnsServer *s;

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

        if (!ordered_set_isempty(domains))
                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_free_ char *temp_path = NULL;
        _cleanup_fclose_ FILE *f = 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: %m");

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

        r = fopen_temporary_label(PRIVATE_RESOLV_CONF, PRIVATE_RESOLV_CONF, &f, &temp_path);
        if (r < 0)
                return log_warning_errno(r, "Failed to open private resolv.conf file for writing: %m");

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

        r = write_resolv_conf_contents(f, dns, domains);
        if (r < 0) {
                log_error_errno(r, "Failed to write private resolv.conf contents: %m");
                goto fail;
        }

        if (rename(temp_path, PRIVATE_RESOLV_CONF) < 0) {
                r = log_error_errno(errno, "Failed to move private resolv.conf file into place: %m");
                goto fail;
        }

        return 0;

fail:
        (void) unlink(PRIVATE_RESOLV_CONF);
        (void) unlink(temp_path);

        return r;
}
Commit	Line	Data
f8dc7e34 LP	1	/***
	2	This file is part of systemd.
	3
	4	Copyright 2014 Tom Gundersen <teg@jklm.no>
	5
	6	systemd is free software; you can redistribute it and/or modify it
	7	under the terms of the GNU Lesser General Public License as published by
	8	the Free Software Foundation; either version 2.1 of the License, or
	9	(at your option) any later version.
	10
	11	systemd is distributed in the hope that it will be useful, but
	12	WITHOUT ANY WARRANTY; without even the implied warranty of
	13	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	14	Lesser General Public License for more details.
	15
	16	You should have received a copy of the GNU Lesser General Public License
	17	along with systemd; If not, see <http://www.gnu.org/licenses/>.
	18	***/
	19
	20	#include <resolv.h>
	21
	22	#include "alloc-util.h"
	23	#include "dns-domain.h"
	24	#include "fd-util.h"
	25	#include "fileio-label.h"
	26	#include "fileio.h"
	27	#include "ordered-set.h"
	28	#include "resolved-conf.h"
59c0fd0e	29	#include "resolved-dns-server.h"
f8dc7e34 LP	30	#include "resolved-resolv-conf.h"
	31	#include "string-util.h"
	32	#include "strv.h"
	33
	34	int manager_read_resolv_conf(Manager *m) {
	35	_cleanup_fclose_ FILE *f = NULL;
	36	struct stat st, own;
	37	char line[LINE_MAX];
f8dc7e34 LP	38	usec_t t;
	39	int r;
	40
	41	assert(m);
	42
	43	/* Reads the system /etc/resolv.conf, if it exists and is not
	44	* symlinked to our own resolv.conf instance */
	45
	46	if (!m->read_resolv_conf)
	47	return 0;
	48
	49	r = stat("/etc/resolv.conf", &st);
	50	if (r < 0) {
	51	if (errno == ENOENT)
bf7fabd6 LP	52	return 0;
	53
	54	r = log_warning_errno(errno, "Failed to stat /etc/resolv.conf: %m");
f8dc7e34 LP	55	goto clear;
	56	}
	57
	58	/* Have we already seen the file? */
	59	t = timespec_load(&st.st_mtim);
	60	if (t == m->resolv_conf_mtime)
	61	return 0;
	62
f8dc7e34	63	/* Is it symlinked to our own file? */
604c9415	64	if (stat(PRIVATE_RESOLV_CONF, &own) >= 0 &&
f8dc7e34	65	st.st_dev == own.st_dev &&
bf7fabd6 LP	66	st.st_ino == own.st_ino)
bf7fabd6 LP	67	return 0;
f8dc7e34 LP	68
	69	f = fopen("/etc/resolv.conf", "re");
	70	if (!f) {
	71	if (errno == ENOENT)
bf7fabd6 LP	72	return 0;
	73
	74	r = log_warning_errno(errno, "Failed to open /etc/resolv.conf: %m");
f8dc7e34 LP	75	goto clear;
	76	}
	77
	78	if (fstat(fileno(f), &st) < 0) {
	79	r = log_error_errno(errno, "Failed to stat open file: %m");
	80	goto clear;
	81	}
	82
4b95f179	83	dns_server_mark_all(m->dns_servers);
a51c1048	84	dns_search_domain_mark_all(m->search_domains);
f8dc7e34 LP	85
f8dc7e34 LP	86	FOREACH_LINE(line, f, r = -errno; goto clear) {
f8dc7e34 LP	87	const char *a;
	88	char *l;
	89
f8dc7e34	90	l = strstrip(line);
4c701096	91	if (IN_SET(*l, '#', ';'))
f8dc7e34 LP	92	continue;
	93
	94	a = first_word(l, "nameserver");
	95	if (a) {
2817157b	96	r = manager_parse_dns_server_string_and_warn(m, DNS_SERVER_SYSTEM, a);
f8dc7e34 LP	97	if (r < 0)
	98	log_warning_errno(r, "Failed to parse DNS server address '%s', ignoring.", a);
	99
	100	continue;
	101	}
a51c1048 LP	102
	103	a = first_word(l, "domain");
	104	if (!a) /* We treat "domain" lines, and "search" lines as equivalent, and add both to our list. */
	105	a = first_word(l, "search");
	106	if (a) {
	107	r = manager_parse_search_domains_and_warn(m, a);
	108	if (r < 0)
	109	log_warning_errno(r, "Failed to parse search domain string '%s', ignoring.", a);
	110	}
f8dc7e34 LP	111	}
f8dc7e34 LP	112
bf7fabd6 LP	113	m->resolv_conf_mtime = t;
bf7fabd6 LP	114
a51c1048 LP	115	/* Flush out all servers and search domains that are still
	116	* marked. Those are then ones that didn't appear in the new
	117	* /etc/resolv.conf */
4b95f179	118	dns_server_unlink_marked(m->dns_servers);
a51c1048	119	dns_search_domain_unlink_marked(m->search_domains);
f8dc7e34 LP	120
	121	/* Whenever /etc/resolv.conf changes, start using the first
	122	* DNS server of it. This is useful to deal with broken
	123	* network managing implementations (like NetworkManager),
	124	* that when connecting to a VPN place both the VPN DNS
	125	* servers and the local ones in /etc/resolv.conf. Without
	126	* resetting the DNS server to use back to the first entry we
	127	* will continue to use the local one thus being unable to
	128	* resolve VPN domains. */
	129	manager_set_dns_server(m, m->dns_servers);
	130
452b4e32 LP	131	/* Unconditionally flush the cache when /etc/resolv.conf is
	132	* modified, even if the data it contained was completely
	133	* identical to the previous version we used. We do this
	134	* because altering /etc/resolv.conf is typically done when
	135	* the network configuration changes, and that should be
	136	* enough to flush the global unicast DNS cache. */
	137	if (m->unicast_scope)
	138	dns_cache_flush(&m->unicast_scope->cache);
	139
59c0fd0e LP	140	/* If /etc/resolv.conf changed, make sure to forget everything we learned about the DNS servers. After all we
	141	* might now talk to a very different DNS server that just happens to have the same IP address as an old one
	142	* (think 192.168.1.1). */
	143	dns_server_reset_features_all(m->dns_servers);
	144
f8dc7e34 LP	145	return 0;
	146
	147	clear:
4b95f179	148	dns_server_unlink_all(m->dns_servers);
a51c1048	149	dns_search_domain_unlink_all(m->search_domains);
f8dc7e34 LP	150	return r;
	151	}
	152
	153	static void write_resolv_conf_server(DnsServer s, FILE f, unsigned *count) {
f8dc7e34 LP	154	assert(s);
	155	assert(f);
	156	assert(count);
	157
2817157b	158	if (!dns_server_string(s)) {
6cb08a89	159	log_warning("Our of memory, or invalid DNS address. Ignoring server.");
f8dc7e34 LP	160	return;
	161	}
	162
b9fe94ca MP	163	/* Check if the DNS server is limited to particular domains;
	164	* resolv.conf does not have a syntax to express that, so it must not
	165	* appear as a global name server to avoid routing unrelated domains to
	166	* it (which is a privacy violation, will most probably fail anyway,
	167	* and adds unnecessary load) */
	168	if (dns_server_limited_domains(s)) {
	169	log_debug("DNS server %s has route-only domains, not using as global name server", dns_server_string(s));
	170	return;
	171	}
	172
f8dc7e34	173	if (*count == MAXNS)
4b61c875	174	fputs_unlocked("# Too many DNS servers configured, the following entries may be ignored.\n", f);
313cefa1	175	(*count)++;
f8dc7e34	176
2817157b	177	fprintf(f, "nameserver %s\n", dns_server_string(s));
f8dc7e34 LP	178	}
	179
	180	static void write_resolv_conf_search(
d2bc1251 MP	181	OrderedSet *domains,
	182	FILE *f) {
	183	unsigned length = 0, count = 0;
	184	Iterator i;
	185	char *domain;
f8dc7e34	186
d2bc1251	187	assert(domains);
f8dc7e34	188	assert(f);
f8dc7e34	189
4b61c875	190	fputs_unlocked("search", f);
f8dc7e34	191
d2bc1251 MP	192	ORDERED_SET_FOREACH(domain, domains, i) {
d2bc1251 MP	193	if (++count > MAXDNSRCH) {
4b61c875	194	fputs_unlocked("\n# Too many search domains configured, remaining ones ignored.", f);
d2bc1251 MP	195	break;
	196	}
	197	length += strlen(domain) + 1;
	198	if (length > 256) {
4b61c875	199	fputs_unlocked("\n# Total length of all search domains is too long, remaining ones ignored.", f);
d2bc1251 MP	200	break;
d2bc1251 MP	201	}
4b61c875 LP	202	fputc_unlocked(' ', f);
4b61c875 LP	203	fputs_unlocked(domain, f);
f8dc7e34 LP	204	}
f8dc7e34 LP	205
4b61c875	206	fputs_unlocked("\n", f);
f8dc7e34 LP	207	}
	208
	209	static int write_resolv_conf_contents(FILE f, OrderedSet dns, OrderedSet *domains) {
	210	Iterator i;
	211
4b61c875 LP	212	fputs_unlocked("# This file is managed by man:systemd-resolved(8). Do not edit.\n#\n"
	213	"# This is a dynamic resolv.conf file for connecting local clients directly to\n"
	214	"# all known DNS servers.\n#\n"
	215	"# Third party programs must not access this file directly, but only through the\n"
	216	"# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,\n"
	217	"# replace this symlink by a static file or a different symlink.\n#\n"
	218	"# See man:systemd-resolved.service(8) for details about the supported modes of\n"
	219	"# operation for /etc/resolv.conf.\n\n", f);
f8dc7e34 LP	220
f8dc7e34 LP	221	if (ordered_set_isempty(dns))
4b61c875	222	fputs_unlocked("# No DNS servers known.\n", f);
f8dc7e34 LP	223	else {
	224	unsigned count = 0;
	225	DnsServer *s;
	226
	227	ORDERED_SET_FOREACH(s, dns, i)
	228	write_resolv_conf_server(s, f, &count);
	229	}
	230
d2bc1251 MP	231	if (!ordered_set_isempty(domains))
d2bc1251 MP	232	write_resolv_conf_search(domains, f);
f8dc7e34 LP	233
	234	return fflush_and_check(f);
	235	}
	236
	237	int manager_write_resolv_conf(Manager *m) {
9176a57c	238
9176a57c	239	_cleanup_ordered_set_free_ OrderedSet dns = NULL, domains = NULL;
f8dc7e34 LP	240	_cleanup_free_ char *temp_path = NULL;
f8dc7e34 LP	241	_cleanup_fclose_ FILE *f = NULL;
f8dc7e34 LP	242	int r;
	243
	244	assert(m);
	245
	246	/* Read the system /etc/resolv.conf first */
7207052d	247	(void) manager_read_resolv_conf(m);
f8dc7e34 LP	248
f8dc7e34 LP	249	/* Add the full list to a set, to filter out duplicates */
9176a57c LP	250	r = manager_compile_dns_servers(m, &dns);
9176a57c LP	251	if (r < 0)
7207052d	252	return log_warning_errno(r, "Failed to compile list of DNS servers: %m");
f8dc7e34	253
6f7da49d	254	r = manager_compile_search_domains(m, &domains, false);
9176a57c	255	if (r < 0)
7207052d	256	return log_warning_errno(r, "Failed to compile list of search domains: %m");
f8dc7e34	257
9176a57c	258	r = fopen_temporary_label(PRIVATE_RESOLV_CONF, PRIVATE_RESOLV_CONF, &f, &temp_path);
f8dc7e34	259	if (r < 0)
7207052d	260	return log_warning_errno(r, "Failed to open private resolv.conf file for writing: %m");
f8dc7e34	261
7207052d	262	(void) fchmod(fileno(f), 0644);
f8dc7e34 LP	263
f8dc7e34 LP	264	r = write_resolv_conf_contents(f, dns, domains);
7207052d LP	265	if (r < 0) {
7207052d LP	266	log_error_errno(r, "Failed to write private resolv.conf contents: %m");
f8dc7e34	267	goto fail;
7207052d	268	}
f8dc7e34	269
9176a57c	270	if (rename(temp_path, PRIVATE_RESOLV_CONF) < 0) {
7207052d	271	r = log_error_errno(errno, "Failed to move private resolv.conf file into place: %m");
f8dc7e34 LP	272	goto fail;
	273	}
	274
	275	return 0;
	276
	277	fail:
9176a57c	278	(void) unlink(PRIVATE_RESOLV_CONF);
f8dc7e34	279	(void) unlink(temp_path);
7207052d	280
f8dc7e34 LP	281	return r;
f8dc7e34 LP	282	}