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Systemd/src/resolve/resolved-resolv-conf.c

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/***
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-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);
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;
}
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