src/resolve/resolved-resolv-conf.c

   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"
  29 #include "resolved-dns-server.h"
  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];
  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)
  52                         return 0;
  53
  54                 r = log_warning_errno(errno, "Failed to stat /etc/resolv.conf: %m");
  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
  63         /* Is it symlinked to our own file? */
  64         if (stat(PRIVATE_UPLINK_RESOLV_CONF, &own) >= 0 &&
  65             st.st_dev == own.st_dev &&
  66             st.st_ino == own.st_ino)
  67                 return 0;
  68
  69         /* Is it symlinked to our own stub file? */
  70         if (stat(PRIVATE_STUB_RESOLV_CONF, &own) >= 0 &&
  71             st.st_dev == own.st_dev &&
  72             st.st_ino == own.st_ino)
  73                 return 0;
  74
  75         f = fopen("/etc/resolv.conf", "re");
  76         if (!f) {
  77                 if (errno == ENOENT)
  78                         return 0;
  79
  80                 r = log_warning_errno(errno, "Failed to open /etc/resolv.conf: %m");
  81                 goto clear;
  82         }
  83
  84         if (fstat(fileno(f), &st) < 0) {
  85                 r = log_error_errno(errno, "Failed to stat open file: %m");
  86                 goto clear;
  87         }
  88
  89         dns_server_mark_all(m->dns_servers);
  90         dns_search_domain_mark_all(m->search_domains);
  91
  92         FOREACH_LINE(line, f, r = -errno; goto clear) {
  93                 const char *a;
  94                 char *l;
  95
  96                 l = strstrip(line);
  97                 if (IN_SET(*l, '#', ';'))
  98                         continue;
  99
 100                 a = first_word(l, "nameserver");
 101                 if (a) {
 102                         r = manager_parse_dns_server_string_and_warn(m, DNS_SERVER_SYSTEM, a);
 103                         if (r < 0)
 104                                 log_warning_errno(r, "Failed to parse DNS server address '%s', ignoring.", a);
 105
 106                         continue;
 107                 }
 108
 109                 a = first_word(l, "domain");
 110                 if (!a) /* We treat "domain" lines, and "search" lines as equivalent, and add both to our list. */
 111                         a = first_word(l, "search");
 112                 if (a) {
 113                         r = manager_parse_search_domains_and_warn(m, a);
 114                         if (r < 0)
 115                                 log_warning_errno(r, "Failed to parse search domain string '%s', ignoring.", a);
 116                 }
 117         }
 118
 119         m->resolv_conf_mtime = t;
 120
 121         /* Flush out all servers and search domains that are still
 122          * marked. Those are then ones that didn't appear in the new
 123          * /etc/resolv.conf */
 124         dns_server_unlink_marked(m->dns_servers);
 125         dns_search_domain_unlink_marked(m->search_domains);
 126
 127         /* Whenever /etc/resolv.conf changes, start using the first
 128          * DNS server of it. This is useful to deal with broken
 129          * network managing implementations (like NetworkManager),
 130          * that when connecting to a VPN place both the VPN DNS
 131          * servers and the local ones in /etc/resolv.conf. Without
 132          * resetting the DNS server to use back to the first entry we
 133          * will continue to use the local one thus being unable to
 134          * resolve VPN domains. */
 135         manager_set_dns_server(m, m->dns_servers);
 136
 137         /* Unconditionally flush the cache when /etc/resolv.conf is
 138          * modified, even if the data it contained was completely
 139          * identical to the previous version we used. We do this
 140          * because altering /etc/resolv.conf is typically done when
 141          * the network configuration changes, and that should be
 142          * enough to flush the global unicast DNS cache. */
 143         if (m->unicast_scope)
 144                 dns_cache_flush(&m->unicast_scope->cache);
 145
 146         /* If /etc/resolv.conf changed, make sure to forget everything we learned about the DNS servers. After all we
 147          * might now talk to a very different DNS server that just happens to have the same IP address as an old one
 148          * (think 192.168.1.1). */
 149         dns_server_reset_features_all(m->dns_servers);
 150
 151         return 0;
 152
 153 clear:
 154         dns_server_unlink_all(m->dns_servers);
 155         dns_search_domain_unlink_all(m->search_domains);
 156         return r;
 157 }
 158
 159 static void write_resolv_conf_server(DnsServer *s, FILE *f, unsigned *count) {
 160         assert(s);
 161         assert(f);
 162         assert(count);
 163
 164         if (!dns_server_string(s)) {
 165                 log_warning("Our of memory, or invalid DNS address. Ignoring server.");
 166                 return;
 167         }
 168
 169         /* Check if the DNS server is limited to particular domains;
 170          * resolv.conf does not have a syntax to express that, so it must not
 171          * appear as a global name server to avoid routing unrelated domains to
 172          * it (which is a privacy violation, will most probably fail anyway,
 173          * and adds unnecessary load) */
 174         if (dns_server_limited_domains(s)) {
 175                 log_debug("DNS server %s has route-only domains, not using as global name server", dns_server_string(s));
 176                 return;
 177         }
 178
 179         if (*count == MAXNS)
 180                 fputs_unlocked("# Too many DNS servers configured, the following entries may be ignored.\n", f);
 181         (*count)++;
 182
 183         fprintf(f, "nameserver %s\n", dns_server_string(s));
 184 }
 185
 186 static void write_resolv_conf_search(
 187                 OrderedSet *domains,
 188                 FILE *f) {
 189         unsigned length = 0, count = 0;
 190         Iterator i;
 191         char *domain;
 192
 193         assert(domains);
 194         assert(f);
 195
 196         fputs_unlocked("search", f);
 197
 198         ORDERED_SET_FOREACH(domain, domains, i) {
 199                 if (++count > MAXDNSRCH) {
 200                         fputs_unlocked("\n# Too many search domains configured, remaining ones ignored.", f);
 201                         break;
 202                 }
 203                 length += strlen(domain) + 1;
 204                 if (length > 256) {
 205                         fputs_unlocked("\n# Total length of all search domains is too long, remaining ones ignored.", f);
 206                         break;
 207                 }
 208                 fputc_unlocked(' ', f);
 209                 fputs_unlocked(domain, f);
 210         }
 211
 212         fputs_unlocked("\n", f);
 213 }
 214
 215 static int write_uplink_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *domains) {
 216         Iterator i;
 217
 218         fputs_unlocked("# This file is managed by man:systemd-resolved(8). Do not edit.\n#\n"
 219                        "# This is a dynamic resolv.conf file for connecting local clients directly to\n"
 220                        "# all known DNS servers.\n#\n"
 221                        "# Third party programs must not access this file directly, but only through the\n"
 222                        "# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,\n"
 223                        "# replace this symlink by a static file or a different symlink.\n#\n"
 224                        "# See man:systemd-resolved.service(8) for details about the supported modes of\n"
 225                        "# operation for /etc/resolv.conf.\n\n", f);
 226
 227         if (ordered_set_isempty(dns))
 228                 fputs_unlocked("# No DNS servers known.\n", f);
 229         else {
 230                 unsigned count = 0;
 231                 DnsServer *s;
 232
 233                 ORDERED_SET_FOREACH(s, dns, i)
 234                         write_resolv_conf_server(s, f, &count);
 235         }
 236
 237         if (!ordered_set_isempty(domains))
 238                 write_resolv_conf_search(domains, f);
 239
 240         return fflush_and_check(f);
 241 }
 242
 243 static int write_stub_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *domains) {
 244         fputs("# This file is managed by man:systemd-resolved(8). Do not edit.\n#\n"
 245               "# 127.0.0.53 is the systemd-resolved stub resolver.\n"
 246               "# run \"systemd-resolve --status\" to see details about the actual nameservers.\n\n"
 247               "nameserver 127.0.0.53\n", f);
 248
 249         if (!ordered_set_isempty(domains))
 250                 write_resolv_conf_search(domains, f);
 251
 252         return fflush_and_check(f);
 253 }
 254
 255 int manager_write_resolv_conf(Manager *m) {
 256
 257         _cleanup_ordered_set_free_ OrderedSet *dns = NULL, *domains = NULL;
 258         _cleanup_free_ char *temp_path_uplink = NULL;
 259         _cleanup_free_ char *temp_path_stub = NULL;
 260         _cleanup_fclose_ FILE *f_uplink = NULL;
 261         _cleanup_fclose_ FILE *f_stub = NULL;
 262         int r;
 263
 264         assert(m);
 265
 266         /* Read the system /etc/resolv.conf first */
 267         (void) manager_read_resolv_conf(m);
 268
 269         /* Add the full list to a set, to filter out duplicates */
 270         r = manager_compile_dns_servers(m, &dns);
 271         if (r < 0)
 272                 return log_warning_errno(r, "Failed to compile list of DNS servers: %m");
 273
 274         r = manager_compile_search_domains(m, &domains, false);
 275         if (r < 0)
 276                 return log_warning_errno(r, "Failed to compile list of search domains: %m");
 277
 278         r = fopen_temporary_label(PRIVATE_UPLINK_RESOLV_CONF, PRIVATE_UPLINK_RESOLV_CONF, &f_uplink, &temp_path_uplink);
 279         if (r < 0)
 280                 return log_warning_errno(r, "Failed to open private resolv.conf file for writing: %m");
 281         r = fopen_temporary_label(PRIVATE_STUB_RESOLV_CONF, PRIVATE_STUB_RESOLV_CONF, &f_stub, &temp_path_stub);
 282         if (r < 0)
 283                 return log_warning_errno(r, "Failed to open private stub-resolv.conf file for writing: %m");
 284         (void) fchmod(fileno(f_uplink), 0644);
 285         (void) fchmod(fileno(f_stub), 0644);
 286
 287         r = write_uplink_resolv_conf_contents(f_uplink, dns, domains);
 288         if (r < 0) {
 289                 log_error_errno(r, "Failed to write private resolv.conf contents: %m");
 290                 goto fail;
 291         }
 292
 293         if (rename(temp_path_uplink, PRIVATE_UPLINK_RESOLV_CONF) < 0) {
 294                 r = log_error_errno(errno, "Failed to move private resolv.conf file into place: %m");
 295                 goto fail;
 296         }
 297
 298         r = write_stub_resolv_conf_contents(f_stub, dns, domains);
 299         if (r < 0) {
 300                 log_error_errno(r, "Failed to write private stub-resolv.conf contents: %m");
 301                 goto fail;
 302         }
 303
 304         if (rename(temp_path_stub, PRIVATE_STUB_RESOLV_CONF) < 0) {
 305                 r = log_error_errno(errno, "Failed to move private stub-resolv.conf file into place: %m");
 306                 goto fail;
 307         }
 308
 309         return 0;
 310
 311 fail:
 312         (void) unlink(PRIVATE_UPLINK_RESOLV_CONF);
 313         (void) unlink(temp_path_uplink);
 314         (void) unlink(PRIVATE_STUB_RESOLV_CONF);
 315         (void) unlink(temp_path_stub);
 316
 317         return r;
 318 }