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-resolv-conf.h"
  30 #include "string-util.h"
  31 #include "strv.h"
  32
  33 int manager_read_resolv_conf(Manager *m) {
  34         _cleanup_fclose_ FILE *f = NULL;
  35         struct stat st, own;
  36         char line[LINE_MAX];
  37         usec_t t;
  38         int r;
  39
  40         assert(m);
  41
  42         /* Reads the system /etc/resolv.conf, if it exists and is not
  43          * symlinked to our own resolv.conf instance */
  44
  45         if (!m->read_resolv_conf)
  46                 return 0;
  47
  48         r = stat("/etc/resolv.conf", &st);
  49         if (r < 0) {
  50                 if (errno == ENOENT)
  51                         return 0;
  52
  53                 r = log_warning_errno(errno, "Failed to stat /etc/resolv.conf: %m");
  54                 goto clear;
  55         }
  56
  57         /* Have we already seen the file? */
  58         t = timespec_load(&st.st_mtim);
  59         if (t == m->resolv_conf_mtime)
  60                 return 0;
  61
  62         /* Is it symlinked to our own file? */
  63         if (stat("/run/systemd/resolve/resolv.conf", &own) >= 0 &&
  64             st.st_dev == own.st_dev &&
  65             st.st_ino == own.st_ino)
  66                 return 0;
  67
  68         f = fopen("/etc/resolv.conf", "re");
  69         if (!f) {
  70                 if (errno == ENOENT)
  71                         return 0;
  72
  73                 r = log_warning_errno(errno, "Failed to open /etc/resolv.conf: %m");
  74                 goto clear;
  75         }
  76
  77         if (fstat(fileno(f), &st) < 0) {
  78                 r = log_error_errno(errno, "Failed to stat open file: %m");
  79                 goto clear;
  80         }
  81
  82         dns_server_mark_all(m->dns_servers);
  83         dns_search_domain_mark_all(m->search_domains);
  84
  85         FOREACH_LINE(line, f, r = -errno; goto clear) {
  86                 const char *a;
  87                 char *l;
  88
  89                 l = strstrip(line);
  90                 if (*l == '#' || *l == ';')
  91                         continue;
  92
  93                 a = first_word(l, "nameserver");
  94                 if (a) {
  95                         r = manager_parse_dns_server_string_and_warn(m, DNS_SERVER_SYSTEM, a);
  96                         if (r < 0)
  97                                 log_warning_errno(r, "Failed to parse DNS server address '%s', ignoring.", a);
  98
  99                         continue;
 100                 }
 101
 102                 a = first_word(l, "domain");
 103                 if (!a) /* We treat "domain" lines, and "search" lines as equivalent, and add both to our list. */
 104                         a = first_word(l, "search");
 105                 if (a) {
 106                         r = manager_parse_search_domains_and_warn(m, a);
 107                         if (r < 0)
 108                                 log_warning_errno(r, "Failed to parse search domain string '%s', ignoring.", a);
 109                 }
 110         }
 111
 112         m->resolv_conf_mtime = t;
 113
 114         /* Flush out all servers and search domains that are still
 115          * marked. Those are then ones that didn't appear in the new
 116          * /etc/resolv.conf */
 117         dns_server_unlink_marked(m->dns_servers);
 118         dns_search_domain_unlink_marked(m->search_domains);
 119
 120         /* Whenever /etc/resolv.conf changes, start using the first
 121          * DNS server of it. This is useful to deal with broken
 122          * network managing implementations (like NetworkManager),
 123          * that when connecting to a VPN place both the VPN DNS
 124          * servers and the local ones in /etc/resolv.conf. Without
 125          * resetting the DNS server to use back to the first entry we
 126          * will continue to use the local one thus being unable to
 127          * resolve VPN domains. */
 128         manager_set_dns_server(m, m->dns_servers);
 129
 130         /* Unconditionally flush the cache when /etc/resolv.conf is
 131          * modified, even if the data it contained was completely
 132          * identical to the previous version we used. We do this
 133          * because altering /etc/resolv.conf is typically done when
 134          * the network configuration changes, and that should be
 135          * enough to flush the global unicast DNS cache. */
 136         if (m->unicast_scope)
 137                 dns_cache_flush(&m->unicast_scope->cache);
 138
 139         return 0;
 140
 141 clear:
 142         dns_server_unlink_all(m->dns_servers);
 143         dns_search_domain_unlink_all(m->search_domains);
 144         return r;
 145 }
 146
 147 static void write_resolv_conf_server(DnsServer *s, FILE *f, unsigned *count) {
 148         assert(s);
 149         assert(f);
 150         assert(count);
 151
 152         if (!dns_server_string(s)) {
 153                 log_warning("Our of memory, or invalid DNS address. Ignoring server.");
 154                 return;
 155         }
 156
 157         if (*count == MAXNS)
 158                 fputs("# Too many DNS servers configured, the following entries may be ignored.\n", f);
 159         (*count)++;
 160
 161         fprintf(f, "nameserver %s\n", dns_server_string(s));
 162 }
 163
 164 static void write_resolv_conf_search(
 165                 OrderedSet *domains,
 166                 FILE *f) {
 167         unsigned length = 0, count = 0;
 168         Iterator i;
 169         char *domain;
 170
 171         assert(domains);
 172         assert(f);
 173
 174         fputs("search", f);
 175
 176         ORDERED_SET_FOREACH(domain, domains, i) {
 177                 if (++count > MAXDNSRCH) {
 178                         fputs("\n# Too many search domains configured, remaining ones ignored.", f);
 179                         break;
 180                 }
 181                 length += strlen(domain) + 1;
 182                 if (length > 256) {
 183                         fputs("\n# Total length of all search domains is too long, remaining ones ignored.", f);
 184                         break;
 185                 }
 186                 fputc(' ', f);
 187                 fputs(domain, f);
 188         }
 189
 190         fputs("\n", f);
 191 }
 192
 193 static int write_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *domains) {
 194         Iterator i;
 195
 196         fputs("# This file is managed by systemd-resolved(8). Do not edit.\n#\n"
 197               "# Third party programs must not access this file directly, but\n"
 198               "# only through the symlink at /etc/resolv.conf. To manage\n"
 199               "# resolv.conf(5) in a different way, replace the symlink by a\n"
 200               "# static file or a different symlink.\n\n", f);
 201
 202         if (ordered_set_isempty(dns))
 203                 fputs("# No DNS servers known.\n", f);
 204         else {
 205                 unsigned count = 0;
 206                 DnsServer *s;
 207
 208                 ORDERED_SET_FOREACH(s, dns, i)
 209                         write_resolv_conf_server(s, f, &count);
 210         }
 211
 212         if (!ordered_set_isempty(domains))
 213                 write_resolv_conf_search(domains, f);
 214
 215         return fflush_and_check(f);
 216 }
 217
 218 int manager_write_resolv_conf(Manager *m) {
 219
 220         _cleanup_ordered_set_free_ OrderedSet *dns = NULL, *domains = NULL;
 221         _cleanup_free_ char *temp_path = NULL;
 222         _cleanup_fclose_ FILE *f = NULL;
 223         int r;
 224
 225         assert(m);
 226
 227         /* Read the system /etc/resolv.conf first */
 228         (void) manager_read_resolv_conf(m);
 229
 230         /* Add the full list to a set, to filter out duplicates */
 231         r = manager_compile_dns_servers(m, &dns);
 232         if (r < 0)
 233                 return log_warning_errno(r, "Failed to compile list of DNS servers: %m");
 234
 235         r = manager_compile_search_domains(m, &domains);
 236         if (r < 0)
 237                 return log_warning_errno(r, "Failed to compile list of search domains: %m");
 238
 239         r = fopen_temporary_label(PRIVATE_RESOLV_CONF, PRIVATE_RESOLV_CONF, &f, &temp_path);
 240         if (r < 0)
 241                 return log_warning_errno(r, "Failed to open private resolv.conf file for writing: %m");
 242
 243         (void) fchmod(fileno(f), 0644);
 244
 245         r = write_resolv_conf_contents(f, dns, domains);
 246         if (r < 0) {
 247                 log_error_errno(r, "Failed to write private resolv.conf contents: %m");
 248                 goto fail;
 249         }
 250
 251         if (rename(temp_path, PRIVATE_RESOLV_CONF) < 0) {
 252                 r = log_error_errno(errno, "Failed to move private resolv.conf file into place: %m");
 253                 goto fail;
 254         }
 255
 256         return 0;
 257
 258 fail:
 259         (void) unlink(PRIVATE_RESOLV_CONF);
 260         (void) unlink(temp_path);
 261
 262         return r;
 263 }