| /* SPDX-License-Identifier: LGPL-2.1+ */ |
| |
| #include <resolv.h> |
| #include <stdio_ext.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" |
| |
| /* A resolv.conf file containing the DNS server and domain data we learnt from uplink, i.e. the full uplink data */ |
| #define PRIVATE_UPLINK_RESOLV_CONF "/run/systemd/resolve/resolv.conf" |
| |
| /* A resolv.conf file containing the domain data we learnt from uplink, but our own DNS server address. */ |
| #define PRIVATE_STUB_RESOLV_CONF "/run/systemd/resolve/stub-resolv.conf" |
| |
| /* A static resolv.conf file containing no domains, but only our own DNS sever address */ |
| #define PRIVATE_STATIC_RESOLV_CONF ROOTLIBEXECDIR "/resolv.conf" |
| |
| static bool file_is_our_own(const struct stat *st) { |
| const char *path; |
| |
| 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 && |
| st->st_dev == own.st_dev && |
| st->st_ino == own.st_ino) |
| return true; |
| } |
| |
| return false; |
| } |
| |
| int manager_read_resolv_conf(Manager *m) { |
| _cleanup_fclose_ FILE *f = NULL; |
| struct stat st; |
| char line[LINE_MAX]; |
| 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 (timespec_load(&st.st_mtim) == m->resolv_conf_mtime) |
| 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); |
| |
| FOREACH_LINE(line, f, r = -errno; goto clear) { |
| const char *a; |
| char *l; |
| |
| 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); |
| } |
| |
| log_syntax(NULL, LOG_DEBUG, "/etc/resolv.conf", n, 0, "Ignoring resolv.conf line: %s", l); |
| } |
| |
| m->resolv_conf_mtime = timespec_load(&st.st_mtim); |
| |
| /* 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("Out 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("# 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("search", f); |
| |
| ORDERED_SET_FOREACH(domain, domains, i) { |
| if (++count > MAXDNSRCH) { |
| fputs("\n# Too many search domains configured, remaining ones ignored.", f); |
| break; |
| } |
| length += strlen(domain) + 1; |
| if (length > 256) { |
| fputs("\n# Total length of all search domains is too long, remaining ones ignored.", f); |
| break; |
| } |
| fputc(' ', f); |
| fputs(domain, f); |
| } |
| |
| fputs("\n", f); |
| } |
| |
| static int write_uplink_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *domains) { |
| Iterator i; |
| |
| fputs("# 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 uplink DNS servers. This file lists all configured search domains.\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("# 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); |
| } |
| |
| static int write_stub_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *domains) { |
| 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 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 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" |
| "nameserver 127.0.0.53\n", f); |
| |
| 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_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: %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_UPLINK_RESOLV_CONF, PRIVATE_UPLINK_RESOLV_CONF, &f_uplink, &temp_path_uplink); |
| if (r < 0) |
| return log_warning_errno(r, "Failed to open private resolv.conf file for writing: %m"); |
| |
| (void) __fsetlocking(f_uplink, FSETLOCKING_BYCALLER); |
| (void) fchmod(fileno(f_uplink), 0644); |
| |
| 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 private stub-resolv.conf file for writing: %m"); |
| |
| (void) __fsetlocking(f_stub, FSETLOCKING_BYCALLER); |
| (void) fchmod(fileno(f_stub), 0644); |
| |
| r = write_uplink_resolv_conf_contents(f_uplink, dns, domains); |
| if (r < 0) { |
| log_error_errno(r, "Failed to write private resolv.conf contents: %m"); |
| goto fail; |
| } |
| |
| if (rename(temp_path_uplink, PRIVATE_UPLINK_RESOLV_CONF) < 0) { |
| r = log_error_errno(errno, "Failed to move private resolv.conf file into place: %m"); |
| goto fail; |
| } |
| |
| r = write_stub_resolv_conf_contents(f_stub, dns, domains); |
| if (r < 0) { |
| log_error_errno(r, "Failed to write private stub-resolv.conf contents: %m"); |
| goto fail; |
| } |
| |
| if (rename(temp_path_stub, PRIVATE_STUB_RESOLV_CONF) < 0) { |
| r = log_error_errno(errno, "Failed to move private stub-resolv.conf file into place: %m"); |
| goto fail; |
| } |
| |
| return 0; |
| |
| fail: |
| (void) unlink(PRIVATE_UPLINK_RESOLV_CONF); |
| (void) unlink(temp_path_uplink); |
| (void) unlink(PRIVATE_STUB_RESOLV_CONF); |
| (void) unlink(temp_path_stub); |
| |
| return r; |
| } |