diff options
Diffstat (limited to 'src/resolve/resolved-resolv-conf.c')
| -rw-r--r-- | src/resolve/resolved-resolv-conf.c | 400 |
1 files changed, 400 insertions, 0 deletions
diff --git a/src/resolve/resolved-resolv-conf.c b/src/resolve/resolved-resolv-conf.c new file mode 100644 index 0000000..5205071 --- /dev/null +++ b/src/resolve/resolved-resolv-conf.c @@ -0,0 +1,400 @@ +/* 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.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" +#include "tmpfile-util-label.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 server address */ +#define PRIVATE_STATIC_RESOLV_CONF ROOTLIBEXECDIR "/resolv.conf" + +int manager_check_resolv_conf(const Manager *m) { + const char *path; + struct stat st; + int r; + + assert(m); + + /* This warns only when our stub listener is disabled and /etc/resolv.conf is a symlink to + * PRIVATE_STATIC_RESOLV_CONF or PRIVATE_STUB_RESOLV_CONF. */ + + if (m->dns_stub_listener_mode != DNS_STUB_LISTENER_NO) + return 0; + + r = stat("/etc/resolv.conf", &st); + if (r < 0) { + if (errno == ENOENT) + return 0; + + return log_warning_errno(errno, "Failed to stat /etc/resolv.conf: %m"); + } + + FOREACH_STRING(path, + 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) { + log_warning("DNSStubListener= is disabled, but /etc/resolv.conf is a symlink to %s " + "which expects DNSStubListener= to be enabled.", path); + return -EOPNOTSUPP; + } + } + + return 0; +} + +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; + 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); + + for (;;) { + _cleanup_free_ char *line = NULL; + const char *a; + char *l; + + r = read_line(f, LONG_LINE_MAX, &line); + if (r < 0) { + log_error_errno(r, "Failed to read /etc/resolv.conf: %m"); + goto clear; + } + if (r == 0) + break; + + 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) { + DnsScope *scope; + + 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 scope this DNS server belongs to is suitable as 'default' route for lookups; 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) */ + scope = dns_server_scope(s); + if (scope && !dns_scope_is_default_route(scope)) { + log_debug("Scope of DNS server %s has only 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" + "options edns0\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; +} |