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-rw-r--r--src/resolve/resolved-resolv-conf.c400
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;
+}