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-rw-r--r--src/resolve/resolved-resolv-conf.c434
1 files changed, 434 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..2071e08
--- /dev/null
+++ b/src/resolve/resolved-resolv-conf.c
@@ -0,0 +1,434 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <resolv.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "alloc-util.h"
+#include "dns-domain.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "fs-util.h"
+#include "label-util.h"
+#include "ordered-set.h"
+#include "path-util.h"
+#include "resolved-conf.h"
+#include "resolved-dns-server.h"
+#include "resolved-resolv-conf.h"
+#include "stat-util.h"
+#include "string-table.h"
+#include "string-util.h"
+#include "strv.h"
+#include "tmpfile-util-label.h"
+
+int manager_check_resolv_conf(const Manager *m) {
+ struct stat st, own;
+
+ assert(m);
+
+ /* This warns only when our stub listener is disabled and /etc/resolv.conf is a symlink to
+ * PRIVATE_STATIC_RESOLV_CONF. */
+
+ if (m->dns_stub_listener_mode != DNS_STUB_LISTENER_NO)
+ return 0;
+
+ if (stat("/etc/resolv.conf", &st) < 0) {
+ if (errno == ENOENT)
+ return 0;
+
+ return log_warning_errno(errno, "Failed to stat /etc/resolv.conf: %m");
+ }
+
+ /* Is it symlinked to our own uplink file? */
+ if (stat(PRIVATE_STATIC_RESOLV_CONF, &own) >= 0 &&
+ stat_inode_same(&st, &own))
+ return log_warning_errno(SYNTHETIC_ERRNO(EOPNOTSUPP),
+ "DNSStubListener= is disabled, but /etc/resolv.conf is a symlink to "
+ PRIVATE_STATIC_RESOLV_CONF " which expects DNSStubListener= to be enabled.");
+
+ return 0;
+}
+
+static bool file_is_our_own(const struct stat *st) {
+ 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 &&
+ stat_inode_same(st, &own))
+ 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 (stat_inode_unmodified(&st, &m->resolv_conf_stat))
+ 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;
+
+ r = read_stripped_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++;
+
+ if (IN_SET(*line, '#', ';', 0))
+ continue;
+
+ a = first_word(line, "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(line, "domain");
+ if (!a) /* We treat "domain" lines, and "search" lines as equivalent, and add both to our list. */
+ a = first_word(line, "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);
+
+ continue;
+ }
+
+ log_syntax(NULL, LOG_DEBUG, "/etc/resolv.conf", n, 0, "Ignoring resolv.conf line: %s", line);
+ }
+
+ m->resolv_conf_stat = st;
+
+ /* 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;
+ }
+
+ /* resolv.conf simply doesn't support any other ports than 53, hence there's nothing much we can
+ * do — we have to suppress these entries */
+ if (dns_server_port(s) != 53) {
+ log_debug("DNS server %s with non-standard UDP port number, suppressing from generated resolv.conf.", dns_server_string(s));
+ 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) {
+ char *domain;
+
+ assert(domains);
+ assert(f);
+
+ fputs("search", f);
+
+ ORDERED_SET_FOREACH(domain, domains) {
+ fputc(' ', f);
+ fputs(domain, f);
+ }
+
+ fputs("\n", f);
+}
+
+static int write_uplink_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *domains) {
+
+ fputs("# This is "PRIVATE_UPLINK_RESOLV_CONF" managed by man:systemd-resolved(8).\n"
+ "# Do not edit.\n"
+ "#\n"
+ "# This file might be symlinked as /etc/resolv.conf. If you're looking at\n"
+ "# /etc/resolv.conf and seeing this text, you have followed the symlink.\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 should typically not access this file directly, but only\n"
+ "# through the symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a\n"
+ "# different way, 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)
+ write_resolv_conf_server(s, f, &count);
+ }
+
+ if (ordered_set_isempty(domains))
+ fputs("search .\n", f); /* Make sure that if the local hostname is chosen as fqdn this does not
+ * imply a search domain */
+ else
+ 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("# This is "PRIVATE_STUB_RESOLV_CONF" managed by man:systemd-resolved(8).\n"
+ "# Do not edit.\n"
+ "#\n"
+ "# This file might be symlinked as /etc/resolv.conf. If you're looking at\n"
+ "# /etc/resolv.conf and seeing this text, you have followed the symlink.\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 should typically not access this file directly, but only\n"
+ "# through the symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a\n"
+ "# different way, 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 trust-ad\n", f);
+
+ if (ordered_set_isempty(domains))
+ fputs("search .\n", f); /* Make sure that if the local hostname is chosen as fqdn this does not
+ * imply a search domain */
+ else
+ 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_(unlink_and_freep) 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, ignoring: %m");
+
+ r = manager_compile_search_domains(m, &domains, false);
+ if (r < 0)
+ return log_warning_errno(r, "Failed to compile list of search domains, ignoring: %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 new %s for writing, ignoring: %m", PRIVATE_UPLINK_RESOLV_CONF);
+
+ (void) fchmod(fileno(f_uplink), 0644);
+
+ r = write_uplink_resolv_conf_contents(f_uplink, dns, domains);
+ if (r < 0)
+ return log_warning_errno(r, "Failed to write new %s, ignoring: %m", PRIVATE_UPLINK_RESOLV_CONF);
+
+ if (m->dns_stub_listener_mode != DNS_STUB_LISTENER_NO) {
+ 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 new %s for writing, ignoring: %m", PRIVATE_STUB_RESOLV_CONF);
+
+ (void) fchmod(fileno(f_stub), 0644);
+
+ r = write_stub_resolv_conf_contents(f_stub, dns, domains);
+ if (r < 0)
+ return log_warning_errno(r, "Failed to write new %s, ignoring: %m", PRIVATE_STUB_RESOLV_CONF);
+
+ r = conservative_rename(temp_path_stub, PRIVATE_STUB_RESOLV_CONF);
+ if (r < 0)
+ log_warning_errno(r, "Failed to move new %s into place, ignoring: %m", PRIVATE_STUB_RESOLV_CONF);
+
+ temp_path_stub = mfree(temp_path_stub); /* free the string explicitly, so that we don't unlink anymore */
+ } else {
+ _cleanup_free_ char *fname = NULL;
+ r = path_extract_filename(PRIVATE_UPLINK_RESOLV_CONF, &fname);
+ if (r < 0)
+ return log_warning_errno(r, "Failed to extract filename from path '" PRIVATE_UPLINK_RESOLV_CONF "', ignoring: %m");
+
+ r = symlink_atomic_label(fname, PRIVATE_STUB_RESOLV_CONF);
+ if (r < 0)
+ log_warning_errno(r, "Failed to symlink %s, ignoring: %m", PRIVATE_STUB_RESOLV_CONF);
+ }
+
+ r = conservative_rename(temp_path_uplink, PRIVATE_UPLINK_RESOLV_CONF);
+ if (r < 0)
+ log_warning_errno(r, "Failed to move new %s into place: %m", PRIVATE_UPLINK_RESOLV_CONF);
+
+ temp_path_uplink = mfree(temp_path_uplink); /* free the string explicitly, so that we don't unlink anymore */
+ return r;
+}
+
+int resolv_conf_mode(void) {
+ static const char * const table[_RESOLV_CONF_MODE_MAX] = {
+ [RESOLV_CONF_UPLINK] = PRIVATE_UPLINK_RESOLV_CONF,
+ [RESOLV_CONF_STUB] = PRIVATE_STUB_RESOLV_CONF,
+ [RESOLV_CONF_STATIC] = PRIVATE_STATIC_RESOLV_CONF,
+ };
+
+ struct stat system_st;
+
+ if (stat("/etc/resolv.conf", &system_st) < 0) {
+ if (errno == ENOENT)
+ return RESOLV_CONF_MISSING;
+
+ return -errno;
+ }
+
+ for (ResolvConfMode m = 0; m < _RESOLV_CONF_MODE_MAX; m++) {
+ struct stat our_st;
+
+ if (!table[m])
+ continue;
+
+ if (stat(table[m], &our_st) < 0) {
+ if (errno != ENOENT)
+ log_debug_errno(errno, "Failed to stat() %s, ignoring: %m", table[m]);
+
+ continue;
+ }
+
+ if (stat_inode_same(&system_st, &our_st))
+ return m;
+ }
+
+ return RESOLV_CONF_FOREIGN;
+}
+
+static const char* const resolv_conf_mode_table[_RESOLV_CONF_MODE_MAX] = {
+ [RESOLV_CONF_UPLINK] = "uplink",
+ [RESOLV_CONF_STUB] = "stub",
+ [RESOLV_CONF_STATIC] = "static",
+ [RESOLV_CONF_MISSING] = "missing",
+ [RESOLV_CONF_FOREIGN] = "foreign",
+};
+DEFINE_STRING_TABLE_LOOKUP(resolv_conf_mode, ResolvConfMode);
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-19 00:01:34 +0000