0a6c074568
While at it, constify the argument.
400 lines
14 KiB
C
400 lines
14 KiB
C
/* SPDX-License-Identifier: LGPL-2.1+ */
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#include <resolv.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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#include <unistd.h>
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#include "alloc-util.h"
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#include "dns-domain.h"
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#include "fd-util.h"
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#include "fileio.h"
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#include "ordered-set.h"
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#include "resolved-conf.h"
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#include "resolved-dns-server.h"
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#include "resolved-resolv-conf.h"
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#include "string-util.h"
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#include "strv.h"
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#include "tmpfile-util-label.h"
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/* A resolv.conf file containing the DNS server and domain data we learnt from uplink, i.e. the full uplink data */
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#define PRIVATE_UPLINK_RESOLV_CONF "/run/systemd/resolve/resolv.conf"
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/* A resolv.conf file containing the domain data we learnt from uplink, but our own DNS server address. */
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#define PRIVATE_STUB_RESOLV_CONF "/run/systemd/resolve/stub-resolv.conf"
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/* A static resolv.conf file containing no domains, but only our own DNS server address */
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#define PRIVATE_STATIC_RESOLV_CONF ROOTLIBEXECDIR "/resolv.conf"
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int manager_check_resolv_conf(const Manager *m) {
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const char *path;
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struct stat st;
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int r;
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assert(m);
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/* This warns only when our stub listener is disabled and /etc/resolv.conf is a symlink to
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* PRIVATE_STATIC_RESOLV_CONF or PRIVATE_STUB_RESOLV_CONF. */
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if (m->dns_stub_listener_mode != DNS_STUB_LISTENER_NO)
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return 0;
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r = stat("/etc/resolv.conf", &st);
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if (r < 0) {
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if (errno == ENOENT)
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return 0;
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return log_warning_errno(errno, "Failed to stat /etc/resolv.conf: %m");
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}
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FOREACH_STRING(path,
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PRIVATE_STUB_RESOLV_CONF,
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PRIVATE_STATIC_RESOLV_CONF) {
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struct stat own;
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/* Is it symlinked to our own uplink file? */
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if (stat(path, &own) >= 0 &&
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st.st_dev == own.st_dev &&
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st.st_ino == own.st_ino) {
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log_warning("DNSStubListener= is disabled, but /etc/resolv.conf is a symlink to %s "
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"which expects DNSStubListener= to be enabled.", path);
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return -EOPNOTSUPP;
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}
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}
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return 0;
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}
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static bool file_is_our_own(const struct stat *st) {
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const char *path;
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assert(st);
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FOREACH_STRING(path,
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PRIVATE_UPLINK_RESOLV_CONF,
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PRIVATE_STUB_RESOLV_CONF,
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PRIVATE_STATIC_RESOLV_CONF) {
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struct stat own;
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/* Is it symlinked to our own uplink file? */
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if (stat(path, &own) >= 0 &&
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st->st_dev == own.st_dev &&
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st->st_ino == own.st_ino)
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return true;
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}
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return false;
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}
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int manager_read_resolv_conf(Manager *m) {
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_cleanup_fclose_ FILE *f = NULL;
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struct stat st;
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unsigned n = 0;
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int r;
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assert(m);
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/* Reads the system /etc/resolv.conf, if it exists and is not
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* symlinked to our own resolv.conf instance */
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if (!m->read_resolv_conf)
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return 0;
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r = stat("/etc/resolv.conf", &st);
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if (r < 0) {
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if (errno == ENOENT)
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return 0;
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r = log_warning_errno(errno, "Failed to stat /etc/resolv.conf: %m");
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goto clear;
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}
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/* Have we already seen the file? */
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if (timespec_load(&st.st_mtim) == m->resolv_conf_mtime)
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return 0;
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if (file_is_our_own(&st))
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return 0;
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f = fopen("/etc/resolv.conf", "re");
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if (!f) {
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if (errno == ENOENT)
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return 0;
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r = log_warning_errno(errno, "Failed to open /etc/resolv.conf: %m");
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goto clear;
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}
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if (fstat(fileno(f), &st) < 0) {
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r = log_error_errno(errno, "Failed to stat open file: %m");
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goto clear;
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}
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if (file_is_our_own(&st))
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return 0;
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dns_server_mark_all(m->dns_servers);
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dns_search_domain_mark_all(m->search_domains);
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for (;;) {
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_cleanup_free_ char *line = NULL;
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const char *a;
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char *l;
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r = read_line(f, LONG_LINE_MAX, &line);
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if (r < 0) {
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log_error_errno(r, "Failed to read /etc/resolv.conf: %m");
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goto clear;
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}
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if (r == 0)
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break;
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n++;
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l = strstrip(line);
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if (IN_SET(*l, '#', ';', 0))
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continue;
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a = first_word(l, "nameserver");
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if (a) {
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r = manager_parse_dns_server_string_and_warn(m, DNS_SERVER_SYSTEM, a);
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if (r < 0)
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log_warning_errno(r, "Failed to parse DNS server address '%s', ignoring.", a);
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continue;
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}
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a = first_word(l, "domain");
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if (!a) /* We treat "domain" lines, and "search" lines as equivalent, and add both to our list. */
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a = first_word(l, "search");
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if (a) {
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r = manager_parse_search_domains_and_warn(m, a);
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if (r < 0)
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log_warning_errno(r, "Failed to parse search domain string '%s', ignoring.", a);
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}
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log_syntax(NULL, LOG_DEBUG, "/etc/resolv.conf", n, 0, "Ignoring resolv.conf line: %s", l);
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}
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m->resolv_conf_mtime = timespec_load(&st.st_mtim);
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/* Flush out all servers and search domains that are still
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* marked. Those are then ones that didn't appear in the new
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* /etc/resolv.conf */
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dns_server_unlink_marked(m->dns_servers);
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dns_search_domain_unlink_marked(m->search_domains);
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/* Whenever /etc/resolv.conf changes, start using the first
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* DNS server of it. This is useful to deal with broken
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* network managing implementations (like NetworkManager),
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* that when connecting to a VPN place both the VPN DNS
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* servers and the local ones in /etc/resolv.conf. Without
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* resetting the DNS server to use back to the first entry we
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* will continue to use the local one thus being unable to
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* resolve VPN domains. */
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manager_set_dns_server(m, m->dns_servers);
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/* Unconditionally flush the cache when /etc/resolv.conf is
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* modified, even if the data it contained was completely
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* identical to the previous version we used. We do this
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* because altering /etc/resolv.conf is typically done when
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* the network configuration changes, and that should be
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* enough to flush the global unicast DNS cache. */
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if (m->unicast_scope)
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dns_cache_flush(&m->unicast_scope->cache);
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/* If /etc/resolv.conf changed, make sure to forget everything we learned about the DNS servers. After all we
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* might now talk to a very different DNS server that just happens to have the same IP address as an old one
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* (think 192.168.1.1). */
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dns_server_reset_features_all(m->dns_servers);
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return 0;
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clear:
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dns_server_unlink_all(m->dns_servers);
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dns_search_domain_unlink_all(m->search_domains);
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return r;
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}
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static void write_resolv_conf_server(DnsServer *s, FILE *f, unsigned *count) {
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DnsScope *scope;
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assert(s);
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assert(f);
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assert(count);
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if (!dns_server_string(s)) {
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log_warning("Out of memory, or invalid DNS address. Ignoring server.");
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return;
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}
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/* Check if the scope this DNS server belongs to is suitable as 'default' route for lookups; resolv.conf does
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* not have a syntax to express that, so it must not appear as a global name server to avoid routing unrelated
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* domains to it (which is a privacy violation, will most probably fail anyway, and adds unnecessary load) */
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scope = dns_server_scope(s);
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if (scope && !dns_scope_is_default_route(scope)) {
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log_debug("Scope of DNS server %s has only route-only domains, not using as global name server", dns_server_string(s));
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return;
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}
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if (*count == MAXNS)
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fputs("# Too many DNS servers configured, the following entries may be ignored.\n", f);
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(*count)++;
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fprintf(f, "nameserver %s\n", dns_server_string(s));
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}
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static void write_resolv_conf_search(
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OrderedSet *domains,
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FILE *f) {
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unsigned length = 0, count = 0;
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Iterator i;
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char *domain;
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assert(domains);
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assert(f);
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fputs("search", f);
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ORDERED_SET_FOREACH(domain, domains, i) {
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if (++count > MAXDNSRCH) {
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fputs("\n# Too many search domains configured, remaining ones ignored.", f);
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break;
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}
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length += strlen(domain) + 1;
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if (length > 256) {
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fputs("\n# Total length of all search domains is too long, remaining ones ignored.", f);
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break;
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}
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fputc(' ', f);
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fputs(domain, f);
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}
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fputs("\n", f);
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}
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static int write_uplink_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *domains) {
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Iterator i;
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fputs("# This file is managed by man:systemd-resolved(8). Do not edit.\n"
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"#\n"
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"# This is a dynamic resolv.conf file for connecting local clients directly to\n"
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"# all known uplink DNS servers. This file lists all configured search domains.\n"
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"#\n"
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"# Third party programs must not access this file directly, but only through the\n"
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"# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,\n"
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"# replace this symlink by a static file or a different symlink.\n"
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"#\n"
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"# See man:systemd-resolved.service(8) for details about the supported modes of\n"
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"# operation for /etc/resolv.conf.\n"
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"\n", f);
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if (ordered_set_isempty(dns))
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fputs("# No DNS servers known.\n", f);
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else {
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unsigned count = 0;
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DnsServer *s;
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ORDERED_SET_FOREACH(s, dns, i)
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write_resolv_conf_server(s, f, &count);
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}
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if (!ordered_set_isempty(domains))
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write_resolv_conf_search(domains, f);
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return fflush_and_check(f);
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}
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static int write_stub_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *domains) {
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fputs_unlocked("# This file is managed by man:systemd-resolved(8). Do not edit.\n"
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"#\n"
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"# This is a dynamic resolv.conf file for connecting local clients to the\n"
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"# internal DNS stub resolver of systemd-resolved. This file lists all\n"
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"# configured search domains.\n"
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"#\n"
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"# Run \"resolvectl status\" to see details about the uplink DNS servers\n"
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"# currently in use.\n"
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"#\n"
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"# Third party programs must not access this file directly, but only through the\n"
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"# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,\n"
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"# replace this symlink by a static file or a different symlink.\n"
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"#\n"
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"# See man:systemd-resolved.service(8) for details about the supported modes of\n"
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"# operation for /etc/resolv.conf.\n"
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"\n"
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"nameserver 127.0.0.53\n"
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"options edns0\n", f);
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if (!ordered_set_isempty(domains))
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write_resolv_conf_search(domains, f);
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return fflush_and_check(f);
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}
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int manager_write_resolv_conf(Manager *m) {
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_cleanup_ordered_set_free_ OrderedSet *dns = NULL, *domains = NULL;
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_cleanup_free_ char *temp_path_uplink = NULL, *temp_path_stub = NULL;
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_cleanup_fclose_ FILE *f_uplink = NULL, *f_stub = NULL;
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int r;
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assert(m);
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/* Read the system /etc/resolv.conf first */
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(void) manager_read_resolv_conf(m);
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/* Add the full list to a set, to filter out duplicates */
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r = manager_compile_dns_servers(m, &dns);
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if (r < 0)
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return log_warning_errno(r, "Failed to compile list of DNS servers: %m");
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r = manager_compile_search_domains(m, &domains, false);
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if (r < 0)
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return log_warning_errno(r, "Failed to compile list of search domains: %m");
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r = fopen_temporary_label(PRIVATE_UPLINK_RESOLV_CONF, PRIVATE_UPLINK_RESOLV_CONF, &f_uplink, &temp_path_uplink);
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if (r < 0)
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return log_warning_errno(r, "Failed to open private resolv.conf file for writing: %m");
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(void) fchmod(fileno(f_uplink), 0644);
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r = fopen_temporary_label(PRIVATE_STUB_RESOLV_CONF, PRIVATE_STUB_RESOLV_CONF, &f_stub, &temp_path_stub);
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if (r < 0)
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return log_warning_errno(r, "Failed to open private stub-resolv.conf file for writing: %m");
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(void) fchmod(fileno(f_stub), 0644);
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r = write_uplink_resolv_conf_contents(f_uplink, dns, domains);
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if (r < 0) {
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log_error_errno(r, "Failed to write private resolv.conf contents: %m");
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goto fail;
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}
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if (rename(temp_path_uplink, PRIVATE_UPLINK_RESOLV_CONF) < 0) {
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r = log_error_errno(errno, "Failed to move private resolv.conf file into place: %m");
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goto fail;
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}
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r = write_stub_resolv_conf_contents(f_stub, dns, domains);
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if (r < 0) {
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log_error_errno(r, "Failed to write private stub-resolv.conf contents: %m");
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goto fail;
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}
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if (rename(temp_path_stub, PRIVATE_STUB_RESOLV_CONF) < 0) {
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r = log_error_errno(errno, "Failed to move private stub-resolv.conf file into place: %m");
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goto fail;
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}
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return 0;
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fail:
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(void) unlink(PRIVATE_UPLINK_RESOLV_CONF);
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(void) unlink(temp_path_uplink);
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(void) unlink(PRIVATE_STUB_RESOLV_CONF);
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(void) unlink(temp_path_stub);
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return r;
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}
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