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resolved: create private stub resolve file for /etc/resolv.conf integration (#7014)

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This creates a second private resolve.conf file which lists the stub resolver
and the resolved acquired search domains.

This runtime file should be used as a symlink target for /etc/resolv.conf such
that non-nss based applications can resolve search domains.

Fixes: #7009
This commit is contained in:
Dimitri John Ledkov 2017-10-24 09:28:41 -04:00 committed by Lennart Poettering
parent ceeb433c39
commit e6b2d948f8
6 changed files with 73 additions and 20 deletions
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8
NEWS
View File

@ -6,6 +6,14 @@ CHANGES WITH 236 in spe:
has been extended to also set the dummy module option numdummies=0,
resolving issues with the kernel creating dummy0.
* systemd-resolved now maintains a new dynamic
/run/systemd/resolve/stub-resolv.conf compatibility file. It is now
recommended to maintain /etc/resolv.conf as a symlink to this new
dynamic file. It points at the systemd-resolved stub DNS 127.0.0.53
resolver and it includes dynamically acquired search domains. This
achieves a more correct DNS resolution by software that bypasses
local DNS APIs (e.g. NSS).
CHANGES WITH 235:
* A new modprobe.d drop-in is now shipped by default that sets the

18
man/systemd-resolved.service.xml
View File

@ -94,7 +94,8 @@
<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details
about systemd's own configuration files for DNS servers. To improve compatibility,
<filename>/etc/resolv.conf</filename> is read in order to discover configured system DNS servers, but only if it is
not a symlink to <filename>/run/systemd/resolve/resolv.conf</filename> (see below).</para>
not a symlink to <filename>/run/systemd/resolve/stub-resolv.conf</filename> or
<filename>/run/systemd/resolve/resolv.conf</filename> (see below).</para>
<para><command>systemd-resolved</command> synthesizes DNS resource records (RRs) for the following cases:</para>
@ -164,15 +165,26 @@
<refsect1>
<title><filename>/etc/resolv.conf</filename></title>
<para>Three modes of handling <filename>/etc/resolv.conf</filename> (see
<para>Four modes of handling <filename>/etc/resolv.conf</filename> (see
<citerefentry project='man-pages'><refentrytitle>resolv.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>) are
supported:</para>
<itemizedlist>
<listitem><para><command>systemd-resolved</command> maintains the
<filename>/run/systemd/resolve/stub-resolv.conf</filename> file for compatibility with traditional Linux
programs. This file may be symlinked from <filename>/etc/resolv.conf</filename>. This file lists the 127.0.0.53
DNS stub (see above) as the only DNS server. It also contains a list of search domains that are in use by
systemd-resolved. The list of search domains is always kept up-to-date. Note that
<filename>/run/systemd/resolve/stub-resolv.conf</filename> should not be used directly by applications, but only
through a symlink from <filename>/etc/resolv.conf</filename>. This file may be symlinked from
<filename>/etc/resolv.conf</filename> in order to connect all local clients that bypass local DNS APIs to
<command>systemd-resolved</command> with correct search domains settings. This mode of operation is
recommended.</para></listitem>
<listitem><para>A static file <filename>/usr/lib/systemd/resolv.conf</filename> is provided that lists
the 127.0.0.53 DNS stub (see above) as only DNS server. This file may be symlinked from
<filename>/etc/resolv.conf</filename> in order to connect all local clients that bypass local DNS APIs to
<command>systemd-resolved</command>. This mode of operation is recommended.</para></listitem>
<command>systemd-resolved</command>. This file does not contain any search domains.</para></listitem>
<listitem><para><command>systemd-resolved</command> maintains the
<filename>/run/systemd/resolve/resolv.conf</filename> file for compatibility with traditional Linux

58
src/resolve/resolved-resolv-conf.c
View File

@ -61,7 +61,13 @@ int manager_read_resolv_conf(Manager *m) {
return 0;
/* Is it symlinked to our own file? */
if (stat(PRIVATE_RESOLV_CONF, &own) >= 0 &&
if (stat(PRIVATE_UPLINK_RESOLV_CONF, &own) >= 0 &&
st.st_dev == own.st_dev &&
st.st_ino == own.st_ino)
return 0;
/* Is it symlinked to our own stub file? */
if (stat(PRIVATE_STUB_RESOLV_CONF, &own) >= 0 &&
st.st_dev == own.st_dev &&
st.st_ino == own.st_ino)
return 0;
@ -206,7 +212,7 @@ static void write_resolv_conf_search(
fputs_unlocked("\n", f);
}
static int write_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *domains) {
static int write_uplink_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *domains) {
Iterator i;
fputs_unlocked("# This file is managed by man:systemd-resolved(8). Do not edit.\n#\n"
@ -234,11 +240,25 @@ static int write_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *doma
return fflush_and_check(f);
}
static int write_stub_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *domains) {
fputs("# This file is managed by man:systemd-resolved(8). Do not edit.\n#\n"
"# 127.0.0.53 is the systemd-resolved stub resolver.\n"
"# run \"systemd-resolve --status\" to see details about the actual nameservers.\n"
"nameserver 127.0.0.53\n\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 = NULL;
_cleanup_fclose_ FILE *f = NULL;
_cleanup_free_ char *temp_path_uplink = NULL;
_cleanup_free_ char *temp_path_stub = NULL;
_cleanup_fclose_ FILE *f_uplink = NULL;
_cleanup_fclose_ FILE *f_stub = NULL;
int r;
assert(m);
@ -255,28 +275,44 @@ int manager_write_resolv_conf(Manager *m) {
if (r < 0)
return log_warning_errno(r, "Failed to compile list of search domains: %m");
r = fopen_temporary_label(PRIVATE_RESOLV_CONF, PRIVATE_RESOLV_CONF, &f, &temp_path);
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");
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) fchmod(fileno(f_uplink), 0644);
(void) fchmod(fileno(f_stub), 0644);
(void) fchmod(fileno(f), 0644);
r = write_resolv_conf_contents(f, dns, domains);
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, PRIVATE_RESOLV_CONF) < 0) {
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_RESOLV_CONF);
(void) unlink(temp_path);
(void) unlink(PRIVATE_UPLINK_RESOLV_CONF);
(void) unlink(temp_path_uplink);
(void) unlink(PRIVATE_STUB_RESOLV_CONF);
(void) unlink(temp_path_stub);
return r;
}

3
src/resolve/resolved-resolv-conf.h
View File

@ -21,7 +21,8 @@
#include "resolved-manager.h"
#define PRIVATE_RESOLV_CONF "/run/systemd/resolve/resolv.conf"
#define PRIVATE_UPLINK_RESOLV_CONF "/run/systemd/resolve/resolv.conf"
#define PRIVATE_STUB_RESOLV_CONF "/run/systemd/resolve/stub-resolv.conf"
int manager_read_resolv_conf(Manager *m);
int manager_write_resolv_conf(Manager *m);

4
src/resolve/resolved.c
View File

@ -117,10 +117,6 @@ int main(int argc, char *argv[]) {
sd_event_get_exit_code(m->event, &r);
finish:
/* systemd-nspawn checks for private resolv.conf to decide whether
or not to mount it into the container. So just delete it. */
(void) unlink(PRIVATE_RESOLV_CONF);
sd_notify(false,
"STOPPING=1\n"
"STATUS=Shutting down...");

2
tmpfiles.d/etc.conf.m4
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@ -14,7 +14,7 @@ m4_ifdef(`HAVE_SMACK_RUN_LABEL',
t /etc/mtab - - - - security.SMACK64=_
)m4_dnl
m4_ifdef(`ENABLE_RESOLVE',
L! /etc/resolv.conf - - - - ../usr/lib/systemd/resolv.conf
L! /etc/resolv.conf - - - - ../run/systemd/resolve/stub-resolv.conf
)m4_dnl
C /etc/nsswitch.conf - - - -
m4_ifdef(`HAVE_PAM',