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dns: write original DNS servers to /var/run/NetworkManager/no-stub-resolv.conf

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When a DNS plugin is enabled (like "main.dns=dnsmasq" or "main.dns=systemd-resolved"),
the name servers announced to the rc-manager are coerced to be 127.0.0.1
or 127.0.0.53.

Depending on the "main.rc-manager" setting, also "/etc/resolv.conf"
contains only this coerced name server to the local caching service.
The same is true for "/var/run/NetworkManager/resolv.conf" file, which
contains what we would write to "/etc/resolv.conf" (depending on
the "main.rc-manager" configuration).

Write a new file "/var/run/NetworkManager/no-stub-resolv.conf", which contains
the original name servers, uncoerced. Like "/var/run/NetworkManager/resolv.conf",
this file is always written.

The effect is, when one enables "main.dns=systemd-resolved", then there
is still a file "no-stub-resolv.conf" with the same content as with
"main.dns=default".

The no-stub-resolv.conf may be a possible solution, when a user wants
NetworkManager to update systemd-resolved, but still have a regular
/etc/resolv.conf [1]. For that, the user could configure

    [main]
    dns=systemd-resolved
    rc-manager=unmanaged

and symlink "/etc/resolv.conf" to "/var/run/NetworkManager/no-stub-resolv.conf".
This is not necessarily the only solution for the problem and does not preclude
options for updating systemd-resolved in combination with other DNS plugins.

[1] https://gitlab.freedesktop.org/NetworkManager/NetworkManager/issues/20
This commit is contained in:
Thomas Haller 2018-09-12 21:16:34 +02:00
parent 95b006c244
commit 0dc673f0a5
2 changed files with 42 additions and 5 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

12
man/NetworkManager.conf.xml
View file

@ -331,15 +331,23 @@ no-auto-default=*
after some time. This behavior can be modified passing the
'all-servers' or 'strict-order' options to dnsmasq (see the
manual page for more details).</para>
<para><literal>systemd-resolved</literal>: NetworkManager will
push the DNS configuration to systemd-resolved</para>
<para><literal>unbound</literal>: NetworkManager will talk
to unbound and dnssec-triggerd, providing a "split DNS"
configuration with DNSSEC support. <filename>/etc/resolv.conf</filename>
will be managed by dnssec-trigger daemon.</para>
<para><literal>systemd-resolved</literal>: NetworkManager will
push the DNS configuration to systemd-resolved</para>
<para><literal>none</literal>: NetworkManager will not
modify resolv.conf. This implies
<literal>rc-manager</literal>&nbsp;<literal>unmanaged</literal></para>
<para>Note that the plugins <literal>dnsmasq</literal>, <literal>systemd-resolved</literal>
and <literal>unbound</literal> are caching local nameservers.
Hence, when NetworkManager writes <filename>&nmrundir;/resolv.conf</filename>
and <filename>/etc/resolv.conf</filename> (according to <literal>rc-manager</literal>
setting below), the name server there will be localhost only.
NetworkManager also writes a file <filename>&nmrundir;/no-stub-resolv.conf</filename>
that contains the original name servers pushed to the DNS plugin.</para>
</listitem>
</varlistentry>

35
src/dns/nm-dns-manager.c
View file

@ -744,9 +744,36 @@ _read_link_cached (const char *path, gboolean *is_cached, char **cached)
return (*cached = g_file_read_link (path, NULL));
}
#define MY_RESOLV_CONF NMRUNDIR "/resolv.conf"
#define MY_RESOLV_CONF_TMP MY_RESOLV_CONF ".tmp"
#define RESOLV_CONF_TMP "/etc/.resolv.conf.NetworkManager"
#define MY_RESOLV_CONF NMRUNDIR"/resolv.conf"
#define MY_RESOLV_CONF_TMP MY_RESOLV_CONF".tmp"
#define RESOLV_CONF_TMP "/etc/.resolv.conf.NetworkManager"
#define NO_STUB_RESOLV_CONF NMRUNDIR "/no-stub-resolv.conf"
static void
update_resolv_conf_no_stub (NMDnsManager *self,
char **searches,
char **nameservers,
char **options)
{
gs_free char *content = NULL;
GError *local = NULL;
content = create_resolv_conf (searches, nameservers, options);
if (!g_file_set_contents (NO_STUB_RESOLV_CONF,
content,
-1,
&local)) {
_LOGD ("update-resolv-no-stub: failure to write file: %s",
local->message);
g_error_free (local);
return;
}
_LOGT ("update-resolv-no-stub: '%s' successfully written",
NO_STUB_RESOLV_CONF);
}
static SpawnResult
update_resolv_conf (NMDnsManager *self,
@ -1421,6 +1448,8 @@ update_dns (NMDnsManager *self,
;
}
update_resolv_conf_no_stub (self, searches, nameservers, options);
/* If caching was successful, we only send 127.0.0.1 to /etc/resolv.conf
* to ensure that the glibc resolver doesn't try to round-robin nameservers,
* but only uses the local caching nameserver.