nixos/systemd: fix NSS database ordering

- The order of NSS (host) modules has been brought in line with upstream
  recommendations:

  - The `myhostname` module is placed before the `resolve` (optional) and `dns`
    entries, but after `file` (to allow overriding via `/etc/hosts` /
    `networking.extraHosts`, and prevent ISPs with catchall-DNS resolvers from
    hijacking `.localhost` domains)
  - The `mymachines` module, which provides hostname resolution for local
    containers (registered with `systemd-machined`) is placed to the front, to
    make sure its mappings are preferred over other resolvers.
  - If systemd-networkd is enabled, the `resolve` module is placed before
    `files` and `myhostname`, as it provides the same logic internally, with
    caching.
  - The `mdns(_minimal)` module has been updated to the new priorities.

  If you use your own NSS host modules, make sure to update your priorities
  according to these rules:

  - NSS modules which should be queried before `resolved` DNS resolution should
    use mkBefore.
  - NSS modules which should be queried after `resolved`, `files` and
    `myhostname`, but before `dns` should use the default priority
  - NSS modules which should come after `dns` should use mkAfter.
This commit is contained in:
Florian Klink 2021-07-17 19:41:45 +02:00
parent b59c06dc92
commit c1536f5c78
6 changed files with 103 additions and 8 deletions

View File

@ -562,6 +562,77 @@
be removed in 22.05.
</para>
</listitem>
<listitem>
<para>
The order of NSS (host) modules has been brought in line with
upstream recommendations:
</para>
<itemizedlist spacing="compact">
<listitem>
<para>
The <literal>myhostname</literal> module is placed before
the <literal>resolve</literal> (optional) and
<literal>dns</literal> entries, but after
<literal>file</literal> (to allow overriding via
<literal>/etc/hosts</literal> /
<literal>networking.extraHosts</literal>, and prevent ISPs
with catchall-DNS resolvers from hijacking
<literal>.localhost</literal> domains)
</para>
</listitem>
<listitem>
<para>
The <literal>mymachines</literal> module, which provides
hostname resolution for local containers (registered with
<literal>systemd-machined</literal>) is placed to the
front, to make sure its mappings are preferred over other
resolvers.
</para>
</listitem>
<listitem>
<para>
If systemd-networkd is enabled, the
<literal>resolve</literal> module is placed before
<literal>files</literal> and
<literal>myhostname</literal>, as it provides the same
logic internally, with caching.
</para>
</listitem>
<listitem>
<para>
The <literal>mdns(_minimal)</literal> module has been
updated to the new priorities.
</para>
</listitem>
</itemizedlist>
<para>
If you use your own NSS host modules, make sure to update your
priorities according to these rules:
</para>
<itemizedlist spacing="compact">
<listitem>
<para>
NSS modules which should be queried before
<literal>resolved</literal> DNS resolution should use
mkBefore.
</para>
</listitem>
<listitem>
<para>
NSS modules which should be queried after
<literal>resolved</literal>, <literal>files</literal> and
<literal>myhostname</literal>, but before
<literal>dns</literal> should use the default priority
</para>
</listitem>
<listitem>
<para>
NSS modules which should come after <literal>dns</literal>
should use mkAfter.
</para>
</listitem>
</itemizedlist>
</listitem>
</itemizedlist>
</section>
</section>

View File

@ -139,3 +139,27 @@ In addition to numerous new and upgraded packages, this release has the followin
- The wordpress module provides a new interface which allows to use different webservers with the new option [`services.wordpress.webserver`](options.html#opt-services.wordpress.webserver). Currently `httpd` and `nginx` are supported. The definitions of wordpress sites should now be set in [`services.wordpress.sites`](options.html#opt-services.wordpress.sites).
Sites definitions that use the old interface are automatically migrated in the new option. This backward compatibility will be removed in 22.05.
- The order of NSS (host) modules has been brought in line with upstream
recommendations:
- The `myhostname` module is placed before the `resolve` (optional) and `dns`
entries, but after `file` (to allow overriding via `/etc/hosts` /
`networking.extraHosts`, and prevent ISPs with catchall-DNS resolvers from
hijacking `.localhost` domains)
- The `mymachines` module, which provides hostname resolution for local
containers (registered with `systemd-machined`) is placed to the front, to
make sure its mappings are preferred over other resolvers.
- If systemd-networkd is enabled, the `resolve` module is placed before
`files` and `myhostname`, as it provides the same logic internally, with
caching.
- The `mdns(_minimal)` module has been updated to the new priorities.
If you use your own NSS host modules, make sure to update your priorities
according to these rules:
- NSS modules which should be queried before `resolved` DNS resolution should
use mkBefore.
- NSS modules which should be queried after `resolved`, `files` and
`myhostname`, but before `dns` should use the default priority
- NSS modules which should come after `dns` should use mkAfter.

View File

@ -124,8 +124,8 @@ with lib;
group = mkBefore [ "files" ];
shadow = mkBefore [ "files" ];
hosts = mkMerge [
(mkBefore [ "files" ])
(mkAfter [ "dns" ])
(mkOrder 998 [ "files" ])
(mkOrder 1499 [ "dns" ])
];
services = mkBefore [ "files" ];
};

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@ -240,8 +240,8 @@ in
system.nssModules = optional cfg.nssmdns pkgs.nssmdns;
system.nssDatabases.hosts = optionals cfg.nssmdns (mkMerge [
(mkOrder 900 [ "mdns_minimal [NOTFOUND=return]" ]) # must be before resolve
(mkOrder 1501 [ "mdns" ]) # 1501 to ensure it's after dns
(mkBefore [ "mdns_minimal [NOTFOUND=return]" ]) # before resolve
(mkAfter [ "mdns" ]) # after dns
]);
environment.systemPackages = [ pkgs.avahi ];

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@ -140,7 +140,8 @@ in
# add resolve to nss hosts database if enabled and nscd enabled
# system.nssModules is configured in nixos/modules/system/boot/systemd.nix
system.nssDatabases.hosts = optional config.services.nscd.enable "resolve [!UNAVAIL=return]";
# added with order 501 to allow modules to go before with mkBefore
system.nssDatabases.hosts = (mkOrder 501 ["resolve [!UNAVAIL=return]"]);
systemd.additionalUpstreamSystemUnits = [
"systemd-resolved.service"

View File

@ -925,9 +925,8 @@ in
system.nssModules = [ systemd.out ];
system.nssDatabases = {
hosts = (mkMerge [
[ "mymachines" ]
(mkOrder 1600 [ "myhostname" ] # 1600 to ensure it's always the last
)
(mkOrder 400 ["mymachines"]) # 400 to ensure it comes before resolve (which is mkBefore'd)
(mkOrder 999 ["myhostname"]) # after files (which is 998), but before regular nss modules
]);
passwd = (mkMerge [
(mkAfter [ "systemd" ])