185 lines
6.7 KiB
Nix
185 lines
6.7 KiB
Nix
{ config, lib, pkgs, ... }:
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with lib;
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let
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cfg = config.services.resolved;
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dnsmasqResolve = config.services.dnsmasq.enable &&
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config.services.dnsmasq.resolveLocalQueries;
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in
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{
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options = {
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services.resolved.enable = mkOption {
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default = false;
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type = types.bool;
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description = lib.mdDoc ''
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Whether to enable the systemd DNS resolver daemon, `systemd-resolved`.
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Search for `services.resolved` to see all options.
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'';
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};
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services.resolved.fallbackDns = mkOption {
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default = null;
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example = [ "8.8.8.8" "2001:4860:4860::8844" ];
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type = types.nullOr (types.listOf types.str);
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description = lib.mdDoc ''
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A list of IPv4 and IPv6 addresses to use as the fallback DNS servers.
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If this option is null, a compiled-in list of DNS servers is used instead.
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Setting this option to an empty list will override the built-in list to an empty list, disabling fallback.
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'';
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};
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services.resolved.domains = mkOption {
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default = config.networking.search;
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defaultText = literalExpression "config.networking.search";
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example = [ "example.com" ];
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type = types.listOf types.str;
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description = lib.mdDoc ''
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A list of domains. These domains are used as search suffixes
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when resolving single-label host names (domain names which
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contain no dot), in order to qualify them into fully-qualified
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domain names (FQDNs).
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For compatibility reasons, if this setting is not specified,
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the search domains listed in
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{file}`/etc/resolv.conf` are used instead, if
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that file exists and any domains are configured in it.
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'';
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};
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services.resolved.llmnr = mkOption {
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default = "true";
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example = "false";
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type = types.enum [ "true" "resolve" "false" ];
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description = lib.mdDoc ''
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Controls Link-Local Multicast Name Resolution support
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(RFC 4795) on the local host.
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If set to
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- `"true"`: Enables full LLMNR responder and resolver support.
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- `"false"`: Disables both.
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- `"resolve"`: Only resolution support is enabled, but responding is disabled.
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'';
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};
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services.resolved.dnssec = mkOption {
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default = "false";
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example = "true";
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type = types.enum [ "true" "allow-downgrade" "false" ];
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description = lib.mdDoc ''
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If set to
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- `"true"`:
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all DNS lookups are DNSSEC-validated locally (excluding
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LLMNR and Multicast DNS). Note that this mode requires a
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DNS server that supports DNSSEC. If the DNS server does
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not properly support DNSSEC all validations will fail.
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- `"allow-downgrade"`:
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DNSSEC validation is attempted, but if the server does not
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support DNSSEC properly, DNSSEC mode is automatically
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disabled. Note that this mode makes DNSSEC validation
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vulnerable to "downgrade" attacks, where an attacker might
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be able to trigger a downgrade to non-DNSSEC mode by
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synthesizing a DNS response that suggests DNSSEC was not
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supported.
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- `"false"`: DNS lookups are not DNSSEC validated.
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At the time of September 2023, systemd upstream advise
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to disable DNSSEC by default as the current code
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is not robust enough to deal with "in the wild" non-compliant
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servers, which will usually give you a broken bad experience
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in addition of insecure.
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'';
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};
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services.resolved.dnsovertls = mkOption {
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default = "false";
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example = "true";
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type = types.enum [ "true" "opportunistic" "false" ];
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description = lib.mdDoc ''
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If set to
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- `"true"`:
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all DNS lookups will be encrypted. This requires
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that the DNS server supports DNS-over-TLS and
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has a valid certificate. If the hostname was specified
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via the `address#hostname` format in {option}`services.resolved.domains`
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then the specified hostname is used to validate its certificate.
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- `"opportunistic"`:
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all DNS lookups will attempt to be encrypted, but will fallback
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to unecrypted requests if the server does not support DNS-over-TLS.
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Note that this mode does allow for a malicious party to conduct a
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downgrade attack by immitating the DNS server and pretending to not
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support encryption.
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- `"false"`:
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all DNS lookups are done unencrypted.
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'';
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};
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services.resolved.extraConfig = mkOption {
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default = "";
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type = types.lines;
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description = lib.mdDoc ''
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Extra config to append to resolved.conf.
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'';
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};
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};
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config = mkIf cfg.enable {
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assertions = [
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{ assertion = !config.networking.useHostResolvConf;
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message = "Using host resolv.conf is not supported with systemd-resolved";
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}
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];
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users.users.systemd-resolve.group = "systemd-resolve";
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# add resolve to nss hosts database if enabled and nscd enabled
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# system.nssModules is configured in nixos/modules/system/boot/systemd.nix
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# added with order 501 to allow modules to go before with mkBefore
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system.nssDatabases.hosts = (mkOrder 501 ["resolve [!UNAVAIL=return]"]);
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systemd.additionalUpstreamSystemUnits = [
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"systemd-resolved.service"
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];
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systemd.services.systemd-resolved = {
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wantedBy = [ "multi-user.target" ];
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aliases = [ "dbus-org.freedesktop.resolve1.service" ];
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restartTriggers = [ config.environment.etc."systemd/resolved.conf".source ];
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};
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environment.etc = {
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"systemd/resolved.conf".text = ''
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[Resolve]
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${optionalString (config.networking.nameservers != [])
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"DNS=${concatStringsSep " " config.networking.nameservers}"}
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${optionalString (cfg.fallbackDns != null)
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"FallbackDNS=${concatStringsSep " " cfg.fallbackDns}"}
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${optionalString (cfg.domains != [])
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"Domains=${concatStringsSep " " cfg.domains}"}
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LLMNR=${cfg.llmnr}
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DNSSEC=${cfg.dnssec}
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DNSOverTLS=${cfg.dnsovertls}
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${config.services.resolved.extraConfig}
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'';
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# symlink the dynamic stub resolver of resolv.conf as recommended by upstream:
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# https://www.freedesktop.org/software/systemd/man/systemd-resolved.html#/etc/resolv.conf
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"resolv.conf".source = "/run/systemd/resolve/stub-resolv.conf";
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} // optionalAttrs dnsmasqResolve {
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"dnsmasq-resolv.conf".source = "/run/systemd/resolve/resolv.conf";
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};
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# If networkmanager is enabled, ask it to interface with resolved.
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networking.networkmanager.dns = "systemd-resolved";
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networking.resolvconf.package = pkgs.systemd;
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};
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}
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