# Stubby for OpenWRT ## Stubby Description [Stubby](https://dnsprivacy.org/wiki/display/DP/DNS+Privacy+Daemon+-+Stubby) is an application that acts as a local DNS Privacy stub resolver (using DNS-over-TLS). Stubby encrypts DNS queries sent from a client machine to a DNS Privacy resolver increasing end user privacy. Stubby is useful on an OpenWRT device, because it can sit between the usual DNS resolver (dnsmasq by default) and the upstream DNS resolver and be used to ensure that DNS traffic is encrypted between the OpenWRT device and the resolver. Stubby is developed by the [getdns](http://getdnsapi.net/) project. For more background and FAQ see the [About Stubby](https://dnsprivacy.org/wiki/display/DP/About+Stubby) page. ## Installation Installation of this package can be achieved at the command line using `opkg install stubby`, or via the LUCI Web Interface. Installing the stubby package will also install the required dependency packages, including the `ca-certificates` package. ## Configuration The default configuration of the package has been chosen to ensure that stubby should work after installation. By default, configuration of stubby is integrated with the OpenWRT UCI system using the file `/etc/config/stubby`. The configuration options available are also documented in that file. If for some reason you wish to configure stubby using the `/etc/stubby/stubby.yml` file, then you simply need to set `option manual '1'` in `/etc/config/stubby` and all other settings in `/etc/config/stubby` will be ignored. ### Stubby port and addresses The default configuration ensures that stubby listens on port 5453 on the loopback interfaces for IPv4 and IPv6. As such, by default, stubby will respond only to lookups from the OpenWRT device itself. By setting the listening ports to non-standard values, this allows users to keep the main name server daemon in place (dnsmasq/unbound/etc.) and have that name server forward to stubby. ### Upstream resolvers The default package configuration uses the CloudFlare resolvers, configured for both IPv4 and IPv6. CloudFlare have not published SPKI pinsets, and even though they are available, they have made no commitment to maintaining them. Using the currently known SPKI pinsets for CloudFlare brings the risk that in the future they may be changed by CloudFlare, and DNS would stop working. The default configuration has those SPKI entries commented out for this reason. [CloudFlare's privacy statement](https://developers.cloudflare.com/1.1.1.1/commitment-to-privacy/) details how they treat data from DNS requests. More resolvers are available in the [upstream stubby example configuration](https://github.com/getdnsapi/stubby/blob/develop/stubby.yml.example) and the [DNS Privacy list](https://dnsprivacy.org/wiki/display/DP/DNS+Privacy+Test+Servers). ## Integration of stubby with dnsmasq The recommended way to use stubby on an OpenWRT device is to integrate it with a caching resolver. The default caching resolver in OpenWRT is dnsmasq. ### Set dnsmasq to send DNS requests to stubby Since dnsmasq responds to LAN DNS requests on port 53 of the OpenWRT device by default, all that is required is to have dnsmasq forward those requests to stubby which is listening on port 5453 of the OpenWRT device. To achieve this, we need to set the `server` option in the dnsmasq configuration in the `/etc/config/dhcp` file to `'127.0.0.1#5453'`. We also need to tell dnsmasq not to use resolvers found in `/etc/resolv.conf` by setting the dnsmasq option `noresolv` to `1` in the same file. This can be achieved by editing the `/etc/config/dhcp` file directly or executing the following commands at the command line: uci add_list dhcp.@dnsmasq[-1].server='127.0.0.1#5453' uci dhcp.@dnsmasq[-1].noresolv=1 uci commit && reload_config The same outcome can be achieved in the LUCI web interface as follows: 1. Select the Network->DHCP and DNS menu entry. 2. In the "General Settings" tab, enter the address `127.0.0.1#5453` as the only entry in the "DNS Forwardings" dialogue. 3. In the "Resolv and Host files" tab tick the "Ignore resolve file" checkbox. ### Disable sending DNS requests to ISP provided DNS servers The configuration changes in the previous section ensure that DNS queries are sent over TLS encrypted connections *once dnsmasq and stubby are started*. When the OpenWRT device is first brought up, there is a possibility that DNS queries can go to ISP provided DNS servers ahead of dnsmasq and stubby being active. In order to mitigate this leakage, it's necessary to ensure that upstream resolvers aren't available, and the only DNS resolver used by the system is dnsmasq+stubby. This requires setting the option `peerdns` to `0` and the option `dns` to the loopback address for both the `wan` and `wan6` interfaces in the `/etc/config/network` file. This can be achieved by editing the `/etc/config/network` file directly, or by executing the following commands: uci set network.wan.peerdns='0' uci set network.wan.dns='127.0.0.1' uci set network.wan6.peerdns='0' uci set network.wan6.dns='0::1' uci commit && reload_config The same outcome can also be achieved using the LUCI web interface as follows: 1. Select the Network->Interfaces menu entry. 2. Click on Edit for the WAN interfaces. 3. Choose the Advanced Settings tab. 4. Unselect the "Use DNS servers advertised by peer" checkbox 5. Enter `127.0.0.1` in the "Use custom DNS servers" dialogue box. 6. Repeat the above steps for the WAN6 interface, but use the address `0::1` instead of `127.0.0.1`. ### Enabling DNSSEC The configuration described above ensures that DNS queries are executed over TLS encrypted links. However, the responses themselves are not validated; DNSSEC provides the ability to validate returned DNS responses, and mitigate against DNS poisoning risks. With the combination of stubby+dnsmasq there are two possible ways to enable DNSSEC: 1. Configure stubby to perform DNSSEC validation, and configure dnsmasq to proxy the DNSSEC data to clients. 2. Configure stubby not to perform DNSSEC validation and configure dnsmasq to require DNSSEC validation. Either option achieves the same outcome, and there appears to be little reason for choosing one over the other other than that the second option is easier to configure in the LUCI web interface. Both options are detailed below, and both require that the `dnsmasq` package on the OpenWRT device is replaced with the `dnsmasq-full` package. That can be achieved by running the following command: opkg install dnsmasq-full --download-only && opkg remove dnsmasq && opkg install dnsmasq-full --cache . && rm *.ipk #### DNSSEC by stubby Configuring stubby to perform DNSSEC validation requires setting the stubby configuration option `dnssec_return_status` to `'1'` in `/etc/config/stubby`, which can be done by editing the file directly or by executing the commands: uci set stubby.global.dnssec_return_status=1 uci commit && reload_config With stubby performing DNSSEC validation, dnsmasq needs to be configured to proxy the DNSSEC data to clients. This requires setting the option `proxydnssec` to 1 in the dnsmasq configuration in `/etc/config/dhcp`. That can be achieved by the following commands: uci set dhcp.@dnsmasq[-1].proxydnssec=1 uci commit && reload_config #### DNSSEC by dnsmasq Configuring dnsmasq to perform DNSSEC validation requires setting the dnsmasq option `dnssec` to `1` in the `/etc/config/dhcp` file. In addition, it is advisable to also set the dnsmasq option `dnsseccheckunsigned` to `1`. this can be achieved by editing the file `/etc/config/dhcp` or by executing the following commands: uci set dhcp.@dnsmasq[-1].dnssec=1 uci set dhcp.@dnsmasq[-1].dnsseccheckunsigned=1 uci commit && reload_config The same options can be set in the LUCI web interface as follows: 1. Select the "Network->DHCP and DNS" menu entry. 2. Select the "Advanced Settings" tab. 3. Ensure both the "DNSSEC" and "DNSSEC check unsigned" check boxes are ticked. #### Validating DNSSEC operation Having configured DNSSEC validation using one of the two approaches above, it's important to check it's actually working. The following command can be used: dig dnssectest.sidn.nl +dnssec +multi @192.168.1.1 This command should return output like the following: ; <<>> DiG 9.11.4-P1-RedHat-9.11.4-5.P1.fc28 <<>> dnssectest.sidn.nl +dnssec +multi @192.168.1.1 ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 26579 ;; flags: qr rd ra ad; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags: do; udp: 512 ;; QUESTION SECTION: ;dnssectest.sidn.nl. IN A ;; ANSWER SECTION: dnssectest.sidn.nl. 14399 IN A 213.136.9.12 dnssectest.sidn.nl. 14399 IN RRSIG A 8 3 14400 ( 20181104071058 20181005071058 42033 sidn.nl. YAQl3tef36M9EQUOmCneHKCCkxox3csLpfUOql5i/6ND zPrQFsNr3g32HPoxOsi+hD2BE5+bEsnARayDSVLyx0qU 6Hpi2rzQ0zGNZZkCJhCsdp3wnM1BWlMgPrCD0iIsJDok +DH5zu+yYufVUdSLQrMqA3MZDFUIqDUqSZuYDF4= ) ;; Query time: 77 msec ;; SERVER: 192.168.1.1#53(192.168.1.1) ;; WHEN: Sat Oct 06 20:36:25 BST 2018 ;; MSG SIZE rcvd: 230 The key thing to note is the `flags: qr rd ra ad` part - the `ad` flag signifies that DNSSEC validation is working. If that flag is absent DNSSEC validation is not working. ## Appendix: stubby configuration options This section details the options available for use in the `/etc/config/stubby` file. The `global` configuration section specifies the configuration parameters for the stubby daemon. One or more `resolver` sections are used to configure upstream resolvers for the stubby daemon to use. ### `global` section options #### `option manual` Specify whether to use this file to configure the stubby service. If this is set to `'1'` stubby will be configured using the file `/etc/stubby/stubby.yml`. If this is set to `'0'`, configuration options will be taken from this file, and the service will be managed through UCI. #### `option trigger` This specifies an interface to trigger stubby start up on; stubby startup will be triggered by a procd signal associated with this interface being ready. If this interface is restarted, stubby will also be restarted. This option can also be set to `'timed'`, in which case a time, specified by the option `triggerdelay`, will be waited before starting stubby. #### `option triggerdelay` If the `trigger` option specifies an interface, this option sets the time that is waited after the procd signal is received before starting stubby. If `trigger` is set to `'timed'` then this is the delay before starting stubby. This option is specified in seconds and defaults to the value `'2'`. #### `list dns_transport` The `dns_transport` list specifies the allowed transports. Allowed values are: `GETDNS_TRANSPORT_UDP`, `GETDNS_TRANSPORT_TCP` and `GETDNS_TRANSPORT_TLS`. The transports are tried in the order listed. #### `option tls_authentication` This option specifies whether TLS authentication is mandatory. A value of `'1'` mandates TLS authentication, and is the default. If this is set to `'0'`, and `GETDNS_TRANSPORT_TCP` or `GETDNS_TRANSPORT_UDP` appears in the `dns_transport` list, stubby is allowed to fall back to non-TLS authenticated lookups. You probably don't want this though. #### `option tls_query_padding_blocksize` This option specifies the block size to pad DNS queries to. You shouldn't need to set this to anything but `'128'` (the default), as recommended by https://tools.ietf.org/html/draft-ietf-dprive-padding-policy-03 #### `option tls_connection_retries` This option specifies the number of connection failures stubby permits before Stubby backs-off from using an individual upstream resolver. You shouldn't need to change this from the default value of `'2'`. #### `option tls_backoff_time` This option specifies the maximum time in seconds Stubby will back-off from using an individual upstream after failures. You shouldn't need to change this from the default value of `'3600'`. #### `option timeout` This option specifies the timeout on getting a response to an individual request. This is specified in milliseconds. You shouldn't need to change this from the default value of ` '5000'`. #### `option dnssec_return_status` This option specifies whether stubby should require DNSSEC validation. Specify to `'1'` to turn on validation, and `'0'` to turn it off. By default it is off. #### `option appdata_dir` This option specifies the location for storing stubby runtime data. In particular, if DNSSEC is turned on, stubby will store its automatically retrieved trust anchor data here. The default value is `'/var/lib/stubby'`. #### `option trust_anchors_backoff_time` When Zero configuration DNSSEC failed, because of network unavailability or failure to write to the appdata directory, stubby will backoff trying to refetch the DNSSEC trust-anchor for a specified amount of time expressed in milliseconds (which defaults to two and a half seconds). #### `option dnssec_trust_anchors` This option sets the location of the file containing the trust anchor data used for DNSSEC validation. If this is not specified, stubby will automatically retrieve a trust anchor at startup. It's unlikely you'll want to manage the trust anchor data manually, so in most cases this is not needed. By default, this is unset. #### `option edns_client_subnet_private` This option specifies whether to enforce ECS client privacy. The default is `'1'`. Set to `'0'` to disable client privacy. For more details see Section 7.1.2 [here](https://tools.ietf.org/html/rfc7871). #### `option idle_timeout` This option specifies the time (in milliseconds) to hold TLS connections open to avoid the overhead of opening a new connection for every query. You should not normally need to change this from the default value (currently `'10000'`). See [here](https://tools.ietf.org/html/rfc7828) for more details. #### `option round_robin_upstreams` This option specifies how stubby will use the upstream DNS resolvers. Set to `'1'` (the default) to instruct stubby to distribute queries across all available name servers - this will use multiple simultaneous connections which can give better performance in most (but not all) cases. Set to `'0'` to treat the upstream resolvers as an ordered list and use a single upstream resolver until it becomes unavailable, then use the next one. #### `list listen_address` This list sets the addresses and ports for the stubby daemon to listen for requests on. the default configuration configures stubby to listen on port 5453 on the loopback interface for both IPv4 and IPv6. #### `option log_level` If set, this option specifies the level of logging from the stubby daemon. By default, this option is not set. The possible levels are: '0': EMERG - System is unusable '1': ALERT - Action must be taken immediately '2': CRIT - Critical conditions '3': ERROR - Error conditions '4': WARN - Warning conditions '5': NOTICE - Normal, but significant, condition '6': INFO - Informational message '7': DEBUG - Debug-level message #### `option command_line_arguments` This option specifies additional command line arguments for stubby daemon. By default, this is an empty string. #### `option tls_cipher_list` If set, this specifies the acceptable ciphers for DNS over TLS. With OpenSSL 1.1.1 this list is for TLS1.2 and older only. Ciphers for TLS1.3 should be set with the `tls_ciphersuites` option. This option can also be given per upstream resolver. By default, this option is not set. #### `option tls_ciphersuites` If set, this specifies the acceptable cipher for DNS over TLS1.3. OpenSSL version 1.1.1 or greater is required for this option. This option can also be given per upstream resolver. By default, this option is not set. #### `option tls_min_version` If set, this specifies the minimum acceptable TLS version. Works with OpenSSL 1.1.1 or greater only. This option can also be given per upstream resolver. By default, this option is not set. #### `option tls_max_version` If set, this specifies the maximum acceptable TLS version. Works with OpenSSL 1.1.1 or greater only. This option can also be given per upstream resolver. By default, this option is not set. ### `resolver` section options #### `option address` This option specifies the resolver IP address, and can either be an IPv4 or an IPv6 address. #### `option tls_auth_name` This option specifies the upstream domain name used for TLS authentication with the supplied server certificate #### `option tls_port` This option specifies the TLS port for the upstream resolver. If not specified, this defaults to 853. #### `option tls_cipher_list` If set, this specifies the acceptable ciphers for DNS over TLS. With OpenSSL 1.1.1 this list is for TLS1.2 and older only. Ciphers for TLS1.3 should be set with the `tls_ciphersuites` option. By default, this option is not set. If set, this overrides the global value. #### `option tls_ciphersuites` If set, this specifies the acceptable cipher for DNS over TLS1.3. OpenSSL version 1.1.1 or greater is required for this option. By default, this option is not set. If set, this overrides the global value. #### `option tls_min_version` If set, this specifies the minimum acceptable TLS version. Works with OpenSSL 1.1.1 or greater only. By default, this option is not set. If set, this overrides the global value. #### `option tls_max_version` If set, this specifies the maximum acceptable TLS version. Works with OpenSSL 1.1.1 or greater only. By default, this options is not set. If set, this overrides the global value. #### `list spki` This list specifies the SPKI pinset which is verified against the keys in the server cerrtificate. The value takes the form `'/value>'`, where the `digest type` is the hashing algorithm used, and the value is the Base64 encoded hash of the public key. At present, only `sha256` is supported for the digest type. This should ONLY be used if the upstream resolver has committed to maintaining the pinset. CloudFlare have made no such commitment, and so we do not specify the SPKI values in the default configuration, even though they are available.