blocker - Domain blocker plugin for CoreDNS

blocker is a CoreDNS plugin which can be used to block a list of domains provided in the AdBlock Plus syntax format. The blocklist will be loaded into memory at start-up and the file’s modified time will be checked periodically. When the blocklist file is updated, the in-memory blocklist will be updated by scanning the blocklist file line-by-line.

Updating the blocklist file itself is beyond the scope of this plugin. I recommend a bash script which downloads common blocklists and updates them into a format without comments. The script blocklist-file-preparer.sh included with this repository is an example of how this can be done using bash and common GNU utilities.

Example blocklist file: (AdBlock Plus syntax)

||buyer.revsci.net^
||ww92.impfr.tradedoubler.com^
||next.chartboost.com^
||pl16442154.alternativecpmgate.com^
||denturesauaid.com^
||pdx-p-con-336.saas.appdynamics.com^
||cdn.ad.citynews.it^
||xxxxxxxamob.acs86.com^
||www.globalhotsale.su^
||zipuploads.com^

Usage

CoreDNS Binary

You can include blocker in the CoreDNS code just as you would include any other CoreDNS plugin.

# Clone coredns to a local location
$ git clone git@github.com:coredns/coredns.git ~/dns-server/coredns

# Clone blocker plugin to a close location
$ git clone git@github.com:icyflame/blocker.git ~/dns-server/blocker

# Symlink blocker location into coredns/plugin/blocker
$ cd ~/dns-server/coredns/plugin
$ ln -s ../blocker ./blocker

# Update plugin.cfg and put the line "blocker:blocker" before the "forward:forward" line

# Build CoreDNS
$ cd ~/dns-server/coredns
$ go generate
$ make
$ ./coredns -conf Corefile

Corefile

The blocker directive inside Corefile requires four arguments. The first argument is the absolute path to the blocklist file. The second argument is the frequency at which the blocklist file is checked for updates. The third argument is the type of blocklist file (hosts and abp are the only two values which are supported at this time.) The fourth argument is the response type from the plugin, either empty for a valid DNS response with 0.0.0.0 or ::6 or nxdomain to respond with a DNS empty response.

The frequency is specified as a string and the value should be a valid argument of the time.ParseDuration function.

blocker /home/user/blocklist_file 1h abp empty

The following is a sample Corefile including the blocker directive. It will block domains that are specified in the blocklist and forward everything else to a full DNS server.

 .:53 {
	metadata

	# prometheus records metrics regarding incoming requests
	prometheus

	# log writes 1 line to the log for every DNS request
	# The last word in the log line will be YES if the request was blocked and NO if it was not
	# blocked.
	# This behaviour is supported by the metadata plugin.
	log . "{common} {/blocker/request-blocked}"

	# blocker blocks domains which are specified in the blocklist
	blocker /home/user/blocklist_file 1h abp empty

	# forward handles any request that is not blocked by blocker
	forward . 127.0.0.1:9053
 }

plugin.cfg

This is a sample middleware configuration file. The order of plugins here is important. This is the order in which plugins will be executed for incoming requests.

metadata:metadata
prometheus:metrics
log:log
blocker:blocker
forward:forward

Interaction with Other CoreDNS Plugins

metadata

The blocker plugin will write the metadata value with the label blocker/request-blocked. This is a boolean value whose value will be either YES (if the request was blocked and the empty IP address was returned as a result to the user) and NO when the request was not blocked.

Release Binaries

For tags which are published to this repository, the GitHub Actions workflow ./.github/workflows/build-binary.yml builds binaries using the latest Go version for Linux under the three most popular architectures: AMD64, ARM (32 bit), and ARM64. The tar.gz files contain a Checksum file which can be used together with sha256sum to verify the integrity of the binary.

$ wget https://github.com/icyflame/blocker/releases/download/v0.0.1-alpha/coredns-linux-amd64.tar.gz
...
coredns-linux-amd64.tar.gz            100%[=======================================================================>]   5.16M   610KB/s    in 14s

2024-07-13 12:26:05 (390 KB/s) - ‘coredns-linux-amd64.tar.gz’ saved [5414731/5414731]

$ tar tvf coredns-linux-amd64.tar.gz
-rwxr-xr-x runner/docker 14110872 2024-07-13 12:26 coredns-linux-amd64
-rw-r--r-- runner/docker       86 2024-07-13 12:26 coredns-linux-amd64.checksum

$ tar zxf coredns-linux-amd64.tar.gz

$ sha256sum -c coredns-linux-amd64.checksum
coredns-linux-amd64: OK

$ ./coredns-linux-amd64 -version
CoreDNS-1.11.1
linux/amd64, go1.22.5, Blocker plugin refs/tags/v0.0.1-alpha 1e6061ee8b7d2ad2ee5c632d3b91851c00481453