Adding DynamicUser to systemd service file, enhancing socket and service (#261)

* Adding nss-lookup.target to the socket Before and Wants directive. Adding current upstream wiki as documentation to service and socket file.
Adding DynamicUser=yes to the service file, alongside various hardening settings (Protect{ControlGroups,KernelModules}. Allowing the service to bind to ports below 1024 by setting CAP_NET_BIND_SERVICE. Adding {Cache,Logs,Runtime}Directory for dnscrypt-proxy. Removing (default) Type=simple. Adding a more default ExecStart location and usage of configuration.

* systemd/dnscrypt-proxy.socket: Adding back ipv6 functionality.

* systemd/dnscrypt-proxy.service: Updating Description to match project name.
Explicitely setting ProtectHome=yes. Adding information on the DynamicUser settings.

* systemd/dnscrypt-proxy.socket: Updating description to match project name.

* systemd/dnscrypt-proxy.service: Adding Requires= and Also= for dnscrypt-proxy.socket in favor of CAP_NET_BIND_SERVICE capabilities.

* dnscrypt-proxy/example-dnscrypt-proxy.toml: Clarifying how to set listen_addresses, when using systemd socket activation.

dnscrypt-proxy/example-dnscrypt-proxy.toml

@@ -26,7 +26,7 @@
 
 
 ## List of local addresses and ports to listen to. Can be IPv4 and/or IPv6.
-## To only use systemd activation sockets, use an empty set: []
+## Note: When using systemd socket activation, choose an empty set (i.e. [] ).
 
 listen_addresses = ['127.0.0.1:53', '[::1]:53']
 

systemd/dnscrypt-proxy.service

@@ -1,27 +1,26 @@
 [Unit]
-Description=DNSCrypt client proxy
-Documentation=man:dnscrypt-proxy(8)
+Description=DNSCrypt-proxy client
+Documentation=https://github.com/jedisct1/dnscrypt-proxy/wiki
 Requires=dnscrypt-proxy.socket
 After=network.target
 Before=nss-lookup.target
 Wants=nss-lookup.target
 
-[Install]
-Also=dnscrypt-proxy.socket
-WantedBy=multi-user.target
-
 [Service]
-Type=simple
 NonBlocking=true
-ProtectHome=true
-
-# Change this
-ExecStart=/opt/dnscrypt-proxy/dnscrypt-proxy
+ExecStart=/usr/bin/dnscrypt-proxy --config /etc/dnscrypt-proxy/dnscrypt-proxy.toml
+ProtectHome=yes
+ProtectControlGroups=yes
+ProtectKernelModules=yes
 
 # Run dnscrypt-proxy as unprivileged user with
 # temporary assigned UID/GID. See man:systemd.exec
 # for more info. Requires systemd 232+.
-#DynamicUser=yes
-#CacheDirectory=dnscrypt-proxy
-#LogsDirectory=dnscrypt-proxy
-#RuntimeDirectory=dnscrypt-proxy
+DynamicUser=yes
+CacheDirectory=dnscrypt-proxy
+LogsDirectory=dnscrypt-proxy
+RuntimeDirectory=dnscrypt-proxy
+
+[Install]
+Also=dnscrypt-proxy.socket
+WantedBy=multi-user.target

systemd/dnscrypt-proxy.socket

@@ -1,5 +1,6 @@
 [Unit]
-Description=dnscrypt-proxy listening socket
+Description=DNSCrypt-proxy socket
+Documentation=https://github.com/jedisct1/dnscrypt-proxy/wiki
 Before=nss-lookup.target
 Wants=nss-lookup.target