feat(dkim): Replace OpenDKIM with DKIM Milter

.github/workflows/test-and-deploy-ipv4only.yaml

@@ -80,7 +80,7 @@ jobs:
 
       - name: set DNS entries
         run: |
-          ssh -o StrictHostKeyChecking=accept-new -v root@staging-ipv4.testrun.org chown opendkim:opendkim -R /etc/dkimkeys
+          ssh -o StrictHostKeyChecking=accept-new -v root@staging-ipv4.testrun.org chown dkim-milter:dkim-milter -R /etc/dkimkeys
           cmdeploy dns --zonefile staging-generated.zone
           cat staging-generated.zone >> .github/workflows/staging-ipv4.testrun.org-default.zone
           cat .github/workflows/staging-ipv4.testrun.org-default.zone

.github/workflows/test-and-deploy.yaml

@@ -82,7 +82,7 @@ jobs:
 
       - name: set DNS entries
         run: |
-          ssh -o StrictHostKeyChecking=accept-new root@staging2.testrun.org chown opendkim:opendkim -R /etc/dkimkeys
+          ssh -o StrictHostKeyChecking=accept-new root@staging2.testrun.org chown dkim-milter:dkim-milter -R /etc/dkimkeys
           cmdeploy dns --zonefile staging-generated.zone --verbose
           cat staging-generated.zone >> .github/workflows/staging.testrun.org-default.zone
           cat .github/workflows/staging.testrun.org-default.zone

cmdeploy/src/cmdeploy/deployers.py

@@ -25,11 +25,11 @@
     configure_remote_units,
     get_resource,
 )
+from .dkim_milter.deployer import DkimMilterDeployer
 from .dovecot.deployer import DovecotDeployer
 from .filtermail.deployer import FiltermailDeployer
 from .mtail.deployer import MtailDeployer
 from .nginx.deployer import NginxDeployer
-from .opendkim.deployer import OpendkimDeployer
 from .postfix.deployer import PostfixDeployer
 from .www import build_webpages, find_merge_conflict, get_paths
 
@@ -572,7 +572,7 @@ def deploy_chatmail(config_path: Path, disable_mail: bool, website_only: bool) -
         WebsiteDeployer(config),
         ChatmailVenvDeployer(config),
         MtastsDeployer(),
-        OpendkimDeployer(mail_domain),
+        DkimMilterDeployer(mail_domain),
         # Dovecot should be started before Postfix
         # because it creates authentication socket
         # required by Postfix.

cmdeploy/src/cmdeploy/dkim_milter/deployer.py

@@ -0,0 +1,169 @@
+"""
+Installs DKIM Milter.
+"""
+
+from pyinfra import facts, host
+from pyinfra.facts.files import File, Sha256File
+from pyinfra.operations import apt, files, server, systemd
+
+from cmdeploy.basedeploy import Deployer, get_resource
+
+
+class DkimMilterDeployer(Deployer):
+    required_users = [("dkim-milter", None, ["dkim-milter"])]
+
+    def __init__(self, mail_domain):
+        self.mail_domain = mail_domain
+        self.need_restart = False
+
+    def install(self):
+        """Builds and installs dkim-milter"""
+
+        # openssl is required to generate the signing key
+        apt.packages(
+            name="Install openssl required by DKIM Milter",
+            packages=["openssl"],
+        )
+
+        (url, sha256sum) = {
+            "x86_64": (
+                "https://github.com/chatmail/dkim-milter/releases/download/0.1.0/dkim-milter-x86_64",
+                "e676837b362ebef461881079e3e1151ed2db2d942d98b7103974921ac69ce5de",
+            ),
+            "aarch64": (
+                "https://github.com/chatmail/dkim-milter/releases/download/0.1.0/dkim-milter-aarch64",
+                "b853ab85a535b7e7e548ae0e4d85a61d4c0fd44f2912c3439662c56ca8a369e6",
+            ),
+        }[host.get_fact(facts.server.Arch)]
+
+        existing_sha256sum = host.get_fact(Sha256File, "/usr/local/sbin/dkim-milter")
+        if existing_sha256sum != sha256sum:
+            server.shell(
+                name="Download DKIM Milter",
+                commands=[
+                    f"(curl -L {url} >/usr/local/sbin/dkim-milter.new && (echo '{sha256sum} /usr/local/sbin/dkim-milter.new' | sha256sum -c) && mv /usr/local/sbin/dkim-milter.new /usr/local/sbin/dkim-milter)",
+                    "chmod 755 /usr/local/sbin/dkim-milter",
+                ],
+            )
+            self.need_restart = True
+
+    def configure(self):
+        """Configures dkim-milter"""
+
+        domain = self.mail_domain
+        # note - we are using "opendkim" for backward compatibility
+        # for relays that were set up before we migrated from OpenDKIM
+        # to DKIM Milter.
+        selector = "opendkim"
+        signing_key_name = selector
+        # for backward compatibility with opendkim-genkey
+        signing_key_filename = f"{signing_key_name}.private"
+        config_common = {
+            "domain": domain,
+            "selector": selector,
+            "signing_key_name": signing_key_name,
+            "signing_key_filename": signing_key_filename,
+        }
+        config_verify = {
+            **config_common,
+            "mode": "verify",
+            "config_file": "/etc/dkim-milter/dkim-milter-verify.conf",
+            "socket_name": "dkim-milter-verify.sock",
+        }
+        config_sign = {
+            **config_common,
+            "mode": "sign",
+            "config_file": "/etc/dkim-milter/dkim-milter-sign.conf",
+            "socket_name": "dkim-milter-sign.sock",
+        }
+
+        self.need_restart |= files.directory(
+            name="Create a directory for DKIM Milter configs",
+            path="/etc/dkim-milter",
+            user="dkim-milter",
+            group="dkim-milter",
+            mode="750",
+            present=True,
+        ).changed
+
+        for config in [config_verify, config_sign]:
+            self.need_restart |= files.template(
+                src=get_resource("dkim_milter/dkim-milter.conf.j2"),
+                dest=config["config_file"],
+                user="dkim-milter",
+                group="dkim-milter",
+                mode="644",
+                config=config,
+            ).changed
+
+        self.need_restart |= files.directory(
+            name="Create dkimkeys directory",
+            path="/etc/dkimkeys",
+            user="dkim-milter",
+            group="dkim-milter",
+            mode="750",
+            present=True,
+        ).changed
+
+        self.need_restart |= files.template(
+            src=get_resource("dkim_milter/signing-keys"),
+            dest="/etc/dkim-milter/signing-keys",
+            user="dkim-milter",
+            group="dkim-milter",
+            mode="644",
+            config=config_common,
+        ).changed
+
+        self.need_restart |= files.template(
+            src=get_resource("dkim_milter/signing-senders"),
+            dest="/etc/dkim-milter/signing-senders",
+            user="dkim-milter",
+            group="dkim-milter",
+            mode="644",
+            config=config_common,
+        ).changed
+
+        self.need_restart |= files.directory(
+            name="Create DKIM Milter unix sockets directory",
+            path="/var/spool/postfix/dkim-milter",
+            user="dkim-milter",
+            group="dkim-milter",
+            mode="770",
+        ).changed
+
+        if not host.get_fact(File, f"/etc/dkimkeys/{signing_key_filename}"):
+            server.shell(
+                name=f"Generate DKIM Milter signing key '{signing_key_name}'",
+                commands=[
+                    f"openssl genpkey -algorithm RSA -out /etc/dkimkeys/{signing_key_filename}"
+                ],
+            )
+            self.need_restart = True
+
+        # enforce restrictive permissions for the signing key
+        self.need_restart |= files.file(
+            path=f"/etc/dkimkeys/{signing_key_filename}",
+            present=True,
+            user="dkim-milter",
+            group="dkim-milter",
+            mode="0400",
+        ).changed
+
+        self.need_restart |= files.put(
+            name="Create dkim-milter service",
+            src=get_resource("dkim_milter/dkim-milter@.service"),
+            dest=f"/etc/systemd/system/dkim-milter@.service",
+        ).changed
+
+    def activate(self):
+        """Start and enable DKIM Milter"""
+        for mode in ["sign", "verify"]:
+            systemd.service(
+                name=f"Start and enable DKIM Milter in {mode} mode",
+                service=f"dkim-milter@{mode}",
+                running=True,
+                enabled=True,
+                daemon_reload=self.need_restart,
+                restarted=self.need_restart,
+            )
+            self.need_restart = False

cmdeploy/src/cmdeploy/dkim_milter/dkim-milter.conf.j2

@@ -0,0 +1,30 @@
+mode = {{ config.mode }}
+
+{% if config.mode == "verify" %}
+# DKIM milter will skip verification for trusted sources,
+# which in our case is everything, since we run DKIM milter on a reinjection port,
+# and all connections are local.
+# We force verification for local connections by not trusting anyone.
+trusted_networks =
+{% endif %}
+
+log_destination = syslog
+log_level = info
+
+canonicalization = relaxed/simple
+
+lookup_timeout = 60s
+
+signing_keys = /etc/dkim-milter/signing-keys
+signing_senders = /etc/dkim-milter/signing-senders
+
+# Signing
+sign_headers = default; autocrypt:content-type
+oversign_headers = signed-extended
+
+# Verification
+required_signed_headers = From*
+forbid_unsigned_content = yes
+reject_failures = missing, no-pass, author-mismatch
+
+socket = unix:/var/spool/postfix/dkim-milter/{{ config.socket_name }}

cmdeploy/src/cmdeploy/dkim_milter/dkim-milter@.service

@@ -0,0 +1,15 @@
+[Unit]
+Description=DKIM Milter %i
+Documentation=man:dkim-milter(8) man:dkim-milter.conf(5)
+After=network-online.target nss-lookup.target
+Wants=network-online.target
+
+[Service]
+User=dkim-milter
+UMask=007
+ExecStart=/usr/local/sbin/dkim-milter -c /etc/dkim-milter/dkim-milter-%i.conf
+ExecReload=/bin/kill -HUP $MAINPID
+Restart=on-failure
+
+[Install]
+WantedBy=multi-user.target

cmdeploy/src/cmdeploy/dkim_milter/signing-keys

@@ -0,0 +1,2 @@
+# Key name                       Signing key
+{{ config.signing_key_name }}    </etc/dkimkeys/{{ config.signing_key_filename }}

cmdeploy/src/cmdeploy/dkim_milter/signing-senders

@@ -0,0 +1,2 @@
+# Sender expression    Domain                 Selector                 Key name
+.{{ config.domain }}   {{ config.domain }}    {{ config.selector }}    {{ config.signing_key_name }}