feat: replace DKIM verification with filtermail v0.5 (#831)

Upgrade to filtermail v0.5, which has a built-in DKIM verifier
and disable OpenDKIM on reinject_incoming.

Signed-off-by: Jagoda Ślązak <jslazak@jslazak.com>

.github/workflows/ci.yaml

@@ -15,7 +15,7 @@ jobs:
         with:
           ref: ${{ github.event.pull_request.head.sha }}
       - name: download filtermail
-        run: curl -L https://github.com/chatmail/filtermail/releases/download/v0.3.0/filtermail-x86_64 -o /usr/local/bin/filtermail && chmod +x /usr/local/bin/filtermail
+        run: curl -L https://github.com/chatmail/filtermail/releases/download/v0.5.1/filtermail-x86_64 -o /usr/local/bin/filtermail && chmod +x /usr/local/bin/filtermail
       - name: run chatmaild tests 
         working-directory: chatmaild
         run: pipx run tox

chatmaild/src/chatmaild/tests/test_filtermail_blackbox.py

@@ -47,6 +47,8 @@ def test_one_mail(
     make_config, make_popen, smtpserver, maildata, filtermail_mode, monkeypatch
 ):
     monkeypatch.setenv("PYTHONUNBUFFERED", "1")
+    # DKIM is tested by cmdeploy tests.
+    monkeypatch.setenv("FILTERMAIL_SKIP_DKIM", "1")
     smtp_inject_port = 20025
     if filtermail_mode == "outgoing":
         settings = dict(
@@ -64,6 +66,10 @@ def test_one_mail(
 
     popen = make_popen(["filtermail", path, filtermail_mode])
     line = popen.stderr.readline().strip()
+
+    # skip a warning that FILTERMAIL_SKIP_DKIM shouldn't be used in prod
+    if b"DKIM verification DISABLED!" in line:
+        line = popen.stderr.readline().strip()
     if b"loop" not in line:
         print(line.decode("ascii"), file=sys.stderr)
         pytest.fail("starting filtermail failed")

cmdeploy/src/cmdeploy/filtermail/deployer.py

@@ -14,10 +14,10 @@ class FiltermailDeployer(Deployer):
 
     def install(self):
         arch = host.get_fact(facts.server.Arch)
-        url = f"https://github.com/chatmail/filtermail/releases/download/v0.3.0/filtermail-{arch}"
+        url = f"https://github.com/chatmail/filtermail/releases/download/v0.5.1/filtermail-{arch}"
         sha256sum = {
-            "x86_64": "f14a31323ae2dad3b59d3fdafcde507521da2f951a9478cd1f2fe2b4463df71d",
+            "x86_64": "adce2ddb461c5fd744df699f3b0b3c33b6d52413c641f18695b93826e5e0d234",
-            "aarch64": "933770d75046c4fd7084ce8d43f905f8748333426ad839154f0fc654755ef09f",
+            "aarch64": "b51cf4248c6c443308f21b1811da1cc919b98b719a2138f4b60940ea093a5422",
         }[arch]
         self.need_restart |= files.download(
             name="Download filtermail",

cmdeploy/src/cmdeploy/opendkim/deployer.py

@@ -37,21 +37,15 @@ class OpendkimDeployer(Deployer):
         )
         need_restart |= main_config.changed
 
-        screen_script = files.put(
+        screen_script = files.file(
-            src=get_resource("opendkim/screen.lua"),
+            path="/etc/opendkim/screen.lua",
-            dest="/etc/opendkim/screen.lua",
+            present=False,
-            user="root",
-            group="root",
-            mode="644",
         )
         need_restart |= screen_script.changed
 
-        final_script = files.put(
+        final_script = files.file(
-            src=get_resource("opendkim/final.lua"),
+            path="/etc/opendkim/final.lua",
-            dest="/etc/opendkim/final.lua",
+            present=False,
-            user="root",
-            group="root",
-            mode="644",
         )
         need_restart |= final_script.changed
 

cmdeploy/src/cmdeploy/opendkim/final.lua

@@ -1,42 +0,0 @@
-mtaname = odkim.get_mtasymbol(ctx, "{daemon_name}")
-if mtaname == "ORIGINATING" then
-	-- Outgoing message will be signed,
-	-- no need to look for signatures.
-	return nil
-end
-
-nsigs = odkim.get_sigcount(ctx)
-if nsigs == nil then
-	return nil
-end
-
-local valid = false
-local error_msg = "No valid DKIM signature found."
-for i = 1, nsigs do
-	sig = odkim.get_sighandle(ctx, i - 1)
-	sigres = odkim.sig_result(sig)
-
-	-- All signatures that do not correspond to From: 
-	-- were ignored in screen.lua and return sigres -1.
-	-- 
-	-- Any valid signature that was not ignored like this
-	-- means the message is acceptable.
-	if sigres == 0 then
-		valid = true
-    else
-        error_msg = "DKIM signature is invalid, error code " .. tostring(sigres) .. ", search https://github.com/trusteddomainproject/OpenDKIM/blob/master/libopendkim/dkim.h#L108"
-	end
-end
-
-if valid then
-	-- Strip all DKIM-Signature headers after successful validation
-	-- Delete in reverse order to avoid index shifting.
-	for i = nsigs, 1, -1 do
-		odkim.del_header(ctx, "DKIM-Signature", i)
-	end
-else
-	odkim.set_reply(ctx, "554", "5.7.1", error_msg)
-	odkim.set_result(ctx, SMFIS_REJECT)
-end
-
-return nil

cmdeploy/src/cmdeploy/opendkim/opendkim.conf

@@ -45,12 +45,6 @@ SignHeaders *,+autocrypt,+content-type
 # Default is empty.
 OversignHeaders from,reply-to,subject,date,to,cc,resent-date,resent-from,resent-sender,resent-to,resent-cc,in-reply-to,references,list-id,list-help,list-unsubscribe,list-subscribe,list-post,list-owner,list-archive,autocrypt
 
-# Script to ignore signatures that do not correspond to the From: domain.
-ScreenPolicyScript /etc/opendkim/screen.lua
-
-# Script to reject mails without a valid DKIM signature.
-FinalPolicyScript /etc/opendkim/final.lua
-
 # In Debian, opendkim runs as user "opendkim". A umask of 007 is required when
 # using a local socket with MTAs that access the socket as a non-privileged
 # user (for example, Postfix). You may need to add user "postfix" to group

cmdeploy/src/cmdeploy/opendkim/screen.lua

@@ -1,21 +0,0 @@
--- Ignore signatures that do not correspond to the From: domain.
-
-from_domain = odkim.get_fromdomain(ctx)
-if from_domain == nil then
-	return nil
-end
-
-n = odkim.get_sigcount(ctx)
-if n == nil then
-	return nil
-end
-
-for i = 1, n do
-	sig = odkim.get_sighandle(ctx, i - 1)
-	sig_domain = odkim.sig_getdomain(sig)
-	if from_domain ~= sig_domain then
-		odkim.sig_ignore(sig)
-	end
-end
-
-return nil

cmdeploy/src/cmdeploy/postfix/master.cf.j2

@@ -86,7 +86,6 @@ filter    unix -        n       n       -       -       lmtp
 # Local SMTP server for reinjecting incoming filtered mail 
 127.0.0.1:{{ config.postfix_reinject_port_incoming }} inet  n       -       n       -       100      smtpd
   -o syslog_name=postfix/reinject_incoming
-  -o smtpd_milters=unix:opendkim/opendkim.sock
 
 # Cleanup `Received` headers for authenticated mail
 # to avoid leaking client IP.

cmdeploy/src/cmdeploy/tests/online/test_1_basic.py

@@ -147,7 +147,7 @@ def test_reject_missing_dkim(cmsetup, maildata, from_addr):
     conn.starttls()
 
     with conn as s:
-        with pytest.raises(smtplib.SMTPDataError, match="No valid DKIM signature"):
+        with pytest.raises(smtplib.SMTPDataError, match="No DKIM signature found"):
             s.sendmail(from_addr=from_addr, to_addrs=recipient.addr, msg=msg)