feat!: Remove IP verification for domain-literals (#90)

BREAKING CHANGE: messages using domain-literal
  addresses don't require to match the origin
  SMTP connection IP anymore.

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

filtermail/README.md

@@ -37,8 +37,7 @@ depending on address type:
    - **domain** - performs a strict DKIM verification and domain alignment check
    (domain of address from `From` header must exactly match the DKIM signature domain),
    rejecting messages that fail.
-   - **domain-literal (IP address)** - rejects message if the IP in domain-literal of `From` header address
+   - **domain-literal (IP address)** - currently no-op.
-   does not match the origin IP received by `XFORWARD` command.
 5. In case of a DKIM failure,
 the message is saved to `/tmp/filtermail-rejected/dkim-verify` directory for later inspection.
 
@@ -104,9 +103,6 @@ with few considerations:
 
 - Filtermail expects to receive messages from a trusted server,
 and thus should not be exposed directly to the internet.
-- In incoming mode it expects to receive `XFORWARD` commands with the origin IP,
-if the other server doesn't support this, 
-it will lead to rejection of every email using domain-literals in it's `From` header address.
 - Issues outside of chatmail relay context are not necessarily considered bugs;
 PRs fixing them are not guaranteed to be accepted.
 (Trivial changes may still be considered, 

filtermail/src/config.rs

@@ -104,3 +104,25 @@ impl Config {
         NonZeroU32::new(10).expect("10 != 0")
     }
 }
+
+#[cfg(test)]
+impl Default for Config {
+    /// Creates a default configuration with example.org domain.
+    ///
+    /// Used for tests.
+    fn default() -> Self {
+        Self {
+            filtermail_smtp_port: Self::default_filtermail_smtp_port(),
+            filtermail_smtp_port_incoming: Self::default_filtermail_smtp_port_incoming(),
+            postfix_reinject_port: Self::default_postfix_reinject_port(),
+            postfix_reinject_port_incoming: Self::default_postfix_reinject_port_incoming(),
+            max_message_size: Self::default_max_message_size(),
+            max_user_send_per_minute: Self::default_max_user_send_per_minute(),
+            max_user_send_burst_size: Self::default_max_user_send_burst_size(),
+            passthrough_senders: Vec::new(),
+            passthrough_recipients: Vec::new(),
+            mail_domain: "example.org".to_string(),
+            mailboxes_dir: None,
+        }
+    }
+}

filtermail/src/inbound.rs

@@ -27,23 +27,16 @@ impl IncomingBeforeQueueHandler {
         })
     }
 
-    /// Verify the origin of the email either by performing DKIM verification or by matching the FROM
+    /// Verify the origin of the email by performing a DKIM verification on a regular domain.
-    /// domain literal with the origin IP.
+    ///
+    /// Currently a no-op for valid domain-literals.
     async fn verify_origin(&self, envelope: &Envelope, from_addr: &str) -> Result<(), String> {
         let from_domain = AddressDomain::from_str(from_addr).map_err(|e| e.smtp_response())?;
 
         match from_domain {
-            AddressDomain::Literal(ip) => {
+            AddressDomain::Literal(_) => {
-                if !envelope.origin_ip.eq_ignore_ascii_case(&ip) {
+                // Subject to change: we currently don't perform any additional authentication
-                    log::warn!(
+                // for domain-literals and rely purely on encryption.
-                        "Received invalid origin address: {ip}, actual: {}",
-                        envelope.origin_ip
-                    );
-                    return Err(format!(
-                        "500 Invalid FROM domain literal: {ip} does not match origin IP {}",
-                        envelope.origin_ip
-                    ));
-                }
             }
             AddressDomain::Name(domain) => {
                 if !self.skip_dkim
@@ -144,3 +137,35 @@ impl SmtpHandler for IncomingBeforeQueueHandler {
         Ok(())
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use rstest::{fixture, rstest};
+    use testresult::TestResult;
+
+    #[fixture]
+    fn config() -> Config {
+        Config::default()
+    }
+
+    /// Test that domain-literals are not rejected by origin check.
+    #[rstest]
+    #[tokio::test]
+    #[case::ipv4(include_bytes!("../test_data/encrypted-ipv4.eml"), "one@[192.0.2.0]")]
+    #[case::ipv6(include_bytes!("../test_data/encrypted-ipv6.eml"), "one@[IPv6:2001:db8::1]")]
+    async fn test_domain_literals_allowed(
+        #[case] eml: &[u8],
+        #[case] address: &str,
+        config: Config,
+    ) -> TestResult {
+        let handler = IncomingBeforeQueueHandler::new(config, false)?;
+        let mut envelope = Envelope {
+            mail_from: address.to_string(),
+            origin_ip: "".to_string(), // Currently shouldn't be relevant.
+            data: eml.to_vec(),
+            rcpt_to: vec!["does.not.matter@example.org".to_string()],
+        };
+        Ok(handler.check_data(&mut envelope).await?)
+    }
+}

filtermail/test_data/encrypted-ipv4.eml

@@ -0,0 +1,66 @@
+From: one@[192.0.2.0]
+To: two@example.org
+Subject: ...
+Date: Sun, 15 Oct 2023 16:43:21 +0000
+Message-ID: <Mr.UVyJWZmkCKM.hGzNc6glBE_@c2.testrun.org>
+In-Reply-To: <Mr.MvmCz-GQbi_.6FGRkhDf05c@c2.testrun.org>
+References: <Mr.3gckbNy5bch.uK3Hd2Ws6-w@c2.testrun.org>
+	<Mr.MvmCz-GQbi_.6FGRkhDf05c@c2.testrun.org>
+Chat-Version: 1.0
+Autocrypt: addr=one@example.org; prefer-encrypt=mutual;
+	keydata=xjMEZSwWjhYJKwYBBAHaRw8BAQdAQBEhqeJh0GueHB6kF/DUQqYCxARNBVokg/AzT+7LqH
+	rNFzxiYXJiYXpAYzIudGVzdHJ1bi5vcmc+wosEEBYIADMCGQEFAmUsFo4CGwMECwkIBwYVCAkKCwID
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+	IXnYw4CKd55UAwl8Zcy+M2diAbkA/0fHHcGV4r78hpbbL1Os52DPOdqYQRauIeJUeG+G6bQO
+MIME-Version: 1.0
+Content-Type: multipart/encrypted; protocol="application/pgp-encrypted";
+	boundary="YFrteb74qSXmggbOxZL9dRnhymywAi"
+
+
+--YFrteb74qSXmggbOxZL9dRnhymywAi
+Content-Description: PGP/MIME version identification
+Content-Type: application/pgp-encrypted
+
+Version: 1
+
+
+--YFrteb74qSXmggbOxZL9dRnhymywAi
+Content-Description: OpenPGP encrypted message
+Content-Disposition: inline; filename="encrypted.asc";
+Content-Type: application/octet-stream; name="encrypted.asc"
+
+-----BEGIN PGP MESSAGE-----
+
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+lkOWnEbCD+XTnbDd
+=agR5
+-----END PGP MESSAGE-----
+
+
+--YFrteb74qSXmggbOxZL9dRnhymywAi--
+
+

filtermail/test_data/encrypted-ipv6.eml

@@ -0,0 +1,66 @@
+From: one@[IPv6:2001:db8::1]
+To: two@example.org
+Subject: ...
+Date: Sun, 15 Oct 2023 16:43:21 +0000
+Message-ID: <Mr.UVyJWZmkCKM.hGzNc6glBE_@c2.testrun.org>
+In-Reply-To: <Mr.MvmCz-GQbi_.6FGRkhDf05c@c2.testrun.org>
+References: <Mr.3gckbNy5bch.uK3Hd2Ws6-w@c2.testrun.org>
+	<Mr.MvmCz-GQbi_.6FGRkhDf05c@c2.testrun.org>
+Chat-Version: 1.0
+Autocrypt: addr=one@example.org; prefer-encrypt=mutual;
+	keydata=xjMEZSwWjhYJKwYBBAHaRw8BAQdAQBEhqeJh0GueHB6kF/DUQqYCxARNBVokg/AzT+7LqH
+	rNFzxiYXJiYXpAYzIudGVzdHJ1bi5vcmc+wosEEBYIADMCGQEFAmUsFo4CGwMECwkIBwYVCAkKCwID
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+	IXnYw4CKd55UAwl8Zcy+M2diAbkA/0fHHcGV4r78hpbbL1Os52DPOdqYQRauIeJUeG+G6bQO
+MIME-Version: 1.0
+Content-Type: multipart/encrypted; protocol="application/pgp-encrypted";
+	boundary="YFrteb74qSXmggbOxZL9dRnhymywAi"
+
+
+--YFrteb74qSXmggbOxZL9dRnhymywAi
+Content-Description: PGP/MIME version identification
+Content-Type: application/pgp-encrypted
+
+Version: 1
+
+
+--YFrteb74qSXmggbOxZL9dRnhymywAi
+Content-Description: OpenPGP encrypted message
+Content-Disposition: inline; filename="encrypted.asc";
+Content-Type: application/octet-stream; name="encrypted.asc"
+
+-----BEGIN PGP MESSAGE-----
+
+wU4DhW3gBZ/VvCYSAQdA8bMs2spwbKdGjVsL1ByPkNrqD7frpB73maeL6I6SzDYg
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+=agR5
+-----END PGP MESSAGE-----
+
+
+--YFrteb74qSXmggbOxZL9dRnhymywAi--
+
+