crates/smtp/src/outbound/dane/dnssec.rs

@@ -2,6 +2,8 @@
  * SPDX-FileCopyrightText: 2020 Stalwart Labs LLC <[email protected]>
  *
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
+ *
+ * Modified by Coffey Labs in 2026 for INBUXA.
  */
 
 use common::{
@@ -13,6 +15,8 @@ use mail_auth::{
     MX, RecordSet,
     common::resolver::ToFqdn,
     hickory_resolver::{
+        TokioResolver,
+        lookup::Lookup,
         net::{DnsError, NetError},
         proto::{
             dnssec::Proof,
@@ -83,16 +87,15 @@ impl TlsaLookup for Server {
             return mail_auth::common::resolver::mock_resolve(key.as_ref());
         }
 
-        let mx_lookup = match self
-            .core
-            .smtp
-            .resolvers
-            .dnssec
-            .resolver
-            .mx_lookup(Name::from_str_relaxed::<&str>(key.as_ref())?)
-            .await
+        let (mx_lookup, forced_insecure) = match validated_lookup(
+            &self.core.smtp.resolvers.dnssec.resolver,
+            self.core.smtp.resolvers.dns.resolver(),
+            Name::from_str_relaxed::<&str>(key.as_ref())?,
+            RecordType::MX,
+        )
+        .await
         {
-            Ok(mx_lookup) => mx_lookup,
+            Ok(validated) => (validated.lookup, validated.insecure),
             Err(err) => {
                 if let Some(denial) = NegativeAnswer::from_error(&err)
                     && denial.response_code == ResponseCode::NoError
@@ -144,7 +147,11 @@ impl TlsaLookup for Server {
             .collect::<Arc<[MX]>>();
         let records = RecordSet {
             rrset,
-            dnssec_status: dnssec_status.unwrap_or(DnssecStatus::Indeterminate),
+            dnssec_status: if forced_insecure {
+                DnssecStatus::Insecure
+            } else {
+                dnssec_status.unwrap_or(DnssecStatus::Indeterminate)
+            },
         };
 
         self.inner
@@ -285,16 +292,15 @@ impl TlsaLookup for Server {
         }
 
         let name = Name::from_str_relaxed::<&str>(key.as_ref())?;
-        let lookup = match self
-            .core
-            .smtp
-            .resolvers
-            .dnssec
-            .resolver
-            .ipv4_lookup(name.clone())
-            .await
+        let (lookup, forced_insecure) = match validated_lookup(
+            &self.core.smtp.resolvers.dnssec.resolver,
+            self.core.smtp.resolvers.dns.resolver(),
+            name.clone(),
+            RecordType::A,
+        )
+        .await
         {
-            Ok(lookup) => lookup,
+            Ok(validated) => (validated.lookup, validated.insecure),
             Err(err) => {
                 if let Some(denial) = NegativeAnswer::from_error(&err)
                     && denial.response_code == ResponseCode::NoError
@@ -325,7 +331,11 @@ impl TlsaLookup for Server {
                     _ => None,
                 })
                 .collect::<Arc<[Ipv4Addr]>>(),
-            dnssec_status: tlsa_base_status(&name, answers, RecordType::A),
+            dnssec_status: if forced_insecure {
+                DnssecStatus::Insecure
+            } else {
+                tlsa_base_status(&name, answers, RecordType::A)
+            },
         };
 
         self.inner
@@ -363,16 +373,15 @@ impl TlsaLookup for Server {
         }
 
         let name = Name::from_str_relaxed::<&str>(key.as_ref())?;
-        let lookup = match self
-            .core
-            .smtp
-            .resolvers
-            .dnssec
-            .resolver
-            .ipv6_lookup(name.clone())
-            .await
+        let (lookup, forced_insecure) = match validated_lookup(
+            &self.core.smtp.resolvers.dnssec.resolver,
+            self.core.smtp.resolvers.dns.resolver(),
+            name.clone(),
+            RecordType::AAAA,
+        )
+        .await
         {
-            Ok(lookup) => lookup,
+            Ok(validated) => (validated.lookup, validated.insecure),
             Err(err) => {
                 if let Some(denial) = NegativeAnswer::from_error(&err)
                     && denial.response_code == ResponseCode::NoError
@@ -403,7 +412,11 @@ impl TlsaLookup for Server {
                     _ => None,
                 })
                 .collect::<Arc<[Ipv6Addr]>>(),
-            dnssec_status: tlsa_base_status(&name, answers, RecordType::AAAA),
+            dnssec_status: if forced_insecure {
+                DnssecStatus::Insecure
+            } else {
+                tlsa_base_status(&name, answers, RecordType::AAAA)
+            },
         };
 
         self.inner
@@ -415,6 +428,115 @@ impl TlsaLookup for Server {
     }
 }
 
+// inbuxa: hickory 0.26.3 calls some valid answers bogus, and the queue then
+// retries those hosts until the message expires. Two cases seen in production:
+//
+// - A zone delegated beneath an unsigned zone, such as `l.google.com` under
+//   `google.com`. To prove the delegation insecure, hickory wants an SOA
+//   record in the DS reply, and public resolvers often send none.
+// - A signed CNAME to a signed name without the record type queried. Hickory
+//   checks the denial of existence against the name first asked for, not the
+//   target's, and rejects it.
+//
+// When hickory says bogus, check the answer again with lookups it gets right.
+// A signed CNAME is followed and the lookup repeated at its target. Otherwise
+// the name's zone and its parents are looked up, nearest first. If one
+// validates as unsigned, nothing below it can be signed, so the plain resolver
+// answers and the result is insecure. If one validates as signed first, the
+// verdict stands.
+
+const MAX_BOGUS_ALIASES: usize = 8;
+
+struct ValidatedLookup {
+    lookup: Lookup,
+    insecure: bool,
+}
+
+enum BogusRecheck {
+    Alias(Name),
+    Insecure,
+    Bogus,
+}
+
+async fn validated_lookup(
+    dnssec: &TokioResolver,
+    plain: &TokioResolver,
+    name: Name,
+    record_type: RecordType,
+) -> Result<ValidatedLookup, NetError> {
+    let mut query = name;
+    let mut aliases = 0;
+
+    loop {
+        let err = match dnssec.lookup(query.clone(), record_type).await {
+            Ok(lookup) => {
+                return Ok(ValidatedLookup {
+                    lookup,
+                    insecure: false,
+                });
+            }
+            Err(err @ NetError::Dns(DnsError::DnssecBogus)) => err,
+            Err(err) => return Err(err),
+        };
+
+        match recheck_bogus(dnssec, &query).await {
+            BogusRecheck::Alias(target) if aliases < MAX_BOGUS_ALIASES => {
+                aliases += 1;
+                query = target;
+            }
+            BogusRecheck::Insecure => {
+                return plain
+                    .lookup(query, record_type)
+                    .await
+                    .map(|lookup| ValidatedLookup {
+                        lookup,
+                        insecure: true,
+                    });
+            }
+            BogusRecheck::Alias(_) | BogusRecheck::Bogus => return Err(err),
+        }
+    }
+}
+
+async fn recheck_bogus(dnssec: &TokioResolver, name: &Name) -> BogusRecheck {
+    if let Ok(lookup) = dnssec.lookup(name.clone(), RecordType::CNAME).await
+        && let Some(target) = secure_alias(name, lookup.answers())
+    {
+        return BogusRecheck::Alias(target);
+    }
+
+    let mut zone = name.clone();
+    while !zone.is_root() {
+        if let Ok(lookup) = dnssec.lookup(zone.clone(), RecordType::SOA).await {
+            match apex_status(&zone, lookup.answers()) {
+                Some(DnssecStatus::Insecure) => return BogusRecheck::Insecure,
+                Some(DnssecStatus::Secure) => return BogusRecheck::Bogus,
+                _ => {}
+            }
+        }
+        zone = zone.base_name();
+    }
+
+    BogusRecheck::Bogus
+}
+
+fn secure_alias(query: &Name, answers: &[Record]) -> Option<Name> {
+    answers.iter().find_map(|record| match &record.data {
+        RData::CNAME(target) if &record.name == query && record.proof.is_secure() => {
+            Some(target.0.clone())
+        }
+        _ => None,
+    })
+}
+
+fn apex_status(zone: &Name, answers: &[Record]) -> Option<DnssecStatus> {
+    answers
+        .iter()
+        .filter(|record| record.record_type() == RecordType::SOA && &record.name == zone)
+        .map(|record| proof_to_dnssec_status(record.proof))
+        .reduce(least_secure)
+}
+
 struct NegativeAnswer {
     response_code: ResponseCode,
     dnssec_status: DnssecStatus,
@@ -511,7 +633,7 @@ pub(crate) fn least_secure(a: DnssecStatus, b: DnssecStatus) -> DnssecStatus {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use mail_auth::hickory_resolver::proto::rr::rdata::{A, CNAME};
+    use mail_auth::hickory_resolver::proto::rr::rdata::{A, CNAME, SOA};
     use std::net::Ipv4Addr;
 
     fn name(value: &str) -> Name {
@@ -624,4 +746,127 @@ mod tests {
             DnssecStatus::Insecure
         );
     }
+
+    fn soa(owner: &str, proof: Proof) -> Record {
+        let mut record = Record::from_rdata(
+            name(owner),
+            3600,
+            RData::SOA(SOA::new(
+                name("ns1.example.org."),
+                name("hostmaster.example.org."),
+                1,
+                900,
+                900,
+                1800,
+                60,
+            )),
+        );
+        record.proof = proof;
+        record
+    }
+
+    #[test]
+    fn secure_alias_follows_signed_cname() {
+        assert_eq!(
+            secure_alias(
+                &name("mail.example.org."),
+                &[alias("mail.example.org.", "mx.example.net.", Proof::Secure)]
+            ),
+            Some(name("mx.example.net."))
+        );
+    }
+
+    #[test]
+    fn secure_alias_ignores_unsigned_or_other_cname() {
+        let query = name("mail.example.org.");
+
+        assert_eq!(
+            secure_alias(
+                &query,
+                &[alias(
+                    "mail.example.org.",
+                    "mx.example.net.",
+                    Proof::Insecure
+                )]
+            ),
+            None
+        );
+        assert_eq!(
+            secure_alias(
+                &query,
+                &[alias(
+                    "other.example.org.",
+                    "mx.example.net.",
+                    Proof::Secure
+                )]
+            ),
+            None
+        );
+    }
+
+    #[test]
+    fn apex_status_reads_the_zone_soa() {
+        let zone = name("example.com.");
+
+        for (proof, expected) in [
+            (Proof::Secure, Some(DnssecStatus::Secure)),
+            (Proof::Insecure, Some(DnssecStatus::Insecure)),
+            (Proof::Bogus, Some(DnssecStatus::Bogus)),
+        ] {
+            assert_eq!(
+                apex_status(&zone, &[soa("example.com.", proof)]),
+                expected,
+                "proof {proof}"
+            );
+        }
+    }
+
+    #[test]
+    fn apex_status_ignores_other_records() {
+        assert_eq!(
+            apex_status(
+                &name("example.com."),
+                &[
+                    soa("sub.example.com.", Proof::Insecure),
+                    address("example.com.", Proof::Insecure),
+                ]
+            ),
+            None
+        );
+    }
+
+    // Needs the network: a signed MX pointing into a zone delegated beneath an
+    // unsigned one. Run with `--ignored` to check a hickory upgrade.
+    #[tokio::test]
+    #[ignore]
+    async fn validated_lookup_proves_delegation_below_unsigned_zone() {
+        use mail_auth::hickory_resolver::{
+            config::{CLOUDFLARE, ResolverConfig, ResolverOpts},
+            net::runtime::TokioRuntimeProvider,
+        };
+
+        let build = |validate: bool| {
+            // Same options as the server's DNSSEC resolver; hickory fails
+            // validation with concurrent requests.
+            let mut opts = ResolverOpts::default();
+            opts.validate = validate;
+            opts.num_concurrent_reqs = 1;
+            opts.cache_size = 0;
+            TokioResolver::builder_with_config(
+                ResolverConfig::udp_and_tcp(&CLOUDFLARE),
+                TokioRuntimeProvider::default(),
+            )
+            .with_options(opts)
+            .build()
+            .unwrap()
+        };
+        let (dnssec, plain) = (build(true), build(false));
+
+        let validated =
+            validated_lookup(&dnssec, &plain, name("aspmx.l.google.com."), RecordType::A)
+                .await
+                .unwrap();
+        assert!(validated.insecure);
+        assert!(!validated.lookup.answers().is_empty());
+    }
 }