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fix(minimald): refuse a deny-all box's names outside the zone at its relay - #2013
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…relay A deny-all box's query to its resolver for any name outside the box zone, of any record type, is answered REFUSED by the relay's DNS gate and never written on to the switch, so no resolver beyond the one Minimal owns for the box sees the name. Zone names, host.min.internal among them, pass as before. Deny-all is the classifier's admits_nothing shape, the section EgressPolicy::deny_all materializes. Allow-list and allow-all boxes are unchanged.
The own-address deny-all stand-in now declares --deny-all-egress, the section the in-force default materializes, and asserts on the wire that names outside the box zone are answered REFUSED, that a lookup fails inside the resolver timeout, that host.min.internal still resolves, and that TCP 53 to the resolver is silently dropped. The stand-in's GET now requires the resolver refusal.
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📝 WalkthroughWalkthroughThe DNS gate now detects deny-all policies and handles queries locally when required. DNS zone checks use parsed labels. Unit, relay, and session checks cover DNS responses, forwarded queries, and TCP port 53 behavior. ChangesDeny-all DNS behavior
Priority: ➖ Normal Estimated code review effort: 3 (Moderate) | ~25 minutes Change: Bug fix Sequence Diagram(s)sequenceDiagram
participant DNSClient
participant DnsGate
participant SwitchResolver
DNSClient->>DnsGate: Send DNS query
alt Deny-all policy and any name is outside switch-resolved zone
DnsGate-->>DNSClient: Return REFUSED
else Name belongs to zone but switch resolver would forward it upstream
DnsGate-->>DNSClient: Return NXDOMAIN
else Zone query includes a non-A question
DnsGate-->>DNSClient: Return NODATA
else Eligible zone A query
DnsGate->>SwitchResolver: Forward query
SwitchResolver-->>DnsGate: Return DNS response
DnsGate-->>DNSClient: Return DNS response
end
Suggested reviewers: Merge Risk: 🔵 Low · up to DNS responses remain supported by the available evidence, but misleading logs could slow diagnosis of some multi-question queries. The change is mergeable with awareness of that bounded issue. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches📝 Generate docstrings
🧪 Generate unit tests (beta)
A rabbit taps a DNS key Comment |
…one A The switch's resolver answers a zone name locally only for type A, and only on an exact, case-sensitive ".min.internal." suffix. Every other type, an upper-case zone suffix, and the apex itself are sent on to the host's resolvers, so a deny-all box could carry data out in a name like TXT <data>.min.internal. For a deny-all box the relay gate now counts a name as the zone only when it sits strictly below the apex and its last two labels are exactly the lowercase "min" and "internal"; anything else is REFUSED. A zone query with any question that is not an A is answered NODATA at the gate, its id and questions kept, and never written to the switch. REFUSED wins over NODATA in a mixed query. is_zone_name now matches by labels, not by string suffix, so a label holding an escaped dot (evil\.min under internal) is not the zone.
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Approved: no findings at Nothing to do. Clobber: none. |
…sed-at-box-gate # Conflicts: # crates/minimald/src/net/dns_gate.rs
…itch forwards The box's resolver (gvproxy) walks every question in a query, so the NET-136 and NET-006 NODATA rules now read every question, not only the first: an A for an outside name in front no longer carries a zone TXT upstream. The resolver also matches the zone by a case-sensitive suffix and never answers the apex, so x.MIN.INTERNAL and min.internal went upstream. Any zone name it would forward is now answered NXDOMAIN at the relay, so no zone name is answered from off the machine (NET-006). Replies echo every question.
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Inline comments:
Review comments at @crates/minimald/src/net/dns_gate.rs:
- Around line 540-542: Update the `answer` decision branches so each log uses
the question that triggered its result, rather than the first question in
`query.queries`. Replace the matching `any` checks in the REFUSED, NXDOMAIN, and
NODATA paths with `find`, then pass the matched question’s normalized name and
query type to `answer`.
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crates/minimald/src/net/dns_gate.rs
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/revise fix ci and resolve code review concerns |
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The run failed: git: git push origin HEAD:refs/heads/fix/deny-all-dns-refused-at-box-gate exited 1: To http://127.0.0.1:8901/git/gominimal/minimal branch Updated 2026-10-07T03:13:00.818Z. |
…abels The relay's log line now names the question that decided its answer, not the first one. The NODATA rule's zone test matches the parsed name's labels, as the switch-answered test does, so a non-ASCII label below the zone is still the zone and its non-A query is never forwarded.
…-all resolver test
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✅ Action performedComments resolved and changes approved. |
Summary
A deny-all box's DNS query for any name outside the box zone, of any record type, is now answered REFUSED (rcode 5) by the box's relay DNS gate. The query is never written on to the switch, so no resolver beyond the one Minimal owns for the box sees the name. A zone query passes only when every question is an A for a name the switch answers itself (strictly below the apex, exact lowercase
min.internalsuffix),host.min.internalamong them. Any other zone type gets NODATA at the gate. This is slice 1 of 3 of the deny-all case. It covers own-address deny-all boxes on native and VM-backed hosts.Requirements
allow_dns_hosts, so every name outside the zone is unmatched. The relay test carries NET-141's verify name,unmatched_name_refused_without_upstream_forward.allow_dns_hostsentry. That includeshost.min.internal(NET-003).Design
admits_nothingshape: everyallow_*dimension is present and empty. That is the sectionEgressPolicy::deny_all()builds, andeffective_session_policymapsEffectiveEgress::DenyAllto it.--deny-all-egressdeclares the same section. The function becomespub(crate), so the gate and the classifier read the same predicate, and the box the classifier puts underdenyis the box whose names the gate refuses.DnsGate::newcomputesdeny_allonce, from the effective policy the gate is built with.DnsGate::intercept_queryalready answers NET-136's AAAA/HTTPS/SVCB NODATA ahead of the switch. For a deny-all box it now checks first whether any question names something outside the zone (super::dns::is_zone_name). If one does, it answers REFUSED with the query's id and questions. Checking every question means a zone name placed first cannot carry a second name out. The relay's existing interception path writes the reply back toward the box and skips both the switch write and the conntrack record, so no onward query is sent and no reply window opens.pkg/services/dns/dns.go) answers a zone name locally only for type A, and only on an exact, case-sensitive.min.internal.suffix. Any other type, an upper-case suffix, and the apex itself go on to the host's resolvers. So for a deny-all box the gate counts a name as the zone only when it sits strictly below the apex and its last two labels are exactly the lowercaseminandinternal.x.MIN.INTERNALandmin.internalget REFUSED. Labels below the zone may have any case.dns::is_zone_namenow matches by labels (hickoryName::zone_of), not by string suffix. A single label holding an escaped dot,evil\.minunderinternal, renders asevil\.min.internalbut is not the zone. This applies to every caller: the pinning gate's allowlist and its zone-answer check too.sessions::core::egress::verdictis UDP-only, so for a deny-all box a TCP frame to the gateway's port 53 falls through to the box's emptyallow_protocolsand is dropped silently.deny_all_still_reaches_the_resolverinsessionsalready asserts this at the verdict, and the e2e below asserts it end to end.Merge with main and follow-ups
maingained #2019 (NET-006: NODATA for non-A queries on box-zone names), which edits the sameDnsGate::intercept_query. The merge commit keeps this PR's deny-all check first (REFUSED outside the zone, NODATA for zone non-A), then fix(minimald): answer NODATA for non-A queries on box-zone names #2019's NODATA rule for every other box, and keeps this PR's label-wiseis_zone_name. Both PRs' tests are kept.[A example.com, TXT x.min.internal]still sent the zone name upstream. The NET-136 and NET-006 NODATA rules now read every question, as the deny-all path already did, and every reply the gate writes echoes every question. Test:every_question_is_read_for_nodata..min.internal.suffix strictly below the apex, whileis_zone_nameis case-insensitive. Sox.MIN.INTERNALand the apexmin.internalwent upstream for every box. NET-006 says zone names are never answered from off the machine. For any box, a query with such a question, of any type, is now answered NXDOMAIN at the relay. The deny-all box keeps its REFUSED for the same names. Test:zone_names_the_switch_would_forward_are_nxdomain.intercept_querynow: deny-all REFUSED, then NXDOMAIN for zone names the switch would forward, then NODATA (NET-136 types, or a zone name of any type but A). Otherwise forward.Tests
net::dns_gate::tests::unmatched_name_refused_without_upstream_forward(relay level): a deny-all box's A, AAAA and TXT queries forexample.comcome back REFUSED from the resolver's address to the query's source port. A sentinel proves the queries never reached the switch, and an unsolicited reply proves they opened no conntrack window. TXT, MX, CNAME and SRV forx.min.internalandhost.min.internalcome back NODATA, and a sentinel proves they never reached the switch.web.min.internal,host.min.internalandx.min.internalA queries are forwarded unchanged.net::dns_gate::tests::deny_all_box_refuses_names_outside_the_zone(gate level): REFUSED for A/AAAA/TXT/MX/HTTPS, with case-folded and lookalike names covered. Zone names, includinghost.min.internaland the apex, are forwarded for A and keep NODATA for AAAA. A two-question query with a zone name first is refused. TXT, MX, CNAME, SRV and NS forx.min.internalandhost.min.internalget NODATA. An A plus a TXT for zone names gets NODATA with both questions echoed. A zone TXT beside a non-zone A gets REFUSED.x.MIN.INTERNAL,x.Min.Internal,x.min.INTERNAL, the apex andevil\.min.internalget REFUSED;X.min.internalA is forwarded. Another port is not the gate's.net::dns_gate::tests::allow_list_and_allow_all_boxes_keep_forwarding: an allow-list box and an allow-all box still forward A/TXT for a non-zone name and still answer AAAA with NODATA.Session e2e (
own_ip_egress_declared_and_enforced): the NET-074 deny-all stand-in now declares--deny-all-egress, the section the in-force default materializes, instead of--deny-subnets 0.0.0.0/0. The same box then shows:example.com, gets rcode 5 on its own id;getent ahostsv4 example.comfails in under 5000 ms, timed inside the box;<nonce>.min.internalgets NODATA (rcode 0, zero answers) on its own id;host.min.internalstill resolves;GET https://example.comnow has to fail at resolution. It used to accept a timeout as well.None of these legs needs the public internet, so they are hard assertions.
Residuals
Validation
CROSS_CONTAINER_OPTS="--env HOME=/tmp" cross test -p minimald --target aarch64-unknown-linux-musl --locked:test result: FAILED. 814 passed; 16 failed; 1 ignored. All three new tests pass. Every failure is a container artifact:hooks(pidfd_open ENOSYS),nsentershims, andswitch/connection/rpcassertions over the process-wide captured log, which other tests' warn lines pollute. The sameswitch,connectionandrpcfailures reproduce onorigin/mainsources.a_laned_box_frame_to_the_proxy_listener_passespasses alone and fails in the same process as any warn-emitting gate test, including the existingdenied_range_resolution_refused.cross test ... --lib -- net::dns net::answerer:test result: ok. 66 passed; 0 failed.--lib -- net:::277 passed; 9 failed, all nine innet::switch; the same eight fail runningnet::switchalone at the previous head (f5d92c4), so they are the captured-log artifact above.net::dns::tests::is_zone_name_matches_the_zone_apex_and_its_names_onlynow also covers an escaped-dot label.cross clippy -p minimald --target aarch64-unknown-linux-musl --all-targets --locked -- -D warnings: clean.just fix,just clippy,just test(macOS scope): clean, with 1003 tests passed.bash -n scripts/session-e2e.shandshellcheck scripts/session-e2e.sh: clean.mainand the follow-ups:cross clippy -p minimald --all-targets --target aarch64-unknown-linux-musl --locked -- -D warningsis clean.cross test ... -- net::dnsgivestest result: ok. 53 passed; 0 failed, which covers both new tests, fix(minimald): answer NODATA for non-A queries on box-zone names #2019'snon_a_zone_queries_are_nodataand this PR's earlier tests.--lib -- net::gives280 passed; 9 failed. All nine failures are innet::switch, and the same nine fail onorigin/main(275 passed; 9 failed). The full-p minimaldrun gives821 passed; 18 failed, all of them in the container-artifact groups listed above.What CI proves
minimaldunit tests, including the three new gate tests (just ci).own_ip_egress_declared_and_enforced. That covers REFUSED on the wire, NODATA for a zone TXT, the fast lookup failure,host.min.internalresolution and the TCP 53 drop, for an own-address deny-all box.Summary by CodeRabbit