Run inside a box, setup-host built a nested boxnet claiming the exact
subnet and gateway of the guest's own uplink: the guest then held
10.88.0.1 as a LOCAL address while its default route pointed at 10.88.0.1
as its GATEWAY, carried two connected routes for the subnet, and suffered
intermittent, self-recovering egress blackouts (~24-36 s, roughly hourly)
that no host-side check could attribute. The flagship use case funnels
agents toward exactly this — working on box, in a box — so the guard, not
the operator, has to catch it.
setup-host now scans the target subnet BEFORE any mutation: the default
route's gateway inside it (the smoking gun — that is this machine's own
uplink), or any non-boxnet interface holding an address in it, refuses
with the way out named (BOX_SUBNET). A prior boxnet owning the subnet is
the one claimant that is NOT a collision — the legitimate re-run — and an
existing bridge on a DIFFERENT subnet refuses too: setup-host converges a
bridge, it never re-addresses one under live leases.
BOX_SUBNET=<a.b.c.0/24> (validated at the gate, alongside BOX_DNS) moves
the whole stack from one place:
· the bridge address derives (ipv4.address=<gw>/24)
· the ACL's gateway carve-out derives — and the ruleset is now converged
via 'network acl edit', not created once: the #80 escape hatch (moving
the bridge) left the old /32 behind, stranding box DNS inside the
10.0.0.0/8 drop, which presents as a dead resolver, never as a stale
ACL
· box-firewall reads the gateway off the live bridge ('|| true' because
under pipefail an absent bridge would kill the script instead of
answering "no bridge yet")
· the drill, multiuser rehearsal and migrate-host probes derive the
prefix from 'incus network get boxnet ipv4.address' instead of
hardcoding 10.88 — a BOX_SUBNET host must not fail its own rehearsals
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Reproduced the drill's E failure on a live stack (Incus 6.0.4, container
box, same setup-host/box-firewall): tcpdump on boxnet shows the SYN
leaving masqueraded as the gateway and the box answering SYN/ACK
instantly — which then dies at the host's input hook. The inet-box input
chain dropped ALL boxnet input except DNS/DHCP, stateless: the reply to
the very connection the door opened. UFW hosts never had this hole
(before.rules accepts RELATED,ESTABLISHED); the nft fallback now matches
that semantics with a ct state established,related accept ahead of the
drop. Boxes still cannot INITIATE toward the host — a box-originated SYN
is a NEW flow, which is what the drop is for.
Also rebuild the chains on every run (add chain + flush + re-add) instead
of skip-if-present: the existence guard pinned every host to the rule set
of the release that first ran there, so an upgraded rule never landed.
Verified end-to-end on the repro stack: curl 127.0.0.1:18091 → HTTP 200;
box→host initiation still times out; DNS carve-out intact; non-exposed
port still dropped; --remove kills the door; re-expose returns 200.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
The drill's E phase moved one layer down: the device now adds, but
127.0.0.1:<hport> never reaches the box. Incus's NAT-mode proxy installs
only the DNAT (prerouting + output); a loopback-sourced packet then dies
twice — the kernel refuses to route it out a non-loopback interface
without route_localnet on the bridge, and the box would reply to its OWN
127.0.0.1 without a masquerade. This is the exact plumbing Docker
installs on docker0 for '-p 127.0.0.1❌y'.
box-firewall.sh now sets route_localnet=1 on boxnet and masquerades
loopback-sourced traffic leaving it (chain expose-snat, table inet box).
route_localnet's known risk — 127/8 becomes a routable destination on
the bridge — is covered by the existing iifname-boxnet input drop, which
fires regardless of destination address. The no-UFW guard now checks the
input CHAIN, not the table, since expose-snat shares the table.
expose warns (root-free, via /proc) when the host firewall predates this
plumbing instead of handing over a door that silently does not answer,
and 'box info' now lists open exposures — the drill's nice-to-have: a
box with a hole says so.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Follow-up to the rename, per operator direction — the divergence is
reversed and the cut is complete:
- Host stack: boxnet (10.88.0.0/24 — a pre-rename host may still carry
claudenet on 10.87, two bridges must not claim one subnet),
box-isolate, nft tables 'inet box'/'bridge box', box-firewall.{sh,
service}. teardown-host now strips BOTH name generations, so one
script uninstalls a host of any age.
- Default template is blank: 'box new --name x' mints bare Debian;
the claude box is '--template claude'. The login hint follows the
EFFECTIVE template read off the instance, so clones of claude boxes
still get it and blank boxes are not told to run a binary they lack.
- The drill validates templates: listing, unknown-template refusal,
the allowlist rejecting BOX_NETWORK by name, and a full blank mint —
default resolves to blank, metadata stamped, box-net placement, exec
lands in 'dev', no claude binary, and isolation parity (egress +
pinned DNS) on the same contract as every template.
- drill/wipe.sh: scorched earth for drill hosts. Both tag generations,
every drill-named instance, networks/ACLs/profiles/firewall of both
generations, cached images, and (--purge-storage) the default pool.
Ends by asserting the ABSENCE of every artifact rather than trusting
the removals' exit codes.
2026-07-14 14:36:39 +00:00
Renamed from host/claudebox-firewall.sh (Browse further)
