[danbugs]

A guest given a network policy and no listen ports could bind any port. Net::allow_bind let every bind through when there was no ListenPorts to ask, while --port's help ("Without this flag or a project's ports, bind() is rejected"), the ListenPorts rustdoc and docs/net.md all promise a guest that cannot serve on a port of its own without one. Found while integrating hyperlight-unikraft guests with urunc (urunc-dev/urunc#1135): hluk run --net with no --port served happily. Targets v0.19.0.

• hostnet: allow_bind refuses every bind but an ephemeral one (port 0) unless the port is listed, whether the guest means to listen on it or to connect from it (source_address). A guest that serves on a port of its own needs --port, a manifest's ports, or listen_ports, as documented, and can still serve on a port the host picks.
• Tests: a unit test for the no-ports case, which fails on the old code; the three python integration tests that serve on a fixed port under a bare AllowAll (tcp_bidir, http_server_client, threaded_select) list it, and the datagram rebind test lists the port it binds. tcp_echo and server_shutdown bind port 0 and are unchanged.
• Conformance: the CPython conformance recipes (bash and pwsh) pass --port all: test_ftplib and test_smtplib bind a source port before connecting and failed under the gate with the bare --net they ran with, and the test host is the boundary there.
• Docs: net.md states the rule next to the ephemeral exception and no longer calls the default "outbound-only", since a port-0 bind still serves; the --port help and the ListenPorts rustdoc say the same; the smolagents README and executor docstring no longer tie "cannot listen" to net_allow being empty (the executor never passes --port, so the guest cannot listen on a port of its own either way, and hluk_args=["--port", ...] opens one); CHANGELOG entry under Fixed.

Behaviour change for embedders: .network(policy) alone no longer lets the guest listen on a port of its own, or choose its source port; add listen_ports. The integrations (smolagents executor, MCP server, ClickHouse driver) never bind and are unaffected. urunc (urunc-dev/urunc#1135) passes --port=all unless a deployment lists ports.

Testing

Rebased onto main after #180, on Linux/KVM: cargo test --lib, the whole cargo test --test python suite and cargo test --test networking pass; cargo fmt --check and cargo clippy --all-targets --locked -- -D warnings are clean. just conformance python test_ftplib test_smtplib with the branch's release build: both PASS (96 and 82 tests), where they failed under the old recipe. By hand, hluk run --initrd python-rootfs.cpio --net examples/python/http_server_client.py fails to bind with Permission denied and --net --port 9997 serves.

[Copilot]

🟢 Approval recommended

The focused bind-policy change, regression coverage, caller updates, and documentation are consistent, with no unresolved blocking findings.

No open issues 🎉

What changed in this PR

This PR makes host networking enforce the documented bind policy: nonzero ports require an explicit listen-port allowance, while port 0 remains permitted for host-assigned ports.

Changes:

• Reject unlisted fixed-port binds, including outbound source-port selection, and add regression coverage.
• Give affected Python tests explicit port permissions and enable all ports in CPython conformance recipes.
• Align CLI help, API documentation, integration documentation, and release notes with the policy.

File	Description
tests/​python.rs	Allow the fixed ports used by three server tests.
src/​net_policy.rs	Clarify listen-port requirements and the ephemeral-port exception.
src/​hostnet.rs	Enforce the bind gate and update unit tests.
src/​cli/​mod.rs	Clarify --port help text.
justfile	Pass --port all in both conformance recipes.
integrations/​smolagents/​src/​smolagents_hyperlight/​executor.py	Correct the executor’s networking docstring.
integrations/​smolagents/​README.md	Clarify outbound policy versus fixed-port permissions.
docs/​net.md	Document bind rejection and source-port restrictions.
CHANGELOG.md	Record the fix and migration guidance for embedders.

_{Review effort: Balanced}