Documentation
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Overview ¶
Package egressfwd installs the in-Sentry egress forwarders for compute-worker sandboxes — the APO-713 data path that makes a worker fetch() actually leave the box. The core sentrystack wires lo+eth0 and then, if an embedder set the ForwarderInstaller hook, hands the stack to us. We register two forwarders, each gated on its own InitStr field:
- TCP (InitStr.EgressHostAddr): a catch-all TCP forwarder. Every outbound SYN the worker issues loops back through eth0 (promiscuous+spoofing), matches no bound listener, and is stolen by the forwarder, which bridges it to the host egress endpoint.
- DNS (InitStr.DNSResolvers): a UDP:53 forwarder. The worker's getaddrinfo query (sent to the sandbox resolv.conf's gateway IP) loops back the same way; the forwarder rewrites the destination to a configured resolver and dials it from the host netns. Its responses feed a per-sandbox IP→name cache the TCP forwarder reads to attribute a later connect() to the hostname the worker resolved it from. Non-DNS UDP fails closed.
With neither field set the same SYN / datagram is RST in the stack (fail-closed) — see the core's egress_demux_test.go.
The forwarder is armed ONLY in a binary that blank-imports this package (init() sets sentrystack.ForwarderInstaller). Production wiring (cmd/workerd-manager) and the Stage-0 spike each opt in explicitly; a standalone core consumer leaves the hook nil and gets a no-egress sandbox. The pure wire framing the forwarder and the host bridge share lives in the side-effect-free sibling package egresswire, so a consumer that only needs to read/write the preamble (the host bridge) does not transitively arm the forwarder by importing this package.
This file carries no build tag so the package always has a buildable Go source on every platform; the forwarder itself is linux-only (forwarder_linux.go, install_linux.go).
Index ¶
Constants ¶
This section is empty.
Variables ¶
var ErrNonDNSUDPDenied = errors.New("non-DNS UDP egress denied (no UDP policy plumbing yet)")
ErrNonDNSUDPDenied is returned by routedUDPDialer.DialUDP when a worker attempts UDP egress to anything other than :53. Worker-side UDP policy is not wired yet; until it is, non-DNS UDP fails closed so a worker can't bypass the egress policy / SSRF backstop (which only see the TCP bridge) by switching protocols. Stable error value — tests rely on it.
Functions ¶
func InstallEgress ¶
func InstallEgress(s *sentrystack.Stack, init *sentrystack.InitStr)
InstallEgress is the sentrystack.ForwarderInstaller: after the core wires lo+eth0, it registers the outbound forwarders. It arms two independent data paths, each gated on its own InitStr field so a resident can enable either without the other:
- TCP egress (init.EgressHostAddr): a catch-all TCP forwarder that bridges every outbound stream to the host egress endpoint. The Sentry stays policy-dumb; the host bridge owns policy + gateway-vs-direct selection.
- DNS (init.DNSResolvers): a UDP:53 forwarder that rewrites the worker's query to a configured resolver and dials it from the host netns. Its responses feed a per-sandbox IP→name cache the TCP dialer reads to attribute a flow to the hostname the worker resolved it from (dstName).
With neither field set, outbound stays fail-closed: the core RSTs the unhandled SYN / UDP datagram rather than silently direct-dialing through the host netns.
Types ¶
This section is empty.
Source Files