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Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS
68 lines
3.4 KiB
Go
68 lines
3.4 KiB
Go
// Package felhomsshd manages the dedicated OOB sshd instance (TASK H1). It is a SECOND sshd —
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// separate port, config, host keys, AuthorizedKeysFile, and systemd unit — that COEXISTS with the
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// customer's/stock sshd on :22 (never touched). Design + safety earned by
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// SPIKE-felhom-sshd-2026-07-05 (§2 claim, §3 SAFE unit, §5 reload-not-restart, §7 AuthorizedKeysFile
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// isolation) and SPIKE-oob-wg-operator-peer-2026-07-05 (the tunnel-only belt).
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//
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// The agent RENDERS the config (Port from the claim) and reloads on change — the wg-felhom pattern.
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// It NEVER declares RuntimeDirectory= (G1 [SF-1]) and NEVER restarts on a config change [SF-2].
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package felhomsshd
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import (
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"fmt"
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"strings"
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)
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const (
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// ConfDir is the dedicated config tree (host-install creates it; the agent renders the config).
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ConfDir = "/etc/felhom-sshd"
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// ConfPath is the rendered sshd config (referenced by the static unit's ExecStart/ExecReload).
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ConfPath = ConfDir + "/sshd_config"
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// HostKeyPath is the dedicated ed25519 host key (host-install generates it; stable across reloads).
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HostKeyPath = ConfDir + "/ssh_host_ed25519_key"
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// AuthKeysDir holds per-user authorized_keys OUTSIDE ~/.ssh, so the customer's sshd (which reads
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// ~/.ssh/authorized_keys) structurally cannot honour the operator key [SF-3/§7].
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AuthKeysDir = ConfDir + "/authorized_keys"
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// PortFile persists the claimed port (idempotent re-pick).
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PortFile = ConfDir + "/port"
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// PidFile is the instance pidfile (NOT a RuntimeDirectory — that is the G1 incident cause).
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PidFile = "/run/felhom-sshd.pid"
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// PrivApply is the root content checker that installs the config and felhom-op's key (R-861, agent v0.146.0).
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PrivApply = "/usr/local/sbin/felhom-priv-apply"
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// Unit is the systemd unit name.
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Unit = "felhom-sshd"
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// OperatorUser is the default operator login (scoped sudo; key in AuthKeysDir only).
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OperatorUser = "felhom-op"
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)
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// renderConfig builds the felhom-sshd config for a claimed port. Pure + deterministic (byte-stable
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// for a given port → a stable conf-hash, no reload churn). The security posture is the SAFE template
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// from the spike §3: key-only, dedicated host key + AuthorizedKeysFile, AllowUsers scoped to
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// root+felhom-op, binds 0.0.0.0 (+ ::) so it never waits on a late interface, no RuntimeDirectory.
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func renderConfig(port int) (string, error) {
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if port < 1 || port > 65535 {
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return "", fmt.Errorf("felhomsshd: port %d out of range", port)
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}
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if port == 22 {
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// The whole point is coexistence — the dedicated instance must NEVER claim :22 [SF-4/trap 5].
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return "", fmt.Errorf("felhomsshd: refusing to render on :22 (the stock/customer sshd port)")
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}
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var b strings.Builder
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b.WriteString("# felhom OOB sshd — agent-managed (H1); DO NOT EDIT\n")
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fmt.Fprintf(&b, "Port %d\n", port)
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b.WriteString("ListenAddress 0.0.0.0\n")
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b.WriteString("ListenAddress ::\n")
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fmt.Fprintf(&b, "HostKey %s\n", HostKeyPath)
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fmt.Fprintf(&b, "PidFile %s\n", PidFile)
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fmt.Fprintf(&b, "AuthorizedKeysFile %s/%%u\n", AuthKeysDir)
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b.WriteString("PasswordAuthentication no\n")
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b.WriteString("PermitRootLogin prohibit-password\n")
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b.WriteString("PubkeyAuthentication yes\n")
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b.WriteString("KbdInteractiveAuthentication no\n")
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b.WriteString("UsePAM yes\n")
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fmt.Fprintf(&b, "AllowUsers root %s\n", OperatorUser)
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b.WriteString("X11Forwarding no\n")
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b.WriteString("Subsystem sftp internal-sftp\n")
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return b.String(), nil
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}
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