glm-5.1
596c89ce24
Rename all crates, CLI commands, constants, type names, doc comments, and documentation from wraith to alknet. Includes wire-protocol changes: ALPN wraith-ssh -> alknet-ssh, reserved destination prefix wraith- -> alknet-, SSH auth username wraith -> alknet.
30 lines
1.7 KiB
Markdown
30 lines
1.7 KiB
Markdown
# ADR-002: TUN Shim as Separate Process
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## Status
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Superseded by ADR-014
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## Context
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TUN interface creation requires root privileges or `CAP_NET_ADMIN` on Linux, Administrator on Windows, or platform-specific VPN APIs on macOS/iOS/Android. If the core alknet binary required these privileges, the attack surface of root-required code would include the entire SSH implementation, key handling, and transport negotiation.
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The primary use cases (SOCKS5 proxy, port forwarding) need no privileges at all. Only the "route all traffic through TUN" use case needs root.
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## Decision
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The TUN functionality is a separate `alknet-tun` binary that:
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1. Creates a TUN device (requires root / CAP_NET_ADMIN)
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2. Reads IP packets from it
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3. Forwards each connection to the core alknet's SOCKS5 port (127.0.0.1:1080)
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4. Proxies bytes between TUN packets and SOCKS5 connections
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The core `alknet connect` binary never needs root. The `alknet-tun` binary is ~200-500 lines and does nothing except TUN ↔ SOCKS5 forwarding.
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## Consequences
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- **Positive**: Root-required code surface is tiny and auditable.
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- **Positive**: Core binary runs unprivileged. SOCKS5 and port forwarding work without any special permissions.
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- **Positive**: TUN process can crash without affecting the SSH session (it just reconnects to SOCKS5).
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- **Positive**: Matches the proven tun2proxy architecture.
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- **Negative**: Two processes to manage instead of one. Requires process supervision (systemd, etc.).
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- **Negative**: SOCKS5 adds a small latency overhead vs. direct TUN → SSH packet routing. This is acceptable for the security benefit.
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## References
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- [tun-shim.md](../tun-shim.md)
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- [tun2proxy](https://github.com/tun2proxy/tun2proxy) — proven architecture for TUN → SOCKS5 proxy |