The tango/tfe-kmod repo is a DKMS Linux kernel module that reconstructs live TCP connections from out-of-band control messages (CMSG), using the TCP_REPAIR_WINDOW socket option to set window state without a handshake and adding special-case handling for protocols such as SSH where the server sends the first packet -- kernel-level infrastructure letting a userspace process ("TFE") transparently take over or inject into an in-progress TCP flow.
使用TCP_REPAIR_WINDOW选项设置socket的窗口大小, 替代窗口回复报文功能; 增加对第一个数据包为服务端先到达的协议的支持
Defense implications
- This confirms TSG middleboxes can reconstruct/take over TCP connection state at the kernel level rather than only issuing RST packets; protocols that depend on strict TCP state continuity being untouched by a MITM should assume the middlebox can synthesize valid in-window packets, not just drop/reset.
Related findings
An internal TSG operations/troubleshooting manual lays out TSG's full traffic pipeline (NIC -> mrzcpd/marsio capture driver -> sapp DPI engine -> firewall/proxy(KNI->TFE)/active-defense/WAN-NAT policy branches) and shows engineers using maat_redis_tool to pull the live Redis-synced blocking policy tables (TSG_SECURITY_COMPILE, TSG_OBJ_IP_ADDR, TSG_OBJ_APP_ID) and filter them by numeric policy/object ID to debug why a block rule isn't firing.
An official "Geedge Networks Confidential And Proprietary" sapp/mrzcpd operations manual documents the packet-injection API (MESA_kill_tcp / MESA_inject_pkt) used for both out-of-band mirror-tap RST injection (relies on the local box's own IP routing table to send) and inline in-path injection (requires mrtunnat.conf tunnel-tracking state -- use_recent_tunnel, use_link_info_table -- keyed on outer/inner MAC and link_id/link_dir), plus the Marsio DPDK-based driver's I/O sub-modes (marsio4, marsio_vxlan, pag_marsio, agent_smith) and its role extracting VXLAN/GTP encapsulation metadata and stamping link/circuit identifiers into mirrored packets' MAC field for session-log correlation.
A 2023 MESA Lab monthly report describes the 'TF' project's active-defense work: test cases for serial ('串联') HTTP hijack/tamper and parallel ('并联') DNS race-injection ('DNS抢答'), performance tuning that scaled active-defense capacity from 3 to 5 units, converting two existing TSG boxes to active-defense mode, and rewriting the active-defense flow-control logic to no longer depend on sapp.
TSG's firewall 'Deny' security-policy action is confirmed implemented via three interchangeable mechanisms: TCP RST injection, forged HTTP 404 response-page injection, and DNS-redirect. Confirmed via commits to MESA_Platform/sapp and tsg/tsg-os-buildimage GitLab repos (git.mesalab.cn).
The tango/tsg-service-chaining-engine (SCE) repo implements TSG's traffic-steering core: it VXLAN-encapsulates and routes both "raw" and "decrypted" copies of a session (four tracked metadata directions) through a chain of up to 32 third-party "Service Functions", with explicit per-flow actions of block, bypass, forward, and rx_drop for both mirrored and inline-steered traffic, coordinating with SAPP, mrzcpd (packet capture/re-injection), and MAAT4 (rule engine) via control-plane messages.
Geedge's production inline-deployment container bundle (tango/tsg_container) wires mrzcpd (capture/inject), sapp (DPI via maat rules), and a third component "tfe" (traffic-forwarding engine) together via Docker Compose; tfe ships a dedicated doh.conf (DNS-over-HTTPS handling) and the firewall-mode container's sapp config includes a send_raw_pkt.conf, a KNI (kernel network interface) config, an "asymmetric_presence_layer.conf" for mirror/asymmetric-routing deployments, and a "pangu" proxy module (pangu_pxy.conf / pangu_http.json).