feat(upstream): native sandbox launcher (Landlock + rlimits) for stdio servers (MCP-34.3)#768
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feat(upstream): native sandbox launcher (Landlock + rlimits) for stdio servers (MCP-34.3)#768Dumbris wants to merge 1 commit into
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…o servers (MCP-34.3)
Implements the `sandbox` spawn branch alongside docker/plain in connectStdio and
buildLauncherCmd, using the Landlock mechanism proven by the MCP-34.1 spike and
wired into the mode-aware selector from MCP-34.2.
Mechanism: a tiny re-exec wrapper. mcpproxy launches itself as
`mcpproxy __sandbox_exec -- <command> [args...]` with the confinement Spec
encoded in the environment; the hidden child applies Landlock + setrlimit, does a
best-effort uid/gid drop, then execs the real command — so confinement is
inherited across execve and the server's stdin/stdout pass straight through with
no mux. Reuses the existing SysProcAttr{Setpgid} process-group cleanup.
- internal/sandbox: WrapCommand/SpecFromEnv (cross-platform), RunChild (unix +
non-unix guard), Available() honest-diagnostic helper.
- internal/upstream/core: wrapWithSandbox + buildSandboxSpec (filesystem WRITE
allowlist: RO "/", RW working_dir + temp + package caches; RLIMIT_CORE=0 +
NOFILE; BestEffort graceful degrade). Wired into both stdio + launcher plain
branches behind ResolveMode == sandbox.
- cmd/mcpproxy: hidden __sandbox_exec subcommand.
- Graceful fallback: non-Linux / Landlock-less kernels degrade to unconfined
(effective "none") with a logged diagnostic; fail-closed when BestEffort=false.
- docs/features/sandbox-isolation.md documents enforcement, honest limits
(no read confinement, uid/gid no-op without root), and platform support.
Tests (red→green): WrapCommand argv/env round-trip, SpecFromEnv absent/malformed,
buildSandboxSpec write-allowlist defaults; Linux end-to-end (cmd construction,
RLIMIT_NOFILE application, write-outside-allowlist denied, stdin/stdout
passthrough) + fail-closed refuses to run unconfined. Landlock enforcement runs
on ubuntu-latest CI (24.04), mirroring the MCP-34.1 spike's empirical proof.
Co-Authored-By: Paperclip <[email protected]>
Deploying mcpproxy-docs with
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Option 2: GitHub CLI gh run download 28144942328 --repo smart-mcp-proxy/mcpproxy-go
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What
Implements the
sandboxspawn branch alongside docker/plain inconnectStdioandbuildLauncherCmd(MCP-34.3), using the Landlock mechanism proven by the MCP-34.1 spike (#754) and wired into the mode-aware selector from MCP-34.2 (#759).Mechanism — re-exec wrapper
Landlock confines the current process and every process it then execs, irreversibly — so it can't be applied in-process before mcp-go spawns the server. Integration is a tiny re-exec wrapper:
with the confinement
SpecJSON-encoded in the env. The hidden child applies Landlock +setrlimit, does a best-effort uid/gid drop, thenexecs the real command. Confinement is inherited acrossexecve; stdin/stdout pass straight through, no mux. Reuses the existingSysProcAttr{Setpgid}process-group cleanup.Scope coverage
RLIMIT_CORE=0,RLIMIT_NOFILE)/, RW = working_dir + temp + package cachesSetuid/Setgidonly when root w/ non-root real user — documented no-op otherwise)none)ResolveMode == sandbox(MCP-34.2 selector) in both stdio + launcher pathsHonest limits (documented in
docs/features/sandbox-isolation.md)CAP_SETUID.dockermode for a hard guarantee.Tests (red→green)
internal/sandbox:WrapCommandargv/env round-trip,SpecFromEnvabsent/malformed.internal/upstream/core:buildSandboxSpecwrite-allowlist defaults; Linux end-to-end via real re-exec — cmd construction,RLIMIT_NOFILEapplication, write-outside-allowlist denied, stdin/stdout passthrough; fail-closed refuses to run unconfined.ubuntu-latestCI (24.04) — same empirical-proof approach as the MCP-34.1 spike (sandbox.Available()skips on kernels without Landlock).Local:
go build ./...,go vet(linux cross),go test ./internal/sandbox/... ./internal/upstream/core/..., gofmt, golangci-lint v2 all clean.Closes MCP-3234.