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docs(sandbox): seccomp BPF filtering design for the bwrap backend - #288
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Proposes adding a strict-allowlist seccomp filter to the bubblewrap sandbox: precompiled per-arch BPF blobs built in CI with libseccomp, handed to bwrap via --add-seccomp-fd through the spawn stdio array. Covers the change map (args.ts, provider.ts, config schema/normalizer, manifest/CI, tests), an audit-first rollout since bwrap has no audit flag, and open questions on degradation policy and config granularity. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Summary
Design doc proposing a seccomp BPF filter for the bubblewrap sandbox backend, closing the gap that namespaces alone leave open: the guest shares the host kernel and today can reach its entire syscall surface, so a single kernel LPE inside the jail is a full host escape.
Key decisions in the doc:
socketrestricted toAF_UNIX, andSCMP_ACT_KILL_PROCESSon the escalation primitives (nested-usernsunshare,keyctl,bpf, module loading,ptrace,userfaultfd, ...).--add-seccomp-fd, with the fd passed through the spawnstdioarray.SECCOMP_RET_LOGvs enforce is baked into separate blobs; the default flips to enforce only after the audit log is quiet across the image toolchain.The doc includes a full change map with file/line anchors (
args.ts,provider.ts, config schema + the desktop normalizer,build-image.ts/manifest, tests), and leaves three open questions for the team: degradation policy on old bwrap, global vs per-sandbox config for v1, and whether to hard-blockptrace.Docs only — no behavior change.
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