fix(mount): create the detached initial-sync script mode 0600 - #39
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📝 WalkthroughWalkthroughChangesThe mount script adds Initial-sync security
Estimated code review effort: 3 (Moderate) | ~30 minutes Merge Risk: 🟡 Moderate · up to The detached initial-sync flow can report a successful sync as failed during cleanup because the generated script is removed before completion is recorded. This can incorrectly fail mount startup, so the change is not merge-ready until the status handling is corrected or explicitly accepted. Sequence Diagram(s)sequenceDiagram
participant MountBuilder
participant GeneratedScript
participant MountProcess
participant ExitSentinel
MountBuilder->>GeneratedScript: create under umask 077
MountBuilder->>GeneratedScript: verify mode 0600
MountBuilder->>MountProcess: launch detached initial sync
MountProcess-->>MountBuilder: return exit status
MountBuilder->>GeneratedScript: remove script
MountBuilder->>ExitSentinel: write exit status
Suggested reviewers: Poem
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Linked Issues checkExplanation The changes address issue ✨ Finishing Touches 💡 1📝 Generate docstrings 💡
🧪 Generate unit tests (beta)
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The detached initial-sync launcher wrote its generated script with a plain `cat >`, so the file landed at the process umask default — 0644 under a 022 umask — and the default token ingress rendered the path-scoped credential into it as a `--token` literal. Any other process able to read the file could recover a reusable credential, and the script outlived the sync that used it. - Create the script inside `(umask 077 && cat > ...)` so the mode is constrained at creation; a chmod after the write would leave a readable window. Verify the mode that actually landed (`stat -c %a`, falling back to `stat -f %Lp`) and refuse to launch if it is not 600. - Add `tokenIngress: 'creds-file'`, which renders no credential literal at all and relies on the mode-0600 creds file already supplied alongside the launch command. It is opt-in rather than implied by `credsFilePath`, because pre-creds binaries ignore the creds-file env var and would fail authentication silently if `--token` were dropped from under them. - Remove the generated script once the detached sync exits, before the exit sentinel is written, so a poller that has observed completion cannot race back and read it. The log, pid and exit sentinels are kept as non-secret failure diagnostics. The tests execute the real launcher through /bin/sh under an explicit 022 umask and assert against the file that lands on disk; a string assertion on the generated shell would not have caught the umask defect. Behaviour verified on dash, bash --posix and zsh. Refs #30 Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Session-Id: 798d531e-b682-47ba-90dc-0a26290aa6e6 Session-Id: b4b52699-ca5c-4331-b702-8989d1e91983 Session-Id: b4b52699-ca5c-4331-b702-8989d1e91983 Session-Id: b4b52699-ca5c-4331-b702-8989d1e91983 Session-Id: b4b52699-ca5c-4331-b702-8989d1e91983
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The "verifies the landed mode" test only grepped the generated launcher for `umask 077` and for the position of the mode check. A grep asserts a proxy: it passes just as happily when the check is present in the generated text but broken at runtime, which is the regression that matters for a credential fix. The property is that the file on disk is 0600 and holds no reusable token. - Add a gating test that runs the check. It mutates the launcher back to the pre-fix creation mode (`umask 022` for `umask 077`) — the exact regression the check exists to catch — executes it under an explicit 022 umask, and asserts the launcher refuses: non-zero exit, a refusal naming the mode that actually landed, the readable script removed, and no pid, log or exit sentinel, because nothing was handed to a detached process. - Assert the landed mode through `stat` by exit code, the way the launcher reads it, alongside the existing `statSync` check. - Assert that under the default argv ingress the credential really is in the file that lands, so the 0600 mode is load-bearing rather than incidental. - Keep the text assertions as a fast unit: creation order is a property of the generated shell, and a chmod-after-write would leave a readable window that a mode assertion on the finished file cannot see. Negative controls: with the `case` arm widened so the mode check tolerates 0644, the text test stays green and the new executing test goes red — cubic's scenario exactly. With `umask 077` removed entirely, 5 of 7 go red; the two build-time invariants are meant to pass in both states. Refs #30 Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Session-Id: 39f5e60a-56d3-46fd-95d8-8f82f024eba2
sandbox#30 — cubic P3 taken; follow-ups filedCommit: Cubic's P3 was correct and is fixed rather than argued. The The gating test now runs the check — Also: the landed mode is asserted by exit code through Negative controls, both run locally:
CI: green per workflow on head Follow-ups filed, deliberately not fixed here:
Not merging. Khaliq owns the merge gate. |
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Inline comments:
In `@src/mount-script.ts`:
- Around line 350-357: Update buildRelayfileMountInitialSyncStatusShell and
startMount’s initial-sync flow to add a completion state that remains
in-progress after the child is reaped but before the exit sentinel is written.
Ensure the status probe does not infer exit 127 from the dead PID during this
window, while preserving script removal before writing the exit sentinel.
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…e path Removing the generated script after the sync is done with it — the credential fix in f7188bc — put a fork+exec between reaping the child and publishing its exit status. Inside that interval the pid file names a dead process, so the status probe's dead-PID heuristic reported `exit 127`, and the orchestrator turns that into `Failed initial relayfile sync` for a sync that exited 0. The window existed before (an `echo` builtin stood in it); this PR widened it to a `rm`, which is where it became reachable in practice. A false failure on a healthy mount is worse than the cosmetic issue it looks like: every consumer of that status learns to distrust it. - The runner marks the completion window the instant `wait` returns, via a bare `: >` redirection so no fork stands between the reap and the mark, and before the `rm` that now lives inside the window. - The status probe reports in-progress while that marker exists and the exit sentinel does not, instead of falling through to the dead-PID check. Script removal stays strictly before the exit sentinel, so a poller that has seen completion still cannot race back and read the script. - The pre-run sweep clears a stale marker, or a previous run's marker would make this run's dead-PID check unreachable. - If the runner is itself killed inside the window the sync now stalls to the caller's deadline rather than reporting 127. An honest "did not finish" beats a false failure on the healthy path, which is the only path that reaches this window. Tests. The must-fire wedges the real runner open inside the window with an `rm` that performs the removal and then blocks, confirms the state is genuinely the window (child reaped, script gone, pid file present, no exit sentinel), and polls the real probe throughout. With the probe branch removed it fails on the first poll with `probe reported {"state":"exited","exitCode":127} inside the completion window`. Must-not-fire: the same on-disk state without the marker still reports 127, and a sync whose mount really fails still reports failure end to end — both pass in either state. Refs #30 Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Session-Id: 39f5e60a-56d3-46fd-95d8-8f82f024eba2
CodeRabbit Major — completion window: fixed and provedCommit: CodeRabbit is right. One correction on provenance that changes nothing about the fix: the window is not new in this PR. Fix — the shape CodeRabbit suggested:
Residual, stated not hidden: if the runner is itself SIGKILLed inside the window, the sync stalls to the caller's deadline rather than reporting 127. Deliberate — an honest "did not finish within Ns" beats a false failure on the healthy path, and the healthy path is the only one that reaches this window. Proved, not asserted. The must-fire wedges the real runner open inside the window with an Must-not-fire, green in both states: the same on-disk state without the marker still reports CI: green per workflow on head Not merging. Khaliq owns the merge gate. |
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Fixes #30.
The defect
The detached initial-sync launcher wrote its generated script with a plain
cat >, so the file was created at the process umask default —0644under a022umask. The default token ingress also rendered the path-scoped credential into that script as a--tokenliteral, and the script outlived the sync that used it. The result was a reusable credential sitting in a file readable by other processes, even though a mode-0600creds file was already being supplied alongside the launch command.Reproduced against the parent commit by running the real launcher under
umask 022: effective mode644, credential literal present, script still on disk after the sync exited. All three now assert the opposite.The fix
Mode, constrained at creation. The script is written inside
(umask 077 && cat > ...). Achmodafter the write would leave a window in which the file exists readable, so the mode is fixed at creation instead. As defence in depth the launcher then reads back the mode that actually landed (stat -c %a, falling back to BSDstat -f %Lp) and refuses to launch if it is not600. Where neitherstatspelling exists the mode cannot be read back, but the umask has already fixed it at creation, so that case is tolerated rather than failing the sandbox shut.No credential literal at all. Adds
tokenIngress: 'creds-file', which renders no token in argv and none in the env prefix — the daemon reads the credential from the mode-0600file named bycredsFilePath, which the option now requires. Protecting the copy is second best; not writing one is the actual fix.This is deliberately opt-in rather than implied by
credsFilePathalone. Per the existingcredsFilePathcontract, pre-creds binaries ignore the unknown env var, so dropping--tokenfor them would convert a working mount into a silent authentication failure. Every existing caller renders byte-identically; a test pins that.Cleanup. The generated script is removed once the detached sync exits, and removed before the exit sentinel is written, so a poller that has observed completion cannot race back and read it. The log, pid and exit sentinels are preserved as the non-secret failure diagnostics.
Tests
Six tests in
src/mount-script.test.ts, underdetached initial-sync script credential hygiene (sandbox#30):creates the generated script at mode exactly 0600 under a 022 umask0600keeps the token literal out of the generated script under creds-file ingressstill renders --token for the default argv ingress (older daemons)rejects creds-file ingress that has no creds file to readremoves the generated script once the detached sync exitsverifies the landed mode before handing the script to a detached processThese execute the real launcher through
/bin/shunder an explicitumask 022and assert against the file that lands on disk — a string assertion on the generated shell would not have caught the umask defect. A blockingrelayfile-mountstand-in makes the timing deterministic rather than sleep-racy.Negative control: with the fix reverted, five of the six fail. The sixth is the backwards-compatibility invariant and passes in both states, as intended.
Portability of the generated shell verified on
dash(Ubuntu CI's/bin/sh),bash --posixandzsh: mode600, correct exit-status propagation, cleanup performed in all four shells. Exit-status propagation is covered specifically because the runner now captures the sync's status around the addedrminstead of reading$?directly.No real credential appears in any fixture, test, or log; the tests use an obvious placeholder.
Scope
Limited to mode, ingress, cleanup and their tests. The credentials-in-argv exposure class (#21, and the corresponding relay-side issue) is intentionally left alone and is not affected by this change: the token still reaches argv under the unchanged
'argv'default, which is what preserves compatibility with older daemon builds.Summary by cubic
Creates the detached initial-sync script with mode 0600 at creation, removes it before the exit sentinel, and marks the completion window to prevent false failures. Previously the script landed 0644 under a 022 umask, could include a --token literal, persisted on disk, and the status probe could report exit 127 while cleanup ran.
(umask 077 && cat > ...), verifies the landed mode viastat, and refuses to launch if not 0600 (removes the script; no pid/log/exit files are created).'creds-file'that emits no token literal and relies on a mode-0600 creds file; requirescredsFilePath. Default remains'argv'for older daemons.exit 127during cleanup.umask 022to gate the 0600 mode and refusal path; assert default'argv'still renders--tokenand'creds-file'keeps the token out of the script; add must-fire/must-not-fire completion-window probes.Migration: To avoid embedding tokens, set
tokenIngressto'creds-file'and providecredsFilePath; otherwise behavior is unchanged.Written for commit ad7fc6f. Summary will update on new commits.