fix(cmux-tui): harden socket start lock files by lawrencecchen · Pull Request #11396 · manaflow-ai/cmux

lawrencecchen · 2026-09-01T08:50:19Z

Summary

reject symlinked or non-regular .spawn-lock files before locking
require the current user to own the lock and keep permissions owner-only
add Unix behavior tests for symlink rejection and mode migration

This isolates the SocketStartLock security portion that exists in PR #11155 but is absent from the current-main #11386 replay. The two commits preserve the red then green test history.

Verification

git diff --check
rustfmt --edition 2024 --check cmux-tui/crates/cmux-tui-core/src/server.rs
hosted cmux-tui focused workflow pending

Related: #11155 #11386

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Summary by cubic

Hardens the socket start lock so symlinked, non-regular, or hard-linked lock paths are rejected before locking, and acquisition fails unless the lock is owned by the current user and private (owner-only, no group or other access).

Rejects symlinks with O_NOFOLLOW (ELOOP), FIFOs with O_NONBLOCK (ENXIO), and hard-linked locks via link count validation.
Enforces owner-only 0600 permissions on the lock, migrating existing locks while keeping them append-only.
Adds Unix tests covering each rejection path, the blocking FIFO case, and mode migration.

^{Written for commit 3390063. Summary will update on new commits.}

Summary by CodeRabbit

Bug Fixes
- Improved security and reliability for the socket startup lock.
- Rejects unsafe lock paths, including symbolic links and non-file entries.
- Verifies that the lock is owned by the current user and restricts access to the owner.
- Automatically updates existing lock files to owner-only permissions.

vercel · 2026-09-01T08:50:26Z

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Project	Deployment	Actions	Updated
cmux166	Canceled		Sep 1, 2026 5:39pm UTC
cmux41	Canceled		Sep 1, 2026 5:39pm UTC

coderabbitai · 2026-09-01T08:51:58Z

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📝 Walkthrough

Walkthrough

SocketStartLock::acquire now uses hardened Unix open flags, validates file type and ownership, and enforces 0o600 permissions. Unix tests cover symlink rejection, nonblocking FIFO rejection, and existing lock permission migration.

Changes

Socket start lock security

Layer / File(s)	Summary
Harden lock acquisition and validate Unix behavior `cmux-tui/crates/cmux-tui-core/src/server.rs`	`SocketStartLock::acquire` uses `O_NOFOLLOW`, `O_CLOEXEC`, and `O_NONBLOCK`, validates regular-file type and effective-user ownership, and enforces `0o600` permissions. Unix tests cover symlink rejection, FIFO rejection, and existing lock-file migration.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: 🔵 Low · up to cf915

The lock hardening strengthens protection against unsafe lock files, but explicitly configured socket paths in shared writable directories can still be prevented from starting if another local user pre-creates the persistent lock. This is a bounded configuration-specific availability risk requiring owner awareness or follow-up.

Suggested reviewers: eggpeat

🚥 Pre-merge checks | ✅ 14 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description explains what changed, why it changed, and how it was verified. It omits the template's Demo Video, Review Trigger, and Checklist sections, and the hosted focused workflow remains pend…	Add the missing Demo Video, Review Trigger, and Checklist sections. Record the hosted cmux-tui focused workflow result before merging.

✅ Passed checks (14 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: hardening socket start lock files.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Cmux Swift Actor Isolation	✅ Passed	PASS: The pull request changes only `cmux-tui/crates/cmux-tui-core/src/server.rs`, a Rust file. The relevant diff contains no Swift production or test changes, so it cannot introduce or worsen the lis…
Cmux Swift Blocking Runtime	✅ Passed	The pull request changes only `cmux-tui/crates/cmux-tui-core/src/server.rs`, a Rust file. The diff adds Rust lock-file handling and Unix Rust tests. It changes no Swift files and introduces no Swift b…
Cmux Browser Automation Off-Main	✅ Passed	PASS. The custom check applies to browser socket automation routing in Swift files and worker policy code. The complete focused PR range from the parent of the first lock-hardening commit changes only…
Cmux Expensive Synchronous Load	✅ Passed	PASS — the custom check applies only to production Swift changes. The pull-request diff from `c3f405901c` to `HEAD` changes only `cmux-tui/crates/cmux-tui-core/src/server.rs`, a Rust file. The diff up…
Cmux Cache Substitution Correctness	✅ Passed	PASS: The pull-request range changes only `cmux-tui/crates/cmux-tui-core/src/server.rs`, a Rust file. The custom check applies only to production Swift, TypeScript, and JavaScript changes. Therefore, …
Cmux No Hacky Sleeps	✅ Passed	PASS: The pull request changes only `cmux-tui/crates/cmux-tui-core/src/server.rs`, which is Rust and outside this check's TypeScript, JavaScript, shell, and build/runtime-script scope. The complete di…
Cmux Algorithmic Complexity	✅ Passed	PASS: The isolated pull request diff changes only `cmux-tui/crates/cmux-tui-core/src/server.rs`, which is Rust. `SocketStartLock::acquire` adds file-opening, metadata, permission checks, and a bounded…
Cmux Swift Concurrency	✅ Passed	PASS: The pull-request-local diff contains one changed file, `cmux-tui/crates/cmux-tui-core/src/server.rs`, which is Rust. It contains no changed `.swift` paths. Therefore, the diff does not introduce…
Cmux Swift `@Concurrent`	✅ Passed	PASS: The pull request changes only `cmux-tui/crates/cmux-tui-core/src/server.rs`, a Rust file. The full diff contains no Swift paths or Swift concurrency annotations. Therefore, the `@concurrent` cus…
Cmux Swift Package Boundaries	✅ Passed	The pull-request security series changes only `cmux-tui/crates/cmux-tui-core/src/server.rs`. The diff is Rust code and tests, with no `.swift` files or `Package.swift` manifests. Therefore, the Swift …

Full details: Description check

Explanation

The description explains what changed, why it changed, and how it was verified. It omits the template's Demo Video, Review Trigger, and Checklist sections, and the hosted focused workflow remains pending.

Full details: Docstring Coverage

Explanation

No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0 files. (1 skipped: 1 too large.)

Full details: Cmux Swift Actor Isolation

Explanation

PASS: The pull request changes only cmux-tui/crates/cmux-tui-core/src/server.rs, a Rust file. The relevant diff contains no Swift production or test changes, so it cannot introduce or worsen the listed Swift actor isolation mistakes.

Full details: Cmux Swift Blocking Runtime

Explanation

The pull request changes only cmux-tui/crates/cmux-tui-core/src/server.rs, a Rust file. The diff adds Rust lock-file handling and Unix Rust tests. It changes no Swift files and introduces no Swift blocking or timing primitive.

Full details: Cmux Browser Automation Off-Main

Explanation

PASS. The custom check applies to browser socket automation routing in Swift files and worker policy code. The complete focused PR range from the parent of the first lock-hardening commit changes only cmux-tui/crates/cmux-tui-core/src/server.rs; it adds Unix spawn-lock flags, ownership and permission checks, and FIFO/symlink tests. No Swift browser automation file, processV2Command, socketWorkerMethods, WebKit/AppKit access, or browser worker policy test changes are introduced. The rule's existing-debt exception also applies because the PR does not alter browser automation routing.

Full details: Cmux Expensive Synchronous Load

Explanation

PASS — the custom check applies only to production Swift changes. The pull-request diff from c3f405901c to HEAD changes only cmux-tui/crates/cmux-tui-core/src/server.rs, a Rust file. The diff updates SocketStartLock::acquire and adds Rust Unix tests; it adds no Swift agent-history load or Swift interactive-path code.

Full details: Cmux Cache Substitution Correctness

Explanation

PASS: The pull-request range changes only cmux-tui/crates/cmux-tui-core/src/server.rs, a Rust file. The custom check applies only to production Swift, TypeScript, and JavaScript changes. Therefore, it is not applicable.

Full details: Cmux No Hacky Sleeps

Explanation

PASS: The pull request changes only cmux-tui/crates/cmux-tui-core/src/server.rs, which is Rust and outside this check's TypeScript, JavaScript, shell, and build/runtime-script scope. The complete diff adds no fixed sleep, timer, polling, or wall-clock wait. The existing std::thread::sleep(Duration::from_millis(25)) is unchanged.

Full details: Cmux Algorithmic Complexity

Explanation

PASS: The isolated pull request diff changes only cmux-tui/crates/cmux-tui-core/src/server.rs, which is Rust. SocketStartLock::acquire adds file-opening, metadata, permission checks, and a bounded retry loop. It does not add nested collection scans, per-target rescans, repeated sorting/filtering, in-memory joins, or a slower collection algorithm. The added collection-like test inputs are fixed-size test data.

Full details: Cmux Swift Concurrency

Explanation

PASS: The pull-request-local diff contains one changed file, cmux-tui/crates/cmux-tui-core/src/server.rs, which is Rust. It contains no changed .swift paths. Therefore, the diff does not introduce or expand Swift concurrency patterns covered by this check.

Full details: Cmux Swift `@Concurrent`

Explanation

PASS: The pull request changes only cmux-tui/crates/cmux-tui-core/src/server.rs, a Rust file. The full diff contains no Swift paths or Swift concurrency annotations. Therefore, the @concurrent custom check is not applicable.

Full details: Cmux Swift Package Boundaries

Explanation

The pull-request security series changes only cmux-tui/crates/cmux-tui-core/src/server.rs. The diff is Rust code and tests, with no .swift files or Package.swift manifests. Therefore, the Swift package boundary rule is not applicable.

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Actionable comments posted: 1

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Inline comments:
In `@cmux-tui/crates/cmux-tui-core/src/server.rs`:
- Around line 4869-4903: Update the symlink-rejection test assertion to expect
the error returned by options.open in SocketStartLock::acquire: verify
error.raw_os_error() equals Some(libc::ELOOP), rather than expecting
ErrorKind::PermissionDenied. Do not alter the later permission checks.

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eaa899c fix(cmux-tui): harden socket start lock files (manaflow-ai#11396)

cubic-dev-ai Bot reviewed Sep 1, 2026

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Comment thread cmux-tui/crates/cmux-tui-core/src/server.rs

lawrencecchen force-pushed the feat/tui-start-lock-security-wave189 branch from aa8a2c1 to dbff9a6 Compare September 1, 2026 08:58

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Comment thread cmux-tui/crates/cmux-tui-core/src/server.rs

lawrencecchen force-pushed the feat/tui-start-lock-security-wave189 branch 2 times, most recently from 0063539 to 771e3ee Compare September 1, 2026 09:33

lawrencecchen force-pushed the feat/tui-start-lock-security-wave189 branch from fd066d3 to cf91548 Compare September 1, 2026 10:02

lawrencecchen force-pushed the feat/tui-start-lock-security-wave189 branch 2 times, most recently from a021f87 to 4040a07 Compare September 1, 2026 14:33

lawrencecchen force-pushed the feat/tui-start-lock-security-wave189 branch from 4040a07 to 7d7e8de Compare September 1, 2026 15:04

lawrencecchen force-pushed the feat/tui-start-lock-security-wave189 branch 2 times, most recently from 4cccf91 to 8256588 Compare September 1, 2026 15:43

lawrencecchen mentioned this pull request Sep 1, 2026

fix(cmux-tui): fence listener cleanup by socket identity #11475

Closed

lawrencecchen added 6 commits September 1, 2026 09:56

test(tui): fence symlinked and shared start locks

dd7653a

fix(tui): harden socket start lock ownership

ee15e6f

test(tui): assert no-follow errno for start locks

e8952f9

fix(tui): keep start lock migration write-only

386abf0

test(tui): reject unsafe start lock files

af89db3

fix(tui): fence unsafe start lock files

3390063

lawrencecchen force-pushed the feat/tui-start-lock-security-wave189 branch from 8256588 to 3390063 Compare September 1, 2026 16:56

lawrencecchen merged commit eaa899c into main Sep 1, 2026
53 of 56 checks passed

lawrencecchen deleted the feat/tui-start-lock-security-wave189 branch September 1, 2026 17:27

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rustybret pushed a commit to rustybret/bmux that referenced this pull request Sep 1, 2026

chore(sync): sync upstream main (1 commits)

a0c7d5d

eaa899c fix(cmux-tui): harden socket start lock files (manaflow-ai#11396)

lawrencecchen mentioned this pull request Sep 1, 2026

Report and stop stale cmux-tui servers #8769

Closed

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fix(cmux-tui): harden socket start lock files - #11396

fix(cmux-tui): harden socket start lock files#11396
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