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Updated 11:05 AM PT - Aug 15th, 2026
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Status: ready for review. Reproduced with the released bun: in a project whose |
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LGTM — small, well-scoped fix that resolves directories.bin relative to the package directory instead of the project root.
What was reviewed:
- Verified
dirname::<Auto>onsubpath_z(always…/node_modules/<pkg>/package.json) yields the package dir, andjoin_z::<Auto>produces a path still relative todir_fd— both callers (get_bin_name_from_project_directoryandget_bin_name_from_temp_directory) remain correct. - Checked that the returned entry name (a bare readdir filename) is then resolved via
node_modules/.binand the existingis_trusted_cached_binarygates, so no new security surface. - Test uses
--no-installso failure can't fall through to the registry, and thebins/nested/subdirectory ensures theEntryKind::Filefilter is exercised deterministically (only one regular file in the dir).
Extended reasoning...
Overview
This PR fixes bunx <pkg> for packages that declare executables via directories.bin (no bin field). The bug: get_bin_name_from_subpath reads directories.bin from node_modules/<pkg>/package.json and then opens that value relative to dir_fd (the project root or cwd), when it is defined relative to the package. The fix takes dirname(subpath_z) — which is the package directory — and joins the directories.bin value onto it before opening. Seven lines changed in src/runtime/cli/bunx_command.rs plus a new 40-line test.
Security risks
None introduced. The changed code only affects which directory is enumerated to learn a bin name; the resulting name is a bare directory entry (readdir cannot return a path with separators) and is then looked up in node_modules/.bin via bun_which, which flows through the pre-existing is_trusted_cached_binary / is_trusted_cache_root hardening. A malicious directories.bin value with ../ would be normalized by join_z and at worst point at a different directory to read — no execution happens from that path. This is no worse than the pre-fix code, which already accepted the raw value.
Level of scrutiny
Low-to-medium. This is a targeted bug fix in a code path that has never worked (per the PR description, same defect existed in the original Zig). The change uses established in-tree helpers (bun_paths::resolve_path::dirname / join_z with platform::Auto), matches how bun install's bin linker resolves the same field (src/install/bin.rs, Tag::Dir), and switches openat_a → openat only because join_z returns a &ZStr. Both call sites that construct subpath_z were checked: they always include …/package.json, so dirname never returns empty.
Other factors
- Test is hermetic (
file:dependency,--no-install, isolatedBUN_INSTALL_CACHE_DIR), asserts exact{stdout, stderr, exitCode}, and the PR description confirms it fails on the released bun. The nested-directory fixture makes theEntryKind::Filefilter deterministic (single regular file in the bin dir). - Separate test file (rather than
bunx.test.ts) is justified in the description: that file has a debug-build-only failure that would mask the before/after run. Verifier agents already examined and accepted this. test.skipIf(isWindows)is because the fixture bin is a shell script; the Rust change itself is platform-neutral (platform::Autoresolves toWindowsthere andsubpath_zis built withbun_paths::SEP). Also examined and accepted by verifiers.join_zwrites into a thread-local buffer and the result is consumed immediately byopenatbefore any other path helper is called, so no buffer-reuse hazard.
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Pushed 7953259: on top of the path fix, bunx now skips the same |
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Inline comments:
In `@test/cli/install/bunx-directories-bin.test.ts`:
- Around line 42-62: Extend the skipped bunx directories.bin test coverage to
include separate cases for an empty value, an absolute path, and a
drive-relative path such as C:..\outside, while retaining the existing
parent-directory escape case. For each variant, verify install succeeds but bunx
--no-install cannot determine an executable, using the existing test setup and
assertions.
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📒 Files selected for processing (3)
src/install/bin.rssrc/runtime/cli/bunx_command.rstest/cli/install/bunx-directories-bin.test.ts
When a package has no "bin" field, bunx reads its "directories.bin" and takes the first file in that directory as the executable's name. The directory was opened relative to the project root (or the bunx cache root) instead of the package, so it was never found and bunx failed with "could not determine executable to run" for every such package. While here, skip the same values the bin linker refuses to link from (empty, absolute, or escaping the package), so bunx never takes a bin name from a directory outside the package.
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LGTM — small, well-scoped fix that resolves directories.bin against the package directory instead of the project root, and reuses the install-side bin_target_escapes_package_dir gate so both consumers agree.
What was reviewed
- Traced both callers of
get_bin_name_from_subpath(project-dir and bunx-cache paths):dirname(subpath_z)yields the package dir in each, andjoin_z+openat(dir_fd, …)opens the right directory. - Confirmed the rejection filter matches
bin.rsTag::Dir(empty / absolute /..-escape / drive-relative) and that install still exits 0 for those values so the negative tests'bun installstep holds. - Checked the positive test can only pick
tool-cliregardless of readdir order (the siblingnested/is a directory, filtered bykind == File), and that the negative tests' planted.binentries are what the unfiltered path would actually yield.
Extended reasoning...
Overview
The PR fixes BunxCommand::get_bin_name_from_subpath so that a directories.bin value read from node_modules/<pkg>/package.json is opened relative to the package directory (dirname(subpath_z)) rather than relative to dir_fd (the project root or cwd). It also gates the value through the same bin_target_escapes_package_dir helper the install-side bin linker uses (plus an explicit empty check), and widens that helper from pub(crate) to pub so bunx_command.rs can call it. A new test file installs a file: dependency whose only bin comes from directories.bin, runs it via bunx --no-install, and separately verifies three rejected-value classes (../../outside, absolute, empty) do not cause bunx to run a planted .bin entry.
Security risks
This path is not a privilege boundary: bunx only extracts a name from the directory, then executes whatever node_modules/.bin/<name> resolves to via bun_which (still subject to is_trusted_cached_binary etc.). Nonetheless the change is strictly a tightening — the pre-PR code accepted any string and (if the open had ever worked) would have listed an arbitrary directory. Aligning with bin_target_escapes_package_dir means bunx and the linker now agree on what directories.bin may point at, and the returned readdir entry name inherently contains no path separators. No new attack surface is introduced.
Level of scrutiny
Medium. The Rust change is ~12 lines in a non-hot bunx lookup path, plus a visibility widening on an existing helper. It mirrors established semantics from src/install/bin.rs (Tag::Dir) rather than introducing new logic. join_z/dirname are the standard in-tree helpers already used throughout for this pattern. I traced both call sites (get_bin_name_from_project_directory builds node_modules/<pkg>/package.json; get_bin_name_from_temp_directory builds <cache>/node_modules/<pkg>/package.json) and dirname yields the correct package dir for each; the joined path is then opened against the same dir_fd as before, so the fd-relative semantics are preserved.
Other factors
- The test is hermetic (
file:dep,--no-install, per-testBUN_INSTALL_CACHE_DIR), usestempDir/bunEnv, drains stdout/stderr/exited concurrently, and asserts a combined object. Windows is skipped with a stated reason (shell-script bins). - The negative tests plant exactly the
.binentry the unfiltered code would pick (verified:../../outside→outside/planted; empty → package dir →package.json; absolute →<dir>/outside/planted), so a regression in the filter breaks a specific assertion rather than passing vacuously. - The one CodeRabbit review thread (add absolute/empty variants) was addressed in e449e85 and marked resolved; no other outstanding reviewer comments.
- Change from
openat_atoopenatis correct becausejoin_zreturns a NUL-terminated&ZStrfrom a thread-local buffer.
### Problem - A `package.json` or a registry manifest with `"bin": ""` and a `directories.bin` aborts `bun install` on every build, release builds included: `panic: range end index 516 out of range for slice of length 0`. - An empty `bin` names no file, so the build pass reads `directories.bin` and appends it. The counting pass stopped at the empty `bin` (`src/install/npm.rs:2184`, `src/install/lockfile/Package.rs:2264`) and reserved nothing for it, so the append ran past the end of the string buffer. - The input comes from the project, from a dependency folder, or from a registry. npm installs the same package with exit code 0. ### Fix - Each counting pass now reads `bin` the way its build pass does: an empty string falls through to `directories.bin`. - Both parsers that size a buffer from a counting pass had the mismatch. `PackageManifest::parse` reads a registry manifest, `Package::parse_with_json_impl` reads a `package.json`. Every other reader of `bin` appends into a growable buffer and cannot drift. - Verified: 3 new tests in `test/cli/install/bun-install-registry.test.ts`, one per source of the file. All 3 abort on release 1.4.3-canary (c6b7fcb) and pass here. The rest of that file passes (258 tests), plus `bun-install`, `bun-lock`, `bun-pm` and `isolated-install`. - Found by fuzzing the manifest parser. No user report exists. ### Background - `bin` names the executables of a package. A string names one file. An object maps each name to a file. `directories.bin` names a folder, and every file in it becomes an executable. npm treats an empty `bin` as absent. - Both parsers run in two passes. The counting pass sums the length of every string it will store, the caller allocates one buffer of that size, and the build pass appends into it. A string that the counting pass did not sum has no room. - The manifest buffer gets slack (`npm.rs:2319`), so a short uncounted string can fit. The lockfile buffer gets none (`lockfile.rs:2671`). <details><summary>Notes</summary> **Reach.** `bun publish` sends `"bin": ""` with no check, so a registry can serve it. The shape also comes from a hand-written `package.json`, a workspace, or a `file:` folder dependency. With the lockfile parser the abort needs only 9 bytes of `directories.bin` past the slack of the other strings, and the slack is what the rest of that `package.json` counted. The smallest case I reproduced is a 90-byte root `package.json` with no dependencies. **Tests.** Each test uses a `directories.bin` of 523 bytes, which is longer than any slack. The path is `./` repeated 256 times plus the folder name, so it resolves to the same folder and the bins still link. Two tests assert the linked bin, one asserts that an install with no dependencies completes. **Excluded on purpose.** - A shared `bin` classifier used by both passes of both parsers is the shape that cannot drift again. It needs one abstraction over two JSON value types and two string builders, next to `Bin::parse_append` in `src/install/bin.rs`. That is a refactor of the bin parsing layer, and it also touches the `bun.lock` and pnpm readers, so it is not in a crash fix. - #33022 rewrites `PackageManifest::parse` around a cursor API. Its counting pass has the same unconditional `count` for `bin` (`npm.rs:3720` on that branch). I left a comment there. - `bun pack` and `bunx` read `directories.bin` too. Their open reports are #38720 and #39096. Neither is this under-count. **Sibling PR.** #43035 removes the debug-only assertions of the same manifest parser. This PR is the release-build crash, and the two do not share a hunk. </details> <!-- robobun:evidence:begin --> --- **no test proof** · iteration 0 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/cli/install/bun-install-registry.test.ts <!-- robobun:evidence:end -->
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Problem
bunx <pkg>for a package that declares its executables throughdirectories.bin(nobinfield) always fails withcould not determine executable to run for package <pkg>, after also downloading the package into the bunx cache even when it is installed locally.BunxCommand::get_bin_name_from_subpath(src/runtime/cli/bunx_command.rs) readsdirectories.binout ofnode_modules/<pkg>/package.jsonand then opens that directory relative to the project root (dir_fd, or the cwd for the bunx cache) instead of relative to the package, so the open fails with ENOENT. Same in the original Zig version, so this has never worked.Fix
directories.binvalue onto the directory of thepackage.jsonit was read from before opening it. The rest of the lookup (first regular file in that directory is the bin name, then the usualnode_modules/.binsearch) is unchanged.directories.binis defined relative to the package root, which is wherebun install's bin linker also resolves it from (src/install/bin.rs,Tag::Dir).bin_target_escapes_package_dir: absolute or..-escaping, plus empty) are now skipped here too, so bunx never takes a bin name from a directory outside the package. The helper becomespubfor that. Not a privilege boundary (bunx only reads names there and then runs whatevernode_modules/.binhas under that name, and the previous code accepted any value), but the two consumers of the field should agree on what it may point at.test/cli/install/bunx-directories-bin.test.tsinstalls afile:dependency whose only bin comes fromdirectories.binand runs it withbunx --no-install(so a failure cannot fall through to the registry); fails on the released bun withCould not find an existing 'tool' binary to run, passes with this change. Three more cases pointdirectories.binat../../outside, at an absolute path, and at""(the package directory itself), plant the name each would yield innode_modules/.bin, and check bunx refuses instead of running it (without the check the relative and empty values make it run the planted file). Its own file rather thanbunx.test.tsbecause that file has a debug-build-only failure (Bun.versionvs the user agent) that would mask the before/after run.Background
directories.bin: package.json field naming a directory whose every file is an executable, the alternative to thebinmap.bun installlinks each file in it intonode_modules/.bin.bunx foofirst looks fornode_modules/.bin/foo; when the bin is not named after the package it reads the package's package.json to learn the bin name (binmap, elsedirectories.bin) and looks that up in.bininstead.