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shell(rm): stop the recursive walk from aborting on entries deeper than PATH_MAX - #39578
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…an PATH_MAX The walk joined each entry onto its directory path inside fixed-size buffers on the worker threads. An entry whose joined path did not fit panicked there. Both joins now spill to a heap buffer when the result does not fit, and the syscall on that path reports ENAMETOOLONG through the normal per-operand error.
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Reproduction on R=$(mktemp -d)
python3 -c 'import os,sys
fd=os.open(sys.argv[1],os.O_RDONLY)
for i in range(25):
os.mkdir("d"*200,dir_fd=fd); n=os.open("d"*200,os.O_RDONLY,dir_fd=fd); os.close(fd); fd=n
os.close(os.open("f.txt",os.O_WRONLY|os.O_CREAT,0o644,dir_fd=fd))' "$R"
bun -e 'const r = await Bun.$`rm -rf ${process.argv[1]}`.nothrow().quiet(); console.log(r.exitCode, r.stderr.toString())' "$R"Before: Fix: #39578 (this PR). The sibling shell sites are #37521 ( |
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Inline comments:
In `@test/js/bun/shell/commands/rm.test.ts`:
- Around line 299-318: Restrict the “recursive rm reports an entry deeper than
PATH_MAX instead of crashing” test to Linux, using the existing platform-based
skip mechanism so the 4060-byte fixture is not created on macOS or other
platforms. Preserve the test’s current behavior and assertions on Linux.
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Inline comments:
In `@test/js/bun/shell/commands/rm.test.ts`:
- Around line 314-320: Update deepDir and the related result-length assertions
to measure filesystem paths in bytes rather than UTF-16 code units: use
Buffer.byteLength for dir-length construction arithmetic and for results.*.entry
length checks, while preserving the existing PATH_MAX boundaries and expected
values.
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Updated 3:31 PM PT - Aug 18th, 2026
✅ @robobun, your commit 6447e487a7cf29e188d07f6b90a36f445609c9a2 passed in 🧪 To try this PR locally: bunx bun-pr 39578That installs a local version of the PR into your bun-39578 --bun |
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LGTM — the macOS PATH_MAX concern from my earlier pass was addressed in fecd9d3 (per-platform sizing) and 7f04ffb (byte-length arithmetic).
Checked that join_z_buf_spill/join_spill are the same helpers already used by the sibling shell/fs sites for this exact overflow, and that the spill Vecs are scoped so the borrowed result is copied into a ZBox before reuse or drop. The test covers both the file join (buf_join in the readdir loop) and the directory join (absolute branch of join), runs in a subprocess so the pre-fix panic surfaces as an assertion, and includes a positive control (plain) that the common path still succeeds.
Extended reasoning...
Overview
Two-file change: src/runtime/shell/builtin/rm.rs swaps resolve_path::join_z_buf → join_z_buf_spill in ShellRmTask::buf_join (adding a spill: &mut Vec<u8> parameter threaded from a per-readdir-loop Vec), and swaps resolve_path::join → join_spill in the absolute branch of ShellRmTask::join. test/js/bun/shell/commands/rm.test.ts adds a subprocess fixture that builds a directory whose absolute path is PATH_MAX - 64 bytes and places a 100-byte file entry and a 100-byte directory entry inside sibling trees, so both changed joins are exercised past the buffer boundary.
Security risks
None. The change widens where an overlong path is written (stack buffer → heap spill) so the syscall receives the whole string and returns ENAMETOOLONG instead of the process aborting on a slice-index panic. No new user-controlled parsing, no path-traversal surface — the join semantics are unchanged for every input that previously fit.
Level of scrutiny
Low-to-moderate. The Rust diff is a mechanical substitution to the established _spill variants (resolve_path.rs:1414, :1433) that #38360/#38368/#38379 already use for the same bug class in fs.watch, Bun.Glob, and shell mkdir/touch. I verified the borrow shape: in the readdir loop the &ZStr returned from buf_join is immediately copied to an owned ZBox before buf/join_spill are re-borrowed on the next iteration, and in join the local spill outlives the ZBox::from_bytes(joined) copy. The reused loop-level Vec is a nice touch — one allocation per directory, not per entry.
Other factors
My previous inline comment flagged that the original fixture hardcoded a 4060-byte tree and would fail setup on macOS (MAX_PATH_BYTES = 1024 there, per src/bun_core/util.rs:718). The author took the per-platform-limit option: the test now derives PATH_MAX as 4096 on Linux / 1024 elsewhere, builds to PATH_MAX - 64, and uses Buffer.byteLength for the arithmetic and the length assertions. That keeps macOS coverage rather than skipping it. All review threads (CodeRabbit's byte-length nit and the comment-cop doc-comment length note) are resolved in 7f04ffb. The author verified fail-before/pass-after on Linux at each revision; the test drains stdout/stderr/exited concurrently, asserts the exact rm: <path>: File name too long line, and checks the parent directory survived and a plain rm -rf still works.
Problem
Bun.$rm -rf <dir>aborts the whole process when the tree under<dir>has an entry whose path is longer than the path buffer:panic: range end index 4160 out of range for slice of length 4094(exit 134). With an absolute operand the message reads... out of range for slice of length 4095..nothrow()does not help.ShellRmTask::buf_join(src/runtime/shell/builtin/rm.rs) joins the directory path and the entry name withjoin_z_bufinto a stackPathBuffer. The join writes the result with plain slice indexing, so a result longer than the buffer panics.ShellRmTask::joindoes the same for an absolute operand withresolve_path::join, which writes into a 4096 byte thread-local buffer. (For a relative operand this branch already builds aVec.)PATH_MAX. Such trees are legal.mkdirrelative to an open directory creates them, and so dotarandgit.Fix
buf_joinjoins throughjoin_z_buf_spill. It uses thePathBufferas before when the result fits, and aVecowned by the readdir loop when it does not.joinusesjoin_spillthe same way.unlinkatoropenatwhole, and the OS rejects it withENAMETOOLONG.rmreports that asrm: <path>: File name too longand exits 1, like every other failed entry.join_z_buf_spillandjoin_spillare the existing helpers thatfs.readdir,Bun.Globandfs.watchuse for the same problem. shell(rm): stop panicking on operands longer than the path scratch buffers #37521 (the preserve-root check inrm) and shell(mkdir, touch): report operands longer than the path buffers instead of aborting #38379 (mkdir,touch) use them for the other shell sites.test/js/bun/shell/commands/rm.test.ts, "recursive rm reports an entry deeper than PATH_MAX instead of crashing". It builds two trees whose deepest directory isPATH_MAX - 64bytes long (PATH_MAXis 4096 on Linux and 1024 on the other POSIX platforms, the same split asMAX_PATH_BYTES), one with a 100 byte file and one with a 100 byte directory inside, so both joins are exercised. It runsrm -rfon each in a child process and expects exit 1 and theFile name too longline for the entry, then a normalrm -rfthat still succeeds. Skipped on Windows, where the path limit is different.USE_SYSTEM_BUN=1 bun test test/js/bun/shell/commands/rm.test.ts -t "deeper than PATH_MAX": fails with the panic above.bun bd test test/js/bun/shell/commands/rm.test.ts: 8 pass.cargo fmt --all -- --check: clean.Background
rm -rin the Bun shell is a tree ofDirTasks. The root task holds the operand as written. When a task reads a directory, it removes each file entry itself and creates a child task for each directory entry. Every task stores the full path of its entry, relative to the shell cwd when the operand was relative, and passes that path tounlinkat,openatorrmdiratwith the shell cwd fd. The two joins in this PR are where those full paths are built.PATH_MAX(4096 on Linux) bounds one path string that the kernel accepts in a syscall. It does not bound how deep a tree can be, because a process can always create an entry relative to an open directory. So a walker that builds full paths has to expect paths longer than its buffers. The OS then rejects the syscall withENAMETOOLONG, which is the error coreutils also shows for such an entry when it cannot use*atcalls.resolve_path::join_z_bufandresolve_path::joinnormalize the joined parts (collapse//, resolve.and..) into a caller buffer or a thread-local buffer. Neither checks the buffer length. The_spillvariants take an extraVec, compute an upper bound of the result from the input lengths, and grow theVecand write there when the bound exceeds the buffer.no test proof · iteration 2 · Platform-specific test(s) that do not run on this machine. Deferring to CI, which covers all platforms: test/js/bun/shell/commands/rm.test.ts