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…rt host file types and nanosecond times, fix the symlink policy refreshMemory() only rebuilt the DataView when the old buffer was detached. A shared memory never detaches on grow, so every hostcall that touched a grown page threw RangeError out of the import. fd_seek returned errno 0 for an unknown whence and for an offset that went negative (writing 2^64-n as the new offset), and threw a plain Error on a descriptor that had never been seeked. It now returns EINVAL and leaves the offset alone. fd_filestat_get and path_filestat_get derived the timestamps from millisecond floats. They now use the BigInt stats and write the exact host nanoseconds. The standard descriptors were hard-coded as character devices with tty rights, so wasi-libc's isatty() was true with stdout redirected to a file or a pipe. Their type and rights now come from the host fd on first use, like any descriptor from path_open. path_symlink accepted any target, while unlink, readlink, rename and lstat refused to touch a link whose target is outside the preopen. The target is now checked against the preopen, and calls that do not follow the final component no longer resolve it.
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Status: ready for review. CI build 106955: 178 of 181 jobs green, Review feedback addressed in ebdf089 (symlink targets follow Node's policy, no Reproduction (Bun 1.4.1 canary, Linux x64), driving
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Included review availability: Your plan provides up to 5 included reviews per hour; 1 remains after this review. WalkthroughWASI now derives standard-descriptor metadata from host descriptors, writes bigint filesystem timestamps, validates seeks, handles final symlinks with preopen containment, and refreshes memory views after buffer changes. Regression tests cover these behaviors. ChangesWASI runtime behavior
Suggested reviewers: Merge Risk: ⚪ Minimal · up to The PR updates WASI memory handling, file-descriptor validation, metadata precision, descriptor typing, and symlink behavior without any actionable merge-blocking risk remaining; it is merge-ready after normal checks and review. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
Full details: Title checkExplanation The title clearly identifies the main WASI changes, including memory refresh, fd_seek validation, descriptor types, nanosecond timestamps, and symlink policy. It is detailed but remains specific and relevant. Full details: Description checkExplanation The description provides a detailed problem statement, implementation summary, verification notes, compatibility background, and test coverage. It does not use the exact template headings, but it contains the required information and is substantially complete. Comment |
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In `@test/js/bun/wasm/wasi.test.js`:
- Around line 323-333: Reorder the assertions in the WASI test so the stdout
JSON validation runs before the exitCode assertion; keep the stderr check before
both, and assert exitCode last to preserve the useful stdout diff when filetype
expectations fail.
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Additional findings (outside the current diff — GitHub can't attach inline comments there):
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src/js/node/wasi.ts— pre-existing:path_linkleft out of thefollowFinal=falsesweep applied to its siblings (path_rename,path_symlink,path_unlink_file,path_readlink,path_rmdir) [also at: src/js/node/wasi.ts:1226 - pre-existing: path_filestat_set_times still ignores its lookupflags — sibling to path_filestat_get left unfixed after…]Extended reasoning...
REVIEW.md requires fixing the whole class in the same PR.
path_link's new-path argument is a name being created (never followed), exactly likepath_rename's new path andpath_symlink's link path — both of which this PR switched toRESOLVE_PATH(..., false). And its old-path argument's follow behavior is governed by_oldFlags & WASI_LOOKUPFLAGS_SYMLINK_FOLLOW, which the new mechanism could honor but is still ignored. After merge, a guest hard-linking a symlink itself (SYMLINK_FOLLOW clear) whose target lies outside the preopen still getsENOTCAPABLEeven though the operation touches only the parent directory — the exact inconsistency this PR fixes forunlink/readlink/rename/lstat. The base branch behaves the same, so this is a partial-fix gap the PR description does not call out; a complete fix passesfollowFinal=falsefornpand(_oldFlags & WASI_LOOKUPFLAGS_SYMLINK_FOLLOW) !== 0forop.Verification: pre-existing —
path_linkat src/js/node/wasi.ts:1229-1240 was left out of thefollowFinalsweep this PR applied to its siblings. Line 1229:path_link: wrap((oldFd, _oldFlags, oldPath, oldPathLen, newFd, newPath, newPathLen) => {—_oldFlags(the WASIlookupflagsfor the source) is underscore-prefixed and ignored, exactly likepath_filestat_get'sflagswas before this PR wired it to…
…es, honor lookupflags in path_filestat_set_times A containment check on a relative symlink target cannot hold: the target is a string that the kernel interprets when the link is followed, against a tree the guest can change afterwards. Match Node instead: refuse an absolute target with EPERM and check the result when a link is followed, which path_open already does. A regular file on fd 0, 1 or 2 shares its offset with the host process and node:fs has no lseek, so its rights no longer include FD_SEEK and FD_TELL. Before, the derived rights advertised them while fd_read kept reading at the host's offset. path_filestat_set_times honors the SYMLINK_FOLLOW lookup flag (lutimes without it) and takes the default times from the target instead of the directory. path_link resolves its new path without following a final symlink, like the other calls that create a name.
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Both issues from the earlier review are addressed: path_symlink now applies only Node's absolute-target refusal (dropping the bypassable lexical containment check in favor of the existing follow-time realpath check), and stdio fds backed by a regular file have FD_SEEK/FD_TELL stripped so a seek on fd 0 fails EPERM as before rather than silently succeeding. I re-reviewed the follow-up commits and didn't find new bugs. Given this reworks the preopen containment path (RESOLVE_PATH followFinal, symlink policy across path_* calls), a human look at the sandbox-escape surface is still worthwhile.
What was reviewed:
RESOLVE_PATH(…, followFinal=false)— parent is still realpath'd and containment-checked; only the final component is left unresolved, so a symlinked intermediate directory pointing outside is still refused.fd_seek— rejected seeks (unknown whence, negative/overflowing result) leavestats.offsetuntouched and write nothing tonewOffsetPtr.fstatSyncbigint migration — all consumers (fd_filestat_get,fd_seekEND,translateFileAttributes, closed-stdio fallback) updated for bigint fields andis*()predicates.refreshMemory()identity check — correct for both detached and shared buffers;memory.bufferis a fresh object after every grow.
Extended reasoning...
Overview
This PR touches src/js/node/wasi.ts (Bun's JS polyfill for node:wasi) and test/js/bun/wasm/wasi.test.js. It fixes several correctness edges: refreshMemory() now compares buffer identity so shared-memory grows are seen; fd_seek validates whence and clamps to [0, 2^63-1] without mutating state on rejection; stat calls use { bigint: true } for full-precision nanosecond timestamps; stdio fds derive their filetype/rights from the real host fd on first use (with FD_SEEK/FD_TELL stripped for regular files since node:fs has no lseek); RESOLVE_PATH gains a followFinal flag so unlink/readlink/rename/rmdir/symlink/link(new)/lstat/lutimes can act on a symlink whose target is outside the preopen or dangling; path_symlink refuses absolute targets with EPERM (matching Node); path_filestat_set_times honors SYMLINK_FOLLOW and stats the target rather than the directory fd. Five new tests exercise each behavior.
Since my previous review, the author pushed follow-up commits that (a) removed the relative-target containment check from path_symlink — I had shown a two-step bypass, and the PR notes explain that resolving from the real parent only relocates the problem, so the check was dropped entirely in favor of Node's policy plus follow-time realpath enforcement — and (b) added the entry.real <= 2 && REGULAR_FILE guard that strips FD_SEEK/FD_TELL from stdio rights, so fd_seek(0, …) on redirected stdin fails EPERM instead of silently succeeding without effect. The stdio test now asserts seek: WASI_EPERM for all three fds.
Security risks
The change directly modifies the WASI preopen sandbox's path-containment logic. RESOLVE_PATH(…, followFinal=false) skips realpath on the final component so operations that act on a link itself can target symlinks pointing outside. I traced this: the parent directory is still realpath'd and containment-checked against realBase, so a symlinked intermediate (e.g., sub -> /etc) is still caught; only the leaf name is appended unresolved. path_symlink no longer attempts creation-time containment of relative targets — this matches Node and is enforced at follow time by the existing realpath loop in RESOLVE_PATH (which path_open uses). path_link's old path is intentionally still resolved with followFinal=true (a hard link to a file outside would be a real escape, and link(2)'s symlink-following is platform-defined). Stdio fds no longer carry a path, so a directory passed as stdin can no longer be used as a path_* base (previously reachable via /dev/stdin). No new escape routes were found, but this is exactly the surface where a subtle mistake becomes a sandbox escape.
Level of scrutiny
High. REVIEW.md flags security-sensitive paths (permissions, path containment) as not-auto-approvable, and this PR reworks the guard that keeps a WASI guest inside its preopened directory across half a dozen path_* hostcalls. The change is well-reasoned, cites Node's observed behavior as the spec per the Node-compat rule, and ships targeted tests including negative cases (following an escaping link is still ENOTCAPABLE, secret.txt outside the preopen is unmodified after the run). But the containment invariant is subtle enough — TOCTOU between realpath and the syscall, lexical vs. real parent, platform link(2) semantics — that a maintainer familiar with the original RESOLVE_PATH design should sign off.
Other factors
Both of my earlier inline findings were addressed by real code changes (not just self-resolved threads), so acknowledging that progress is warranted. The bug hunt ran to dry_streak with no new findings. The fstatSync bigint migration is consistent across all call sites I checked (fd_filestat_get, fd_seek END arm, translateFileAttributes via is*() predicates, and the closed-stdio fallback object). Tests follow harness conventions (tempDir, bunExe/bunEnv, stderr asserted befo
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Problem
memory.grow(), every hostcall that touches a new page throwsRangeError: Out of bounds accessinto the guest.refreshMemory()(src/js/node/wasi.ts) only rebuilt itsDataViewwhen the buffer was detached. ASharedArrayBuffernever detaches.fd_seekreturned errno 0 for an unknownwhenceand for a negative result (writing2^64-n). On a never-seeked descriptor it threw a plainError.path_filestat_gettruncated times to ms. fd 0-2 were hard-coded as tty character devices, soisatty()was true with stdout redirected.unlink,readlink,rename,lstatrefused a symlink whose target is outside the preopen.Fix
refreshMemory()compares buffer identity.memory.bufferis a new object after every grow.fd_seekreturnsEINVALfor an unknownwhenceor a result outside[0, 2^63-1], and stores nothing then.{ bigint: true }. fd 0-2 get type and rights fromfstaton first use, through the existingstat()path. A regular file there gets noFD_SEEK/FD_TELL: the host owns its offset.RESOLVE_PATHgets afollowFinalflag. Calls that act on a link itself passfalse, so only the parent goes through realpath.path_symlinkrefuses absolute targets withEPERM, like Node.path_filestat_set_timeshonorsSYMLINK_FOLLOW.test/js/bun/wasm/wasi.test.js(5 new tests, fail on 1.4.1). Alsohello-wasi.wasmwith stdout to a file,/dev/null, a pipe, a pty.Background
node:wasiis a JS polyfill. Each hostcall reads guest memory throughthis.view, aDataViewovermemory.buffer.path_open.isatty()isfd_fdstat_getreturningCHARACTER_DEVICEwith neitherFD_SEEKnorFD_TELL.Notes
Oracle: Node v26.3.0, driving
wasi.getImportObject().wasi_snapshot_preview1with a hand-assembled module that only exports a memory. Results for the same cells:args_sizes_get/clock_time_getin the new page: 0 (Bun: RangeError)fd_seekwhence 3 / 255: 28; negative result via SET/CUR: 28;SEEK_END -3on a 10-byte file: 0, offset 7 (Bun before: 0, 0, 0 with offset 2^64-5)path_filestat_getandfd_filestat_getmtim: identical to the hostst_mtimin ns (Bun before:...851000064and...851749756for a host...851749745; the second one went through a float ms value)fd_fdstat_get(1)with stdout to a file: filetype 4; to a pipe: 6 (Bun before: 2 for both)path_symlink: absolute target 63 (EPERM);../x,sub/../../x,..,a/../../xall 0. Node performsunlink,readlink,rename,lstatandlutimeson a link whose target is outside; Bun now does too.path_filestat_set_timeswith lookupflags 0 on a symlink sets the link's own time in Node and leaves the target alone.Other details:
fd_seekwith a whence of 3 on a fresh descriptor threwError: stats.offset must be definedout of the import.wrap()only convertsWASIErrorand errors with a stringcode.sub -> ., thensub/link -> ../secret). Resolving from the real parent only moves the problem (sub/up -> .., thenlink -> sub/up/../secret, or creating the link before its intermediate directories exist), so the check was dropped in favor of Node's policy plus the follow-time check.FD_SEEK/FD_TELLfor a regular file on fd 0.fd_readon fd 0 reads at the host's offset, so a seek would have succeeded without effect. Before this PR such a seek failed withEPERM, and it still does.path_linkkeeps resolving its old path through a final symlink whatever the lookup flags say. Whetherlink(2)follows a symlink is platform defined, and a hard link to a file outside the preopen would be a real escape. Its new path is resolved without following, like the other calls that create a name.path_filestat_set_timestook its default times (the one of atim/mtim not being set) from the directory fd. They now come from the target. WithoutSYMLINK_FOLLOWit callslutimes.translateFileAttributescall instat()passed the WASI fd tobindings.isTTY, not the host fd. It now passesentry.real.fstatSync()now returns BigInt fields and theis*()predicates, becausestat()can reach it for fd 0-2.path, so they can never be the base of apath_*call (before, a directory passed as stdin could be listed and opened through/dev/stdin).fd_fdstat_set_rightstest readFD_MAP.get(0).rightsbefore any hostcall. It now callsfd_fdstat_get(0)first, since the rights are derived on first use.src/js/node/wasi.ts(node:wasi: bounds-check guest pointers in every hostcall and return EOVERFLOW #39100 pointer bounds checks, node:wasi: return EOVERFLOW for out-of-bounds iovecs instead of throwing/logging #34468 iovec bounds, node:wasi: fix clock_res_get endianness and missing refreshMemory #34471clock_res_get, node:wasi: honor returnOnExit so proc_exit does not kill the host process #34474proc_exit, node: implement node:wasi v26 WASI class surface (+23 tests) #35709 the Node v26 class surface). None of them changes these behaviors. Re-verified on this build that their targets (proc_exitkilling the host,poll_oneoffclock TypeError,dev/tty-> fd 0,clock_res_getbyte order, iovec OOBconsole.log, missinggetImportObject/initialize,fd_renumber(x, x)) are still present and untouched here.no test proof · iteration 0 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/bun/wasm/wasi.test.js