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Give path exports the permissions open() would - #525
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The atomic writers created their temp file with tempfile.mkstemp, which is always 0o600, and os.replace carried that onto the target: every to_html, write_image, write_images and facet export was owner-only, even when it replaced an existing 0o644 file. Create the temp file with 0o666 so the umask applies, and keep an existing target's mode.
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| Layer / File(s) | Summary |
|---|---|
Atomic export permission handling python/xy/export.py, tests/test_figure.py, tests/test_export_permissions.py, spec/api/export.md, news/525.bugfix.md |
Byte and text writers apply publication permissions before replacing targets. Tests cover new and existing files, temporary-file permissions, groups, ACLs, failure handling, and cleanup. The API specification and release note describe the behavior. |
Priority:
Estimated code review effort: 3 (Moderate) | ~20 minutes
Change: Bug fix
Suggested reviewers: alek99
Merge Risk: 
1fe27
-
Path exports now get the permissions open() would give them, and existing files keep their permissions. The remaining edge case is a narrow, brief exposure of an unpublished export when replacing another user's file in a sticky directory. It does not block merging.
Security architecture risk: 
32de4
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Exports that were previously owner-only can now be readable by other users under ordinary filesystem permissions. This enables the intended sharing behavior, but applications exporting confidential charts must account for it. Permission selection can also be influenced by a writable destination directory.
Retained concerns
- Medium · security · inferred: New exports inherit directory-governed permissions rather than remaining owner-only. Under a typical 022 umask, other local users can read chart files if directory traversal permits it; confidential-export callers must now enforce their intended filesystem policy.
- Medium · security · inferred: Mode lookup is not bound to the inode replaced. In an attacker-writable export directory, a planted symlink or a destination change between lookup and replacement can cause the writer to publish content with permissions taken from a different file or an earlier destination state. The prior writer published owner-only files regardless of that lookup.
Security review details
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Security Blast Radius
- inferred — Exposure is bounded to files written by path-export callers and to identities able to traverse their destination directories. The available evidence does not identify deployed tenants, serving accounts, or directory policies.
Security Findings and Attack Paths
- inferred — A user with write access to an export directory could plant a symlink whose referent has permissive bits before another identity exports to that name. The writer follows it for mode selection but replaces the pathname, potentially leaving the exported content readable to that user. Practical reachability depends on directory ownership and permissions not established here.
Trust Boundaries and Controls
- observed — The temporary file remains owner-only through fsync, and mode-probe failure falls back to owner-only publication. Neither control binds an existing-target mode lookup to the inode present at replacement time.
Resilience and Maintainability Implications
- inferred — Atomic replacement protects readers from partial content, but concurrent destination changes can make permission selection stale. The provided tests do not establish behavior under concurrent exporters or destination mutation.
Hardening Proposals
- proposed — For confidential exports, require a restrictive destination policy or explicit permission choice rather than relying on default umask behavior; avoid deriving the published mode from an untrusted or mutable pathname.
Pre-merge checks: 
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Check name Status Explanation Description Check Check skipped - CodeRabbit’s high-level summary is enabled. Title check The title accurately and concisely describes the main change: path exports now receive the permissions that open()would assign.Docstring Coverage Docstring coverage is inconclusive: files from earlier reviews still need to be rechecked within the check's analysis limits. Not blocking. Linked Issues check Check skipped because no linked issues were found for this pull request. Out of Scope Changes check Check skipped because no linked issues were found for this pull request.
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 [Medium impact] The change reaches files written through chart export paths. Preserve the existing file's group before merging, so re-exporting cannot grant another group read access. Findings
SummaryPath exports now apply normal file permission bits after writing a private temporary file.
Reviews (5) · Last reviewed commit: "Merge branch 'main' into fix/export-file..." · Reviewed by Greptile |
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Actionable comments posted: 2
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Inline comments:
In `@python/xy/export.py`:
- Line 240: Update the temporary-file creation flow around os.open: when mode
indicates an existing target, create the replacement with private permissions,
then use os.fchmod on fd to apply mode; keep 0o666 creation for new targets so
umask-based open-style permissions are preserved.
In `@tests/test_figure.py`:
- Line 1276: Update the mode assertion in the test using `_sibling_temp` to
compare the export’s mode with a reference file created by `open`, so the test
follows the same default-ACL behavior. Also revise the export specification to
clarify that the umask determines a new file’s mode only when no parent default
ACL applies.
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📒 Files selected for processing (4)
news/525.bugfix.mdpython/xy/export.pyspec/api/export.mdtests/test_figure.py
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Review follow-up. The temp file is created 0o600 by mkstemp again, so no other user can open it while the export is being written; after fsync the final mode is set through the descriptor (fchmod), right before the replace. A new file's mode is read from an empty probe created with 0o666, so a directory default ACL applies just as it does for open(). The test compares against a file made with open(), covers to_svg(path) and write_images, and checks the temp file is 0o600 while it is written.
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The probe is one more file in the target directory; if it cannot be made (no free inode), keep the finished export owner-only instead of failing it.
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A filesystem without chmod (vfat, some FUSE/NFS mounts) now keeps the owner-only export instead of failing it. The fallback test covers both the probe and fchmod failures, uses errno constants, and asserts the 0o600 fallback.
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One change is required: the platform guard in _publish_mode (inline comment). It does not skip Windows on Python 3.13+. There, a re-export over a read-only target leaks the .tmp file and replaces the real error with a PermissionError.
What I checked at e2d2187 (Linux, Python 3.13):
- On
main,to_html,write_imagepng/svg/pdf, and a pre-existing0o664target all land as0o600. On this PR they land as0o644, and the0o664file keeps0o664. Results matchopen()with umask027and002. Afacet_chart(...).to_html(path)export also gets0o644. No.tmpor.modefiles are left behind. - Live check: I served both output directories as an unprivileged user (
nobody) and loaded them in headless Chromium. The PR exports load: the HTML chart renders its canvases, the facet page renders, the PNG/SVG are served, and there are no console errors. Themainexports cannot be read by that user. - The new tests and the existing atomic-replace tests pass. The export, facet, and svg subset passes (443 passed). Ruff check and format are clean. The new functions are under the C901 threshold.
- The news fragment and the spec update are present.
Note: only the review bots have run on this head. The repository CI workflows have not run on it yet.
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Merging this PR will not alter performance1 warning, 1 note
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Footnotes
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All reported issues were addressed across 4 files (changes from recent commits).
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Every path export writes through
_atomic_write_bytes/_atomic_write_text. Both create their temp file withtempfile.mkstemp, which always uses mode0o600, andos.replacethen moves that mode onto the target. This affectsto_html(path),write_image,write_images,to_svg(path), and the facet-grid writers. As a result every exported chart is owner-only (rw-------), whatever the umask says, and it even replaces the mode of an existing0o644file.This matters when the export is meant to be read by someone else. A chart written into a directory served by nginx or Apache (running as another user) returns 403, a report dropped into a shared or group directory can't be opened by the group, and a file that was already
0o644becomes0o600after one re-export.Repro (main @ 72a069f, umask 022)
Fix
The temp file is still created by
mkstemp(0o600), so nothing can read it while it is being written. Afterfsync,_publish_modeapplies the modeopen(path, "w")would leave, usingos.fchmodon the open descriptor, and thenos.replaceruns. That mode is the existing file's permission bits, or for a new file0o666filtered by the umask or the directory's default ACL (read back from an empty probe file, so the process-wide umask is never flipped). Atomicity, fsync, temp naming, and cleanup are unchanged.spec/api/export.mdstates the rule next to the atomic-write contract.Tests
tests/test_figure.py::test_path_exports_get_the_permissions_open_would_givehas five cases:to_html,write_imagepng,to_svg(path),write_imagepdf, andwrite_images. Each case checks three things:open()in that directory.0o664target keeps0o664.0o600at everyfsync.The test is POSIX only.
test_export_still_lands_when_the_mode_cannot_be_applied(added after review) checks that applying the mode is best effort: when the probe cannot be created (ENOSPC) orfchmodis unsupported (EPERM), the export is still published, owner-only (0o600). Results:0o600vs0o644). With the fix, 5/5 pass, and the existing*_keeps_existing_file_on_atomic_replace_failuretests still pass.make check-security(security_export) passes.ruff check,ruff format --check, andty check pythonreport no new diagnostics compared with main.Checklist
news/525.bugfix.mdspec/api/export.md(atomic write paragraph)make check-securityrun for the path-write changeSummary by CodeRabbit