Reject tar hard link targets that escape the output directory - #5437
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shaggyinsomniac wants to merge 1 commit into
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Reject tar hard link targets that escape the output directory#5437shaggyinsomniac wants to merge 1 commit into
shaggyinsomniac wants to merge 1 commit into
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TarArchiveReader.extract validated member names only. A hard link member whose relative linkname contains '..' makes tarfile's os.link() alias an existing file outside the output directory; a later write through the alias overwrites it. The realpath-based check cannot detect this because it does not resolve hard links. Mirror tarfile's link-target resolution and apply the same containment check to it.
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Fixes #5436.
What
TarArchiveReader.extractnow resolves a hard link member's target the same waytarfilewill (absolute linknames re-rooted at the output directory, relative ones joined against the member's directory) and applies the existing_is_attempting_path_traversalcontainment check to it.Why
The member-name guard could not catch this class:
os.path.realpathdoes not resolve hard links, so an alias created byos.linkpointing outside the output directory still appears contained. Details and a standalone stdlib PoC in #5436.Testing
pytest src/clusterfuzz/_internal/tests/core/system/archive_test.py— both new tests pass; no other tests changed behavior (one unrelated pre-existing env-sensitive zip-chmod mock test fails identically with and without this change).