Ensure that FileManager.copyItem cannot copy directory metadata to files #1081
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Dec 11, 2024
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…les (swiftlang#1081) * (135575520) Ensure that FileManager.copyItem cannot copy directory metadata to files * Fix whitespacing * Fix Windows test failure
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FileManager.copyItem(atPath:toPath:)has a TOCTOU bug due to how it recursively copies directories. As we recursively copy directories, we copy the directory itself with default metadata/permissions, copy the contents of the directory, then copy the metadata over (which may change permissions on the directory, including potentially making it read-only). This TOCTOU bug allows another process with write access to the source directory to (with the right timing) cause a process that usesFileManager.copyItemto copy and apply metadata to a file rather than a directory.To fix the TOCTOU issue, the post-order traversal which copies the metadata now:
fstatsthe source and destination directories to validate that they are directories (and not files)fcopyfileon Darwin, and a custom function on Linux wherefcopyfiledoes not existThis ensures that we only copy metadata between directories and cannot accidentally apply metadata to a file.