tarfile `data`/`tar` filter bypass via hard link to a symlink

[StanFromIreland]

On CPython 3.13.15 for Linux, an attacker-controlled tar archive extracted with the tar or data filter can make tarfile change the permissions and modification time of an existing file outside the extraction directory. The archive also leaves a path inside the extracted tree that resolves to the outside file. Opening that path returns the outside file's content.

This was incidentally fixed by 5a57248 for 3.14+ which changed os.link to use AT_SYMLINK_FOLLOW.

Linked PRs

• gh-157190: Follow symlinks when extracting tarfile hard links #157191
• [3.13] gh-157190: Fix tarfile data/tar filter bypass via hard link to a symlink #157192
• [3.14] gh-157190: Follow symlinks when extracting tarfile hard links (GH-157191) #157261
• [3.15] gh-157190: Follow symlinks when extracting tarfile hard links (GH-157191) #157262
• [3.12] gh-157190: Fix tarfile data/tar filter bypass via hard link to a symlink (GH-157191) (GH-157192) #157454