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gh-156026: document tar filter link targets #156056

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14 changes: 13 additions & 1 deletion Doc/library/tarfile.rst
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Expand Up @@ -1056,7 +1056,8 @@ can be:

* the string ``'tar'``: Honor most *tar*-specific features (i.e. features of
UNIX-like filesystems), but block features that are very likely to be
surprising or malicious. See :func:`tar_filter` for details.
surprising or malicious. Note that this filter does not limit the targets of
symbolic links. See :func:`tar_filter` for details.

* the string ``'data'``: Ignore or block most features specific to UNIX-like
filesystems. Intended for extracting cross-platform data archives.
Expand Down Expand Up @@ -1124,6 +1125,17 @@ reused in custom filters:

Return the modified ``TarInfo`` member.

.. warning::
This filter does not check :attr:`TarInfo.linkname`. This means it does
not limit where a symbolic link member points. An absolute symbolic-link
target will remain absolute, and a relative target may resolve outside the
extraction destination. The destination path protection described above
concerns only where the archive member itself is written, not where a
symbolic link resolves. The stricter :func:`data_filter` rejects these
unsafe link targets, raising :class:`~tarfile.AbsoluteLinkError` for
absolute link targets or :class:`~tarfile.LinkOutsideDestinationError`
for link targets outside the destination.

.. versionchanged:: next

Filenames containing ``..`` components are now normalized.
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