Python safe_tarfile: further adjustments for old python

Douglas Bagnallrequested to merge
samba-team/devel/samba:douglas-safe-tarfile-again-and-again into master

This is used only by domain backup restore. With old versions (< 3.8) of Python, a bad tarfile could write in the wrong place (CVE-2007-4559). This sounds worse than it is, because writing in the right place already gives the attacker domain admin.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=16103

Checklist

  • Commits have Signed-off-by: with name/author being identical to the commit author
  • (optional) This MR is just one part towards a larger feature.
  • (optional, if backport required) Bugzilla bug filed and BUG: tag added
  • Test suite updated with functionality tests
  • Test suite updated with negative tests
  • Documentation updated
  • CI timeout is 3h or higher (see Settings/CICD/General pipelines/ Timeout)

Reviewer's checklist:

  • There is a test suite reasonably covering new functionality or modifications
  • Function naming, parameters, return values, types, etc., are consistent and according to README.Coding.md
  • This feature/change has adequate documentation added
  • No obvious mistakes in the code

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