[Bug 2091865] Re: Invalid null-pointer dereference in TagSection.keys()

[Sudhakar Verma]

The USN is out - @juliank will you handle the debian side or should I
raise a PR to https://salsa.debian.org/apt-team/python-apt/

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https://bugs.launchpad.net/bugs/2091865

Title:
  Invalid null-pointer dereference in TagSection.keys()

Status in python-apt package in Ubuntu:
  Fix Released

Bug description:
  [Impact]
  deb822 files with non-Unicode keys cause a NULL value to be generated and subsequently passed to PyList_Append() and Py_DECREF(), the latter than trying to dereference it and causing a segmentation fault.

  This is causing process-upload to crash on broken uploads.

  [Test plan]
  The unit tests are run at build time, as well as during autopkgtests.

  To reproduce the issue, the following test case is added:

  +    def test_invalid_unicode_key(self):
  +        ts = apt_pkg.TagSection(b"T\xc3st: Value\n", bytes=True)
  +        self.assertEqual(len(ts), 1)
  +        self.assertRaises(UnicodeDecodeError, ts.keys)

  `T\xc3st` is `Tést` = `T\xc3\xa9st` with the continuation byte
  removed, causing a UnicodeDecodeError.

  [Where problems could occur]
  The `.keys()` function can now raise the `UnicodeDecodeError` exception (or other exceptions from PyString_FromStringAndSize). It should have always crashed in those conditions before (they always resulted in NULL pointer dereference), but it's worth pointing out.

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