gh-143377: fix crashes in _interpreters.capture_exception

[picnixz]

• Issue: Heap buffer overflow in _format_TracebackException when TracebackException.format omits newline #143377

[serhiy-storchaka]

LGTM. 👍

[picnixz]

so there is a consistant iOS failure for this test. It looks like unraisable hooks are not well-supported (?) though I don't know why. Who should I ping for help here?

[picnixz]

ASAN isn't happy either. Which is weird.

[vstinner]

The failure on Android, iOS and ASAN:

  ERROR: test_capture_exception_unraisable_exception (test.test_crossinterp.CaptureExceptionTests.test_capture_exception_unraisable_exception)
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "/data/user/0/org.python.testbed/files/python/lib/python3.15/test/test_crossinterp.py", line 1536, in test_capture_exception_unraisable_exception
      self.assertEqual(cm.unraisable.exc_type, TypeError)
                       ^^^^^^^^^^^^^^^^^^^^^^
  AttributeError: 'NoneType' object has no attribute 'exc_type'

[picnixz]

Yes but I don't understand why unraisable exceptions are not supported for those platforms. The same goes for ASAN which is an Ubuntu machine. So I'm worried something else is wrong somewhere else but I don't know where.

[vstinner]

The failure on Android, iOS and ASAN

Oh, the unraisable exception is only raised if Python is built with --with-pydebug.

Extract of Python/crossinterp.c:

        info->errdisplay = _format_TracebackException(tbexc);
        Py_DECREF(tbexc);
        if (info->errdisplay == NULL) {
#ifdef Py_DEBUG
            PyErr_FormatUnraisable("Exception ignored while formatting TracebackException");
#endif
            PyErr_Clear();
        }

If the Py_DEBUG macro is not defined, PyErr_FormatUnraisable() is not raised.

@picnixz: You can skip the test if test.support.Py_DEBUG is false.

[picnixz]

Oh I thought all of them were built with DEBUG!

[picnixz]

Thanks Victor for the investigation! and thanks Serhiy for the suggestions!

[miss-islington-app]

Thanks @picnixz for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @picnixz, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker ce6bae92da671e31013b00901591ce2b595b61ce 3.13

[bedevere-app]

GH-143652 is a backport of this pull request to the 3.14 branch.

[bedevere-app]

GH-143653 is a backport of this pull request to the 3.13 branch.