class SafeStream has a potentially unsafe __getattr__ implementation (potentially yielding an infinite recursion when attempting to pickle it)

	@thehcma reported
Trac ID	trac#9612
Type	defect
Created	2019-04-05 17:14:47Z

The problem happens when a SafeStream object gets pickled/unpickled.

This happens due to the implementation not safeguarding against the potential for infinite recursion when getattr would invoke its own __getattr__.

Here is an example of the recursion:

  File "/home/blah/local/lib/python2.7/site-packages/twisted/trial/reporter.py", line 56, in __getattr__
    return getattr(self.original, name)
  File "/home/blah/lib/python2.7/site-packages/twisted/trial/reporter.py", line 56, in __getattr__
    return getattr(self.original, name)
  File "/home/blah/local/lib/python2.7/site-packages/twisted/trial/reporter.py", line 56, in __getattr__

Here is an exact description of the problem (and solution):

https://stackoverflow.com/questions/22781872/python-pickle-got-acycle-recursion-with-getattr

In fact, the first suggested solution works to prevent the potential for infinite recursion.

Here is the alternative implementation that addresses the problem:

 def __getattr__(self, name):
      original = object.__getattribute__(self, 'original')
      return getattr(original, name)

trac-id__9612 9612
type__defect defect
reporter__thehcma thehcma
priority__normal normal
milestone__None None
branch__ 
branch_author__ 
status__new new
resolution__None None
component__core core
keywords__None None
time__1554484487597160 1554484487597160
changetime__1554493322402629 1554493322402629
version__None None
owner__None None

Start in twisted/trial/reporter.py at SafeStream.getattr, then reproduce the pickle/unpickle case described in the issue. Verify that accessing a missing attribute during unpickling no longer recurses indefinitely and add or update a focused regression test for that behavior.