SIGSEGV in ffi callback preparation

[viraptor]

I'm not sure where actual issue is, but I'll start here. Maybe someone's got an idea.

I've got the following py-bt output from cpython 3.5.2 on arch linux when initializing the backend:

Traceback (most recent call first):
  File "/home/viraptor/Projects/anchor/.tox/py35d/lib/python3.5/site-packages/cryptography/hazmat/bindings/openssl/binding.py", line 80, in wrapper
    callback = ffi.callback(signature, **kwargs)(func)
  File "/home/viraptor/Projects/anchor/.tox/py35d/lib/python3.5/site-packages/cryptography/hazmat/bindings/openssl/binding.py", line 87, in <module>
    error=-1)
  <built-in method exec of module object at remote 0x3450f6c5c58>
  File "<frozen importlib._bootstrap>", line 222, in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 665, in exec_module
  File "<frozen importlib._bootstrap>", line 673, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 958, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 969, in _find_and_load
  <built-in method __import__ of module object at remote 0x3450f6c5c58>
  File "<frozen importlib._bootstrap>", line 222, in _call_with_frames_removed
  File "<frozen importlib._bootstrap>", line 1016, in _handle_fromlist
  <built-in method __import__ of module object at remote 0x3450f6c5c58>
  File "/home/viraptor/Projects/anchor/.tox/py35d/lib/python3.5/site-packages/cryptography/hazmat/backends/openssl/backend.py", line 47, in <module>
    from cryptography.hazmat.bindings.openssl import binding
  <built-in method exec of module object at remote 0x3450f6c5c58>
  File "<frozen importlib._bootstrap>", line 222, in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 665, in exec_module
  File "<frozen importlib._bootstrap>", line 673, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 958, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 969, in _find_and_load
  <built-in method __import__ of module object at remote 0x3450f6c5c58>
  File "/home/viraptor/Projects/anchor/.tox/py35d/lib/python3.5/site-packages/cryptography/hazmat/backends/openssl/__init__.py", line 7, in <module>
    from cryptography.hazmat.backends.openssl.backend import backend
  <built-in method exec of module object at remote 0x3450f6c5c58>
  File "<frozen importlib._bootstrap>", line 222, in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 665, in exec_module
  File "<frozen importlib._bootstrap>", line 673, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 958, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 969, in _find_and_load
  <built-in method __import__ of module object at remote 0x3450f6c5c58>
  File "/home/viraptor/Projects/anchor/.tox/py35d/lib/python3.5/site-packages/pkg_resources/__init__.py", line 2274, in resolve
    module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "/home/viraptor/Projects/anchor/.tox/py35d/lib/python3.5/site-packages/cryptography/hazmat/backends/__init__.py", line 27, in <listcomp>
    for ep in pkg_resources.iter_entry_points(
  File "/home/viraptor/Projects/anchor/.tox/py35d/lib/python3.5/site-packages/cryptography/hazmat/backends/__init__.py", line 28, in _available_backends
    "cryptography.backends"
  File "/home/viraptor/Projects/anchor/.tox/py35d/lib/python3.5/site-packages/cryptography/hazmat/backends/__init__.py", line 41, in default_backend
    _default_backend = MultiBackend(_available_backends())

and the top frames of actual bt:

#0  0x0000034505d23d9b in ffi_prep_closure_loc () from /usr/lib/libffi.so.6
#1  0x0000034505f4263f in b_callback (self=self@entry=0x0, args=args@entry=(<_cffi_backend.CTypeDescr at remote 0x345058e7418>, <function at remote 0x345058d5788>, -1, None)) at c/_cffi_backend.c:5284
#2  0x0000034505f42900 in _ffi_callback_decorator (outer_args=(<_cffi_backend.CTypeDescr at remote 0x345058e7418>, <function at remote 0x345058d5788>, -1, None), fn=<optimized out>) at c/ffi_obj.c:776
#3  0x000000000053909d in call_function (pp_stack=pp_stack@entry=0x384ea2ea018, oparg=oparg@entry=1) at Python/ceval.c:4690
#4  0x00000000005361f2 in PyEval_EvalFrameEx (

This didn't happen in python 3.4. The installed versions are as follows:

• cffi (1.8.3)
• cryptography (1.5.2)
• cpython 3.5.2
• openssl 1.0.2j

Happy to provide more details if there are any questions.

[viraptor]

Let this be a warning to others I guess. cffi allocates RWX memory, which upsets grsec kernels. Use pax flags to allow it to work.

[tiran]

Yes, libffi uses WX memory to create dynamic closures for its callbacks. I fixed it in #2481. Later the fix was undone for Python 3.5 because it caused segfaults in another place. #3201 or OpenSSL 1.1.0 will the root cause once and for all. #3201 is currently blocked by legal issues.