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Explicitly add DLL directories for Windows before importing #558

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Merged
jacobperron merged 5 commits into from
May 18, 2020
Merged

Explicitly add DLL directories for Windows before importing #558

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e561a30
Explicitly add DLL directories for Windows before importing
jacobperron May 14, 2020
241a02c
Refactor patch and add check for os.add_dll_directory
jacobperron May 14, 2020
4f1676c
Make same patch to test_rclpy module import
jacobperron May 14, 2020
a795304
Move logic to common package rpyutils
jacobperron May 15, 2020
4f5cc27
alphabetize
jacobperron May 16, 2020
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17 changes: 16 additions & 1 deletion rclpy/rclpy/impl/__init__.py
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Expand Up @@ -17,8 +17,20 @@


def _import(name):
dll_dir_handles = []
try:
return importlib.import_module(name, package='rclpy')
# New in Python 3.8: on Windows we should call 'add_dll_directory()' for directories
# containing DLLs we depend on.
# https://docs.python.org/3/whatsnew/3.8.html#bpo-36085-whatsnew
if os.name == 'nt':
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path_env = os.environ['PATH'].split(';')

@dirk-thomas dirk-thomas May 14, 2020 •
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There is a reason why Python chose to not use all paths in PATH. Maybe it would be better to not bypass this mechanism entirely but select specific paths only to be added, e.g. rclpy.

@dirk-thomas dirk-thomas May 14, 2020

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Message packages should probably contain their own logic to ensure their path is added too.

@jacobperron jacobperron May 14, 2020 •
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There is a reason why Python chose to not use all paths in PATH

What I gather from the issue[1] is that where DLLs are loaded from was not consistent before Python 3.8 (e.g. in general, you couldn't assume that PATH was ever searched for DLLs; it was using the process default ordering[2]), which has some security implications[3]. The change in Python 3.8 forces a consistent search order.

The reason to not include PATH in the search order is a little above my head, but I think it boils down to a minimizing the risk of a so-called DLL preloading attack. I agree we could try down-selecting to just what we need, though I'm not sure of a proper way to achieve this. Maybe using CMake variables that are exported by packages producing DLLs? Also, I guess there will be other DLLs installed on the system we rely on that should also be added (e.g. OpenSSL).

[1] https://bugs.python.org/issue36085
[2] https://docs.microsoft.com/en-us/windows/win32/dlls/dynamic-link-library-search-order
[3] https://docs.microsoft.com/en-us/windows/win32/dlls/dynamic-link-library-security

@jacobperron jacobperron May 14, 2020

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Yeah, you're right. rosidl_generator_py needs a similar patch. Pretty much anywhere we use importlib.import_module.

for prefix_path in path_env:
if os.path.exists(prefix_path):
dll_dir_handles.append(os.add_dll_directory(prefix_path))

imported_module = importlib.import_module(name, package='rclpy')

return imported_module
except ImportError as e:
if e.path is not None and os.path.isfile(e.path):
e.msg += \
Expand All @@ -27,3 +39,6 @@ def _import(name):
(e.path, 'https://index.ros.org/doc/ros2/Troubleshooting/'
'#import-failing-even-with-library-present-on-the-system')
raise
finally:
for handle in dll_dir_handles:
handle.close()