Bug in generator if the generator in created in a C thread
Hi, bugs.python.org is down so I'm reporting the bug here :-) We have a crash in our product when tracing is enabled by sys.settrace() and threading.settrace(). If a Python generator is created in a C thread, calling the generator later in another thread may crash if Python tracing is enabled. - the C thread calls PyGILState_Ensure() which creates a temporary Python thread state - a generator is created, the generator has a reference to a Python frame which keeps a reference to the temporary Python thread state - the C thread calls PyGILState_Releases() which destroys the temporary Python thread state - when the generator is called later in another thread, call_trace() reads the Python thread state from the generator frame, which is the destroyed frame => it does crash on a pointer dereference if the memory was reallocated (by malloc()) and the data were erased To reproduce the crash, unpack the attached generator_frame_bug.tar.gz, compile the C module using "python setup.py build" and then run "PYTHONPATH=$(ls -d build/lib*/) python test.py" (or just "python test.py if you installed the _test module). You may need to use Valgrind to see the error, or call memset(tstate, 0xFF, sizeof(*tstate)) before free(tstate) in tstate_delete_common(). Calling the generator should update its reference to the Python state thread in its frame. The generator may also clears frame->f_tstate (to detect bugs earlier), as it does for frame->f_back (to avoid a reference cycle). Attached patch implements this fix for Python 3.3. Victor
participants (3)
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Guido van Rossum
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Tim Lesher
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Victor Stinner