Description of problem: I've been writing an experimental static analysis tool to detect bugs commonly occurring within C Python extension modules: https://fedorahosted.org/gcc-python-plugin/ http://gcc-python-plugin.readthedocs.org/en/latest/cpychecker.html http://fedoraproject.org/wiki/Features/StaticAnalysisOfPythonRefcounts I ran the latest version of the tool (in git master; post 0.9) on clearsilver-0.10.5-17.fc17.src.rpm, and it reports various errors. You can see a list of errors here, triaged into categories (from most significant to least significant): http://fedorapeople.org/~dmalcolm/gcc-python-plugin/2012-02-16/clearsilver-0.10.5-17.fc17/ I've manually inspected the results. The issue reported in "Reference count too low" appears to be a genuine bug: the code should use: Py_RETURN_NONE; here, rather than return Py_None; to ensure that the reference count of Py_None is incremented (otherwise repeated calls of the setUploadCB method will lead to python crashing). The 5 issues reported in "Reference leak within initialization" appear to be very minor, given that this appears to be one-time initialization, rather than ongoing code. The issue reported in "Segfaults within error-handling paths: neo_cgi.c:python_upload_cb:dereferencing NULL (result->ob_refcnt) at neo_cgi.c:146 appears to be a genuine segfaulter: if the callback raises an exception, returning NULL, then: result = PyEval_CallObject(cb, args); will be NULL, and, if I'm reading it right, this code will be called: 144 r = PyInt_AsLong(result); 145 Py_DECREF(result); which will segfault the interpreter. The issue reported in "Possible reference leaks" may well be just a false-positive. There may of course be other bugs in my checker tool. Hope this is helpful; let me know if you need help reading the logs that the tool generates - I know that it could use some improvement. Version-Release number of selected component (if applicable): clearsilver-0.10.5-17.fc17 gcc-python-plugin post-0.9 git 073d390de53ef52136bd90e5ac06f1ef833d047d running the checker in an *f16* chroot
Fascinating. . .thank you! It looks like these haven't been addressed in upstream releases or SVN as of this writing. I've started a patch. For the segfaulter, my C is less than it should be, is simply testing result's NULLness and free()ing it as appropriate likely to be sufficient here?
(In reply to comment #1) > Fascinating. . .thank you! It looks like these haven't been addressed in > upstream releases or SVN as of this writing. I've started a patch. Thanks! > For the segfaulter, my C is less than it should be, is simply testing result's > NULLness and free()ing it as appropriate likely to be sufficient here? That doesn't sound correct to me - you don't typically free() python objects. If I'm reading python_upload_cb right, the case where result is non-NULL *is* being correctly cleaned up. The issue is when result is NULL: something ought to check for result == NULL and do something appropriate, similar to the error-handling for the case when the callback returns a non-int value. FWIW, a guide to the C Python API can be seen here: http://docs.python.org/extending/index.html and detailed notes are here: http://docs.python.org/c-api/index.html though if you're not yet familiar with this API, it's probably best to engage with upstream. Hope this is helpful Dave
Ah, I see. I think it's nearly correct, except it looks like not all cases. What if I modified: if (result != NULL && !PyInt_Check(result)) { Py_DECREF(result); result = NULL; PyErr_SetString(PyExc_TypeError, "upload_cb () returned non-integer"); self->upload_error = 1; return 1; } r = PyInt_AsLong(result); Py_DECREF(result); result = NULL; return r; thusly: if (result != NULL) { if (!PyInt_Check(result)) { { Py_DECREF(result); result = NULL; PyErr_SetString(PyExc_TypeError, "upload_cb () returned non-integer"); self->upload_error = 1; return 1; } } else { r = PyInt_AsLong(result); Py_DECREF(result); result = NULL; return r; } This way, in no case does the result get defererenced if NULL. At least here. :)
Created attachment 563952 [details] Patch to protect against exception in callback (NULL) (In reply to comment #3) > if (result != NULL) { > if (!PyInt_Check(result)) { > { > Py_DECREF(result); > result = NULL; > PyErr_SetString(PyExc_TypeError, > "upload_cb () returned non-integer"); > self->upload_error = 1; > return 1; > } > } else { > r = PyInt_AsLong(result); > Py_DECREF(result); > result = NULL; > return r; > } Am I right in thinking you still have the trailing "return r" at the end? Isn't r still uninitialized at this point? Am attaching a patch that (I hope) covers this case. Applies cleanly, but untested though.
No, my version went to the end of the function. So I suppose that would have left open the possibility of not returning anything. I'll try your patch.
Maybe I'm foggy today, but how can I run this against my patched RPM?
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