[Patches] [ python-Patches-784825 ] fix obscure crash in descriptor handling

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Tue Aug 12 04:21:53 EDT 2003


Patches item #784825, was opened at 2003-08-07 16:32
Message generated for change (Comment added) made by mwh
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Category: Core (C code)
Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Michael Hudson (mwh)
>Assigned to: Raymond Hettinger (rhettinger)
Summary: fix obscure crash in descriptor handling

Initial Comment:
Ages & ages back twouters pointed out a potential hole in 
PyObject_GenericGetAttr.  I've come up with a testcase & a 
fix, attached to this report.

Are there any other bits of code shaped like 
PyObject_GenericGetAttr?  I've fixed type_getattro.


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>Comment By: Michael Hudson (mwh)
Date: 2003-08-12 11:21

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First two comments: thanks, I've uploaded a new version with
these taken on board.

> In object.c, the DECREF on line 1459 should be a XDECREF 

No.  Look where f came from.

> and the final exit path (running PyErr_Format) also needs a 
> XDECREF.

I object to putting in Py_XDECREF(foo) when I know foo ==
NULL.  Or am I missing something? (this same applies to the
similar comment about typeobject.c).

> This is labelled as a Py2.4 patch but it should probably be 
> backported also.

Oh yes, this applies to 2.3 and almost surely 2.2, too.

Back to you.

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Comment By: Raymond Hettinger (rhettinger)
Date: 2003-08-12 01:36

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In typeobject.c, eliminate the else-block so that it is obvious 
that the incref always gets executed before the block ends.

Also, the first XDECREF (on line 2022) needs to be 
repositioned (to later in the block) because, in MSVC++, the 
descrgetfunc declaration (two lines below) needs to be the 
first line in the code block.

The final exit path (marked "give up") also need a DECREF.

In object.c, the DECREF on line 1459 should be a XDECREF 
and the final exit path (running PyErr_Format) also needs a 
XDECREF.

This is labelled as a Py2.4 patch but it should probably be 
backported also.



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Comment By: Michael Hudson (mwh)
Date: 2003-08-11 18:42

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trying to attach again, grr

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Comment By: Michael Hudson (mwh)
Date: 2003-08-11 18:38

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upload new patch that has a test that doesn't call gc.get_referrers 
on the integer 1 and thus create uncollectable cycles (or 
something like that, anyway).

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