Thread: Segfault in PL/Python

Segfault in PL/Python

From
Peter Eisentraut
Date:
I have discovered an obscure segfault condition in PL/Python.  In
PLy_output(), when the elog() call in the TRY branch throws an exception
(this can happen when a statement timeout kicks in, for example), the
PyErr_SetString() call in the CATCH branch can cause a segfault, because
the Py_XDECREF(so) call before it releases memory that is still used by
the sv variable that PyErr_SetString() uses as argument, because sv
points into memory owned by so.

Patch is attached.  This should be backpatched back to 8.0, where this
code was introduced.

I also threw in a couple of volatile declarations for variables that are
used before and after the TRY.  I don't think they caused the crash that
I observed, but they could become issues.

Attachment

Re: Segfault in PL/Python

From
Peter Eisentraut
Date:
On Sat, 2009-10-31 at 14:24 +0200, Peter Eisentraut wrote:
> I have discovered an obscure segfault condition in PL/Python.  In
> PLy_output(), when the elog() call in the TRY branch throws an exception
> (this can happen when a statement timeout kicks in, for example), the
> PyErr_SetString() call in the CATCH branch can cause a segfault, because
> the Py_XDECREF(so) call before it releases memory that is still used by
> the sv variable that PyErr_SetString() uses as argument, because sv
> points into memory owned by so.
> 
> Patch is attached.  This should be backpatched back to 8.0, where this
> code was introduced.
> 
> I also threw in a couple of volatile declarations for variables that are
> used before and after the TRY.  I don't think they caused the crash that
> I observed, but they could become issues.

This patch has been applied to 8.0 - 8.5.