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Fix obscure segfault condition in PL/Python

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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.

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 commit is contained in:
Peter Eisentraut 2009-11-03 08:59:16 +00:00
parent 01adc8afd5
commit 59052a5122
1 changed files with 7 additions and 4 deletions

11
src/pl/plpython/plpython.c

@ -1,7 +1,7 @@
/********************************************************************** /**********************************************************************
* plpython.c - python as a procedural language for PostgreSQL * plpython.c - python as a procedural language for PostgreSQL
* *
* $PostgreSQL: pgsql/src/pl/plpython/plpython.c,v 1.122 2009/06/11 14:49:14 momjian Exp $ * $PostgreSQL: pgsql/src/pl/plpython/plpython.c,v 1.122.2.1 2009/11/03 08:59:16 petere Exp $
* *
********************************************************************* *********************************************************************
*/ */
@ -2893,9 +2893,9 @@ PLy_fatal(PyObject *self, PyObject *args)
static PyObject * static PyObject *
PLy_output(volatile int level, PyObject *self, PyObject *args) PLy_output(volatile int level, PyObject *self, PyObject *args)
{ {
PyObject *so; PyObject *volatile so;
char *volatile sv; char *volatile sv;
MemoryContext oldcontext; volatile MemoryContext oldcontext;
so = PyObject_Str(args); so = PyObject_Str(args);
if (so == NULL || ((sv = PyString_AsString(so)) == NULL)) if (so == NULL || ((sv = PyString_AsString(so)) == NULL))
@ -2914,6 +2914,10 @@ PLy_output(volatile int level, PyObject *self, PyObject *args)
MemoryContextSwitchTo(oldcontext); MemoryContextSwitchTo(oldcontext);
PLy_error_in_progress = CopyErrorData(); PLy_error_in_progress = CopyErrorData();
FlushErrorState(); FlushErrorState();
PyErr_SetString(PLy_exc_error, sv);
/* Note: If sv came from PyString_AsString(), it points into
* storage owned by so. So free so after using sv. */
Py_XDECREF(so); Py_XDECREF(so);
/* /*
@ -2921,7 +2925,6 @@ PLy_output(volatile int level, PyObject *self, PyObject *args)
* control passes back to PLy_procedure_call, we check for PG * control passes back to PLy_procedure_call, we check for PG
* exceptions and re-throw the error. * exceptions and re-throw the error.
*/ */
PyErr_SetString(PLy_exc_error, sv);
return NULL; return NULL;
} }
PG_END_TRY(); PG_END_TRY();