Avoid possible longjmp-induced logic error in PLy_trigger_build_args.

The "pltargs" variable wasn't marked volatile, which makes it unsafe
to change its value within the PG_TRY block.  It looks like the worst
outcome would be to fail to release a refcount on Py_None during an
(improbable) error exit, which would likely go unnoticed in the field.
Still, it's a bug.  A one-liner fix could be to mark pltargs volatile,
but on the whole it seems cleaner to arrange things so that we don't
change its value within PG_TRY.

Per report from Xing Guo.  This has been there for quite awhile,
so back-patch to all supported branches.

Discussion: https://postgr.es/m/CACpMh+DLrk=fDv07MNpBT4J413fDAm+gmMXgi8cjPONE+jvzuw@mail.gmail.com

diff --git a/src/pl/plpython/plpy_exec.c b/src/pl/plpython/plpy_exec.c
index 993a4e2ea9078e19eb1c67b5245b4a3828a68737..953c2d4819f8fd60d52f964bce0b56eb5c812a48 100644 (file)
--- a/src/pl/plpython/plpy_exec.c
+++ b/src/pl/plpython/plpy_exec.c
@@ -691,7 +691,7 @@ PLy_trigger_build_args(FunctionCallInfo fcinfo, PLyProcedure *proc, HeapTuple *r
               *pltrelid,
               *plttablename,
               *plttableschema,
-              *pltargs = NULL,
+              *pltargs,
               *pytnew,
               *pytold,
               *pltdata;
@@ -715,6 +715,11 @@ PLy_trigger_build_args(FunctionCallInfo fcinfo, PLyProcedure *proc, HeapTuple *r
            return NULL;
        }
    }
+   else
+   {
+       Py_INCREF(Py_None);
+       pltargs = Py_None;
+   }
 
    PG_TRY();
    {
@@ -858,7 +863,7 @@ PLy_trigger_build_args(FunctionCallInfo fcinfo, PLyProcedure *proc, HeapTuple *r
            PyObject   *pltarg;
 
            /* pltargs should have been allocated before the PG_TRY block. */
-           Assert(pltargs);
+           Assert(pltargs && pltargs != Py_None);
 
            for (i = 0; i < tdata->tg_trigger->tgnargs; i++)
            {
@@ -872,8 +877,7 @@ PLy_trigger_build_args(FunctionCallInfo fcinfo, PLyProcedure *proc, HeapTuple *r
        }
        else
        {
-           Py_INCREF(Py_None);
-           pltargs = Py_None;
+           Assert(pltargs == Py_None);
        }
        PyDict_SetItemString(pltdata, "args", pltargs);
        Py_DECREF(pltargs);