From 675a313b545d416d614bc36341556bfbc866dee2 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 8 Feb 2007 18:38:31 +0000
Subject: [PATCH] Fix an ancient logic error in plpgsql's exec_stmt_block: it
 thought it could get away with not (re)initializing a local variable if the
 variable is marked "isconst" and not "isnull".  Unfortunately it makes this
 decision after having already freed the old value, meaning that something
 like

   for i in 1..10 loop
     declare c constant text := 'hi there';

leads to subsequent accesses to freed memory, and hence probably crashes.
(In particular, this is why Asif Ali Rehman's bug leads to crash and not
just an unexpectedly-NULL value for SQLERRM: SQLERRM is marked CONSTANT
and so triggers this error.)

The whole thing seems wrong on its face anyway: CONSTANT means that you can't
change the variable inside the block, not that the initializer expression is
guaranteed not to change value across successive block entries.  Hence,
remove the "optimization" instead of trying to fix it.
---
 src/pl/plpgsql/src/pl_exec.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/src/pl/plpgsql/src/pl_exec.c b/src/pl/plpgsql/src/pl_exec.c
index 193e80c1528..07791ffc86d 100644
--- a/src/pl/plpgsql/src/pl_exec.c
+++ b/src/pl/plpgsql/src/pl_exec.c
@@ -3,7 +3,7 @@
  *			  procedural language
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/pl/plpgsql/src/pl_exec.c,v 1.65.2.4 2005/06/20 20:45:06 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/pl/plpgsql/src/pl_exec.c,v 1.65.2.5 2007/02/08 18:38:31 tgl Exp $
  *
  *	  This software is copyrighted by Jan Wieck - Hamburg.
  *
@@ -767,26 +767,26 @@ exec_stmt_block(PLpgSQL_execstate * estate, PLpgSQL_stmt_block * block)
 				{
 					PLpgSQL_var *var = (PLpgSQL_var *) (estate->datums[n]);
 
+					/* free any old value, in case re-entering block */
 					if (var->freeval)
 					{
 						pfree((void *) (var->value));
 						var->freeval = false;
 					}
 
-					if (!var->isconst || var->isnull)
+					/* Initially it contains a NULL */
+					var->value = (Datum) 0;
+					var->isnull = true;
+
+					if (var->default_val == NULL)
 					{
-						if (var->default_val == NULL)
-						{
-							var->value = (Datum) 0;
-							var->isnull = true;
-							if (var->notnull)
-								elog(ERROR, "variable '%s' declared NOT NULL cannot default to NULL", var->refname);
-						}
-						else
-						{
-							exec_assign_expr(estate, (PLpgSQL_datum *) var,
-											 var->default_val);
-						}
+						if (var->notnull)
+							elog(ERROR, "variable '%s' declared NOT NULL cannot default to NULL", var->refname);
+					}
+					else
+					{
+						exec_assign_expr(estate, (PLpgSQL_datum *) var,
+										 var->default_val);
 					}
 				}
 				break;