Improved version of patch to protect pg_get_expr() against misuse:

look through join alias Vars to avoid breaking join queries, and
move the test to someplace where it will catch more possible ways
of calling a function.  We still ought to throw away the whole thing
in favor of a data-type-based solution, but that's not feasible in
the back branches.

This needs to be back-patched further than 9.0, but I don't have time
to do so today.  Committing now so that the fix gets into 9.0beta4.

src/backend/parser/parse_expr.c

@@ -8,16 +8,13 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/parser/parse_expr.c,v 1.256 2010/07/06 19:18:57 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/parser/parse_expr.c,v 1.257 2010/07/29 23:16:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
 
 #include "postgres.h"
 
-#include "catalog/pg_attrdef.h"
-#include "catalog/pg_constraint.h"
-#include "catalog/pg_proc.h"
 #include "catalog/pg_type.h"
 #include "commands/dbcommands.h"
 #include "miscadmin.h"
@@ -33,7 +30,6 @@
 #include "parser/parse_target.h"
 #include "parser/parse_type.h"
 #include "utils/builtins.h"
-#include "utils/fmgroids.h"
 #include "utils/lsyscache.h"
 #include "utils/xml.h"
 
@@ -1214,7 +1210,6 @@ transformFuncCall(ParseState *pstate, FuncCall *fn)
 {
 	List	   *targs;
 	ListCell   *args;
-	Node	   *result;
 
 	/* Transform the list of arguments ... */
 	targs = NIL;
@@ -1225,7 +1220,7 @@ transformFuncCall(ParseState *pstate, FuncCall *fn)
 	}
 
 	/* ... and hand off to ParseFuncOrColumn */
-	result = ParseFuncOrColumn(pstate,
+	return ParseFuncOrColumn(pstate,
 							 fn->funcname,
 							 targs,
 							 fn->agg_order,
@@ -1235,87 +1230,6 @@ transformFuncCall(ParseState *pstate, FuncCall *fn)
 							 fn->over,
 							 false,
 							 fn->location);
-
-	/*
-	 * pg_get_expr() is a system function that exposes the expression
-	 * deparsing functionality in ruleutils.c to users. Very handy, but it was
-	 * later realized that the functions in ruleutils.c don't check the input
-	 * rigorously, assuming it to come from system catalogs and to therefore
-	 * be valid. That makes it easy for a user to crash the backend by passing
-	 * a maliciously crafted string representation of an expression to
-	 * pg_get_expr().
-	 *
-	 * There's a lot of code in ruleutils.c, so it's not feasible to add
-	 * water-proof input checking after the fact. Even if we did it once, it
-	 * would need to be taken into account in any future patches too.
-	 *
-	 * Instead, we restrict pg_rule_expr() to only allow input from system
-	 * catalogs instead. This is a hack, but it's the most robust and easiest
-	 * to backpatch way of plugging the vulnerability.
-	 *
-	 * This is transparent to the typical usage pattern of
-	 * "pg_get_expr(systemcolumn, ...)", but will break "pg_get_expr('foo',
-	 * ...)", even if 'foo' is a valid expression fetched earlier from a
-	 * system catalog. Hopefully there's isn't many clients doing that out
-	 * there.
-	 */
-	if (result && IsA(result, FuncExpr) &&!superuser())
-	{
-		FuncExpr   *fe = (FuncExpr *) result;
-
-		if (fe->funcid == F_PG_GET_EXPR || fe->funcid == F_PG_GET_EXPR_EXT)
-		{
-			Expr	   *arg = linitial(fe->args);
-			bool		allowed = false;
-
-			/*
-			 * Check that the argument came directly from one of the allowed
-			 * system catalog columns
-			 */
-			if (IsA(arg, Var))
-			{
-				Var		   *var = (Var *) arg;
-				RangeTblEntry *rte;
-
-				rte = GetRTEByRangeTablePosn(pstate,
-											 var->varno, var->varlevelsup);
-
-				switch (rte->relid)
-				{
-					case IndexRelationId:
-						if (var->varattno == Anum_pg_index_indexprs ||
-							var->varattno == Anum_pg_index_indpred)
-							allowed = true;
-						break;
-
-					case AttrDefaultRelationId:
-						if (var->varattno == Anum_pg_attrdef_adbin)
-							allowed = true;
-						break;
-
-					case ProcedureRelationId:
-						if (var->varattno == Anum_pg_proc_proargdefaults)
-							allowed = true;
-						break;
-
-					case ConstraintRelationId:
-						if (var->varattno == Anum_pg_constraint_conbin)
-							allowed = true;
-						break;
-
-					case TypeRelationId:
-						if (var->varattno == Anum_pg_type_typdefaultbin)
-							allowed = true;
-						break;
-				}
-			}
-			if (!allowed)
-				ereport(ERROR,
-						(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
-						 errmsg("argument to pg_get_expr() must come from system catalogs")));
-		}
-	}
-	return result;
 }
 
 static Node *

src/backend/parser/parse_func.c

@@ -8,15 +8,18 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/parser/parse_func.c,v 1.224 2010/05/30 18:10:40 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/parser/parse_func.c,v 1.225 2010/07/29 23:16:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
 #include "postgres.h"
 
+#include "catalog/pg_attrdef.h"
+#include "catalog/pg_constraint.h"
 #include "catalog/pg_proc.h"
 #include "catalog/pg_type.h"
 #include "funcapi.h"
+#include "miscadmin.h"
 #include "nodes/makefuncs.h"
 #include "nodes/nodeFuncs.h"
 #include "parser/parse_agg.h"
@@ -26,6 +29,7 @@
 #include "parser/parse_target.h"
 #include "parser/parse_type.h"
 #include "utils/builtins.h"
+#include "utils/fmgroids.h"
 #include "utils/lsyscache.h"
 #include "utils/syscache.h"
 
@@ -494,6 +498,9 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 		retval = (Node *) wfunc;
 	}
 
+	/* Hack to protect pg_get_expr() against misuse */
+	check_pg_get_expr_args(pstate, funcid, fargs);
+
 	return retval;
 }
 
@@ -1580,3 +1587,107 @@ LookupAggNameTypeNames(List *aggname, List *argtypes, bool noError)
 
 	return oid;
 }
+
+
+/*
+ * pg_get_expr() is a system function that exposes the expression
+ * deparsing functionality in ruleutils.c to users. Very handy, but it was
+ * later realized that the functions in ruleutils.c don't check the input
+ * rigorously, assuming it to come from system catalogs and to therefore
+ * be valid. That makes it easy for a user to crash the backend by passing
+ * a maliciously crafted string representation of an expression to
+ * pg_get_expr().
+ *
+ * There's a lot of code in ruleutils.c, so it's not feasible to add
+ * water-proof input checking after the fact. Even if we did it once, it
+ * would need to be taken into account in any future patches too.
+ *
+ * Instead, we restrict pg_rule_expr() to only allow input from system
+ * catalogs. This is a hack, but it's the most robust and easiest
+ * to backpatch way of plugging the vulnerability.
+ *
+ * This is transparent to the typical usage pattern of
+ * "pg_get_expr(systemcolumn, ...)", but will break "pg_get_expr('foo',
+ * ...)", even if 'foo' is a valid expression fetched earlier from a
+ * system catalog. Hopefully there aren't many clients doing that out there.
+ */
+void
+check_pg_get_expr_args(ParseState *pstate, Oid fnoid, List *args)
+{
+	bool		allowed = false;
+	Node	   *arg;
+	int			netlevelsup;
+
+	/* if not being called for pg_get_expr, do nothing */
+	if (fnoid != F_PG_GET_EXPR && fnoid != F_PG_GET_EXPR_EXT)
+		return;
+
+	/* superusers are allowed to call it anyway (dubious) */
+	if (superuser())
+		return;
+
+	/*
+	 * The first argument must be a Var referencing one of the allowed
+	 * system-catalog columns.  It could be a join alias Var, though.
+	 */
+	Assert(list_length(args) > 1);
+	arg = (Node *) linitial(args);
+	netlevelsup = 0;
+
+restart:
+	if (IsA(arg, Var))
+	{
+		Var		   *var = (Var *) arg;
+		RangeTblEntry *rte;
+
+		netlevelsup += var->varlevelsup;
+		rte = GetRTEByRangeTablePosn(pstate, var->varno, netlevelsup);
+
+		if (rte->rtekind == RTE_JOIN)
+		{
+			/* Expand join alias reference */
+			if (var->varattno > 0 &&
+				var->varattno <= list_length(rte->joinaliasvars))
+			{
+				arg = (Node *) list_nth(rte->joinaliasvars, var->varattno - 1);
+				goto restart;
+			}
+		}
+		else if (rte->rtekind == RTE_RELATION)
+		{
+			switch (rte->relid)
+			{
+				case IndexRelationId:
+					if (var->varattno == Anum_pg_index_indexprs ||
+						var->varattno == Anum_pg_index_indpred)
+						allowed = true;
+					break;
+
+				case AttrDefaultRelationId:
+					if (var->varattno == Anum_pg_attrdef_adbin)
+						allowed = true;
+					break;
+
+				case ProcedureRelationId:
+					if (var->varattno == Anum_pg_proc_proargdefaults)
+						allowed = true;
+					break;
+
+				case ConstraintRelationId:
+					if (var->varattno == Anum_pg_constraint_conbin)
+						allowed = true;
+					break;
+
+				case TypeRelationId:
+					if (var->varattno == Anum_pg_type_typdefaultbin)
+						allowed = true;
+					break;
+			}
+		}
+	}
+
+	if (!allowed)
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+				 errmsg("argument to pg_get_expr() must come from system catalogs")));
+}

src/backend/parser/parse_oper.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/parser/parse_oper.c,v 1.113 2010/02/26 02:00:52 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/parser/parse_oper.c,v 1.114 2010/07/29 23:16:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -869,6 +869,9 @@ make_op(ParseState *pstate, List *opname, Node *ltree, Node *rtree,
 
 	ReleaseSysCache(tup);
 
+	/* Hack to protect pg_get_expr() against misuse */
+	check_pg_get_expr_args(pstate, result->opfuncid, args);
+
 	return (Expr *) result;
 }
 
@@ -997,6 +1000,9 @@ make_scalar_array_op(ParseState *pstate, List *opname,
 
 	ReleaseSysCache(tup);
 
+	/* Hack to protect pg_get_expr() against misuse */
+	check_pg_get_expr_args(pstate, result->opfuncid, args);
+
 	return (Expr *) result;
 }
 

src/include/parser/parse_func.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/parser/parse_func.h,v 1.68 2010/01/02 16:58:07 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/parser/parse_func.h,v 1.69 2010/07/29 23:16:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -82,4 +82,6 @@ extern Oid LookupFuncNameTypeNames(List *funcname, List *argtypes,
 extern Oid LookupAggNameTypeNames(List *aggname, List *argtypes,
 					   bool noError);
 
+extern void check_pg_get_expr_args(ParseState *pstate, Oid fnoid, List *args);
+
 #endif   /* PARSE_FUNC_H */