Allow LEAKPROOF functions for better performance of security views.

We don't normally allow quals to be pushed down into a view created
with the security_barrier option, but functions without side effects
are an exception: they're OK.  This allows much better performance in
common cases, such as when using an equality operator (that might
even be indexable).

There is an outstanding issue here with the CREATE FUNCTION / ALTER
FUNCTION syntax: there's no way to use ALTER FUNCTION to unset the
leakproof flag.  But I'm committing this as-is so that it doesn't
have to be rebased again; we can fix up the grammar in a future
commit.

KaiGai Kohei, with some wordsmithing by me.

doc/src/sgml/catalogs.sgml

@@ -4423,6 +4423,18 @@
       function)</entry>
      </row>
 
+     <row>
+      <entry><structfield>proleakproof</structfield></entry>
+      <entry><type>bool</type></entry>
+      <entry></entry>
+      <entry>
+       The function has no side effects.  No information about the
+       arguments is conveyed except via the return value.  Any function
+       that might throw an error depending on the values of its arguments
+       is not leakproof.
+      </entry>
+     </row>
+
      <row>
       <entry><structfield>proisstrict</structfield></entry>
       <entry><type>bool</type></entry>

doc/src/sgml/ref/alter_function.sgml

@@ -33,7 +33,7 @@ ALTER FUNCTION <replaceable>name</replaceable> ( [ [ <replaceable class="paramet
 <phrase>where <replaceable class="PARAMETER">action</replaceable> is one of:</phrase>
 
     CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT
-    IMMUTABLE | STABLE | VOLATILE
+    IMMUTABLE | STABLE | VOLATILE | LEAKPROOF
     [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER
     COST <replaceable class="parameter">execution_cost</replaceable>
     ROWS <replaceable class="parameter">result_rows</replaceable>
@@ -191,6 +191,17 @@ ALTER FUNCTION <replaceable>name</replaceable> ( [ [ <replaceable class="paramet
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>LEAKPROOF</literal></term>
+    <listitem>
+     <para>
+      Change whether the function is considered leakproof or not.
+      See <xref linkend="sql-createfunction"> for more information about
+      this capability.
+     </para>
+    </listitem>
+   </varlistentry>
+
     <varlistentry>
      <term><literal>COST</literal> <replaceable class="parameter">execution_cost</replaceable></term>
 

doc/src/sgml/ref/create_function.sgml

@@ -26,7 +26,7 @@ CREATE [ OR REPLACE ] FUNCTION
       | RETURNS TABLE ( <replaceable class="parameter">column_name</replaceable> <replaceable class="parameter">column_type</replaceable> [, ...] ) ]
   { LANGUAGE <replaceable class="parameter">lang_name</replaceable>
     | WINDOW
-    | IMMUTABLE | STABLE | VOLATILE
+    | IMMUTABLE | STABLE | VOLATILE | LEAKPROOF
     | CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT
     | [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER
     | COST <replaceable class="parameter">execution_cost</replaceable>
@@ -324,6 +324,23 @@ CREATE [ OR REPLACE ] FUNCTION
      </listitem>
     </varlistentry>
 
+    <varlistentry>
+     <term><literal>LEAKPROOF</literal></term>
+     <listitem>
+      <para>
+       <literal>LEAKPROOF</literal> indicates that the function has no side
+       effects.  It reveals no information about its arguments other than by
+       its return value.  For example, a function which throws an error message
+       for some argument values but not others, or which includes the argument
+       values in any error message, is not leakproof.   The query planner may
+       push leakproof functions (but not others) into views created with the
+       <literal>security_barrier</literal> option.  See
+       <xref linkend="sql-createview"> and <xref linkend="rules-privileges">.
+       This option can only be set by the superuser.
+      </para>
+     </listitem>
+    </varlistentry>
+
     <varlistentry>
      <term><literal>CALLED ON NULL INPUT</literal></term>
      <term><literal>RETURNS NULL ON NULL INPUT</literal></term>

doc/src/sgml/rules.sgml

@@ -1890,6 +1890,20 @@ CREATE VIEW phone_number WITH (security_barrier) AS
     enabled by default.
 </para>
 
+<para>
+    The query planner has more flexibility when dealing with functions that
+    have no side effects.  Such functions are referred to as LEAKPROOF, and
+    include many simple, commonly used operators, such as many equality
+    operators.  The query planner can safely allow such functions to be evaluated
+    at any point in the query execution process, since invoking them on rows
+    invisible to the user will not leak any information about the unseen rows.
+    In contrast, a function that might throw an error depending on the values
+    received as arguments (such as one that throws an error in the event of
+    overflow or division by zero) are not leak-proof, and could provide
+    significant information about the unseen rows if applied before the security
+    view's row filters.
+</para>
+
 <para>
     It is important to understand that even a view created with the
     <literal>security_barrier</literal> option is intended to be secure only

src/backend/catalog/pg_aggregate.c

@@ -241,6 +241,7 @@ AggregateCreate(const char *aggName,
 							  false,	/* isWindowFunc */
 							  false,	/* security invoker (currently not
 										 * definable for agg) */
+							  false,	/* isLeakProof */
 							  false,	/* isStrict (not needed for agg) */
 							  PROVOLATILE_IMMUTABLE,	/* volatility (not
 														 * needed for agg) */

src/backend/catalog/pg_proc.c

@@ -76,6 +76,7 @@ ProcedureCreate(const char *procedureName,
 				bool isAgg,
 				bool isWindowFunc,
 				bool security_definer,
+				bool isLeakProof,
 				bool isStrict,
 				char volatility,
 				oidvector *parameterTypes,
@@ -334,6 +335,7 @@ ProcedureCreate(const char *procedureName,
 	values[Anum_pg_proc_proisagg - 1] = BoolGetDatum(isAgg);
 	values[Anum_pg_proc_proiswindow - 1] = BoolGetDatum(isWindowFunc);
 	values[Anum_pg_proc_prosecdef - 1] = BoolGetDatum(security_definer);
+	values[Anum_pg_proc_proleakproof - 1] = BoolGetDatum(isLeakProof);
 	values[Anum_pg_proc_proisstrict - 1] = BoolGetDatum(isStrict);
 	values[Anum_pg_proc_proretset - 1] = BoolGetDatum(returnsSet);
 	values[Anum_pg_proc_provolatile - 1] = CharGetDatum(volatility);

src/backend/commands/functioncmds.c

@@ -446,6 +446,7 @@ compute_common_attribute(DefElem *defel,
 						 DefElem **volatility_item,
 						 DefElem **strict_item,
 						 DefElem **security_item,
+						 DefElem **leakproof_item,
 						 List **set_items,
 						 DefElem **cost_item,
 						 DefElem **rows_item)
@@ -471,6 +472,13 @@ compute_common_attribute(DefElem *defel,
 
 		*security_item = defel;
 	}
+	else if (strcmp(defel->defname, "leakproof") == 0)
+	{
+		if (*leakproof_item)
+			goto duplicate_error;
+
+		*leakproof_item = defel;
+	}
 	else if (strcmp(defel->defname, "set") == 0)
 	{
 		*set_items = lappend(*set_items, defel->arg);
@@ -564,6 +572,7 @@ compute_attributes_sql_style(List *options,
 							 char *volatility_p,
 							 bool *strict_p,
 							 bool *security_definer,
+							 bool *leakproof_p,
 							 ArrayType **proconfig,
 							 float4 *procost,
 							 float4 *prorows)
@@ -575,6 +584,7 @@ compute_attributes_sql_style(List *options,
 	DefElem    *volatility_item = NULL;
 	DefElem    *strict_item = NULL;
 	DefElem    *security_item = NULL;
+	DefElem    *leakproof_item = NULL;
 	List	   *set_items = NIL;
 	DefElem    *cost_item = NULL;
 	DefElem    *rows_item = NULL;
@@ -611,6 +621,7 @@ compute_attributes_sql_style(List *options,
 										  &volatility_item,
 										  &strict_item,
 										  &security_item,
+										  &leakproof_item,
 										  &set_items,
 										  &cost_item,
 										  &rows_item))
@@ -653,6 +664,8 @@ compute_attributes_sql_style(List *options,
 		*strict_p = intVal(strict_item->arg);
 	if (security_item)
 		*security_definer = intVal(security_item->arg);
+	if (leakproof_item)
+		*leakproof_p = intVal(leakproof_item->arg);
 	if (set_items)
 		*proconfig = update_proconfig_value(NULL, set_items);
 	if (cost_item)
@@ -805,7 +818,8 @@ CreateFunction(CreateFunctionStmt *stmt, const char *queryString)
 	Oid			requiredResultType;
 	bool		isWindowFunc,
 				isStrict,
-				security;
+				security,
+				isLeakProof;
 	char		volatility;
 	ArrayType  *proconfig;
 	float4		procost;
@@ -828,6 +842,7 @@ CreateFunction(CreateFunctionStmt *stmt, const char *queryString)
 	isWindowFunc = false;
 	isStrict = false;
 	security = false;
+	isLeakProof = false;
 	volatility = PROVOLATILE_VOLATILE;
 	proconfig = NULL;
 	procost = -1;				/* indicates not set */
@@ -837,7 +852,7 @@ CreateFunction(CreateFunctionStmt *stmt, const char *queryString)
 	compute_attributes_sql_style(stmt->options,
 								 &as_clause, &language,
 								 &isWindowFunc, &volatility,
-								 &isStrict, &security,
+								 &isStrict, &security, &isLeakProof,
 								 &proconfig, &procost, &prorows);
 
 	/* Look up the language and validate permissions */
@@ -874,6 +889,16 @@ CreateFunction(CreateFunctionStmt *stmt, const char *queryString)
 
 	ReleaseSysCache(languageTuple);
 
+	/*
+	 * Only superuser is allowed to create leakproof functions because
+	 * it possibly allows unprivileged users to reference invisible tuples
+	 * to be filtered out using views for row-level security.
+	 */
+	if (isLeakProof && !superuser())
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+				 errmsg("only superuser can define a leakproof function")));
+
 	/*
 	 * Convert remaining parameters of CREATE to form wanted by
 	 * ProcedureCreate.
@@ -960,6 +985,7 @@ CreateFunction(CreateFunctionStmt *stmt, const char *queryString)
 					false,		/* not an aggregate */
 					isWindowFunc,
 					security,
+					isLeakProof,
 					isStrict,
 					volatility,
 					parameterTypes,
@@ -1238,6 +1264,7 @@ AlterFunction(AlterFunctionStmt *stmt)
 	DefElem    *volatility_item = NULL;
 	DefElem    *strict_item = NULL;
 	DefElem    *security_def_item = NULL;
+	DefElem    *leakproof_item = NULL;
 	List	   *set_items = NIL;
 	DefElem    *cost_item = NULL;
 	DefElem    *rows_item = NULL;
@@ -1274,6 +1301,7 @@ AlterFunction(AlterFunctionStmt *stmt)
 									 &volatility_item,
 									 &strict_item,
 									 &security_def_item,
+									 &leakproof_item,
 									 &set_items,
 									 &cost_item,
 									 &rows_item) == false)
@@ -1286,6 +1314,14 @@ AlterFunction(AlterFunctionStmt *stmt)
 		procForm->proisstrict = intVal(strict_item->arg);
 	if (security_def_item)
 		procForm->prosecdef = intVal(security_def_item->arg);
+	if (leakproof_item)
+	{
+		if (intVal(leakproof_item->arg) && !superuser())
+			ereport(ERROR,
+					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+					 errmsg("only superuser can define a leakproof function")));
+		procForm->proleakproof = intVal(leakproof_item->arg);
+	}
 	if (cost_item)
 	{
 		procForm->procost = defGetNumeric(cost_item);

src/backend/commands/proclang.c

@@ -131,6 +131,7 @@ CreateProceduralLanguage(CreatePLangStmt *stmt)
 										 false, /* isAgg */
 										 false, /* isWindowFunc */
 										 false, /* security_definer */
+										 false,	/* isLeakProof */
 										 false, /* isStrict */
 										 PROVOLATILE_VOLATILE,
 										 buildoidvector(funcargtypes, 0),
@@ -166,6 +167,7 @@ CreateProceduralLanguage(CreatePLangStmt *stmt)
 											false,		/* isAgg */
 											false,		/* isWindowFunc */
 											false,		/* security_definer */
+											false,		/* isLeakProof */
 											true,		/* isStrict */
 											PROVOLATILE_VOLATILE,
 											buildoidvector(funcargtypes, 1),
@@ -204,6 +206,7 @@ CreateProceduralLanguage(CreatePLangStmt *stmt)
 										 false, /* isAgg */
 										 false, /* isWindowFunc */
 										 false, /* security_definer */
+										 false,	/* isLeakProof */
 										 true,	/* isStrict */
 										 PROVOLATILE_VOLATILE,
 										 buildoidvector(funcargtypes, 1),

src/backend/commands/typecmds.c

@@ -1521,6 +1521,7 @@ makeRangeConstructors(const char *name, Oid namespace,
 								  false,		/* isAgg */
 								  false,		/* isWindowFunc */
 								  false,		/* security_definer */
+								  false,		/* leakproof */
 								  false,		/* isStrict */
 								  PROVOLATILE_IMMUTABLE,		/* volatility */
 								  constructorArgTypesVector,	/* parameterTypes */

src/backend/optimizer/path/allpaths.c

@@ -1042,16 +1042,9 @@ set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
 			RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);
 			Node	   *clause = (Node *) rinfo->clause;
 
-			/*
-			 * XXX.  You might wonder why we're testing rte->security_barrier
-			 * qual-by-qual here rather than hoisting the test up into the
-			 * surrounding if statement; after all, the answer will be the
-			 * same for all quals.  The answer is that we expect to shortly
-			 * change this logic to allow pushing down some quals that use only
-			 * "leakproof" operators even through a security barrier.
-			 */
 			if (!rinfo->pseudoconstant &&
-				!rte->security_barrier &&
+				(!rte->security_barrier ||
+				 !contain_leaky_functions(clause)) &&
 				qual_is_pushdown_safe(subquery, rti, clause, differentTypes))
 			{
 				/* Push it down */