Support explicit placement of the temporary-table schema within search_path.

This is needed to allow a security-definer function to set a truly secure
value of search_path.  Without it, a malicious user can use temporary objects
to execute code with the privileges of the security-definer function.  Even
pushing the temp schema to the back of the search path is not quite good
enough, because a function or operator at the back of the path might still
capture control from one nearer the front due to having a more exact datatype
match.  Hence, disable searching the temp schema altogether for functions and
operators.

Security: CVE-2007-2138

doc/src/sgml/config.sgml

@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.36.2.7 2006/11/04 18:20:40 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.36.2.8 2007/04/20 02:38:04 tgl Exp $
 -->
 <chapter Id="runtime-config">
   <title>Server Configuration</title>
@@ -3103,9 +3103,17 @@ SELECT * FROM parent WHERE key = 2400;
         mentioned in the path then it will be searched in the specified
         order.  If <literal>pg_catalog</> is not in the path then it will
         be searched <emphasis>before</> searching any of the path items.
-        It should also be noted that the temporary-table schema,
+       </para>
-        <literal>pg_temp_<replaceable>nnn</></>, is implicitly searched before any of
+
-        these.
+       <para>
+        Likewise, the current session's temporary-table schema,
+        <literal>pg_temp_<replaceable>nnn</></>, is always searched if it
+        exists.  It can be explicitly listed in the path by using the
+        alias <literal>pg_temp</>.  If it is not listed in the path then
+        it is searched first (before even <literal>pg_catalog</>).  However,
+        the temporary schema is only searched for relation (table, view,
+        sequence, etc) and data type names.  It will never be searched for
+        function or operator names.
        </para>
 
        <para>

doc/src/sgml/ref/create_function.sgml

@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/create_function.sgml,v 1.67 2005/11/01 21:09:50 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/create_function.sgml,v 1.67.2.1 2007/04/20 02:38:04 tgl Exp $
 -->
 
 <refentry id="SQL-CREATEFUNCTION">
@@ -473,6 +473,54 @@ SELECT * FROM dup(42);
   </para>
  </refsect1>
 
+ <refsect1 id="sql-createfunction-security">
+  <title>Writing <literal>SECURITY DEFINER</literal> Functions Safely</title>
+
+   <para>
+    Because a <literal>SECURITY DEFINER</literal> function is executed
+    with the privileges of the user that created it, care is needed to
+    ensure that the function cannot be misused.  For security,
+    <xref linkend="guc-search-path"> should be set to exclude any schemas
+    writable by untrusted users.  This prevents
+    malicious users from creating objects that mask objects used by the
+    function.  Particularly important is in this regard is the
+    temporary-table schema, which is searched first by default, and
+    is normally writable by anyone.  A secure arrangement can be had
+    by forcing the temporary schema to be searched last.  To do this,
+    write <literal>pg_temp</> as the last entry in <varname>search_path</>.
+    This function illustrates safe usage:
+   </para>
+
+<programlisting>
+CREATE FUNCTION check_password(uname TEXT, pass TEXT)
+RETURNS BOOLEAN AS $$
+DECLARE passed BOOLEAN;
+        old_path TEXT;
+BEGIN
+        -- Save old search_path; notice we must qualify current_setting
+        -- to ensure we invoke the right function
+        old_path := pg_catalog.current_setting('search_path');
+
+        -- Set a secure search_path: trusted schemas, then 'pg_temp'.
+        -- We set is_local = true so that the old value will be restored
+        -- in event of an error before we reach the function end.
+        PERFORM pg_catalog.set_config('search_path', 'admin, pg_temp', true);
+
+        -- Do whatever secure work we came for.
+        SELECT  (pwd = $2) INTO passed
+        FROM    pwds
+        WHERE   username = $1;
+
+        -- Restore caller's search_path
+        PERFORM pg_catalog.set_config('search_path', old_path, true);
+
+        RETURN passed;
+END;
+$$ LANGUAGE plpgsql SECURITY DEFINER;
+</programlisting>
+
+ </refsect1>
+
  
  <refsect1 id="sql-createfunction-compat">
   <title>Compatibility</title>

doc/src/sgml/release.sgml

@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/release.sgml,v 1.400.2.41 2007/04/19 13:02:30 momjian Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/release.sgml,v 1.400.2.42 2007/04/20 02:38:04 tgl Exp $ -->
 <!--
 
 Typical markup:
@@ -28,7 +28,8 @@ For new features, add links to the documentation sections.
    </note>
 
    <para>
-    This release contains fixes from 8.1.8.
+    This release contains a variety of fixes from 8.1.8,
+    including a security fix.
    </para>
 
    <sect2>
@@ -49,39 +50,57 @@ For new features, add links to the documentation sections.
 
      <listitem>
      <para>
-      Fix <function>to_char()</> so it properly upper/lower cases localized day or month
+      Support explicit placement of the temporary-table schema within
-      names (Pavel Stehule)
+      <varname>search_path</>, and disable searching it for functions
+      and operators (Tom)
+     </para>
+     <para>
+      This is needed to allow a security-definer function to set a
+      truly secure value of <varname>search_path</>.  Without it,
+      an unprivileged SQL user can use temporary objects to execute code
+      with the privileges of the security-definer function (CVE-2007-2138).
+      See <xref linkend="sql-createfunction"
+      endterm="sql-createfunction-title"> for more information.
      </para>
      </listitem>
 
      <listitem>
      <para>
-      <filename>/contrib/tsearch2</> fixes (Teodor)
+      <filename>/contrib/tsearch2</> crash fixes (Teodor)
      </para>
      </listitem>
 
      <listitem>
      <para>
-      Require <command>COMMIT TRANSACTION</> to be executed in the same database as
+      Require <command>COMMIT PREPARED</> to be executed in the same
-      it was prepared (Heikki)
+      database as the transaction was prepared in (Heikki)
      </para>
      </listitem>
 
      <listitem>
      <para>
-      Improve detection of <acronym>POSIX</>-style time zone names (Tom)
+      Fix potential-data-corruption bug in how <command>VACUUM FULL</> handles
+      <command>UPDATE</> chains (Tom, Pavan Deolasee)
      </para>
      </listitem>
 
      <listitem>
      <para>
-      Fix bug in how <command>VACUUM FULL</> handles <command>UPDATE</> chains (Tom, Pavan Deolasee)
+      Planner fixes, including improving outer join and bitmap scan
+      selection logic (Tom)
      </para>
      </listitem>
 
      <listitem>
      <para>
-      Improve outer join and bitmap join selection logic (Tom)
+      Fix PANIC during enlargement of a hash index (bug introduced in 8.1.6)
+      (Tom)
+     </para>
+     </listitem>
+
+     <listitem>
+     <para>
+      Fix POSIX-style timezone specs to follow new USA DST rules (Tom)
      </para>
      </listitem>
 
@@ -3047,7 +3066,8 @@ psql -t -f fixseq.sql db1 | psql -e db1
    </note>
 
    <para>
-    This release contains fixes from 8.0.12.
+    This release contains a variety of fixes from 8.0.12,
+    including a security fix.
    </para>
 
    <sect2>
@@ -3068,25 +3088,43 @@ psql -t -f fixseq.sql db1 | psql -e db1
 
      <listitem>
      <para>
-      <filename>/contrib/tsearch2</> fixes (Teodor)
+      Support explicit placement of the temporary-table schema within
+      <varname>search_path</>, and disable searching it for functions
+      and operators (Tom)
+     </para>
+     <para>
+      This is needed to allow a security-definer function to set a
+      truly secure value of <varname>search_path</>.  Without it,
+      an unprivileged SQL user can use temporary objects to execute code
+      with the privileges of the security-definer function (CVE-2007-2138).
+      See <xref linkend="sql-createfunction"
+      endterm="sql-createfunction-title"> for more information.
      </para>
      </listitem>
 
      <listitem>
      <para>
-      Improve detection of <acronym>POSIX</>-style time zone names (Tom)
+      <filename>/contrib/tsearch2</> crash fixes (Teodor)
      </para>
      </listitem>
 
      <listitem>
      <para>
-      Fix bug in how <command>VACUUM FULL</> handles <command>UPDATE</> chains (Tom, Pavan Deolasee)
+      Fix potential-data-corruption bug in how <command>VACUUM FULL</> handles
+      <command>UPDATE</> chains (Tom, Pavan Deolasee)
      </para>
      </listitem>
 
      <listitem>
      <para>
-      <filename>/contrib/tsearch2</> fixes (Teodor)
+      Fix PANIC during enlargement of a hash index (bug introduced in 8.0.10)
+      (Tom)
+     </para>
+     </listitem>
+
+     <listitem>
+     <para>
+      Fix POSIX-style timezone specs to follow new USA DST rules (Tom)
      </para>
      </listitem>
 
@@ -6537,7 +6575,8 @@ typedefs (Michael)</para></listitem>
    </note>
 
    <para>
-    This release contains a variety of fixes from 7.4.16.
+    This release contains fixes from 7.4.16,
+    including a security fix.
    </para>
 
    <sect2>
@@ -6558,13 +6597,37 @@ typedefs (Michael)</para></listitem>
 
      <listitem>
      <para>
-      <filename>/contrib/tsearch2</> fixes (Teodor)
+      Support explicit placement of the temporary-table schema within
+      <varname>search_path</>, and disable searching it for functions
+      and operators (Tom)
+     </para>
+     <para>
+      This is needed to allow a security-definer function to set a
+      truly secure value of <varname>search_path</>.  Without it,
+      an unprivileged SQL user can use temporary objects to execute code
+      with the privileges of the security-definer function (CVE-2007-2138).
+      See <xref linkend="sql-createfunction"
+      endterm="sql-createfunction-title"> for more information.
      </para>
      </listitem>
 
      <listitem>
      <para>
-      Fix bug in how <command>VACUUM FULL</> handles <command>UPDATE</> chains (Tom, Pavan Deolasee)
+      <filename>/contrib/tsearch2</> crash fixes (Teodor)
+     </para>
+     </listitem>
+
+     <listitem>
+     <para>
+      Fix potential-data-corruption bug in how <command>VACUUM FULL</> handles
+      <command>UPDATE</> chains (Tom, Pavan Deolasee)
+     </para>
+     </listitem>
+
+     <listitem>
+     <para>
+      Fix PANIC during enlargement of a hash index (bug introduced in 7.4.15)
+      (Tom)
      </para>
      </listitem>
 
@@ -9697,7 +9760,8 @@ DROP SCHEMA information_schema CASCADE;
    </note>
 
    <para>
-    This release contains a variety of fixes from 7.3.18.
+    This release contains fixes from 7.3.18,
+    including a security fix.
    </para>
 
    <sect2>
@@ -9718,7 +9782,24 @@ DROP SCHEMA information_schema CASCADE;
 
      <listitem>
      <para>
-      Fix bug in how <command>VACUUM FULL</> handles <command>UPDATE</> chains (Tom, Pavan Deolasee)
+      Support explicit placement of the temporary-table schema within
+      <varname>search_path</>, and disable searching it for functions
+      and operators (Tom)
+     </para>
+     <para>
+      This is needed to allow a security-definer function to set a
+      truly secure value of <varname>search_path</>.  Without it,
+      an unprivileged SQL user can use temporary objects to execute code
+      with the privileges of the security-definer function (CVE-2007-2138).
+      See <xref linkend="sql-createfunction"
+      endterm="sql-createfunction-title"> for more information.
+     </para>
+     </listitem>
+
+     <listitem>
+     <para>
+      Fix potential-data-corruption bug in how <command>VACUUM FULL</> handles
+      <command>UPDATE</> chains (Tom, Pavan Deolasee)
      </para>
      </listitem>
 

src/backend/catalog/aclchk.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/catalog/aclchk.c,v 1.120.2.1 2005/11/22 18:23:06 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/catalog/aclchk.c,v 1.120.2.2 2007/04/20 02:38:04 tgl Exp $
  *
  * NOTES
  *	  See acl.h.
@@ -1746,7 +1746,7 @@ pg_namespace_aclmask(Oid nsp_oid, Oid roleid,
 	 */
 	if (isTempNamespace(nsp_oid))
 	{
-		if (pg_database_aclcheck(MyDatabaseId, GetUserId(),
+		if (pg_database_aclcheck(MyDatabaseId, roleid,
 								 ACL_CREATE_TEMP) == ACLCHECK_OK)
 			return mask & ACL_ALL_RIGHTS_NAMESPACE;
 		else

src/backend/catalog/namespace.c

@@ -13,7 +13,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/catalog/namespace.c,v 1.79.2.2 2006/02/10 19:01:22 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/catalog/namespace.c,v 1.79.2.3 2007/04/20 02:38:04 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -64,14 +64,32 @@
  * SQL99.  Also, this provides a way to search the system namespace first
  * without thereby making it the default creation target namespace.)
  *
+ * For security reasons, searches using the search path will ignore the temp
+ * namespace when searching for any object type other than relations and
+ * types.  (We must allow types since temp tables have rowtypes.)
+ *
  * The default creation target namespace is normally equal to the first
  * element of the explicit list, but is the "special" namespace when one
  * has been set.  If the explicit list is empty and there is no special
  * namespace, there is no default target.
  *
- * In bootstrap mode, the search path is set equal to 'pg_catalog', so that
+ * The textual specification of search_path can include "$user" to refer to
+ * the namespace named the same as the current user, if any.  (This is just
+ * ignored if there is no such namespace.)  Also, it can include "pg_temp"
+ * to refer to the current backend's temp namespace.  This is usually also
+ * ignorable if the temp namespace hasn't been set up, but there's a special
+ * case: if "pg_temp" appears first then it should be the default creation
+ * target.  We kluge this case a little bit so that the temp namespace isn't
+ * set up until the first attempt to create something in it.  (The reason for
+ * klugery is that we can't create the temp namespace outside a transaction,
+ * but initial GUC processing of search_path happens outside a transaction.)
+ * tempCreationPending is TRUE if "pg_temp" appears first in the string but
+ * is not reflected in defaultCreationNamespace because the namespace isn't
+ * set up yet.
+ *
+ * In bootstrap mode, the search path is set equal to "pg_catalog", so that
  * the system namespace is the only one searched or inserted into.
- * The initdb script is also careful to set search_path to 'pg_catalog' for
+ * The initdb script is also careful to set search_path to "pg_catalog" for
  * its post-bootstrap standalone backend runs.	Otherwise the default search
  * path is determined by GUC.  The factory default path contains the PUBLIC
  * namespace (if it exists), preceded by the user's personal namespace
@@ -99,7 +117,10 @@ static Oid	defaultCreationNamespace = InvalidOid;
 /* first explicit member of list; usually same as defaultCreationNamespace */
 static Oid	firstExplicitNamespace = InvalidOid;
 
-/* The above four values are valid only if namespaceSearchPathValid */
+/* if TRUE, defaultCreationNamespace is wrong, it should be temp namespace */
+static bool tempCreationPending = false;
+
+/* The above five values are valid only if namespaceSearchPathValid */
 static bool namespaceSearchPathValid = true;
 
 /*
@@ -244,6 +265,14 @@ RangeVarGetCreationNamespace(const RangeVar *newRelation)
 
 	if (newRelation->schemaname)
 	{
+		/* check for pg_temp alias */
+		if (strcmp(newRelation->schemaname, "pg_temp") == 0)
+		{
+			/* Initialize temp namespace if first time through */
+			if (!OidIsValid(myTempNamespace))
+				InitTempTableNamespace();
+			return myTempNamespace;
+		}
 		/* use exact schema given */
 		namespaceId = GetSysCacheOid(NAMESPACENAME,
 									 CStringGetDatum(newRelation->schemaname),
@@ -259,6 +288,12 @@ RangeVarGetCreationNamespace(const RangeVar *newRelation)
 	{
 		/* use the default creation namespace */
 		recomputeNamespacePath();
+		if (tempCreationPending)
+		{
+			/* Need to initialize temp namespace */
+			InitTempTableNamespace();
+			return myTempNamespace;
+		}
 		namespaceId = defaultCreationNamespace;
 		if (!OidIsValid(namespaceId))
 			ereport(ERROR,
@@ -531,12 +566,16 @@ FuncnameGetCandidates(List *names, int nargs)
 		}
 		else
 		{
-			/* Consider only procs that are in the search path */
+			/*
+			 * Consider only procs that are in the search path and are not
+			 * in the temp namespace.
+			 */
 			ListCell   *nsp;
 
 			foreach(nsp, namespaceSearchPath)
 			{
-				if (procform->pronamespace == lfirst_oid(nsp))
+				if (procform->pronamespace == lfirst_oid(nsp) &&
+					procform->pronamespace != myTempNamespace)
 					break;
 				pathpos++;
 			}
@@ -765,12 +804,16 @@ OpernameGetCandidates(List *names, char oprkind)
 		}
 		else
 		{
-			/* Consider only opers that are in the search path */
+			/*
+			 * Consider only opers that are in the search path and are not
+			 * in the temp namespace.
+			 */
 			ListCell   *nsp;
 
 			foreach(nsp, namespaceSearchPath)
 			{
-				if (operform->oprnamespace == lfirst_oid(nsp))
+				if (operform->oprnamespace == lfirst_oid(nsp) &&
+					operform->oprnamespace != myTempNamespace)
 					break;
 				pathpos++;
 			}
@@ -931,6 +974,9 @@ OpclassnameGetOpcid(Oid amid, const char *opcname)
 	{
 		Oid			namespaceId = lfirst_oid(l);
 
+		if (namespaceId == myTempNamespace)
+			continue;			/* do not look in temp namespace */
+
 		opcid = GetSysCacheOid(CLAAMNAMENSP,
 							   ObjectIdGetDatum(amid),
 							   PointerGetDatum(opcname),
@@ -1013,6 +1059,9 @@ ConversionGetConid(const char *conname)
 	{
 		Oid			namespaceId = lfirst_oid(l);
 
+		if (namespaceId == myTempNamespace)
+			continue;			/* do not look in temp namespace */
+
 		conid = GetSysCacheOid(CONNAMENSP,
 							   PointerGetDatum(conname),
 							   ObjectIdGetDatum(namespaceId),
@@ -1139,6 +1188,19 @@ LookupExplicitNamespace(const char *nspname)
 	Oid			namespaceId;
 	AclResult	aclresult;
 
+	/* check for pg_temp alias */
+	if (strcmp(nspname, "pg_temp") == 0)
+	{
+		if (OidIsValid(myTempNamespace))
+			return myTempNamespace;
+		/*
+		 * Since this is used only for looking up existing objects, there
+		 * is no point in trying to initialize the temp namespace here;
+		 * and doing so might create problems for some callers.
+		 * Just fall through and give the "does not exist" error.
+		 */
+	}
+
 	namespaceId = GetSysCacheOid(NAMESPACENAME,
 								 CStringGetDatum(nspname),
 								 0, 0, 0);
@@ -1159,7 +1221,11 @@ LookupExplicitNamespace(const char *nspname)
  * LookupCreationNamespace
  *		Look up the schema and verify we have CREATE rights on it.
  *
- * This is just like LookupExplicitNamespace except for the permission check.
+ * This is just like LookupExplicitNamespace except for the permission check,
+ * and that we are willing to create pg_temp if needed.
+ *
+ * Note: calling this may result in a CommandCounterIncrement operation,
+ * if we have to create or clean out the temp namespace.
  */
 Oid
 LookupCreationNamespace(const char *nspname)
@@ -1167,6 +1233,15 @@ LookupCreationNamespace(const char *nspname)
 	Oid			namespaceId;
 	AclResult	aclresult;
 
+	/* check for pg_temp alias */
+	if (strcmp(nspname, "pg_temp") == 0)
+	{
+		/* Initialize temp namespace if first time through */
+		if (!OidIsValid(myTempNamespace))
+			InitTempTableNamespace();
+		return myTempNamespace;
+	}
+
 	namespaceId = GetSysCacheOid(NAMESPACENAME,
 								 CStringGetDatum(nspname),
 								 0, 0, 0);
@@ -1192,21 +1267,28 @@ LookupCreationNamespace(const char *nspname)
  * Note: this does not apply any permissions check.  Callers must check
  * for CREATE rights on the selected namespace when appropriate.
  *
- * This is *not* used for tables.  Hence, the TEMP table namespace is
+ * Note: calling this may result in a CommandCounterIncrement operation,
- * never selected as the creation target.
+ * if we have to create or clean out the temp namespace.
  */
 Oid
 QualifiedNameGetCreationNamespace(List *names, char **objname_p)
 {
 	char	   *schemaname;
-	char	   *objname;
 	Oid			namespaceId;
 
 	/* deconstruct the name list */
-	DeconstructQualifiedName(names, &schemaname, &objname);
+	DeconstructQualifiedName(names, &schemaname, objname_p);
 
 	if (schemaname)
 	{
+		/* check for pg_temp alias */
+		if (strcmp(schemaname, "pg_temp") == 0)
+		{
+			/* Initialize temp namespace if first time through */
+			if (!OidIsValid(myTempNamespace))
+				InitTempTableNamespace();
+			return myTempNamespace;
+		}
 		/* use exact schema given */
 		namespaceId = GetSysCacheOid(NAMESPACENAME,
 									 CStringGetDatum(schemaname),
@@ -1221,6 +1303,12 @@ QualifiedNameGetCreationNamespace(List *names, char **objname_p)
 	{
 		/* use the default creation namespace */
 		recomputeNamespacePath();
+		if (tempCreationPending)
+		{
+			/* Need to initialize temp namespace */
+			InitTempTableNamespace();
+			return myTempNamespace;
+		}
 		namespaceId = defaultCreationNamespace;
 		if (!OidIsValid(namespaceId))
 			ereport(ERROR,
@@ -1228,7 +1316,6 @@ QualifiedNameGetCreationNamespace(List *names, char **objname_p)
 					 errmsg("no schema has been selected to create in")));
 	}
 
-	*objname_p = objname;
 	return namespaceId;
 }
 
@@ -1419,6 +1506,10 @@ FindConversionByName(List *name)
 		foreach(l, namespaceSearchPath)
 		{
 			namespaceId = lfirst_oid(l);
+
+			if (namespaceId == myTempNamespace)
+				continue;			/* do not look in temp namespace */
+
 			conoid = FindConversion(conversion_name, namespaceId);
 			if (OidIsValid(conoid))
 				return conoid;
@@ -1444,6 +1535,9 @@ FindDefaultConversionProc(int4 for_encoding, int4 to_encoding)
 	{
 		Oid			namespaceId = lfirst_oid(l);
 
+		if (namespaceId == myTempNamespace)
+			continue;			/* do not look in temp namespace */
+
 		proc = FindDefaultConversion(namespaceId, for_encoding, to_encoding);
 		if (OidIsValid(proc))
 			return proc;
@@ -1465,6 +1559,7 @@ recomputeNamespacePath(void)
 	List	   *oidlist;
 	List	   *newpath;
 	ListCell   *l;
+	bool		temp_missing;
 	Oid			firstNS;
 	MemoryContext oldcxt;
 
@@ -1492,6 +1587,7 @@ recomputeNamespacePath(void)
 	 * already been accepted.)	Don't make duplicate entries, either.
 	 */
 	oidlist = NIL;
+	temp_missing = false;
 	foreach(l, namelist)
 	{
 		char	   *curname = (char *) lfirst(l);
@@ -1521,6 +1617,21 @@ recomputeNamespacePath(void)
 					oidlist = lappend_oid(oidlist, namespaceId);
 			}
 		}
+		else if (strcmp(curname, "pg_temp") == 0)
+		{
+			/* pg_temp --- substitute temp namespace, if any */
+			if (OidIsValid(myTempNamespace))
+			{
+				if (!list_member_oid(oidlist, myTempNamespace))
+					oidlist = lappend_oid(oidlist, myTempNamespace);
+			}
+			else
+			{
+				/* If it ought to be the creation namespace, set flag */
+				if (oidlist == NIL)
+					temp_missing = true;
+			}
+		}
 		else
 		{
 			/* normal namespace reference */
@@ -1536,7 +1647,9 @@ recomputeNamespacePath(void)
 	}
 
 	/*
-	 * Remember the first member of the explicit list.
+	 * Remember the first member of the explicit list.  (Note: this is
+	 * nominally wrong if temp_missing, but we need it anyway to distinguish
+	 * explicit from implicit mention of pg_catalog.)
 	 */
 	if (oidlist == NIL)
 		firstNS = InvalidOid;
@@ -1576,9 +1689,16 @@ recomputeNamespacePath(void)
 	 */
 	firstExplicitNamespace = firstNS;
 	if (OidIsValid(mySpecialNamespace))
+	{
 		defaultCreationNamespace = mySpecialNamespace;
+		/* don't have to create temp in this state */
+		tempCreationPending = false;
+	}
 	else
+	{
 		defaultCreationNamespace = firstNS;
+		tempCreationPending = temp_missing;
+	}
 
 	/* Mark the path valid. */
 	namespaceSearchPathValid = true;
@@ -1600,6 +1720,8 @@ InitTempTableNamespace(void)
 	char		namespaceName[NAMEDATALEN];
 	Oid			namespaceId;
 
+	Assert(!OidIsValid(myTempNamespace));
+
 	/*
 	 * First, do permission check to see if we are authorized to make temp
 	 * tables.	We use a nonstandard error message here since "databasename:
@@ -1798,8 +1920,9 @@ assign_search_path(const char *newval, bool doit, GucSource source)
 	{
 		/*
 		 * Verify that all the names are either valid namespace names or
-		 * "$user".  We do not require $user to correspond to a valid
+		 * "$user" or "pg_temp".  We do not require $user to correspond to a
-		 * namespace.  We do not check for USAGE rights, either; should we?
+		 * valid namespace, and pg_temp might not exist yet.  We do not check
+		 * for USAGE rights, either; should we?
 		 *
 		 * When source == PGC_S_TEST, we are checking the argument of an ALTER
 		 * DATABASE SET or ALTER USER SET command.	It could be that the
@@ -1813,6 +1936,8 @@ assign_search_path(const char *newval, bool doit, GucSource source)
 
 			if (strcmp(curname, "$user") == 0)
 				continue;
+			if (strcmp(curname, "pg_temp") == 0)
+				continue;
 			if (!SearchSysCacheExists(NAMESPACENAME,
 									  CStringGetDatum(curname),
 									  0, 0, 0))
@@ -1857,6 +1982,7 @@ InitializeSearchPath(void)
 		MemoryContextSwitchTo(oldcxt);
 		defaultCreationNamespace = PG_CATALOG_NAMESPACE;
 		firstExplicitNamespace = PG_CATALOG_NAMESPACE;
+		tempCreationPending = false;
 		namespaceSearchPathValid = true;
 		namespaceUser = GetUserId();
 	}
@@ -1892,6 +2018,9 @@ NamespaceCallback(Datum arg, Oid relid)
  *
  * The returned list includes the implicitly-prepended namespaces only if
  * includeImplicit is true.
+ *
+ * Note: calling this may result in a CommandCounterIncrement operation,
+ * if we have to create or clean out the temp namespace.
  */
 List *
 fetch_search_path(bool includeImplicit)
@@ -1900,6 +2029,19 @@ fetch_search_path(bool includeImplicit)
 
 	recomputeNamespacePath();
 
+	/*
+	 * If the temp namespace should be first, force it to exist.  This is
+	 * so that callers can trust the result to reflect the actual default
+	 * creation namespace.  It's a bit bogus to do this here, since
+	 * current_schema() is supposedly a stable function without side-effects,
+	 * but the alternatives seem worse.
+	 */
+	if (tempCreationPending)
+	{
+		InitTempTableNamespace();
+		recomputeNamespacePath();
+	}
+
 	result = list_copy(namespaceSearchPath);
 	if (!includeImplicit)
 	{

src/test/regress/expected/temp.out

@@ -109,3 +109,61 @@ CREATE TEMP TABLE temptest4(col int REFERENCES temptest3);
 COMMIT;
 ERROR:  unsupported ON COMMIT and foreign key combination
 DETAIL:  Table "temptest4" references "temptest3" via foreign key constraint "temptest4_col_fkey", but they do not have the same ON COMMIT setting.
+-- Test manipulation of temp schema's placement in search path
+create table public.whereami (f1 text);
+insert into public.whereami values ('public');
+create temp table whereami (f1 text);
+insert into whereami values ('temp');
+create function public.whoami() returns text
+  as $$select 'public'::text$$ language sql;
+create function pg_temp.whoami() returns text
+  as $$select 'temp'::text$$ language sql;
+-- default should have pg_temp implicitly first, but only for tables
+select * from whereami;
+  f1  
+------
+ temp
+(1 row)
+
+select whoami();
+ whoami 
+--------
+ public
+(1 row)
+
+-- can list temp first explicitly, but it still doesn't affect functions
+set search_path = pg_temp, public;
+select * from whereami;
+  f1  
+------
+ temp
+(1 row)
+
+select whoami();
+ whoami 
+--------
+ public
+(1 row)
+
+-- or put it last for security
+set search_path = public, pg_temp;
+select * from whereami;
+   f1   
+--------
+ public
+(1 row)
+
+select whoami();
+ whoami 
+--------
+ public
+(1 row)
+
+-- you can invoke a temp function explicitly, though
+select pg_temp.whoami();
+ whoami 
+--------
+ temp
+(1 row)
+
+drop table public.whereami;

src/test/regress/sql/temp.sql

@@ -99,3 +99,36 @@ BEGIN;
 CREATE TEMP TABLE temptest3(col int PRIMARY KEY) ON COMMIT DELETE ROWS;
 CREATE TEMP TABLE temptest4(col int REFERENCES temptest3);
 COMMIT;
+
+-- Test manipulation of temp schema's placement in search path
+
+create table public.whereami (f1 text);
+insert into public.whereami values ('public');
+
+create temp table whereami (f1 text);
+insert into whereami values ('temp');
+
+create function public.whoami() returns text
+  as $$select 'public'::text$$ language sql;
+
+create function pg_temp.whoami() returns text
+  as $$select 'temp'::text$$ language sql;
+
+-- default should have pg_temp implicitly first, but only for tables
+select * from whereami;
+select whoami();
+
+-- can list temp first explicitly, but it still doesn't affect functions
+set search_path = pg_temp, public;
+select * from whereami;
+select whoami();
+
+-- or put it last for security
+set search_path = public, pg_temp;
+select * from whereami;
+select whoami();
+
+-- you can invoke a temp function explicitly, though
+select pg_temp.whoami();
+
+drop table public.whereami;