Make standard maintenance operations (including VACUUM, ANALYZE, REINDEX,

and CLUSTER) execute as the table owner rather than the calling user, using
the same privilege-switching mechanism already used for SECURITY DEFINER
functions.  The purpose of this change is to ensure that user-defined
functions used in index definitions cannot acquire the privileges of a
superuser account that is performing routine maintenance.  While a function
used in an index is supposed to be IMMUTABLE and thus not able to do anything
very interesting, there are several easy ways around that restriction; and
even if we could plug them all, there would remain a risk of reading sensitive
information and broadcasting it through a covert channel such as CPU usage.

To prevent bypassing this security measure, execution of SET SESSION
AUTHORIZATION and SET ROLE is now forbidden within a SECURITY DEFINER context.

Thanks to Itagaki Takahiro for reporting this vulnerability.

Security: CVE-2007-6600

doc/src/sgml/ref/set_session_auth.sgml

@@ -1,4 +1,4 @@
-<!-- $Header: /cvsroot/pgsql/doc/src/sgml/ref/set_session_auth.sgml,v 1.11 2003/09/11 21:42:20 momjian Exp $ -->
+<!-- $Header: /cvsroot/pgsql/doc/src/sgml/ref/set_session_auth.sgml,v 1.11.2.1 2008/01/03 21:25:33 tgl Exp $ -->
 <refentry id="SQL-SET-SESSION-AUTHORIZATION">
  <refmeta>
   <refentrytitle id="sql-set-session-authorization-title">SET SESSION AUTHORIZATION</refentrytitle>
@@ -27,7 +27,7 @@ RESET SESSION AUTHORIZATION
 
   <para>
    This command sets the session user identifier and the current user
-   identifier of the current SQL-session context to be <replaceable
+   identifier of the current SQL session to be <replaceable
    class="parameter">username</replaceable>.  The user name may be
    written as either an identifier or a string literal.  Using this
    command, it is possible, for example, to temporarily become an
@@ -38,7 +38,7 @@ RESET SESSION AUTHORIZATION
    The session user identifier is initially set to be the (possibly
    authenticated) user name provided by the client.  The current user
    identifier is normally equal to the session user identifier, but
-   may change temporarily in the context of <quote>setuid</quote>
+   might change temporarily in the context of <literal>SECURITY DEFINER</>
    functions and similar mechanisms.  The current user identifier is
    relevant for permission checking.
   </para>
@@ -63,6 +63,15 @@ RESET SESSION AUTHORIZATION
   </para>
  </refsect1>
 
+ <refsect1>
+  <title>Notes</title>
+
+  <para>
+   <command>SET SESSION AUTHORIZATION</> cannot be used within a
+   <literal>SECURITY DEFINER</> function.
+  </para>
+ </refsect1>
+
  <refsect1>
   <title>Examples</title>
 

src/backend/access/transam/xact.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.156.2.4 2007/04/26 23:25:40 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.156.2.5 2008/01/03 21:25:33 tgl Exp $
  *
  * NOTES
  *		Transaction aborts can now occur two ways:
@@ -204,6 +204,8 @@ static TransactionStateData CurrentTransactionStateData = {
 
 static TransactionState CurrentTransactionState = &CurrentTransactionStateData;
 
+static AclId prevUser;			/* CurrentUserId at transaction start */
+
 /*
  *	User-tweakable parameters
  */
@@ -849,6 +851,7 @@ static void
 StartTransaction(void)
 {
 	TransactionState s = CurrentTransactionState;
+	bool		prevSecDefCxt;
 
 	/*
 	 * check the current transaction state
@@ -882,6 +885,10 @@ StartTransaction(void)
 	s->commandId = FirstCommandId;
 	s->startTime = GetCurrentAbsoluteTimeUsec(&(s->startTimeUsec));
 
+	GetUserIdAndContext(&prevUser, &prevSecDefCxt);
+	/* SecurityDefinerContext should never be set outside a transaction */
+	Assert(!prevSecDefCxt);
+
 	/*
 	 * initialize the various transaction subsystems
 	 */
@@ -1074,9 +1081,16 @@ AbortTransaction(void)
 	AtAbort_Memory();
 
 	/*
-	 * Reset user id which might have been changed transiently
+	 * Reset user ID which might have been changed transiently.  We need this
+	 * to clean up in case control escaped out of a SECURITY DEFINER function
+	 * or other local change of CurrentUserId; therefore, the prior value
+	 * of SecurityDefinerContext also needs to be restored.
+	 *
+	 * (Note: it is not necessary to restore session authorization
+	 * setting here because that can only be changed via GUC, and GUC will
+	 * take care of rolling it back if need be.)
 	 */
-	SetUserId(GetSessionUserId());
+	SetUserIdAndContext(prevUser, false);
 
 	/*
 	 * do abort processing

src/backend/catalog/index.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/catalog/index.c,v 1.219.2.2 2007/11/08 23:23:23 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/catalog/index.c,v 1.219.2.3 2008/01/03 21:25:33 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -1332,6 +1332,8 @@ index_build(Relation heapRelation,
 			IndexInfo *indexInfo)
 {
 	RegProcedure procedure;
+	AclId		save_userid;
+	bool		save_secdefcxt;
 
 	/*
 	 * sanity checks
@@ -1342,6 +1344,13 @@ index_build(Relation heapRelation,
 	procedure = indexRelation->rd_am->ambuild;
 	Assert(RegProcedureIsValid(procedure));
 
+	/*
+	 * Switch to the table owner's userid, so that any index functions are
+	 * run as that user.
+	 */
+	GetUserIdAndContext(&save_userid, &save_secdefcxt);
+	SetUserIdAndContext(heapRelation->rd_rel->relowner, true);
+
 	/*
 	 * Call the access method's build procedure
 	 */
@@ -1349,6 +1358,9 @@ index_build(Relation heapRelation,
 					 PointerGetDatum(heapRelation),
 					 PointerGetDatum(indexRelation),
 					 PointerGetDatum(indexInfo));
+
+	/* Restore userid */
+	SetUserIdAndContext(save_userid, save_secdefcxt);
 }
 
 

src/backend/commands/schemacmds.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/schemacmds.c,v 1.16 2003/08/04 02:39:58 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/schemacmds.c,v 1.16.4.1 2008/01/03 21:25:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -46,9 +46,10 @@ CreateSchemaCommand(CreateSchemaStmt *stmt)
 	const char *owner_name;
 	AclId		owner_userid;
 	AclId		saved_userid;
+	bool		saved_secdefcxt;
 	AclResult	aclresult;
 
-	saved_userid = GetUserId();
+	GetUserIdAndContext(&saved_userid, &saved_secdefcxt);
 
 	/*
 	 * Figure out user identities.
@@ -71,7 +72,7 @@ CreateSchemaCommand(CreateSchemaStmt *stmt)
 		 * (This will revert to session user on error or at the end of
 		 * this routine.)
 		 */
-		SetUserId(owner_userid);
+		SetUserIdAndContext(owner_userid, true);
 	}
 	else
 	{
@@ -151,7 +152,7 @@ CreateSchemaCommand(CreateSchemaStmt *stmt)
 	PopSpecialNamespace(namespaceId);
 
 	/* Reset current user */
-	SetUserId(saved_userid);
+	SetUserIdAndContext(saved_userid, saved_secdefcxt);
 }
 
 

src/backend/commands/vacuum.c

@@ -13,7 +13,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/vacuum.c,v 1.263.2.3 2007/03/14 18:49:26 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/vacuum.c,v 1.263.2.4 2008/01/03 21:25:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -742,6 +742,8 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
 	LockRelId	onerelid;
 	Oid			toast_relid;
 	bool		result;
+	AclId		save_userid;
+	bool		save_secdefcxt;
 
 	/* Begin a transaction for vacuuming this relation */
 	StartTransactionCommand();
@@ -846,6 +848,14 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
 	 */
 	toast_relid = onerel->rd_rel->reltoastrelid;
 
+	/*
+	 * Switch to the table owner's userid, so that any index functions are
+	 * run as that user.  (This is unnecessary, but harmless, for lazy
+	 * VACUUM.)
+	 */
+	GetUserIdAndContext(&save_userid, &save_secdefcxt);
+	SetUserIdAndContext(onerel->rd_rel->relowner, true);
+
 	/*
 	 * Do the actual work --- either FULL or "lazy" vacuum
 	 */
@@ -856,6 +866,9 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
 
 	result = true;				/* did the vacuum */
 
+	/* Restore userid */
+	SetUserIdAndContext(save_userid, save_secdefcxt);
+
 	/* all done with this class, but hold lock until commit */
 	relation_close(onerel, NoLock);
 

src/backend/commands/variable.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/variable.c,v 1.88.2.3 2006/02/12 22:33:28 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/variable.c,v 1.88.2.4 2008/01/03 21:25:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -773,6 +773,22 @@ assign_session_authorization(const char *value, bool doit, bool interactive)
 		/* not a saved ID, so look it up */
 		HeapTuple	userTup;
 
+		if (InSecurityDefinerContext())
+		{
+			/*
+			 * Disallow SET SESSION AUTHORIZATION inside a security definer
+			 * context.  We need to do this because when we exit the context,
+			 * GUC won't be notified, leaving things out of sync.  Note that
+			 * this test is positioned so that restoring a previously saved
+			 * setting isn't prevented.
+			 */
+			if (interactive)
+				ereport(ERROR,
+						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+						 errmsg("cannot set session authorization within security-definer function")));
+			return NULL;
+		}
+
 		if (!IsTransactionState())
 		{
 			/*

src/backend/utils/adt/ri_triggers.c

@@ -17,7 +17,7 @@
  *
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  *
- * $Header: /cvsroot/pgsql/src/backend/utils/adt/ri_triggers.c,v 1.63.2.1 2004/10/13 22:22:03 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/utils/adt/ri_triggers.c,v 1.63.2.2 2008/01/03 21:25:33 tgl Exp $
  *
  * ----------
  */
@@ -2967,7 +2967,8 @@ ri_PlanCheck(const char *querystr, int nargs, Oid *argtypes,
 {
 	void	   *qplan;
 	Relation	query_rel;
-	AclId		save_uid;
+	AclId		save_userid;
+	bool		save_secdefcxt;
 
 	/*
 	 * The query is always run against the FK table except when this is an
@@ -2981,8 +2982,8 @@ ri_PlanCheck(const char *querystr, int nargs, Oid *argtypes,
 		query_rel = fk_rel;
 
 	/* Switch to proper UID to perform check as */
-	save_uid = GetUserId();
+	GetUserIdAndContext(&save_userid, &save_secdefcxt);
-	SetUserId(RelationGetForm(query_rel)->relowner);
+	SetUserIdAndContext(RelationGetForm(query_rel)->relowner, true);
 
 	/* Create the plan */
 	qplan = SPI_prepare(querystr, nargs, argtypes);
@@ -2991,7 +2992,7 @@ ri_PlanCheck(const char *querystr, int nargs, Oid *argtypes,
 		elog(ERROR, "SPI_prepare returned %d for %s", SPI_result, querystr);
 
 	/* Restore UID */
-	SetUserId(save_uid);
+	SetUserIdAndContext(save_userid, save_secdefcxt);
 
 	/* Save the plan if requested */
 	if (cache_plan)
@@ -3019,7 +3020,8 @@ ri_PerformCheck(RI_QueryKey *qkey, void *qplan,
 	bool		useCurrentSnapshot;
 	int			limit;
 	int			spi_result;
-	AclId		save_uid;
+	AclId		save_userid;
+	bool		save_secdefcxt;
 	Datum		vals[RI_MAX_NUMKEYS * 2];
 	char		nulls[RI_MAX_NUMKEYS * 2];
 
@@ -3095,15 +3097,15 @@ ri_PerformCheck(RI_QueryKey *qkey, void *qplan,
 	limit = (expect_OK == SPI_OK_SELECT) ? 1 : 0;
 
 	/* Switch to proper UID to perform check as */
-	save_uid = GetUserId();
+	GetUserIdAndContext(&save_userid, &save_secdefcxt);
-	SetUserId(RelationGetForm(query_rel)->relowner);
+	SetUserIdAndContext(RelationGetForm(query_rel)->relowner, true);
 
 	/* Finally we can run the query. */
 	spi_result = SPI_execp_current(qplan, vals, nulls,
 								   useCurrentSnapshot, limit);
 
 	/* Restore UID */
-	SetUserId(save_uid);
+	SetUserIdAndContext(save_userid, save_secdefcxt);
 
 	/* Check result */
 	if (spi_result < 0)

src/backend/utils/fmgr/fmgr.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/utils/fmgr/fmgr.c,v 1.76.2.1 2007/07/31 15:50:17 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/utils/fmgr/fmgr.c,v 1.76.2.2 2008/01/03 21:25:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -654,6 +654,7 @@ fmgr_security_definer(PG_FUNCTION_ARGS)
 	FmgrInfo   *save_flinfo;
 	struct fmgr_security_definer_cache *fcache;
 	AclId		save_userid;
+	bool		save_secdefcxt;
 	HeapTuple	tuple;
 
 	if (!fcinfo->flinfo->fn_extra)
@@ -679,16 +680,18 @@ fmgr_security_definer(PG_FUNCTION_ARGS)
 	else
 		fcache = fcinfo->flinfo->fn_extra;
 
+	GetUserIdAndContext(&save_userid, &save_secdefcxt);
+	SetUserIdAndContext(fcache->userid, true);
+
 	save_flinfo = fcinfo->flinfo;
 	fcinfo->flinfo = &fcache->flinfo;
 
-	save_userid = GetUserId();
-	SetUserId(fcache->userid);
 	result = FunctionCallInvoke(fcinfo);
-	SetUserId(save_userid);
 
 	fcinfo->flinfo = save_flinfo;
 
+	SetUserIdAndContext(save_userid, save_secdefcxt);
+
 	return result;
 }
 

src/backend/utils/init/miscinit.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/utils/init/miscinit.c,v 1.116 2003/09/26 15:27:37 petere Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/utils/init/miscinit.c,v 1.116.2.1 2008/01/03 21:25:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -235,6 +235,9 @@ SetDataDir(const char *dir)
  * are implemented.  Conceptually there is a stack, whose bottom
  * is the session user.  You are yourself responsible to save and
  * restore the current user id if you need to change it.
+ *
+ * SecurityDefinerContext is TRUE if we are within a SECURITY DEFINER function
+ * or another context that temporarily changes CurrentUserId.
  * ----------------------------------------------------------------
  */
 static AclId AuthenticatedUserId = 0;
@@ -243,8 +246,13 @@ static AclId CurrentUserId = 0;
 
 static bool AuthenticatedUserIsSuperuser = false;
 
+static bool SecurityDefinerContext = false;
+
+
 /*
- * This function is relevant for all privilege checks.
+ * GetUserId - get the current effective user ID.
+ *
+ * Note: there's no SetUserId() anymore; use SetUserIdAndContext().
  */
 AclId
 GetUserId(void)
@@ -254,14 +262,6 @@ GetUserId(void)
 }
 
 
-void
-SetUserId(AclId newid)
-{
-	AssertArg(AclIdIsValid(newid));
-	CurrentUserId = newid;
-}
-
-
 /*
  * This value is only relevant for informational purposes.
  */
@@ -273,17 +273,57 @@ GetSessionUserId(void)
 }
 
 
-void
+static void
 SetSessionUserId(AclId newid)
 {
+	AssertState(!SecurityDefinerContext);
 	AssertArg(AclIdIsValid(newid));
 	SessionUserId = newid;
-	/* Current user defaults to session user. */
+	CurrentUserId = newid;
-	if (!AclIdIsValid(CurrentUserId))
-		CurrentUserId = newid;
 }
 
 
+/*
+ * GetUserIdAndContext/SetUserIdAndContext - get/set the current user ID
+ * and the SecurityDefinerContext flag.
+ *
+ * Unlike GetUserId, GetUserIdAndContext does *not* Assert that the current
+ * value of CurrentUserId is valid; nor does SetUserIdAndContext require
+ * the new value to be valid.  In fact, these routines had better not
+ * ever throw any kind of error.  This is because they are used by
+ * StartTransaction and AbortTransaction to save/restore the settings,
+ * and during the first transaction within a backend, the value to be saved
+ * and perhaps restored is indeed invalid.  We have to be able to get
+ * through AbortTransaction without asserting in case InitPostgres fails.
+ */
+void
+GetUserIdAndContext(AclId *userid, bool *sec_def_context)
+{
+	*userid = CurrentUserId;
+	*sec_def_context = SecurityDefinerContext;
+}
+
+void
+SetUserIdAndContext(AclId userid, bool sec_def_context)
+{
+	CurrentUserId = userid;
+	SecurityDefinerContext = sec_def_context;
+}
+
+
+/*
+ * InSecurityDefinerContext - are we inside a SECURITY DEFINER context?
+ */
+bool
+InSecurityDefinerContext(void)
+{
+	return SecurityDefinerContext;
+}
+
+
+/*
+ * Initialize user identity during normal backend startup
+ */
 void
 InitializeSessionUserId(const char *username)
 {
@@ -378,7 +418,6 @@ SetSessionAuthorization(AclId userid, bool is_superuser)
 			  errmsg("permission denied to set session authorization")));
 
 	SetSessionUserId(userid);
-	SetUserId(userid);
 
 	SetConfigOption("is_superuser",
 					is_superuser ? "on" : "off",

src/include/miscadmin.h

@@ -12,7 +12,7 @@
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: miscadmin.h,v 1.134 2003/09/24 18:54:01 tgl Exp $
+ * $Id: miscadmin.h,v 1.134.2.1 2008/01/03 21:25:34 tgl Exp $
  *
  * NOTES
  *	  some of the information in this file should be moved to
@@ -220,9 +220,10 @@ extern void SetDatabasePath(const char *path);
 
 extern char *GetUserNameFromId(AclId userid);
 extern AclId GetUserId(void);
-extern void SetUserId(AclId userid);
 extern AclId GetSessionUserId(void);
-extern void SetSessionUserId(AclId userid);
+extern void GetUserIdAndContext(AclId *userid, bool *sec_def_context);
+extern void SetUserIdAndContext(AclId userid, bool sec_def_context);
+extern bool InSecurityDefinerContext(void);
 extern void InitializeSessionUserId(const char *username);
 extern void InitializeSessionUserIdStandalone(void);
 extern void SetSessionAuthorization(AclId userid, bool is_superuser);