Prevent indirect security attacks via changing session-local state within

an allegedly immutable index function.  It was previously recognized that
we had to prevent such a function from executing SET/RESET ROLE/SESSION
AUTHORIZATION, or it could trivially obtain the privileges of the session
user.  However, since there is in general no privilege checking for changes
of session-local state, it is also possible for such a function to change
settings in a way that might subvert later operations in the same session.
Examples include changing search_path to cause an unexpected function to
be called, or replacing an existing prepared statement with another one
that will execute a function of the attacker's choosing.

The present patch secures VACUUM, ANALYZE, and CREATE INDEX/REINDEX against
these threats, which are the same places previously deemed to need protection
against the SET ROLE issue.  GUC changes are still allowed, since there are
many useful cases for that, but we prevent security problems by forcing a
rollback of any GUC change after completing the operation.  Other cases are
handled by throwing an error if any change is attempted; these include temp
table creation, closing a cursor, and creating or deleting a prepared
statement.  (In 7.4, the infrastructure to roll back GUC changes doesn't
exist, so we settle for rejecting changes of "search_path" in these contexts.)

Original report and patch by Gurjeet Singh, additional analysis by
Tom Lane.

Security: CVE-2009-4136

1 files changed, 13 insertions, 11 deletions

diff --git a/src/backend/utils/adt/ri_triggers.c b/src/backend/utils/adt/ri_triggers.c
index 32925146f92..d614c732923 100644
--- a/src/backend/utils/adt/ri_triggers.c
+++ b/src/backend/utils/adt/ri_triggers.c
@@ -17,7 +17,7 @@
  *
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  *
- * $PostgreSQL: pgsql/src/backend/utils/adt/ri_triggers.c,v 1.76.4.3 2008/01/03 21:25:00 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/utils/adt/ri_triggers.c,v 1.76.4.4 2009/12/09 21:58:55 tgl Exp $
  *
  * ----------
  */
@@ -3001,7 +3001,7 @@ ri_PlanCheck(const char *querystr, int nargs, Oid *argtypes,
 	void	   *qplan;
 	Relation	query_rel;
 	AclId		save_userid;
-	bool		save_secdefcxt;
+	int			save_sec_context;
 
 	/*
 	 * The query is always run against the FK table except when this is an
@@ -3015,8 +3015,9 @@ ri_PlanCheck(const char *querystr, int nargs, Oid *argtypes,
 		query_rel = fk_rel;
 
 	/* Switch to proper UID to perform check as */
-	GetUserIdAndContext(&save_userid, &save_secdefcxt);
-	SetUserIdAndContext(RelationGetForm(query_rel)->relowner, true);
+	GetUserIdAndSecContext(&save_userid, &save_sec_context);
+	SetUserIdAndSecContext(RelationGetForm(query_rel)->relowner,
+						   save_sec_context | SECURITY_LOCAL_USERID_CHANGE);
 
 	/* Create the plan */
 	qplan = SPI_prepare(querystr, nargs, argtypes);
@@ -3024,8 +3025,8 @@ ri_PlanCheck(const char *querystr, int nargs, Oid *argtypes,
 	if (qplan == NULL)
 		elog(ERROR, "SPI_prepare returned %d for %s", SPI_result, querystr);
 
-	/* Restore UID */
-	SetUserIdAndContext(save_userid, save_secdefcxt);
+	/* Restore UID and security context */
+	SetUserIdAndSecContext(save_userid, save_sec_context);
 
 	/* Save the plan if requested */
 	if (cache_plan)
@@ -3055,7 +3056,7 @@ ri_PerformCheck(RI_QueryKey *qkey, void *qplan,
 	int			limit;
 	int			spi_result;
 	AclId		save_userid;
-	bool		save_secdefcxt;
+	int			save_sec_context;
 	Datum		vals[RI_MAX_NUMKEYS * 2];
 	char		nulls[RI_MAX_NUMKEYS * 2];
 
@@ -3134,8 +3135,9 @@ ri_PerformCheck(RI_QueryKey *qkey, void *qplan,
 	limit = (expect_OK == SPI_OK_SELECT) ? 1 : 0;
 
 	/* Switch to proper UID to perform check as */
-	GetUserIdAndContext(&save_userid, &save_secdefcxt);
-	SetUserIdAndContext(RelationGetForm(query_rel)->relowner, true);
+	GetUserIdAndSecContext(&save_userid, &save_sec_context);
+	SetUserIdAndSecContext(RelationGetForm(query_rel)->relowner,
+						   save_sec_context | SECURITY_LOCAL_USERID_CHANGE);
 
 	/* Finally we can run the query. */
 	spi_result = SPI_execute_snapshot(qplan,
@@ -3143,8 +3145,8 @@ ri_PerformCheck(RI_QueryKey *qkey, void *qplan,
 									  test_snapshot, crosscheck_snapshot,
 									  false, false, limit);
 
-	/* Restore UID */
-	SetUserIdAndContext(save_userid, save_secdefcxt);
+	/* Restore UID and security context */
+	SetUserIdAndSecContext(save_userid, save_sec_context);
 
 	/* Check result */
 	if (spi_result < 0)