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, 17 insertions, 9 deletions

diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index f9fce596a36..eb0ba4afef2 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -13,7 +13,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.317.2.8 2009/11/10 18:01:11 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.317.2.9 2009/12/09 21:58:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -44,6 +44,7 @@
 #include "utils/builtins.h"
 #include "utils/flatfiles.h"
 #include "utils/fmgroids.h"
+#include "utils/guc.h"
 #include "utils/inval.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
@@ -962,7 +963,8 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
 	Oid			toast_relid;
 	bool		result;
 	Oid			save_userid;
-	bool		save_secdefcxt;
+	int			save_sec_context;
+	int			save_nestlevel;
 	bool		heldoff;
 
 	/* Begin a transaction for vacuuming this relation */
@@ -1075,12 +1077,15 @@ 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.)
+	 * Switch to the table owner's userid, so that any index functions are run
+	 * as that user.  Also lock down security-restricted operations and
+	 * arrange to make GUC variable changes local to this command.
+	 * (This is unnecessary, but harmless, for lazy VACUUM.)
 	 */
-	GetUserIdAndContext(&save_userid, &save_secdefcxt);
-	SetUserIdAndContext(onerel->rd_rel->relowner, true);
+	GetUserIdAndSecContext(&save_userid, &save_sec_context);
+	SetUserIdAndSecContext(onerel->rd_rel->relowner,
+						   save_sec_context | SECURITY_RESTRICTED_OPERATION);
+	save_nestlevel = NewGUCNestLevel();
 
 	/*
 	 * Do the actual work --- either FULL or "lazy" vacuum
@@ -1092,8 +1097,11 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
 
 	result = true;				/* did the vacuum */
 
-	/* Restore userid */
-	SetUserIdAndContext(save_userid, save_secdefcxt);
+	/* Roll back any GUC changes executed by index functions */
+	AtEOXact_GUC(false, save_nestlevel);
+
+	/* Restore userid and security context */
+	SetUserIdAndSecContext(save_userid, save_sec_context);
 
 	/* all done with this class, but hold lock until commit */
 	relation_close(onerel, NoLock);