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

4 files changed, 51 insertions, 24 deletions

diff --git a/src/backend/commands/analyze.c b/src/backend/commands/analyze.c
index 91a0cc05b35..5eaf7a2ecf9 100644
--- a/src/backend/commands/analyze.c
+++ b/src/backend/commands/analyze.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/analyze.c,v 1.80.4.1 2008/01/03 21:25:00 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/analyze.c,v 1.80.4.2 2009/12/09 21:58:54 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -34,6 +34,7 @@
 #include "utils/builtins.h"
 #include "utils/datum.h"
 #include "utils/fmgroids.h"
+#include "utils/guc.h"
 #include "utils/lsyscache.h"
 #include "utils/syscache.h"
 #include "utils/tuplesort.h"
@@ -111,7 +112,8 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt)
 	double		totalrows;
 	HeapTuple  *rows;
 	AclId		save_userid;
-	bool		save_secdefcxt;
+	int			save_sec_context;
+	int			save_nestlevel;
 
 	if (vacstmt->verbose)
 		elevel = INFO;
@@ -202,11 +204,14 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt)
 					RelationGetRelationName(onerel))));
 
 	/*
-	 * Switch to the table owner's userid, so that any index functions are
-	 * run as that user.
+	 * 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.
 	 */
-	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();
 
 	/*
 	 * Determine which columns to analyze
@@ -444,8 +449,11 @@ cleanup:
 	 */
 	relation_close(onerel, NoLock);
 
-	/* 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);
 }
 
 /*
diff --git a/src/backend/commands/schemacmds.c b/src/backend/commands/schemacmds.c
index 49e931013a5..d255e3a5cb2 100644
--- a/src/backend/commands/schemacmds.c
+++ b/src/backend/commands/schemacmds.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/schemacmds.c,v 1.27.4.1 2008/01/03 21:25:00 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/schemacmds.c,v 1.27.4.2 2009/12/09 21:58:54 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -46,10 +46,10 @@ CreateSchemaCommand(CreateSchemaStmt *stmt)
 	const char *owner_name;
 	AclId		owner_userid;
 	AclId		saved_userid;
-	bool		saved_secdefcxt;
+	int			save_sec_context;
 	AclResult	aclresult;
 
-	GetUserIdAndContext(&saved_userid, &saved_secdefcxt);
+	GetUserIdAndSecContext(&saved_userid, &save_sec_context);
 
 	/*
 	 * Figure out user identities.
@@ -72,7 +72,8 @@ CreateSchemaCommand(CreateSchemaStmt *stmt)
 		 * (This will revert to session user on error or at the end of
 		 * this routine.)
 		 */
-		SetUserIdAndContext(owner_userid, true);
+		SetUserIdAndSecContext(owner_userid,
+							   save_sec_context | SECURITY_LOCAL_USERID_CHANGE);
 	}
 	else
 	{
@@ -151,8 +152,8 @@ CreateSchemaCommand(CreateSchemaStmt *stmt)
 	/* Reset search path to normal state */
 	PopSpecialNamespace(namespaceId);
 
-	/* Reset current user */
-	SetUserIdAndContext(saved_userid, saved_secdefcxt);
+	/* Reset current user and security context */
+	SetUserIdAndSecContext(saved_userid, save_sec_context);
 }
 
 
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 8001b0798c4..3c1cbae6955 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.142.4.10 2008/05/27 21:13:50 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.142.4.11 2009/12/09 21:58:54 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -296,6 +296,16 @@ DefineRelation(CreateStmt *stmt, char relkind)
 			  errmsg("ON COMMIT can only be used on temporary tables")));
 
 	/*
+	 * Security check: disallow creating temp tables from security-restricted
+	 * code.  This is needed because calling code might not expect untrusted
+	 * tables to appear in pg_temp at the front of its search path.
+	 */
+	if (stmt->relation->istemp && InSecurityRestrictedOperation())
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+				 errmsg("cannot create temporary table within security-restricted operation")));
+
+	/*
 	 * Look up the namespace in which we are supposed to create the
 	 * relation.  Check we have permission to create there. Skip check if
 	 * bootstrapping, since permissions machinery may not be working yet.
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index dc481f30f5f..ccef7141092 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 1.299.4.5 2009/11/10 18:01:26 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.299.4.6 2009/12/09 21:58:55 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -43,6 +43,7 @@
 #include "utils/acl.h"
 #include "utils/builtins.h"
 #include "utils/fmgroids.h"
+#include "utils/guc.h"
 #include "utils/inval.h"
 #include "utils/lsyscache.h"
 #include "utils/relcache.h"
@@ -884,7 +885,8 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
 	Oid			toast_relid;
 	bool		result;
 	AclId		save_userid;
-	bool		save_secdefcxt;
+	int			save_sec_context;
+	int			save_nestlevel;
 	bool		heldoff;
 
 	/* Begin a transaction for vacuuming this relation */
@@ -1001,12 +1003,15 @@ 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
@@ -1018,8 +1023,11 @@ 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);