Avoid repeated name lookups during table and index DDL.

If the name lookups come to different conclusions due to concurrent
activity, we might perform some parts of the DDL on a different table
than other parts.  At least in the case of CREATE INDEX, this can be
used to cause the permissions checks to be performed against a
different table than the index creation, allowing for a privilege
escalation attack.

This changes the calling convention for DefineIndex, CreateTrigger,
transformIndexStmt, transformAlterTableStmt, CheckIndexCompatible
(in 9.2 and newer), and AlterTable (in 9.1 and older).  In addition,
CheckRelationOwnership is removed in 9.2 and newer and the calling
convention is changed in older branches.  A field has also been added
to the Constraint node (FkConstraint in 8.4).  Third-party code calling
these functions or using the Constraint node will require updating.

Report by Andres Freund.  Patch by Robert Haas and Andres Freund,
reviewed by Tom Lane.

Security: CVE-2014-0062

1 files changed, 25 insertions, 48 deletions

diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
index f4d25bd1edd..d1621add7d8 100644
--- a/src/backend/tcop/utility.c
+++ b/src/backend/tcop/utility.c
@@ -79,49 +79,6 @@ static void ExecDropStmt(DropStmt *stmt, bool isTopLevel);
 
 
 /*
- * Verify user has ownership of specified relation, else ereport.
- *
- * If noCatalogs is true then we also deny access to system catalogs,
- * except when allowSystemTableMods is true.
- */
-void
-CheckRelationOwnership(RangeVar *rel, bool noCatalogs)
-{
-	Oid			relOid;
-	HeapTuple	tuple;
-
-	/*
-	 * XXX: This is unsafe in the presence of concurrent DDL, since it is
-	 * called before acquiring any lock on the target relation.  However,
-	 * locking the target relation (especially using something like
-	 * AccessExclusiveLock) before verifying that the user has permissions is
-	 * not appealing either.
-	 */
-	relOid = RangeVarGetRelid(rel, NoLock, false);
-
-	tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relOid));
-	if (!HeapTupleIsValid(tuple))		/* should not happen */
-		elog(ERROR, "cache lookup failed for relation %u", relOid);
-
-	if (!pg_class_ownercheck(relOid, GetUserId()))
-		aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
-					   rel->relname);
-
-	if (noCatalogs)
-	{
-		if (!allowSystemTableMods &&
-			IsSystemClass(relOid, (Form_pg_class) GETSTRUCT(tuple)))
-			ereport(ERROR,
-					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
-					 errmsg("permission denied: \"%s\" is a system catalog",
-							rel->relname)));
-	}
-
-	ReleaseSysCache(tuple);
-}
-
-
-/*
  * CommandIsReadOnly: is an executable query read-only?
  *
  * This is a much stricter test than we apply for XactReadOnly mode;
@@ -1019,7 +976,8 @@ ProcessUtilitySlow(Node *parsetree,
 					if (OidIsValid(relid))
 					{
 						/* Run parse analysis ... */
-						stmts = transformAlterTableStmt(atstmt, queryString);
+						stmts = transformAlterTableStmt(relid, atstmt,
+														queryString);
 
 						/* ... and do it */
 						foreach(l, stmts)
@@ -1160,18 +1118,36 @@ ProcessUtilitySlow(Node *parsetree,
 			case T_IndexStmt:	/* CREATE INDEX */
 				{
 					IndexStmt  *stmt = (IndexStmt *) parsetree;
+					Oid			relid;
+					LOCKMODE	lockmode;
 
 					if (stmt->concurrent)
 						PreventTransactionChain(isTopLevel,
 												"CREATE INDEX CONCURRENTLY");
 
-					CheckRelationOwnership(stmt->relation, true);
+					/*
+					 * Look up the relation OID just once, right here at the
+					 * beginning, so that we don't end up repeating the name
+					 * lookup later and latching onto a different relation
+					 * partway through.  To avoid lock upgrade hazards, it's
+					 * important that we take the strongest lock that will
+					 * eventually be needed here, so the lockmode calculation
+					 * needs to match what DefineIndex() does.
+					 */
+					lockmode = stmt->concurrent ? ShareUpdateExclusiveLock
+						: ShareLock;
+					relid =
+						RangeVarGetRelidExtended(stmt->relation, lockmode,
+												 false, false,
+												 RangeVarCallbackOwnsRelation,
+												 NULL);
 
 					/* Run parse analysis ... */
-					stmt = transformIndexStmt(stmt, queryString);
+					stmt = transformIndexStmt(relid, stmt, queryString);
 
 					/* ... and do it */
-					DefineIndex(stmt,
+					DefineIndex(relid,	/* OID of heap relation */
+								stmt,
 								InvalidOid,		/* no predefined OID */
 								false,	/* is_alter_table */
 								true,	/* check_rights */
@@ -1276,7 +1252,8 @@ ProcessUtilitySlow(Node *parsetree,
 
 			case T_CreateTrigStmt:
 				(void) CreateTrigger((CreateTrigStmt *) parsetree, queryString,
-									 InvalidOid, InvalidOid, false);
+									 InvalidOid, InvalidOid, InvalidOid,
+									 InvalidOid, false);
 				break;
 
 			case T_CreatePLangStmt: