Fix priv checks for ALTER <object> DEPENDS ON EXTENSION

Marking an object as dependant on an extension did not have any
privilege check whatsoever; this allowed any user to mark objects as
droppable by anyone able to DROP EXTENSION, which could be used to cause
system-wide havoc.  Disallow by checking that the calling user owns the
mentioned object.

(No constraints are placed on the extension.)

Security: CVE-2020-1720
Reported-by: Tom Lane
Discussion: 31605.1566429043@sss.pgh.pa.us

diff --git a/src/backend/commands/alter.c b/src/backend/commands/alter.c
index 4d443c13292c9559395cd28306378575e194c3c7..302f496b7d97a856bbe6ef608a7ee811af7994ee 100644 (file)
--- a/src/backend/commands/alter.c
+++ b/src/backend/commands/alter.c
@@ -432,6 +432,17 @@ ExecAlterObjectDependsStmt(AlterObjectDependsStmt *stmt, ObjectAddress *refAddre
        get_object_address_rv(stmt->objectType, stmt->relation, (List *) stmt->object,
                              &rel, AccessExclusiveLock, false);
 
+   /*
+    * Verify that the user is entitled to run the command.
+    *
+    * We don't check any privileges on the extension, because that's not
+    * needed.  The object owner is stipulating, by running this command, that
+    * the extension owner can drop the object whenever they feel like it,
+    * which is not considered a problem.
+    */
+   check_object_ownership(GetUserId(),
+                          stmt->objectType, address, stmt->object, rel);
+
    /*
     * If a relation was involved, it would have been opened and locked. We
     * don't need the relation here, but we'll retain the lock until commit.