From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BA941CA9EAF for ; Thu, 24 Oct 2019 19:17:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 974D520684 for ; Thu, 24 Oct 2019 19:17:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2437249AbfJXTRT (ORCPT ); Thu, 24 Oct 2019 15:17:19 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:59946 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S2437179AbfJXTRS (ORCPT ); Thu, 24 Oct 2019 15:17:18 -0400 Received: (qmail 6262 invoked by uid 2102); 24 Oct 2019 15:17:18 -0400 Received: from localhost (sendmail-bs@127.0.0.1) by localhost with SMTP; 24 Oct 2019 15:17:18 -0400 Date: Thu, 24 Oct 2019 15:17:18 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Andrey Konovalov cc: syzbot , "Jacky . Cao @ sony . com" , Felipe Balbi , Chunfeng Yun , Greg Kroah-Hartman , LKML , USB list , syzkaller-bugs Subject: Re: divide error in dummy_timer In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 24 Oct 2019, Andrey Konovalov wrote: > On Thu, Oct 24, 2019 at 7:57 PM Alan Stern wrote: > > > > On Thu, 24 Oct 2019, Andrey Konovalov wrote: > > > > > > Is this really the sort of thing we need to catch? It isn't a bug in > > > > any existing kernel code, as far as I know. Maybe only gadgetfs and > > > > configfs need to worry about it. > > > > > > Hi Alan, > > > > > > Do you mean that the gadget driver must ensure that the max packet > > > size in the endpoint descriptor is not zero? Do HCDs rely on that? I > > > can add this check into the driver we use for USB fuzzing. > > > > Well, if there are any gadget drivers in the kernel which do set an > > endpoint's maxpacket size to 0, they should be fixed. I'm not aware of > > any. > > > > Of course, gadget drivers in userspace are always suspect. That's why > > I suggested having gadgetfs and configfs perform this check. Even so > > it's not really a _security_ risk, because only the superuser is > > allowed to run a userspace gadget driver. (Although obviously it is > > better to have a clean failure than to crash the system when a buggy > > program runs with superuser privileges.) > > > > Yes, HCDs do depend on endpoints having reasonable maxpacket values. I > > suppose the core should check for this. Currently we check for values > > that are too large or invalid in other ways (like high-speed bulk > > endpoints with maxpacket != 512), but we don't check for 0. > > Oh, I think I've confused the terms here. I meant to ask about UDCs. > The question is whether it's OK to try and emulate a gadget with > maxpacket = 0 on a board with a hardware UDC? Or can it cause issues? > The fact that HCDs must ensure correct maxpacket values of course > makes sense. It doesn't make any sense to have an endpoint with maxpacket = 0 -- either real or emulated. The USB spec doesn't prohibit them (probably an oversight), but such endpoints would be useless since it would not be possible to transfer any data to/from them. And as you surmised, it wouldn't be at all surprising for UDC drivers to crash (much like dummy-hcd does) when faced with an endpoint having maxpacket = 0. Best to rule out the possibility entirely. Alan Stern