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=-5.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 F0921C433FF for ; Wed, 7 Aug 2019 14:39:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D254E21EF2 for ; Wed, 7 Aug 2019 14:39:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388309AbfHGOji (ORCPT ); Wed, 7 Aug 2019 10:39:38 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:42622 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S2387891AbfHGOjh (ORCPT ); Wed, 7 Aug 2019 10:39:37 -0400 Received: (qmail 18918 invoked by uid 2102); 7 Aug 2019 10:39:36 -0400 Received: from localhost (sendmail-bs@127.0.0.1) by localhost with SMTP; 7 Aug 2019 10:39:36 -0400 Date: Wed, 7 Aug 2019 10:39:36 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Andrey Konovalov cc: syzbot , Greg Kroah-Hartman , LKML , USB list , Cesar Miquel , , syzkaller-bugs Subject: Re: possible deadlock in open_rio In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Wed, 7 Aug 2019, Andrey Konovalov wrote: > On Wed, Aug 7, 2019 at 4:01 PM Alan Stern wrote: > > > > On Wed, 7 Aug 2019, Andrey Konovalov wrote: > > > > > On Tue, Aug 6, 2019 at 9:13 PM Alan Stern wrote: > > > > > > > > On Thu, 1 Aug 2019, syzbot wrote: > > > > > > > > > Hello, > > > > > > > > > > syzbot found the following crash on: > > > > > > > > > > HEAD commit: 7f7867ff usb-fuzzer: main usb gadget fuzzer driver > > > > > git tree: https://github.com/google/kasan.git usb-fuzzer > > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=136b6aec600000 > > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=792eb47789f57810 > > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=7bbcbe9c9ff0cd49592a > > > > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > > > > > > > > > Unfortunately, I don't have any reproducer for this crash yet. > > > > > > > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > > > > Reported-by: syzbot+7bbcbe9c9ff0cd49592a@syzkaller.appspotmail.com > > > > > > > > > > ====================================================== > > > > > WARNING: possible circular locking dependency detected > > > > > 5.3.0-rc2+ #23 Not tainted > > > > > ------------------------------------------------------ > > > > > > > > Andrey: > > > > > > > > This should be completely reproducible, since it's a simple ABBA > > > > locking violation. Maybe just introducing a time delay (to avoid races > > > > and give the open() call time to run) between the gadget creation and > > > > gadget removal would be enough to do it. > > > > > > I've tried some simple approaches to reproducing this, but failed. > > > Should this require two rio500 devices to trigger? > > > > No, one device should be enough. Just plug it in and then try to open > > the character device file. > > OK, I've reproduced it, so I can test a patch manually. The reason > syzbot couldn't do that, is because it doesn't open character devices. > Right now the USB fuzzing instance only opens /dev/input*, > /dev/hidraw* and /dev/usb/hiddev* (only the devices that are created > by USB HID devices as I've been working on adding USB HID targeted > fuzzing support lately). > > I guess we should open /dev/chr/* as well. The problem is that there > 300+ devices there even without connecting USB devices and opening > them blindly probably won't work. Is there a way to know which > character devices are created by USB devices? Maybe they are exposed > over /sys/bus/usb or via some other way? I don't have any devices that use this API, so I can't be certain. However, I believe the devices do get registered under /sys/class/usb/. (Note that this directory doesn't exist when there aren't any USB class files.) In any case, the USB character device files all have their major numbers set to 180 (USB_MAJOR defined in include/linux/usb.h), so you can identify them that way. Alan Stern