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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 19C45C433EF for ; Fri, 3 Jun 2022 16:03:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343605AbiFCQDg (ORCPT ); Fri, 3 Jun 2022 12:03:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48676 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343617AbiFCQDf (ORCPT ); Fri, 3 Jun 2022 12:03:35 -0400 Received: from netrider.rowland.org (netrider.rowland.org [192.131.102.5]) by lindbergh.monkeyblade.net (Postfix) with SMTP id ACC5F37BCF for ; Fri, 3 Jun 2022 09:03:33 -0700 (PDT) Received: (qmail 305407 invoked by uid 1000); 3 Jun 2022 12:03:32 -0400 Date: Fri, 3 Jun 2022 12:03:32 -0400 From: Alan Stern To: Greg KH Cc: Andy Shevchenko , syzbot , hdanton@sina.com, lenb@kernel.org, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, rafael.j.wysocki@intel.com, rafael@kernel.org, rjw@rjwysocki.net, syzkaller-bugs@googlegroups.com, linux-usb@vger.kernel.org Subject: Re: [syzbot] general protection fault in __device_attach Message-ID: References: <000000000000bb7f1c05da29b601@google.com> <00000000000010b7d305e08837c8@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org On Fri, Jun 03, 2022 at 05:52:38PM +0200, Greg KH wrote: > On Fri, Jun 03, 2022 at 11:42:19AM -0400, Alan Stern wrote: > > On Fri, Jun 03, 2022 at 02:04:04PM +0300, Andy Shevchenko wrote: > > > On Fri, Jun 03, 2022 at 03:02:07AM -0700, syzbot wrote: > > > > syzbot has bisected this issue to: > > > > > > > > commit a9c4cf299f5f79d5016c8a9646fa1fc49381a8c1 > > > > Author: Andy Shevchenko > > > > Date: Fri Jun 18 13:41:27 2021 +0000 > > > > > > > > ACPI: sysfs: Use __ATTR_RO() and __ATTR_RW() macros > > > > > > Hmm... It's not obvious at all how this change can alter the behaviour so > > > drastically. device_add() is called from USB core with intf->dev.name == NULL > > > by some reason. A-ha, seems like fault injector, which looks like > > > > > > dev_set_name(&intf->dev, "%d-%s:%d.%d", dev->bus->busnum, > > > dev->devpath, configuration, ifnum); > > > > > > missed the return code check. > > > > > > But I'm not familiar with that code at all, adding Linux USB ML and Alan. > > > > I can't see any connection between this bug and acpi/sysfs.c. Is it a > > bad bisection? > > > > It looks like you're right about dev_set_name() failing. In fact, the > > kernel appears to be littered with calls to that routine which do not > > check the return code (the entire subtree below drivers/usb/ contains > > only _one_ call that does check the return code!). The function doesn't > > have any __must_check annotation, and its kerneldoc doesn't mention the > > return code or the possibility of a failure. > > > > Apparently the assumption is that if dev_set_name() fails then > > device_add() later on will also fail, and the problem will be detected > > then. > > > > So now what should happen when device_add() for an interface fails in > > usb_set_configuration()? > > But how can that really fail on a real system? > > Is this just due to error-injection stuff? If so, I'm really loath to > rework the world for something that can never happen in real life. > > Or is this a real syzbot-found-with-reproducer issue? Aren't there quite a few reasons why device_add() might fail? (Although most of them probably are memory allocation errors...) Basically, you have to make up your mind. If a function can fail, you should be prepared to handle the failure. If it can't fail, there's no point in even checking the return code. Alan Stern