Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751461AbdFHLlD (ORCPT ); Thu, 8 Jun 2017 07:41:03 -0400 Received: from mail-yb0-f175.google.com ([209.85.213.175]:34544 "EHLO mail-yb0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751132AbdFHLlB (ORCPT ); Thu, 8 Jun 2017 07:41:01 -0400 MIME-Version: 1.0 In-Reply-To: References: From: Andrey Konovalov Date: Thu, 8 Jun 2017 13:40:59 +0200 Message-ID: Subject: Re: usb/gadget: another GPF in usb_gadget_unregister_driver To: Alan Stern Cc: Felipe Balbi , Greg Kroah-Hartman , Peter Chen , Krzysztof Opasiak , Colin Ian King , =?UTF-8?Q?Felix_H=C3=A4dicke?= , Roger Quadros , USB list , LKML , Dmitry Vyukov , Kostya Serebryany , syzkaller Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3185 Lines: 84 On Wed, Jun 7, 2017 at 11:20 PM, Alan Stern wrote: > On Wed, 7 Jun 2017, Andrey Konovalov wrote: > >> On Wed, Jun 7, 2017 at 4:43 PM, Alan Stern wrote: >> > On Wed, 7 Jun 2017, Andrey Konovalov wrote: >> > >> >> Hi, >> >> >> >> I've got the following error report while fuzzing the kernel with syzkaller. >> >> >> >> On commit b29794ec95c6856b316c2295904208bf11ffddd9 (4.12-rc4+). >> >> >> >> This looks quite similar to >> >> https://groups.google.com/forum/#!topic/syzkaller/HDawLBeeORI >> > >> > It does look very similar, but that problem was supposed to have been >> > fixed by commit 7b0173811260 ("usb: gadget: udc: core: fix return code >> > of usb_gadget_probe_driver()"). >> > >> >> I'm able to reproduce this, so I can collect some debug traces if needed. >> > >> > Can you provide an strace or the equivalent? >> >> Here's the syzkaller program (which is actually two programs executed >> consequently): >> https://gist.github.com/xairy/fe0a7531e00df5e8bc23e2e56e413510 >> >> Here's the strace log: >> https://gist.github.com/xairy/5fadc3b5d8b2b80c97e566538de08bc4 > > Do you know which of the two programs got the GPF? I can't tell from > the strace log. > >> Unfortunately there's a lot of unrelated garbage, but I can't extract >> a simple C reproducer. > > That's okay, it's easy enough to see what's going on. One program > opens /dev/gadget/dummy_udc, writes an invalid setup string, then > writes a valid setup string, and then exits. The other program just > opens the file and then exits. > >> I can also apply patches with debug printk's, run the reproducer and >> send you the result if that will help. I've extract another crash log, which is a little simpler: https://gist.github.com/xairy/b8c814cbd731e4632e8e8fa0f51a29e8 > > Maybe you can patch usb_gadget_probe_driver() in > drivers/usb/gadget/udc/core.c. Find out whether the "if > (!driver->match_existing_only)" test is executed and whether it > succeeds, and find out whether the code following "found:" is executed. > I would expect that the test is not executed and the jump to "found:" > is taken, so udc_bind_to_driver() is called and returns 0. Thus, > udc->driver should be set to driver. Here's the funcgraph for usb_gadget_probe_driver: https://gist.github.com/xairy/3221e2cb9c59514880d24c955de30b80 The (!driver->match_existing_only) test is not executed. The code following "found:" is executed. > > Also, in usb_gadget_unregister_driver(), in the list_for_each_entry() > loop, we should have udc->driver == driver and therefore ret should get > set to 0. Consequently, the list_del() near the end should not be > executed and so the GPF should not occur. Here's the funcgraph for usb_gadget_unregister_driver: https://gist.github.com/xairy/887c52a12af8c9f9fe8ba3e4fa0ef1f0 What you described happens during the first call of usb_gadget_unregister_driver(), however there's another one after that, which is probably triggered by the second program. > > In particular, do these subroutines get called more than once? usb_gadget_unregister_driver() is called twice, the GPF happens during the second call. > > Alan Stern >