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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 26B36C388F7 for ; Tue, 10 Nov 2020 15:56:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D344320795 for ; Tue, 10 Nov 2020 15:56:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730819AbgKJP4w (ORCPT ); Tue, 10 Nov 2020 10:56:52 -0500 Received: from netrider.rowland.org ([192.131.102.5]:48703 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1730299AbgKJP4w (ORCPT ); Tue, 10 Nov 2020 10:56:52 -0500 Received: (qmail 193217 invoked by uid 1000); 10 Nov 2020 10:56:50 -0500 Date: Tue, 10 Nov 2020 10:56:50 -0500 From: Alan Stern To: Kyungtae Kim Cc: Felipe Balbi , Greg KH , USB list , syzkaller Subject: Re: WARNING in usb_composite_setup_continue Message-ID: <20201110155650.GC190146@rowland.harvard.edu> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org Felipe: On Mon, Nov 09, 2020 at 02:29:42PM -0500, Kyungtae Kim wrote: > We report a bug (in linux-5.8.13) found by FuzzUSB (a modified version > of syzkaller). > > (corrected analysis) > This bug happens while continuing a delayed setup message in mass > storage gadget. > To be specific, composite_setup() sets FSG_STATE_CONFIG_CHANGE via > fsg_set_alt() (line 1793), > and followed by cdev->delayed_status++ (line 1798). > Meanwile, the mass gadget tries check cdev->delayed_status == 0 > through handle_exception() (line 2428), > which occurs in between the two operations above. > Such a race causes invalid operations eventually. Do you know who maintains composite.c (or the composite framework) these days? This is a real race, and it needs to be fixed. Part of the problem seems to be that cdev->delayed_status is sometimes accessed without the protection of cdev->lock. But I don't know when it is safe to take that lock, so I can't tell what changes to make. Another part of the problem is that cdev->delayed_status doesn't count things properly. That is, its value is incremented each time a function driver asks for a delayed status and decremented each time a function driver calls usb_composite_setup_continue(), and the delayed status response is sent when the value reaches 0. But there's nothing to stop this from happening (imagine a gadget with two functions A and B): Function driver A asks for delayed status; Function driver A calls setup_continue(): Now the value of the counter is 0 so a status message is queued too early; Function driver B asks for delayed status; Function driver B calls setup_continue(): Now a second status message is queued. I'm willing to help fix these issues, but I need assistance from someone who fully understands the composite framework. Alan Stern