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=-2.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 35099C2B9F8 for ; Mon, 24 May 2021 18:50:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 111B361413 for ; Mon, 24 May 2021 18:50:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233045AbhEXSvu (ORCPT ); Mon, 24 May 2021 14:51:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35448 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232746AbhEXSvu (ORCPT ); Mon, 24 May 2021 14:51:50 -0400 Received: from mail-pj1-x1033.google.com (mail-pj1-x1033.google.com [IPv6:2607:f8b0:4864:20::1033]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0B6CDC061574 for ; Mon, 24 May 2021 11:50:21 -0700 (PDT) Received: by mail-pj1-x1033.google.com with SMTP id ep16-20020a17090ae650b029015d00f578a8so11697626pjb.2 for ; Mon, 24 May 2021 11:50:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=fQgHvnfIC6ECXr/JZNhUc4xHmYDETUNJEbI4WCNlKJ4=; b=AQxrTgiRwV25d4OHYDxMnBkKHtkIzePoDNyvsSm2daB6J1FXuECrte7Rn0vl13l//X 87/84APa6vR0EPGBJ91bQ8LKfLi5SL+FRYWuyAPo+RukbKfCbd94+NKFhmKsZh86FSfs sn2sz31Q6nZvHEHXE+IotQbx/Rs6KiUiAXyNl3QpQYJ1/Y8EHr4TJe1POqFkNKN1s/P6 pbjkxTjPrv5SEUhQMPxgPpZ03q20CyvdcflhcHKkhsXC/aVFdSZf3rygaCuy5LG1l++X 7+wq2AFYGBONNMfenzNmLfyZv0yYBk2KZYDhRiwfqPdNqal40OAxZoEiTJ7mTG968RSn S++w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=fQgHvnfIC6ECXr/JZNhUc4xHmYDETUNJEbI4WCNlKJ4=; b=PvbHH8pGADKiE8e8GrGdvYd3wyeWzP303kV7iNbb7bCYsWxcUJb55AKCeqvRfkOu+D wZMH5u0bmuG6iv7w6ohoFItB+JBrelcGVuVxUoWtrasAD2rlMSzG0ZP49yJeRTE8gHIx dYErSjDK6oZHcX/15WyWdlEbeSVZvMWMAE4TxeTzH7gpakInES2INg7b0HJQiIUGSCy7 HvVuXbL4hrRdBL4BLcRIWiSCI2QM9KcW+5ldFVCAbdKVNjX6L+LHDilSQscY1VNJ2fDZ uV05yfwZMxD841DZqY1+apItR6HoDofvcjfBy9KE2Ls0CGtAZN1XpVntuP03YXgekLOV +4Vg== X-Gm-Message-State: AOAM533TeaZLMhIiIA0lcp5lilSnrkJOy0dAnNvfN6n4Po/eMzHNEljP j2tSX+hMfufJpeCvdJFuAHg= X-Google-Smtp-Source: ABdhPJzxeSsOQjRMhPQr78up8q9/1X745LDof09uXAN1RSz+SdOqU3+447W/de+5a96IodwbelF/Ng== X-Received: by 2002:a17:902:b70f:b029:f4:5445:cd9f with SMTP id d15-20020a170902b70fb02900f45445cd9fmr27115533pls.32.1621882220529; Mon, 24 May 2021 11:50:20 -0700 (PDT) Received: from google.com ([2620:15c:202:201:870d:a395:9098:674]) by smtp.gmail.com with ESMTPSA id o24sm12043940pgl.55.2021.05.24.11.50.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 May 2021 11:50:19 -0700 (PDT) Date: Mon, 24 May 2021 11:50:17 -0700 From: Dmitry Torokhov To: Bui Quang Minh Cc: Greg Kroah-Hartman , linux-usb@vger.kernel.org Subject: Re: [BUG REPORT] usb: usb-skeleton: Race condition between skel_open and skel_disconnect Message-ID: References: <2f3f0176-244c-d76b-3d7d-15b332c87041@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2f3f0176-244c-d76b-3d7d-15b332c87041@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org Hi, On Mon, May 17, 2021 at 09:31:57PM +0700, Bui Quang Minh wrote: > Hi, > > I spotted this bug through code review and I don't know how to make a Proof > of Concept for this bug so maybe I'm wrong. > > Between skel_open() and skel_disconnect(), this scenario can happen > > skel_open() skel_disconnect() > dev = usb_get_intfdata(interface); > usb_set_intfdata(interface, NULL); > kref_put(&dev->kref, skel_delete); > kref_get(&dev->kref); > > In case dev's refcount is 1 before these events, kref_put() in > skel_disconnect() will call the skel_delete to free dev. As a result, a UAF > will happen when we try to access dev->kref in skel_open(). I can see this > pattern in other USB drivers as well such as usblcd.c, yurex.c, ... > > Please correct me if I am wrong. I think it is mostly OK. As far as I can see the minor_rwsem in drivers/usb/core/file.c makes sure that usb_open()/skel_open() either complete if they happen before call to usb_deregister_dev() in skel_disconnect() or usb_open() errors out and not call into skel_open() if usb_deregister_dev() already completed. So there is no issue with bumping refcount while the structure is being deleted. This only leaves usb_get_intfdata() returning NULL because we set it to NULL too early in skel_disconnect(). I'd recommend moving "usb_set_intfdata(interface, NULL)" to happen after call to usb_deregister_dev() in skel_disconnect(). Thanks. -- Dmitry