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=-3.8 required=3.0 tests=BAYES_00, 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 BF11EC433E6 for ; Sat, 6 Feb 2021 08:29:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8F57764FDF for ; Sat, 6 Feb 2021 08:29:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229703AbhBFI3f (ORCPT ); Sat, 6 Feb 2021 03:29:35 -0500 Received: from mx2.suse.de ([195.135.220.15]:57974 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229537AbhBFI3e (ORCPT ); Sat, 6 Feb 2021 03:29:34 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id EAAA7AC88; Sat, 6 Feb 2021 08:28:51 +0000 (UTC) Date: Sat, 06 Feb 2021 09:28:51 +0100 Message-ID: From: Takashi Iwai To: Mikhail Gavrilov Cc: Hillf Danton , zonque@gmail.com, LKML , alsa-devel@alsa-project.org, linux-usb@vger.kernel.org Subject: Re: BUG: KASAN: use-after-free in snd_complete_urb+0x109e/0x1740 [snd_usb_audio] (5.11-rc6) In-Reply-To: References: <20210206054533.120-1-hdanton@sina.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 Emacs/25.3 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Sat, 06 Feb 2021 08:48:05 +0100, Takashi Iwai wrote: > > On Sat, 06 Feb 2021 06:45:32 +0100, > Hillf Danton wrote: > > > > Due to the reconnecting key word mentioned, no fix to > > d0f09d1e4a88 ("ALSA: usb-audio: Refactoring endpoint URB deactivation") > > will be added. > > > > What is added is to capture EP_FLAG_STOPPING and remove the one > > second wait limit if the reconnecting acts may make it easier to > > repro the uaf. The diff is only for idea show. > > If my understanding is right, this won't change. The problem is > rather the lack of this function call itself, i.e. the missing > synchronization for the stream stop. > > It worked casually in the past because the endpoint resource is > released at a later point that is after all streams are really closed. > Now it's released earlier and hitting the UAF. ... and reading the code in a closer look, my guess was also wrong. The sync should have happened in snd_usb_endpoint_release(), and this didn't change for quite some time. So my previous fix won't be effective, too, I'm afraid. (And Hilif's patch won't help, either; if it's effective, there must have been a timeout error in the original case.) That said, I don't think this is a newly introduced regression, and race the condition could be in a hairy detail. Mikhail, can you reproduce this bug reliably? Takashi