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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 0CFE6C433FF for ; Sat, 10 Aug 2019 18:23:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DBE0A208C3 for ; Sat, 10 Aug 2019 18:23:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="CfXBw9LL" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726112AbfHJSXV (ORCPT ); Sat, 10 Aug 2019 14:23:21 -0400 Received: from mail-pf1-f193.google.com ([209.85.210.193]:34216 "EHLO mail-pf1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726014AbfHJSXV (ORCPT ); Sat, 10 Aug 2019 14:23:21 -0400 Received: by mail-pf1-f193.google.com with SMTP id b13so47707951pfo.1 for ; Sat, 10 Aug 2019 11:23:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=1wMbnmcvYThr8v75tXw+NLJxxgTL8aTm8bPoijuWeXk=; b=CfXBw9LLS2F5CcDSorlej7BcL3a8HeAP9pALu5KvwWwkMSPiuKBuVIY9XQmieFUYCE lFxYg0yhxmEmzZCTXKoFTjfqBxXQsPTI1k2u20Amu4jFI6EvtZeKX7o+G7ygYkeu9GJf w/8ZmCDP/svUHzPv4FGiys1oJaPjVepGIg1vo= 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=1wMbnmcvYThr8v75tXw+NLJxxgTL8aTm8bPoijuWeXk=; b=UzQwnLtR4exgGTAYUf6ue2kXrZ7O7oyhwMgvKdzxGpNnVUiuP3JNO1nMY/RleOmqVh JKpqEBnq7WJZjD9L+mMVG+RlGqsRQxuxxNvA5B16+2KkF6hV44vuCkdb1KOJFw0kPaPW /4F+78vxaY9rEy1YgXlF3Wx6kevMuYRnXTKY7ETiTDvtZv+UJu+UzuijgBMQVukrGTIh sUeIEIFQOmZD9SO91xM+aLJ1Ji4ffMgtnyx4HRtcRgRugKN+EMU1hXMPoAvtgfRuvKwg luxldgERjYdy12o/3aOeAi5htGVqDqbEQyv7GgXltf37jt7O8kTIidOOL5J6fPmQQ+l6 orOg== X-Gm-Message-State: APjAAAWJLnaRJ4dUOO/BK87VTeTQVTfBueF9255d1FLnoQA0/jb7OiUU LmrMrXUdXewR2OA84zxpBB7tDg== X-Google-Smtp-Source: APXvYqwv9kKazhsFHfQH/poO6zFrpDEO8Q9vVz6A2xAvqR+Dr3CXy+nbi3/t+heCuUrDlMSmH7frYw== X-Received: by 2002:a17:90a:bf03:: with SMTP id c3mr14911536pjs.112.1565461400408; Sat, 10 Aug 2019 11:23:20 -0700 (PDT) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id a1sm72180032pgh.61.2019.08.10.11.23.19 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sat, 10 Aug 2019 11:23:19 -0700 (PDT) Date: Sat, 10 Aug 2019 11:23:18 -0700 From: Kees Cook To: Alan Stern Cc: Greg KH , syzbot , Michael Hund , akpm@linux-foundation.org, andreyknvl@google.com, cai@lca.pw, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-usb@vger.kernel.org, syzkaller-bugs@googlegroups.com, tglx@linutronix.de Subject: Re: BUG: bad usercopy in ld_usb_read Message-ID: <201908101120.BE5034521A@keescook> References: <20190809085545.GB21320@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Fri, Aug 09, 2019 at 11:13:00AM -0400, Alan Stern wrote: > In fact, I don't see why any of the computations here should overflow > or wrap around, or even give rise to a negative value. If syzbot had a > reproducer we could get more debugging output -- but it doesn't. Yeah, this is odd. The only thing I could see here with more study was that ring_tail is used/updated outside of the rbsl lock in ld_usb_read(). I couldn't convince myself there wasn't a race against the interrupt, but I also couldn't think of a way it could break... -- Kees Cook