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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 237E2ECDE43 for ; Mon, 22 Oct 2018 08:06:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D90262083A for ; Mon, 22 Oct 2018 08:05:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D90262083A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727843AbeJVQXY (ORCPT ); Mon, 22 Oct 2018 12:23:24 -0400 Received: from mga12.intel.com ([192.55.52.136]:32555 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727523AbeJVQXY (ORCPT ); Mon, 22 Oct 2018 12:23:24 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga106.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 22 Oct 2018 01:05:57 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.54,411,1534834800"; d="scan'208";a="101516638" Received: from lahna.fi.intel.com (HELO lahna) ([10.237.72.157]) by orsmga001.jf.intel.com with SMTP; 22 Oct 2018 01:05:54 -0700 Received: by lahna (sSMTP sendmail emulation); Mon, 22 Oct 2018 11:05:53 +0300 Date: Mon, 22 Oct 2018 11:05:53 +0300 From: Mika Westerberg To: Wenwen Wang Cc: Kangjie Lu , Andreas Noever , Michael Jamet , Yehezkel Bernat , open list Subject: Re: [PATCH] thunderbolt: fix a missing-check bug Message-ID: <20181022080553.GM2302@lahna.fi.intel.com> References: <1540064869-17849-1-git-send-email-wang6495@umn.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1540064869-17849-1-git-send-email-wang6495@umn.edu> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Oct 20, 2018 at 02:47:49PM -0500, Wenwen Wang wrote: > In ring_work(), the first while loop is used to collect all completed > frames from the ring buffer. In each iteration of this loop, the flag of > the frame, i.e., 'ring->descriptors[ring->tail].flags' is firstly check to > see whether the frame is completed. If yes, the descriptor of the frame, > including the flag, is then copied. It is worth noting that the descriptor > is actually in a DMA region, which is allocated through > dma_alloc_coherent() in tb_ring_alloc(). Given that the device can also > access the DMA region, a malicious device controlled by an attacker can > race to modify the flag of the frame after the check but before the copy. > By doing so, the attacker can bypass the check and supply uncompleted > frame, which can cause undefined behavior of the kernel and introduce > potential security risk. > > This patch firstly copies the flag into a local variable 'desc_flags' and > then performs the check and copy using 'desc_flags'. Through this way, the > above issue can be avoided. Ditto :)