Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754527AbdCHViE (ORCPT ); Wed, 8 Mar 2017 16:38:04 -0500 Received: from quartz.orcorp.ca ([184.70.90.242]:40227 "EHLO quartz.orcorp.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753773AbdCHViD (ORCPT ); Wed, 8 Mar 2017 16:38:03 -0500 Date: Wed, 8 Mar 2017 13:52:36 -0700 From: Jason Gunthorpe To: "Hon Ching(Vicky) Lo" Cc: tpmdd-devel@lists.sourceforge.net, Ashley Lai , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Peter Huewe Subject: Re: [tpmdd-devel] [PATCH] vTPM: Fix missing NULL check Message-ID: <20170308205236.GA28643@obsidianresearch.com> References: <1488839535-11822-1-git-send-email-honclo@linux.vnet.ibm.com> <20170306231946.GA23953@obsidianresearch.com> <1488946363.15595.17.camel@vtpm2014.ibm.com> <20170308171729.GC16709@obsidianresearch.com> <1489004891.15595.37.camel@vtpm2014.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1489004891.15595.37.camel@vtpm2014.ibm.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Broken-Reverse-DNS: no host name found for IP address 10.0.0.156 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1735 Lines: 40 On Wed, Mar 08, 2017 at 03:28:11PM -0500, Hon Ching(Vicky) Lo wrote: > On Wed, 2017-03-08 at 10:17 -0700, Jason Gunthorpe wrote: > > On Tue, Mar 07, 2017 at 11:12:43PM -0500, Hon Ching(Vicky) Lo wrote: > > > On Mon, 2017-03-06 at 16:19 -0700, Jason Gunthorpe wrote: > > > > > > Also, how does locking work here? Does the vio core prevent > > > > tpm_ibmvtpm_get_desired_dma and tpm_ibmvtpm_remove from running > > > > concurrently? > > > > > > No, vio core doesn't prevent tpm_ibmvtpm_get_desired_dma and tpm_ibmvtpm_remove > > > from running concurrently. > > > > > > vio_bus_probe calls vio_cmo_bus_probe which calls tpm_ibmvtpm_get_desired_dma. > > > tpm_ibmvtpm_get_desired_dma is called before the code enters critical section. > > > > > > There is no locking mechanism around tpm_ibmvtpm_remove in vio_bus_remove. > > > > > > What's the concern here? > > > > tpm_ibmvtpm_remove makes the pointer that tpm_ibmvtpm_get_desired_dma > > is accessing invalid, so some kind of locking is technically required > > so that the two things do not create a use after free race: > > I don't think we need to worry about locking in this specific case. > tpm_ibmvtpm_get_desired_dma was designed to return a default value > in the case when the chip is not available. You have to worry about it to prevent a use after free race: CPU0 CPU1 tpm_ibmvtpm_remove() tpm_ibmvtpm_get_desired_dma() chip = dev_get_drvdata(dev); dev_set_drvdata(&vdev->dev, NULL); if (chip) ibmvtpm = dev_get_drvdata(&chip->dev); kfree(ibmvtpm); // *ibmvtpm is now a use-after-free Jason