Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752856AbbGHW1R (ORCPT ); Wed, 8 Jul 2015 18:27:17 -0400 Received: from quartz.orcorp.ca ([184.70.90.242]:57106 "EHLO quartz.orcorp.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752634AbbGHW1G (ORCPT ); Wed, 8 Jul 2015 18:27:06 -0400 Date: Wed, 8 Jul 2015 16:26:49 -0600 From: Jason Gunthorpe To: Greg Kroah-Hartman , Dmitry Torokhov Cc: Jens Wiklander , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org, Arnd Bergmann , Rob Herring , Herbert Xu , valentin.manea@huawei.com, jean-michel.delorme@st.com, emmanuel.michel@st.com, javier@javigon.com, Mark Rutland , Michal Simek Subject: Re: [PATCH v4 3/5] tee: generic TEE subsystem Message-ID: <20150708222649.GA20068@obsidianresearch.com> References: <1436350592-7732-1-git-send-email-jens.wiklander@linaro.org> <1436350592-7732-4-git-send-email-jens.wiklander@linaro.org> <20150708171026.GA11740@obsidianresearch.com> <20150708211129.GA29824@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150708211129.GA29824@kroah.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-Broken-Reverse-DNS: no host name found for IP address 10.0.0.192 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2803 Lines: 80 On Wed, Jul 08, 2015 at 02:11:29PM -0700, Greg Kroah-Hartman wrote: > > > + cdev_init(&teedev->cdev, &tee_fops); > > > + teedev->cdev.owner = teedesc->owner; > > > > This also needs to set teedev->cdev.kobj.parent. > > I'm guessing: > > > > teedev->cdev.kobj.parent = &teedev->dev.kobj; > > > > TPM had the same mistake.. > > Really? As of a few years ago, A cdev's kobject should not be touched > by anything other than the cdev core. It's not a "real" kobject in that > it is never registered in sysfs, and no one sees it. I keep meaning to Well, when I looked at it, it looked like it was necessary to maintain the refcount on the memory that is holding cdev. The basic issue is that cdev_del doesn't seem to be synchronizing. The use after free race is then something like: struct tpm_chip { struct device dev; struct cdev cdev; CPU0 CPU1 ================= ====================== tpm_chip = kalloc cdev_add(&tpm_chip->cdev) device_add(&tpm_chip->dev) chrdev_open filp->f_op->open cdev_del(&tpm_chip->cdev) device_unregister (&tpm_chip->dev) kfree(tpm_chip) tpm_chip = container_of fput cdev_put(.. cdev) Ie we need cdev to hold a ref on tpm_chip->dev until cdev_put is called. > just use something else one of these days for that structure, as lots of > people get it wrong. Or has things changed there? Not recently, but this is the commit: commit 2f0157f13f42800aa3d9017ebb0fb80a65f7b2de Author: Dmitry Torokhov Date: Sun Oct 21 17:57:19 2012 -0700 char_dev: pin parent kobject In certain cases (for example when a cdev structure is embedded into another object whose lifetime is controlled by a separate kobject) it is beneficial to tie lifetime of another object to the lifetime of character device so that related object is not freed until after char_dev object is freed. To achieve this let's pin kobject's parent when doing cdev_add() and unpin when last reference to cdev structure is being released. Signed-off-by: Dmitry Torokhov Acked-by: Al Viro Signed-off-by: Linus Torvalds It doesn't seem the be the best situation, this is the 3rd time this week I've noticed cdev with a kalloc'd struct being used improperly. Perhaps cdev_init should accept the module and kref parent as an argument? Jason -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/