From mboxrd@z Thu Jan 1 00:00:00 1970 From: jgunthorpe@obsidianresearch.com (Jason Gunthorpe) Date: Wed, 8 Jul 2015 16:26:49 -0600 Subject: [PATCH v4 3/5] tee: generic TEE subsystem In-Reply-To: <20150708211129.GA29824@kroah.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> Message-ID: <20150708222649.GA20068@obsidianresearch.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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