From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933995AbcECQCo (ORCPT ); Tue, 3 May 2016 12:02:44 -0400 Received: from www381.your-server.de ([78.46.137.84]:44820 "EHLO www381.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933775AbcECQCm (ORCPT ); Tue, 3 May 2016 12:02:42 -0400 Subject: Re: [PATCH] media: fix use-after-free in cdev_put() when app exits after driver unbind To: Shuah Khan , mchehab@osg.samsung.com, laurent.pinchart@ideasonboard.com, sakari.ailus@iki.fi References: <1461969452-9276-1-git-send-email-shuahkh@osg.samsung.com> <57272910.8090500@metafoo.de> <5728BE73.7020505@osg.samsung.com> Cc: linux-media@vger.kernel.org, linux-kernel@vger.kernel.org From: Lars-Peter Clausen Message-ID: <5728CB9D.2090509@metafoo.de> Date: Tue, 3 May 2016 18:02:37 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Icedove/38.7.0 MIME-Version: 1.0 In-Reply-To: <5728BE73.7020505@osg.samsung.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Authenticated-Sender: lars@metafoo.de Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/03/2016 05:06 PM, Shuah Khan wrote: > On 05/02/2016 04:16 AM, Lars-Peter Clausen wrote: >> On 04/30/2016 12:37 AM, Shuah Khan wrote: >> [...] >>> diff --git a/include/media/media-devnode.h b/include/media/media-devnode.h >>> index 5bb3b0e..ce9b051 100644 >>> --- a/include/media/media-devnode.h >>> +++ b/include/media/media-devnode.h >>> @@ -72,6 +72,7 @@ struct media_file_operations { >>> * @fops: pointer to struct &media_file_operations with media device ops >>> * @dev: struct device pointer for the media controller device >>> * @cdev: struct cdev pointer character device >>> + * @kobj: struct kobject >>> * @parent: parent device >>> * @minor: device node minor number >>> * @flags: flags, combination of the MEDIA_FLAG_* constants >>> @@ -91,6 +92,7 @@ struct media_devnode { >>> /* sysfs */ >>> struct device dev; /* media device */ >>> struct cdev cdev; /* character device */ >>> + struct kobject kobj; /* set as cdev parent kobj */ >> >> As said during the previous review, the struct device should be used for >> reference counting. Otherwise a use-after-free can still occur since you now >> have two reference counted data structures with independent counters in the >> same structure. For one of them the counter goes to zero before the other >> and then you have the use-after-free. >> > > struct device is embedded in the media_devnode and media_devnode > will not be released until cdev releases the kobject since it is > set as cdeev kobj.parent. I am not seeing any use-fater-free with > this scheme. There might still be a reference to the struct device at that point, so if you free the media_devnode there is a use-after-free.