From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932910AbcFOVvK (ORCPT ); Wed, 15 Jun 2016 17:51:10 -0400 Received: from lists.s-osg.org ([54.187.51.154]:34116 "EHLO lists.s-osg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753129AbcFOVuv (ORCPT ); Wed, 15 Jun 2016 17:50:51 -0400 Subject: Re: [PATCH 3/3] drivers/media/media-device: fix double free bug in _unregister() To: linux-media@vger.kernel.org, mchehab@osg.samsung.com, linux-kernel@vger.kernel.org, Shuah Khan References: <146602170216.9818.6967531646383934202.stgit@woodpecker.blarg.de> <146602171226.9818.8828702464432665144.stgit@woodpecker.blarg.de> <5761BB4A.9040309@osg.samsung.com> <20160615203753.GA30666@swift.blarg.de> From: Shuah Khan Message-ID: <5761CDB7.9020001@osg.samsung.com> Date: Wed, 15 Jun 2016 15:50:47 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.8.0 MIME-Version: 1.0 In-Reply-To: <20160615203753.GA30666@swift.blarg.de> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/15/2016 02:37 PM, Max Kellermann wrote: > On 2016/06/15 22:32, Shuah Khan wrote: >> This change introduces memory leaks, since drivers are relying on >> media_device_unregister() to free interfaces. > > This is what I thought, too, until I checked the code paths. Who adds > entries to that list? Only media_gobj_create() does, and only when > type==MEDIA_GRAPH_INTF_DEVNODE. That is called via > media_interface_init(), via media_devnode_create(). > > In the whole kernel, there are two calls to media_devnode_create(): > one in dvbdev.c and another one in v4l2-dev.c. Both callers take care > for freeing their interface. Both would crash if somebody else would > free it for them before they get a chance to do it. Which is the very > thing my patch addresses. > > Did I miss something? > Yes media_devnode_create() creates the interfaces links and these links are deleted by media_devnode_remove(). media_device_unregister() still needs to delete the interfaces links. The reason for that is the API dynalic use-case. Drivers (other than dvb-core and v4l2-core) can create and delete media devnode interfaces during run-time, hence media_devnode_remove() has to call media_remove_intf_links(). However, driver isn't required to call media_devnode_remove() and media-core can't enforce that. So it is safe for media_device_unregister() to remove interface links if the list isn't empty. If driver does delete them, media_device_unregister() has nothing to do since the list is going to be empty. So removing kfree() from media_device_unregister() isn't the correct fix. I don't see the stack trace for the double free error you are seeing? Could it be that there is a driver problem in the order in which it is calling media_device_unregister()? thanks, -- Shuah