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envelope-from=gregkh@linuxfoundation.org; receiver=) Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=0R1tizG1; dkim-atps=neutral Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4MwyjM6q7Lz2xl5 for ; Tue, 25 Oct 2022 01:52:39 +1100 (AEDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 62D49B816A2; Mon, 24 Oct 2022 14:52:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 52EFBC433C1; Mon, 24 Oct 2022 14:52:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1666623153; bh=iIf7CBp4DRtS4RK5w27tn1+7LfTAdJA8NimWQF9sSvg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=0R1tizG1JTD1VZMfei9eZUwBceJMo27F3IPhrwxgizVbdIXR/VebztKIjUAfm+TJ2 cpiPAbSdylVk4YR/PmDNZIIZzoMbWnp7XnOykqA3Po0XqNtgjvxOXuMeqXyiEX1VR+ i+cMHZA9GYInHS3HEvmT7UEBSkL+YkXi0BemMqzI= Date: Mon, 24 Oct 2022 16:53:22 +0200 From: Greg KH To: Yang Yingliang Subject: Re: [PATCH v2] kset: fix memory leak when kset_register() returns error Message-ID: References: <20221024121910.1169801-1-yangyingliang@huawei.com> <8281fc72-948a-162d-6e5f-a9fe29d8ee46@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8281fc72-948a-162d-6e5f-a9fe29d8ee46@huawei.com> X-BeenThere: linux-erofs@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Development of Linux EROFS file system List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: rafael@kernel.org, qemu-devel@nongnu.org, liushixin2@huawei.com, joseph.qi@linux.alibaba.com, linux-mtd@lists.infradead.org, huangjianan@oppo.com, richard@nod.at, mark@fasheh.com, mst@redhat.com, amd-gfx@lists.freedesktop.org, luben.tuikov@amd.com, hsiangkao@linux.alibaba.com, somlo@cmu.edu, jlbec@evilplan.org, jaegeuk@kernel.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, alexander.deucher@amd.com, akpm@linux-foundation.org, linux-erofs@lists.ozlabs.org, ocfs2-devel@oss.oracle.com Errors-To: linux-erofs-bounces+linux-erofs=archiver.kernel.org@lists.ozlabs.org Sender: "Linux-erofs" On Mon, Oct 24, 2022 at 10:39:44PM +0800, Yang Yingliang wrote: > > On 2022/10/24 21:52, Greg KH wrote: > > On Mon, Oct 24, 2022 at 08:19:10PM +0800, Yang Yingliang wrote: > > > Inject fault while loading module, kset_register() may fail. > > > If it fails, the name allocated by kobject_set_name() which > > > is called before kset_register() is leaked, because refcount > > > of kobject is hold in kset_init(). > > > > > > As a kset may be embedded in a larger structure which needs > > > be freed in release() function or error path in callers, we > > > can not call kset_put() in kset_register(), or it will cause > > > double free, so just call kfree_const() to free the name and > > > set it to NULL. > > > > > > With this fix, the callers don't need to care about the name > > > freeing and call an extra kset_put() if kset_register() fails. > > > > > > Suggested-by: Luben Tuikov > > > Signed-off-by: Yang Yingliang > > > --- > > > v1 -> v2: > > > Free name inside of kset_register() instead of calling kset_put() > > > in drivers. > > > --- > > > lib/kobject.c | 8 +++++++- > > > 1 file changed, 7 insertions(+), 1 deletion(-) > > > > > > diff --git a/lib/kobject.c b/lib/kobject.c > > > index a0b2dbfcfa23..3409a89c81e5 100644 > > > --- a/lib/kobject.c > > > +++ b/lib/kobject.c > > > @@ -834,6 +834,9 @@ EXPORT_SYMBOL_GPL(kobj_sysfs_ops); > > > /** > > > * kset_register() - Initialize and add a kset. > > > * @k: kset. > > > + * > > > + * NOTE: On error, the kset.kobj.name allocated by() kobj_set_name() > > > + * which is called before kset_register() in caller need be freed. > > This comment doesn't make any sense anymore. No caller needs to worry > > about this, right? > With this fix, the name is freed inside of kset_register(), it can not be > accessed, Agreed. > if it allocated dynamically, but callers don't know this if no comment here, > they may use it in error path (something like to print error message with > it), > so how about comment like this to tell callers not to use the name: > > NOTE: On error, the kset.kobj.name allocated by() kobj_set_name() > is freed, it can not be used any more. Sure, that's a better way to word it. > > > */ > > > int kset_register(struct kset *k) > > > { > > > @@ -844,8 +847,11 @@ int kset_register(struct kset *k) > > > kset_init(k); > > > err = kobject_add_internal(&k->kobj); > > > - if (err) > > > + if (err) { > > > + kfree_const(k->kobj.name); > > > + k->kobj.name = NULL; > > Why are you setting the name here to NULL? > I set it to NULL to avoid accessing bad pointer in callers, > if callers use it in error path, current callers won't use this > name pointer in error path, so we can remove this assignment? Ah, I didn't think about using it on error paths. Ideally that would never happen, but that's good to set just to make it obvious. How about adding a small comment here saying why you are setting it so we all remember it in 5 years when we look at the code again. thanks, greg k-h