From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 072D5C433E0 for ; Tue, 2 Jun 2020 14:57:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D22552074B for ; Tue, 2 Jun 2020 14:57:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="N1Ne1IWH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726693AbgFBO5k (ORCPT ); Tue, 2 Jun 2020 10:57:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35310 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726261AbgFBO5j (ORCPT ); Tue, 2 Jun 2020 10:57:39 -0400 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5290DC08C5C0 for ; Tue, 2 Jun 2020 07:57:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=YkOeRP7ixrxUjRV41/evzXHhbGKPE5POCnQ7Px2to4s=; b=N1Ne1IWHT2VVZ68QfUBRERhVcC GLswuMI2i2LAwW8nAzxA8I1Yfb53j2eysHhgitbdFiHKsmzagBHgFrsiO2HfHvAaFEurQQcYhO7J4 K0pSmAG5vkOn+0trmGxLRAx9miQYYaDKKLJBYkuge22VELS7MF8N2m/omJGQeQGSB+ucFnmnfKlSS QThqXz1xS/fjO17Vuqf81wJo3ukUeNgf8ZcH0i3SyfSZB29gBScvUktbi65QpirPDSKon8OrGN5nL HT6omhcISpUFqrdk73ah/c1H+Cvn4FX5cgJBGwualPA1OxmvLys7amsfwQMvDx1kM1qiP+04xPrG1 9Gn5Z92g==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jg8Lx-0005bR-AX; Tue, 02 Jun 2020 14:57:21 +0000 Date: Tue, 2 Jun 2020 07:57:21 -0700 From: Matthew Wilcox To: Greg Kroah-Hartman Cc: Wang Hai , cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, khlebnikov@yandex-team.ru, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: kobject_init_and_add is easy to misuse Message-ID: <20200602145721.GM19604@bombadil.infradead.org> References: <20200602115033.1054-1-wanghai38@huawei.com> <20200602121035.GL19604@bombadil.infradead.org> <20200602140404.GA3280145@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200602140404.GA3280145@kroah.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 02, 2020 at 04:04:04PM +0200, Greg Kroah-Hartman wrote: > On Tue, Jun 02, 2020 at 05:10:35AM -0700, Matthew Wilcox wrote: > > On Tue, Jun 02, 2020 at 07:50:33PM +0800, Wang Hai wrote: > > > syzkaller reports for memory leak when kobject_init_and_add() > > > returns an error in the function sysfs_slab_add() [1] > > > > > > When this happened, the function kobject_put() is not called for the > > > corresponding kobject, which potentially leads to memory leak. > > > > > > This patch fixes the issue by calling kobject_put() even if > > > kobject_init_and_add() fails. > > > > I think this speaks to a deeper problem with kobject_init_and_add() > > -- the need to call kobject_put() if it fails is not readily apparent > > to most users. This same bug appears in the first three users of > > kobject_init_and_add() that I checked -- > > arch/ia64/kernel/topology.c > > drivers/firmware/dmi-sysfs.c > > drivers/firmware/efi/esrt.c > > drivers/scsi/iscsi_boot_sysfs.c > > > > Some do get it right -- > > arch/powerpc/kernel/cacheinfo.c > > drivers/gpu/drm/ttm/ttm_bo.c > > drivers/gpu/drm/ttm/ttm_memory.c > > drivers/infiniband/hw/mlx4/sysfs.c > > Why are random individual drivers calling kobject* functions? That > speaks to a larger problem here... There's around 120 callers in the kernel today ... large, indeed. > Anyway, yes, it's a tricky function, but the issue usually is that the > kobject is embedded in something else and if you call init_and_add() you > want to tear things down _before_ the final put happens. > > The good thing is, that function is really hard to get to fail except if > you abuse it with syzkaller :) Yes ;-) > > I'd argue that the current behaviour is wrong, that kobject_init_and_add() > > should call kobject_put() if the add fails. This would need a tree-wide > > audit. But somebody needs to do that anyway because based on my random > > sampling, half of the users currently get it wrong. > > As said above, this is "tricky", and might break things. My audit may not be correct then. The kobject_put() may be appropriately being called at a higher level rather than in the same function as the kobject_init_and_add().