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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 725ACC433DF for ; Tue, 2 Jun 2020 14:04:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 45B37207D8 for ; Tue, 2 Jun 2020 14:04:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591106650; bh=5Bxzrru4Pb1u+SpPGmIbHIvhtZs/e62GqDODmBighQg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=l78CqbBJ1bwWAAsGVH3+kTlpwRVD4l0z8sNif05RREle9eyELhLpDVSMBcW8ZGFxB rN7ha3IJmYrK4xFq5AZONX/Gmw1PRaCo5EPbD/LOeSqBM+4f3LwwxR56v2IU3+97yn +w+/5H9YubXcZUd2lRIdpOdpFaLfczHPVvaLzK0A= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727785AbgFBOEJ (ORCPT ); Tue, 2 Jun 2020 10:04:09 -0400 Received: from mail.kernel.org ([198.145.29.99]:57406 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726019AbgFBOEJ (ORCPT ); Tue, 2 Jun 2020 10:04:09 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0E9F22074B; Tue, 2 Jun 2020 14:04:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591106647; bh=5Bxzrru4Pb1u+SpPGmIbHIvhtZs/e62GqDODmBighQg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=07jfzjuY1I6kgihd31CPlafeKfxtbWqOo28rFCuEXtnbt1gXeldBNx/pvJIGnyD43 p1upWaLE0jnZZquRFBN6IwxKr9l32PHeyRZDpISndr7LKUQ9FGFjwgGwRwtJBeUBJX RmiCjViV8am8lLB8oIa3PJ89VexmtLgvCWDc7rns= Date: Tue, 2 Jun 2020 16:04:04 +0200 From: Greg Kroah-Hartman To: Matthew Wilcox 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: <20200602140404.GA3280145@kroah.com> References: <20200602115033.1054-1-wanghai38@huawei.com> <20200602121035.GL19604@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200602121035.GL19604@bombadil.infradead.org> 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 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... 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 :) > 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. thanks, greg k-h