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 A1A06C433E0 for ; Tue, 2 Jun 2020 14:05:16 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6146620659 for ; Tue, 2 Jun 2020 14:05:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="07jfzjuY" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6146620659 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id CF5BA80011; Tue, 2 Jun 2020 10:05:15 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CA6F880010; Tue, 2 Jun 2020 10:05:15 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BBB5680011; Tue, 2 Jun 2020 10:05:15 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0166.hostedemail.com [216.40.44.166]) by kanga.kvack.org (Postfix) with ESMTP id 9D43080010 for ; Tue, 2 Jun 2020 10:05:15 -0400 (EDT) Received: from smtpin09.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 4EEFCF04D for ; Tue, 2 Jun 2020 14:05:15 +0000 (UTC) X-FDA: 76884443790.09.mice19_5e601a52bd902 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin09.hostedemail.com (Postfix) with ESMTP id F2987180477DD for ; Tue, 2 Jun 2020 14:04:08 +0000 (UTC) X-HE-Tag: mice19_5e601a52bd902 X-Filterd-Recvd-Size: 3444 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf15.hostedemail.com (Postfix) with ESMTP for ; Tue, 2 Jun 2020 14:04:08 +0000 (UTC) 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> X-Rspamd-Queue-Id: F2987180477DD X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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