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=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 D26C4C433FF for ; Mon, 29 Jul 2019 04:53:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 97CE52070B for ; Mon, 29 Jul 2019 04:53:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="key not found in DNS" (0-bit key) header.d=codeaurora.org header.i=@codeaurora.org header.b="h8r5poRK"; dkim=fail reason="key not found in DNS" (0-bit key) header.d=codeaurora.org header.i=@codeaurora.org header.b="SY9t6Q5j" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726436AbfG2Exr (ORCPT ); Mon, 29 Jul 2019 00:53:47 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:58522 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726164AbfG2Exr (ORCPT ); Mon, 29 Jul 2019 00:53:47 -0400 Received: by smtp.codeaurora.org (Postfix, from userid 1000) id 6C8306074F; Mon, 29 Jul 2019 04:53:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1564376025; bh=v+vCZH4yEGr9MM8pQs4DZYDjxgNgaGjO9aKWbuFV6Qg=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=h8r5poRKZDyjpLTBUiQl0R4XG0baxj+5kotrng8T0pwi7igBn12nNsxHRyq8IG1Ra m8sJhMWRGPU5nkQPDEwk8mJmalaxbvGJB1XS03qRQ0mBYwIgzaQ3KQv05Kgqa9Ru44 dCuWC2IR3XAX1d/uwDtlcPD6IhzNWGjkTbLkR7QA= Received: from [10.204.79.19] (blr-c-bdr-fw-01_globalnat_allzones-outside.qualcomm.com [103.229.19.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: prsood@smtp.codeaurora.org) by smtp.codeaurora.org (Postfix) with ESMTPSA id 92A3B60247; Mon, 29 Jul 2019 04:53:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1564376023; bh=v+vCZH4yEGr9MM8pQs4DZYDjxgNgaGjO9aKWbuFV6Qg=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=SY9t6Q5jDt0qnOgzOlg166y6nBzKiOPHhUsmWudRChh/wWaaM0ZmunX7Tzz/m9xiD 3zsO0eISG1gN1nW23KNBlUOcDU16HdteEdJ42Vogqc7FsvkHmh7Lw073BlZaTpnBZ4 jwU0DAyFH/XPbmzdhQ2m3YSo+vVdqIIzLTFn6WKU= DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 92A3B60247 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=prsood@codeaurora.org Subject: Re: [PATCH v7] driver core: Fix use-after-free and double free on glue directory To: Muchun Song , gregkh@linuxfoundation.org, rafael@kernel.org, mojha@codeaurora.org Cc: benh@kernel.crashing.org, gkohli@codeaurora.org, songmuchun@bytedance.com, linux-kernel@vger.kernel.org References: <20190727032122.24639-1-smuchun@gmail.com> From: Prateek Sood Message-ID: <3a1884e1-7453-a938-8136-a31e5168a6f9@codeaurora.org> Date: Mon, 29 Jul 2019 10:23:39 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190727032122.24639-1-smuchun@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/27/19 8:51 AM, Muchun Song wrote: > There is a race condition between removing glue directory and adding a new > device under the glue dir. It can be reproduced in following test: > > CPU1: CPU2: > > device_add() > get_device_parent() > class_dir_create_and_add() > kobject_add_internal() > create_dir() // create glue_dir > > device_add() > get_device_parent() > kobject_get() // get glue_dir > > device_del() > cleanup_glue_dir() > kobject_del(glue_dir) > > kobject_add() > kobject_add_internal() > create_dir() // in glue_dir > sysfs_create_dir_ns() > kernfs_create_dir_ns(sd) > > sysfs_remove_dir() // glue_dir->sd=NULL > sysfs_put() // free glue_dir->sd > > // sd is freed > kernfs_new_node(sd) > kernfs_get(glue_dir) > kernfs_add_one() > kernfs_put() > > Before CPU1 remove last child device under glue dir, if CPU2 add a new > device under glue dir, the glue_dir kobject reference count will be > increase to 2 via kobject_get() in get_device_parent(). And CPU2 has > been called kernfs_create_dir_ns(), but not call kernfs_new_node(). > Meanwhile, CPU1 call sysfs_remove_dir() and sysfs_put(). This result in > glue_dir->sd is freed and it's reference count will be 0. Then CPU2 call > kernfs_get(glue_dir) will trigger a warning in kernfs_get() and increase > it's reference count to 1. Because glue_dir->sd is freed by CPU1, the next > call kernfs_add_one() by CPU2 will fail(This is also use-after-free) > and call kernfs_put() to decrease reference count. Because the reference > count is decremented to 0, it will also call kmem_cache_free() to free > the glue_dir->sd again. This will result in double free. > > In order to avoid this happening, we also should make sure that kernfs_node > for glue_dir is released in CPU1 only when refcount for glue_dir kobj is > 1 to fix this race. > > The following calltrace is captured in kernel 4.14 with the following patch > applied: > > commit 726e41097920 ("drivers: core: Remove glue dirs from sysfs earlier") > > -------------------------------------------------------------------------- > [ 3.633703] WARNING: CPU: 4 PID: 513 at .../fs/kernfs/dir.c:494 > Here is WARN_ON(!atomic_read(&kn->count) in kernfs_get(). > .... > [ 3.633986] Call trace: > [ 3.633991] kernfs_create_dir_ns+0xa8/0xb0 > [ 3.633994] sysfs_create_dir_ns+0x54/0xe8 > [ 3.634001] kobject_add_internal+0x22c/0x3f0 > [ 3.634005] kobject_add+0xe4/0x118 > [ 3.634011] device_add+0x200/0x870 > [ 3.634017] _request_firmware+0x958/0xc38 > [ 3.634020] request_firmware_into_buf+0x4c/0x70 > .... > [ 3.634064] kernel BUG at .../mm/slub.c:294! > Here is BUG_ON(object == fp) in set_freepointer(). > .... > [ 3.634346] Call trace: > [ 3.634351] kmem_cache_free+0x504/0x6b8 > [ 3.634355] kernfs_put+0x14c/0x1d8 > [ 3.634359] kernfs_create_dir_ns+0x88/0xb0 > [ 3.634362] sysfs_create_dir_ns+0x54/0xe8 > [ 3.634366] kobject_add_internal+0x22c/0x3f0 > [ 3.634370] kobject_add+0xe4/0x118 > [ 3.634374] device_add+0x200/0x870 > [ 3.634378] _request_firmware+0x958/0xc38 > [ 3.634381] request_firmware_into_buf+0x4c/0x70 > -------------------------------------------------------------------------- > > Fixes: 726e41097920 ("drivers: core: Remove glue dirs from sysfs earlier") > > Signed-off-by: Muchun Song > Reviewed-by: Mukesh Ojha > --- > > Change in v7: > 1. Update commit message. > Change in v6: > 1. Remove hardcoding "1 " > Change in v5: > 1. Revert to the v1 fix. > 2. Add some comment to explain why we need do this in > cleanup_glue_dir(). > Change in v4: > 1. Add some kerneldoc comment. > 2. Remove unlock_if_glue_dir(). > 3. Rename get_device_parent_locked_if_glue_dir() to > get_device_parent_locked. > 4. Update commit message. > Change in v3: > Add change log. > Change in v2: > Fix device_move() also. > > drivers/base/core.c | 53 ++++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 52 insertions(+), 1 deletion(-) > > diff --git a/drivers/base/core.c b/drivers/base/core.c > index 4aeaa0c92bda..edc55160c5f0 100644 > --- a/drivers/base/core.c > +++ b/drivers/base/core.c > @@ -1820,12 +1820,63 @@ static inline struct kobject *get_glue_dir(struct device *dev) > */ > static void cleanup_glue_dir(struct device *dev, struct kobject *glue_dir) > { > + unsigned int ref; > + > /* see if we live in a "glue" directory */ > if (!live_in_glue_dir(glue_dir, dev)) > return; > > mutex_lock(&gdp_mutex); > - if (!kobject_has_children(glue_dir)) > + /** > + * There is a race condition between removing glue directory > + * and adding a new device under the glue directory. > + * > + * CPU1: CPU2: > + * > + * device_add() > + * get_device_parent() > + * class_dir_create_and_add() > + * kobject_add_internal() > + * create_dir() // create glue_dir > + * > + * device_add() > + * get_device_parent() > + * kobject_get() // get glue_dir > + * > + * device_del() > + * cleanup_glue_dir() > + * kobject_del(glue_dir) > + * > + * kobject_add() > + * kobject_add_internal() > + * create_dir() // in glue_dir > + * sysfs_create_dir_ns() > + * kernfs_create_dir_ns(sd) > + * > + * sysfs_remove_dir() // glue_dir->sd=NULL > + * sysfs_put() // free glue_dir->sd > + * > + * // sd is freed > + * kernfs_new_node(sd) > + * kernfs_get(glue_dir) > + * kernfs_add_one() > + * kernfs_put() > + * > + * Before CPU1 remove last child device under glue dir, if CPU2 add > + * a new device under glue dir, the glue_dir kobject reference count > + * will be increase to 2 in kobject_get(k). And CPU2 has been called > + * kernfs_create_dir_ns(). Meanwhile, CPU1 call sysfs_remove_dir() > + * and sysfs_put(). This result in glue_dir->sd is freed. > + * > + * Then the CPU2 will see a stale "empty" but still potentially used > + * glue dir around in kernfs_new_node(). > + * > + * In order to avoid this happening, we also should make sure that > + * kernfs_node for glue_dir is released in CPU1 only when refcount > + * for glue_dir kobj is 1. > + */ > + ref = kref_read(&glue_dir->kref); > + if (!kobject_has_children(glue_dir) && !--ref) > kobject_del(glue_dir); > kobject_put(glue_dir); > mutex_unlock(&gdp_mutex); > Looks good to me and inline with https://lkml.org/lkml/2019/5/1/3 Signed-off-by: Prateek Sood Thanks Prateek -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc., is a member of Code Aurora Forum, a Linux Foundation Collaborative Project