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=-8.0 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 92347C7618B for ; Thu, 25 Jul 2019 06:22:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4C7C6206B8 for ; Thu, 25 Jul 2019 06:22:42 +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="WNGvJYT+"; dkim=fail reason="key not found in DNS" (0-bit key) header.d=codeaurora.org header.i=@codeaurora.org header.b="Up777VAn" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729482AbfGYGWl (ORCPT ); Thu, 25 Jul 2019 02:22:41 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:50114 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728120AbfGYGWk (ORCPT ); Thu, 25 Jul 2019 02:22:40 -0400 Received: by smtp.codeaurora.org (Postfix, from userid 1000) id 1C3106115B; Thu, 25 Jul 2019 06:22:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1564035759; bh=SvR1FBNe7K5O5cm1ba72bKfw4qSdIk39uPKzCT7hxmY=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=WNGvJYT+2dEUTc2GE/D47u8cdeCCNxdT5zOUV4CJnnLXR4fM1dLK0D8bc/aVywXto dYf8OESeClQxTdWo7f9n6nhhsy/JB5DzBH5///Ut/IlKmToBzpaWBoKky9tCvDzS0j oFZ4mzqxN8G5jcCrAiF2aeY+T0ZkWp9RQ1FRl9Qc= 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 4D1AE6044E; Thu, 25 Jul 2019 06:22:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1564035754; bh=SvR1FBNe7K5O5cm1ba72bKfw4qSdIk39uPKzCT7hxmY=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=Up777VAnCma9qLktUYeneCS8CUejajmN3Wh7Yl76x+VUrmt0JsKYtIbnhVEiVg1zL lBdiZAnFbi5SU1n6ReGMK6+48IVIb06SvFfRBEVCJfHFaqni9REu/IuLuUwT8bhh3B wNfETIUTrIsFIqcT6tcNIWGzsW5fcIJaKn7F6CV0= DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 4D1AE6044E 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 v6] 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, linux-kernel@vger.kernel.org References: <20190724160006.21013-1-smuchun@gmail.com> From: Prateek Sood Message-ID: <8cf0bd10-5ae4-b1aa-abf3-c5d2a0f3a214@codeaurora.org> Date: Thu, 25 Jul 2019 11:52:24 +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: <20190724160006.21013-1-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 7/24/19 9:30 PM, Muchun Song wrote: > There is a race condition between removing glue directory and adding a new > device under the glue directory. It can be reproduced in following test: > > path 1: Add the child device under glue dir > device_add() > get_device_parent() > mutex_lock(&gdp_mutex); > .... > /*find parent from glue_dirs.list*/ > list_for_each_entry(k, &dev->class->p->glue_dirs.list, entry) > if (k->parent == parent_kobj) { > kobj = kobject_get(k); > break; > } > .... > mutex_unlock(&gdp_mutex); > .... > .... > kobject_add() > kobject_add_internal() > create_dir() > sysfs_create_dir_ns() > if (kobj->parent) > parent = kobj->parent->sd; > .... > kernfs_create_dir_ns(parent) > kernfs_new_node() > kernfs_get(parent) > .... > /* link in */ > rc = kernfs_add_one(kn); > if (!rc) > return kn; > > kernfs_put(kn) > .... > repeat: > kmem_cache_free(kn) > kn = parent; > > if (kn) { > if (atomic_dec_and_test(&kn->count)) > goto repeat; > } > .... > > path2: Remove last child device under glue dir > device_del() > cleanup_glue_dir() > mutex_lock(&gdp_mutex); > if (!kobject_has_children(glue_dir)) > kobject_del(glue_dir); > kobject_put(glue_dir); > mutex_unlock(&gdp_mutex); > > Before path2 remove last child device under glue dir, If path1 add a new > device under glue dir, the glue_dir kobject reference count will be > increase to 2 via kobject_get(k) in get_device_parent(). And path1 has > been called kernfs_new_node(), but not call kernfs_get(parent). > Meanwhile, path2 call kobject_del(glue_dir) beacause 0 is returned by > kobject_has_children(). This result in glue_dir->sd is freed and it's > reference count will be 0. Then path1 call kernfs_get(parent) will trigger > a warning in kernfs_get()(WARN_ON(!atomic_read(&kn->count))) and increase > it's reference count to 1. Because glue_dir->sd is freed by path2, the next > call kernfs_add_one() by path1 will fail(This is also use-after-free) > and call atomic_dec_and_test() to decrease reference count. Because the > reference count is decremented to 0, it will also call kmem_cache_free() > to free 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 path2 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 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 | 57 ++++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 56 insertions(+), 1 deletion(-) > > diff --git a/drivers/base/core.c b/drivers/base/core.c > index 4aeaa0c92bda..49bcb01e44cd 100644 > --- a/drivers/base/core.c > +++ b/drivers/base/core.c > @@ -1820,12 +1820,67 @@ 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. > + * > + * path 1: Add the child device under glue dir > + * device_add() > + * get_device_parent() > + * mutex_lock(&gdp_mutex); > + * .... > + * list_for_each_entry(k, &dev->class->p->glue_dirs.list, > + * entry) > + * if (k->parent == parent_kobj) { > + * kobj = kobject_get(k); > + * break; > + * } > + * .... > + * mutex_unlock(&gdp_mutex); > + * .... > + * .... > + * kobject_add() > + * kobject_add_internal() > + * create_dir() > + * .... > + * if (kobj->parent) > + * parent = kobj->parent->sd; > + * .... > + * kernfs_create_dir_ns(parent) > + * .... > + * > + * path2: Remove last child device under glue dir > + * device_del() > + * cleanup_glue_dir() > + * .... > + * mutex_lock(&gdp_mutex); > + * if (!kobject_has_children(glue_dir)) > + * kobject_del(glue_dir); > + * .... > + * mutex_unlock(&gdp_mutex); > + * > + * Before path2 remove last child device under glue dir, if path1 add > + * a new device under glue dir, the glue_dir kobject reference count > + * will be increase to 2 via kobject_get(k) in get_device_parent(). > + * And path1 has been called kernfs_create_dir_ns(). Meanwhile, > + * path2 call kobject_del(glue_dir) beacause 0 is returned by > + * kobject_has_children(). This result in glue_dir->sd is freed. > + * Then the path1 will see a stale "empty" but still potentially used > + * glue dir around. > + * > + * In order to avoid this happening, we also should make sure that > + * kernfs_node for glue_dir is released in path2 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); > I would recommend to describe the issue as done in patch https://lkml.org/lkml/2019/5/1/3 It helps in visualizing the race condition. 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