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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 34F3EC3A5A6 for ; Thu, 19 Sep 2019 22:28:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 02610217D6 for ; Thu, 19 Sep 2019 22:28:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1568932118; bh=pnUsMLbsmExaJMsZKCYpdrEFQVqfDxcORJDW2EbhTcM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=RBYKEFaP7YbQhJs/Ten8YXlb5FGW3ubg9Dyl0t4ZbMSL/ySGM2QoJ3eUBmVMiM+Wb F7JvR/7rNE7pzayl9lHIqsmj2SeXLlZIEzJg/mxCyNA2I4b/Qyo1XosP4RaofAvxBj HtsgGKnxs4hzsQ+JmZIxQimdeIjLRCewd64469/I= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2407315AbfISW2h (ORCPT ); Thu, 19 Sep 2019 18:28:37 -0400 Received: from mail.kernel.org ([198.145.29.99]:60944 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2406619AbfISWTG (ORCPT ); Thu, 19 Sep 2019 18:19:06 -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 068B621BE5; Thu, 19 Sep 2019 22:19:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1568931545; bh=pnUsMLbsmExaJMsZKCYpdrEFQVqfDxcORJDW2EbhTcM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=VVMjhJOWA7ozzk6ItS3B4TMYqVhVw3HdWkEAih9Of5ZxJEleKa1byTMgviF//XsDt hL3q7Q0rLaxxNmeU1xKWZQse05LvamUpr7INNnJbGGwpj7tJdhyoZJ7JN/Hb8/Pmcv WyDzuYtD8hNwGpff1FonX4HMUuy1xuHahkw+YqEI= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Muchun Song , Mukesh Ojha , Prateek Sood Subject: [PATCH 4.9 25/74] driver core: Fix use-after-free and double free on glue directory Date: Fri, 20 Sep 2019 00:03:38 +0200 Message-Id: <20190919214807.268647700@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20190919214800.519074117@linuxfoundation.org> References: <20190919214800.519074117@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Muchun Song commit ac43432cb1f5c2950408534987e57c2071e24d8f upstream. 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 Signed-off-by: Prateek Sood Link: https://lore.kernel.org/r/20190727032122.24639-1-smuchun@gmail.com Signed-off-by: Greg Kroah-Hartman --- drivers/base/core.c | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 52 insertions(+), 1 deletion(-) --- a/drivers/base/core.c +++ b/drivers/base/core.c @@ -857,12 +857,63 @@ static inline struct kobject *get_glue_d */ 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 = atomic_read(&glue_dir->kref.refcount); + if (!kobject_has_children(glue_dir) && !--ref) kobject_del(glue_dir); kobject_put(glue_dir); mutex_unlock(&gdp_mutex);