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=-9.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 5D9FCC7618F for ; Sat, 27 Jul 2019 03:21:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 20EDA217D9 for ; Sat, 27 Jul 2019 03:21:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="nsQ65Ko1" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728151AbfG0DVg (ORCPT ); Fri, 26 Jul 2019 23:21:36 -0400 Received: from mail-pg1-f195.google.com ([209.85.215.195]:45356 "EHLO mail-pg1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726184AbfG0DVf (ORCPT ); Fri, 26 Jul 2019 23:21:35 -0400 Received: by mail-pg1-f195.google.com with SMTP id o13so25601730pgp.12 for ; Fri, 26 Jul 2019 20:21:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id; bh=qdYopa8yacP8k3G7bShYLnBRz0nWK8PU35rQCw1ZN1U=; b=nsQ65Ko1z5pzcCks5lqtmh6ul2FpWxtYovxWQau5L16ZcX1lv8mP+0BBd/aRPiHkAN g7exeNQE5zRnvFLjl8K2Z/ctY9jHbKKyBTnShPFN0/kccJi0vx1kObSwnS3mvOv960vi IEY3NwTrYHMSa/UdidNcYNWVMOLXdXVm9561Pj3UomW5fqptdjGwcMVm0bVL+zQsZtHr Gsl998I75up31k+Fm3DlKOOMMo+q0sw8Ppe2u8mKG7+NRSDvRUCzdHjlc7ORFiboDvwe jCMKu7vtfH712BTGbv9t7lD4sT8p6i1/gjRyzUFev7fd33H0pq9WYW3UbvmNVGfz/PXd bUqg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id; bh=qdYopa8yacP8k3G7bShYLnBRz0nWK8PU35rQCw1ZN1U=; b=XIvphwoeED0RuicpGKtEe1+WyITd+NEZJg7dbUrMZyvlJtfh3NJi8cccuxAVX2sJd5 nk5Dsn4SpKPq5SxW2gR/3DVj7WUCYQ7F+eZmn2KxdE38jGY/5NULMcd+uuHMbKFe9RIS uGk+l8Jybnk8F7zMucin8dwvxEu1ALGNUPAcCB48ZPPEiJ4hOrRdLP8Th1uXQnAuZILQ 7Y+vcxDGqmksAmaHNGJHs+pyRI/qvwGGp22CUSg3cA7uu0oyJR+lrSgR+N1tejMxW+hg 5ykIR40QTbEDd5uup6UV9ms+xohfarMzN9UqKquEjafuz3KmRVTwsFl55Liq/cCKtyBL WclQ== X-Gm-Message-State: APjAAAXgZapRsoC+UhhjDZqXntwG/By0dbXe13YRJ5o1zW0dshA3NVW0 pOr9CiMENfCdyT9mKT67WYAd8RxrUgU= X-Google-Smtp-Source: APXvYqzl+AiJCet1QIj0gHRy0lsfILO65tC8BHEjApS/9NVSPIPN9YvqLiq2CfgBfXks+3U4hgjzfQ== X-Received: by 2002:a62:5252:: with SMTP id g79mr25145264pfb.18.1564197694522; Fri, 26 Jul 2019 20:21:34 -0700 (PDT) Received: from ubuntu.localdomain ([104.238.150.158]) by smtp.gmail.com with ESMTPSA id b190sm44632040pga.37.2019.07.26.20.21.31 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 26 Jul 2019 20:21:33 -0700 (PDT) From: Muchun Song To: gregkh@linuxfoundation.org, rafael@kernel.org, mojha@codeaurora.org Cc: benh@kernel.crashing.org, prsood@codeaurora.org, gkohli@codeaurora.org, songmuchun@bytedance.com, linux-kernel@vger.kernel.org Subject: [PATCH v7] driver core: Fix use-after-free and double free on glue directory Date: Sat, 27 Jul 2019 11:21:22 +0800 Message-Id: <20190727032122.24639-1-smuchun@gmail.com> X-Mailer: git-send-email 2.17.1 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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); -- 2.17.1