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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 B4BF1C4332F for ; Sat, 4 Sep 2021 12:12:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9B084610A1 for ; Sat, 4 Sep 2021 12:12:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236368AbhIDMNj (ORCPT ); Sat, 4 Sep 2021 08:13:39 -0400 Received: from szxga08-in.huawei.com ([45.249.212.255]:15239 "EHLO szxga08-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236376AbhIDMNj (ORCPT ); Sat, 4 Sep 2021 08:13:39 -0400 Received: from dggemv704-chm.china.huawei.com (unknown [172.30.72.54]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4H1tnK4hCwz1DDrN; Sat, 4 Sep 2021 20:11:49 +0800 (CST) Received: from dggpeml500025.china.huawei.com (7.185.36.35) by dggemv704-chm.china.huawei.com (10.3.19.47) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Sat, 4 Sep 2021 20:12:35 +0800 Received: from huawei.com (10.175.124.27) by dggpeml500025.china.huawei.com (7.185.36.35) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Sat, 4 Sep 2021 20:12:35 +0800 From: Hou Tao To: Josef Bacik , Jens Axboe , CC: , , Subject: [PATCH v2 3/3] nbd: fix race between nbd_alloc_config() and module removal Date: Sat, 4 Sep 2021 20:25:19 +0800 Message-ID: <20210904122519.1963983-4-houtao1@huawei.com> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20210904122519.1963983-1-houtao1@huawei.com> References: <20210904122519.1963983-1-houtao1@huawei.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7BIT Content-Type: text/plain; charset=US-ASCII X-Originating-IP: [10.175.124.27] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To dggpeml500025.china.huawei.com (7.185.36.35) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org When nbd module is being removing, nbd_alloc_config() may be called concurrently by nbd_genl_connect(), although try_module_get() will return false, but nbd_alloc_config() doesn't handle it. The race may lead to the leak of nbd_config and its related resources (e.g, recv_workq) and oops in nbd_read_stat() due to the unload of nbd module as shown below: BUG: kernel NULL pointer dereference, address: 0000000000000040 Oops: 0000 [#1] SMP PTI CPU: 5 PID: 13840 Comm: kworker/u17:33 Not tainted 5.14.0+ #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996) Workqueue: knbd16-recv recv_work [nbd] RIP: 0010:nbd_read_stat.cold+0x130/0x1a4 [nbd] Call Trace: recv_work+0x3b/0xb0 [nbd] process_one_work+0x1ed/0x390 worker_thread+0x4a/0x3d0 kthread+0x12a/0x150 ret_from_fork+0x22/0x30 Fixing it by checking the return value of try_module_get() in nbd_alloc_config(). As nbd_alloc_config() may return ERR_PTR(-ENODEV), assign nbd->config only when nbd_alloc_config() succeeds to ensure the value of nbd->config is binary (valid or NULL). Also adding a debug message to check the reference counter of nbd_config during module removal. Signed-off-by: Hou Tao --- drivers/block/nbd.c | 28 +++++++++++++++++++--------- 1 file changed, 19 insertions(+), 9 deletions(-) diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index cedd3648e1a7..fa6c069b79dc 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -1473,15 +1473,20 @@ static struct nbd_config *nbd_alloc_config(void) { struct nbd_config *config; + if (!try_module_get(THIS_MODULE)) + return ERR_PTR(-ENODEV); + config = kzalloc(sizeof(struct nbd_config), GFP_NOFS); - if (!config) - return NULL; + if (!config) { + module_put(THIS_MODULE); + return ERR_PTR(-ENOMEM); + } + atomic_set(&config->recv_threads, 0); init_waitqueue_head(&config->recv_wq); init_waitqueue_head(&config->conn_wait); config->blksize = NBD_DEF_BLKSIZE; atomic_set(&config->live_connections, 0); - try_module_get(THIS_MODULE); return config; } @@ -1508,12 +1513,13 @@ static int nbd_open(struct block_device *bdev, fmode_t mode) mutex_unlock(&nbd->config_lock); goto out; } - config = nbd->config = nbd_alloc_config(); - if (!config) { - ret = -ENOMEM; + config = nbd_alloc_config(); + if (IS_ERR(config)) { + ret = PTR_ERR(config); mutex_unlock(&nbd->config_lock); goto out; } + nbd->config = config; refcount_set(&nbd->config_refs, 1); refcount_inc(&nbd->refs); mutex_unlock(&nbd->config_lock); @@ -1905,13 +1911,14 @@ static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info) nbd_put(nbd); return -EINVAL; } - config = nbd->config = nbd_alloc_config(); - if (!nbd->config) { + config = nbd_alloc_config(); + if (IS_ERR(config)) { mutex_unlock(&nbd->config_lock); nbd_put(nbd); pr_err("nbd: couldn't allocate config\n"); - return -ENOMEM; + return PTR_ERR(config); } + nbd->config = config; refcount_set(&nbd->config_refs, 1); set_bit(NBD_RT_BOUND, &config->runtime_flags); @@ -2486,6 +2493,9 @@ static void __exit nbd_cleanup(void) while (!list_empty(&del_list)) { nbd = list_first_entry(&del_list, struct nbd_device, list); list_del_init(&nbd->list); + if (refcount_read(&nbd->config_refs)) + pr_err("possibly leaking nbd_config (ref %d)\n", + refcount_read(&nbd->config_refs)); if (refcount_read(&nbd->refs) != 1) pr_err("possibly leaking a device\n"); nbd_put(nbd); -- 2.29.2