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=-15.2 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_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 744E3C432BE for ; Sun, 29 Aug 2021 13:47:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4F58360F25 for ; Sun, 29 Aug 2021 13:47:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229504AbhH2Nsp (ORCPT ); Sun, 29 Aug 2021 09:48:45 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:51693 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229463AbhH2Nsp (ORCPT ); Sun, 29 Aug 2021 09:48:45 -0400 Received: from fsav116.sakura.ne.jp (fsav116.sakura.ne.jp [27.133.134.243]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 17TDlYN3005221; Sun, 29 Aug 2021 22:47:34 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav116.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav116.sakura.ne.jp); Sun, 29 Aug 2021 22:47:34 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav116.sakura.ne.jp) Received: from [192.168.1.9] (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 17TDlYeu005218 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NO); Sun, 29 Aug 2021 22:47:34 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: [PATCH v3] loop: reduce the loop_ctl_mutex scope From: Tetsuo Handa To: Christoph Hellwig , Jens Axboe Cc: Hillf Danton , Pavel Tatashin , Tyler Hicks , linux-block References: <2642808b-a7d0-28ff-f288-0f4eabc562f7@i-love.sakura.ne.jp> <20210827184302.GA29967@lst.de> <73c53177-be1b-cff1-a09e-ef7979a95200@i-love.sakura.ne.jp> <20210828071832.GA31755@lst.de> <33a0a1e5-a79f-1887-6417-c5a81f58e47d@i-love.sakura.ne.jp> Message-ID: Date: Sun, 29 Aug 2021 22:47:31 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <33a0a1e5-a79f-1887-6417-c5a81f58e47d@i-love.sakura.ne.jp> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org syzbot is reporting circular locking problem at __loop_clr_fd() [1], for commit a160c6159d4a0cf8 ("block: add an optional probe callback to major_names") is calling the module's probe function with major_names_lock held. Fortunately, since commit 990e78116d38059c ("block: loop: fix deadlock between open and remove") stopped holding loop_ctl_mutex in lo_open(), current role of loop_ctl_mutex is to serialize access to loop_index_idr and loop_add()/loop_remove(); in other words, management of id for IDR. To avoid holding loop_ctl_mutex during whole add/remove operation, use a bool flag to indicate whether the loop device is ready for use. loop_unregister_transfer() which is called from cleanup_cryptoloop() currently has possibility of use-after-free access due to lack of serialization between kfree() from loop_remove() from loop_control_remove() and mutex_lock() from unregister_transfer_cb(). But since lo->lo_encryption should be already NULL when this function is called due to module unload, and commit 222013f9ac30b9ce ("cryptoloop: add a deprecation warning") indicates that we will remove this function shortly, this patch updates this function to emit warning instead of checking lo->lo_encryption. Holding loop_ctl_mutex in loop_exit() is pointless, for all users must close /dev/loop-control and /dev/loop$num (in order to drop module's refcount to 0) before loop_exit() starts, and nobody can open /dev/loop-control or /dev/loop$num afterwards. Link: https://syzkaller.appspot.com/bug?id=7bb10e8b62f83e4d445cdf4c13d69e407e629558 [1] Reported-by: syzbot Signed-off-by: Tetsuo Handa --- Changes in v3: Don't use cmpxchg(), for kernel test robot reported that some archtectures do not support cmpxchg() on bool. Add data_race() annotation to loop_control_get_free(). Changes in v2: Don't replace loop_ctl_mutex mutex with loop_idr_spinlock spinlock. Don't traverse on loop_index_idr at loop_unregister_transfer(). Don't use refcount for handling duplicated removal requests. --- drivers/block/loop.c | 75 +++++++++++++++++++++++++++++--------------- drivers/block/loop.h | 1 + 2 files changed, 50 insertions(+), 26 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index f0cdff0c5fbf..478ff6650dab 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -2113,18 +2113,6 @@ int loop_register_transfer(struct loop_func_table *funcs) return 0; } -static int unregister_transfer_cb(int id, void *ptr, void *data) -{ - struct loop_device *lo = ptr; - struct loop_func_table *xfer = data; - - mutex_lock(&lo->lo_mutex); - if (lo->lo_encryption == xfer) - loop_release_xfer(lo); - mutex_unlock(&lo->lo_mutex); - return 0; -} - int loop_unregister_transfer(int number) { unsigned int n = number; @@ -2132,9 +2120,20 @@ int loop_unregister_transfer(int number) if (n == 0 || n >= MAX_LO_CRYPT || (xfer = xfer_funcs[n]) == NULL) return -EINVAL; + /* + * This function is called from only cleanup_cryptoloop(). + * Given that each loop device that has a transfer enabled holds a + * reference to the module implementing it we should never get here + * with a transfer that is set (unless forced module unloading is + * requested). Thus, check module's refcount and warn if this is + * not a clean unloading. + */ +#ifdef CONFIG_MODULE_UNLOAD + if (xfer->owner && module_refcount(xfer->owner) != -1) + pr_err("Danger! Unregistering an in use transfer function.\n"); +#endif xfer_funcs[n] = NULL; - idr_for_each(&loop_index_idr, &unregister_transfer_cb, xfer); return 0; } @@ -2325,8 +2324,9 @@ static int loop_add(int i) } else { err = idr_alloc(&loop_index_idr, lo, 0, 0, GFP_KERNEL); } + mutex_unlock(&loop_ctl_mutex); if (err < 0) - goto out_unlock; + goto out_free_dev; i = err; err = -ENOMEM; @@ -2392,15 +2392,19 @@ static int loop_add(int i) disk->private_data = lo; disk->queue = lo->lo_queue; sprintf(disk->disk_name, "loop%d", i); + /* Make this loop device reachable from pathname. */ add_disk(disk); + /* Show this loop device. */ + mutex_lock(&loop_ctl_mutex); + lo->idr_visible = true; mutex_unlock(&loop_ctl_mutex); return i; out_cleanup_tags: blk_mq_free_tag_set(&lo->tag_set); out_free_idr: + mutex_lock(&loop_ctl_mutex); idr_remove(&loop_index_idr, i); -out_unlock: mutex_unlock(&loop_ctl_mutex); out_free_dev: kfree(lo); @@ -2410,9 +2414,14 @@ static int loop_add(int i) static void loop_remove(struct loop_device *lo) { + /* Make this loop device unreachable from pathname. */ del_gendisk(lo->lo_disk); blk_cleanup_disk(lo->lo_disk); blk_mq_free_tag_set(&lo->tag_set); + mutex_lock(&loop_ctl_mutex); + idr_remove(&loop_index_idr, lo->lo_number); + mutex_unlock(&loop_ctl_mutex); + /* There is no route which can find this loop device. */ mutex_destroy(&lo->lo_mutex); kfree(lo); } @@ -2436,31 +2445,40 @@ static int loop_control_remove(int idx) return -EINVAL; } + /* Hide this loop device for serialization. */ ret = mutex_lock_killable(&loop_ctl_mutex); if (ret) return ret; - lo = idr_find(&loop_index_idr, idx); - if (!lo) { + if (!lo || !lo->idr_visible) ret = -ENODEV; - goto out_unlock_ctrl; - } + else + lo->idr_visible = false; + mutex_unlock(&loop_ctl_mutex); + if (ret) + return ret; + /* Check whether this loop can be removed. */ ret = mutex_lock_killable(&lo->lo_mutex); if (ret) - goto out_unlock_ctrl; + goto mark_visible; if (lo->lo_state != Lo_unbound || atomic_read(&lo->lo_refcnt) > 0) { mutex_unlock(&lo->lo_mutex); ret = -EBUSY; - goto out_unlock_ctrl; + goto mark_visible; } + /* Mark this loop device no longer open()-able. */ lo->lo_state = Lo_deleting; mutex_unlock(&lo->lo_mutex); - idr_remove(&loop_index_idr, lo->lo_number); loop_remove(lo); -out_unlock_ctrl: + return 0; + +mark_visible: + /* Show this loop device again. */ + mutex_lock(&loop_ctl_mutex); + lo->idr_visible = true; mutex_unlock(&loop_ctl_mutex); return ret; } @@ -2474,7 +2492,8 @@ static int loop_control_get_free(int idx) if (ret) return ret; idr_for_each_entry(&loop_index_idr, lo, id) { - if (lo->lo_state == Lo_unbound) + /* Hitting a race results in creating a new loop device which is harmless. */ + if (lo->idr_visible && data_race(lo->lo_state) == Lo_unbound) goto found; } mutex_unlock(&loop_ctl_mutex); @@ -2590,10 +2609,14 @@ static void __exit loop_exit(void) unregister_blkdev(LOOP_MAJOR, "loop"); misc_deregister(&loop_misc); - mutex_lock(&loop_ctl_mutex); + /* + * There is no need to use loop_ctl_mutex here, for nobody else can + * access loop_index_idr when this module is unloading (unless forced + * module unloading is requested). If this is not a clean unloading, + * we have no means to avoid kernel crash. + */ idr_for_each_entry(&loop_index_idr, lo, id) loop_remove(lo); - mutex_unlock(&loop_ctl_mutex); idr_destroy(&loop_index_idr); } diff --git a/drivers/block/loop.h b/drivers/block/loop.h index 1988899db63a..04c88dd6eabd 100644 --- a/drivers/block/loop.h +++ b/drivers/block/loop.h @@ -68,6 +68,7 @@ struct loop_device { struct blk_mq_tag_set tag_set; struct gendisk *lo_disk; struct mutex lo_mutex; + bool idr_visible; }; struct loop_cmd { -- 2.25.1