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=-9.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,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 972DDC2BA83 for ; Thu, 13 Feb 2020 08:14:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 67A6220848 for ; Thu, 13 Feb 2020 08:14:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726545AbgBMIOF (ORCPT ); Thu, 13 Feb 2020 03:14:05 -0500 Received: from szxga04-in.huawei.com ([45.249.212.190]:10616 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726232AbgBMIOF (ORCPT ); Thu, 13 Feb 2020 03:14:05 -0500 Received: from DGGEMS411-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id 89CD216CD1DB96080775; Thu, 13 Feb 2020 16:14:00 +0800 (CST) Received: from huawei.com (10.175.124.28) by DGGEMS411-HUB.china.huawei.com (10.3.19.211) with Microsoft SMTP Server id 14.3.439.0; Thu, 13 Feb 2020 16:13:50 +0800 From: yu kuai To: , , , , , , , CC: , , , , , Subject: [PATCH V2] block: rename 'q->debugfs_dir' and 'q->blk_trace->dir' in blk_unregister_queue() Date: Thu, 13 Feb 2020 16:12:52 +0800 Message-ID: <20200213081252.32395-1-yukuai3@huawei.com> X-Mailer: git-send-email 2.17.2 MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.175.124.28] X-CFilter-Loop: Reflected Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org syzbot is reporting use after free bug in debugfs_remove[1]. This is because in request_queue, 'q->debugfs_dir' and 'q->blk_trace->dir' could be the same dir. And in __blk_release_queue(), blk_mq_debugfs_unregister() will remove everything inside the dir. With futher investigation of the reporduce repro, the problem can be reporduced by following procedure: 1. LOOP_CTL_ADD, create a request_queue q1, blk_mq_debugfs_register() will create the dir. 2. LOOP_CTL_REMOVE, blk_release_queue() will add q1 to release queue. 3. LOOP_CTL_ADD, create another request_queue q2,blk_mq_debugfs_register() will fail because the dir aready exist. 4. BLKTRACESETUP, create two files(msg and dropped) inside the dir. 5. call __blk_release_queue() for q1, debugfs_remove_recursive() will delete the files created in step 4. 6. LOOP_CTL_REMOVE, blk_release_queue() will add q2 to release queue. And when __blk_release_queue() is called for q2, blk_trace_shutdown() will try to release the two files created in step 4, wich are aready released in step 5. thread1 |kworker |thread2 ----------------------- | ------------------------ | -------------------- loop_control_ioctl | | loop_add | | blk_mq_debugfs_register| | debugfs_create_dir | | loop_control_ioctl | | loop_remove | | blk_release_queue | | schedule_work | | | |loop_control_ioctl | | loop_add | | ... | |blk_trace_ioctl | | __blk_trace_setup | | debugfs_create_file |__blk_release_queue | | blk_mq_debugfs_unregister| | debugfs_remove_recursive| | |loop_control_ioctl | | loop_remove | | ... |__blk_release_queue | | blk_trace_shutdown | | debugfs_remove | commit dc9edc44de6c ("block: Fix a blk_exit_rl() regression") pushed the final release of request_queue to a workqueue, so, when loop_add() is called again(step 3), __blk_release_queue() might not been called yet, which causes the problem. Fix the problem by renaming 'q->debugfs_dir' or 'q->blk_trace->dir' in blk_unregister_queue() if they exist. [1] https://syzkaller.appspot.com/bug?extid=903b72a010ad6b7a40f2 References: CVE-2019-19770 Fixes: commit dc9edc44de6c ("block: Fix a blk_exit_rl() regression") Reported-by: syzbot Signed-off-by: yu kuai --- Changes in V2: add device name to the new dir name fix compile err when 'CONFIG_BLK_DEBUG_FS' is not enabled add treatment of 'q->blk_trace->dir' block/blk-sysfs.c | 42 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+) diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index fca9b158f4a0..1da8d4a4915a 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -11,6 +11,7 @@ #include #include #include +#include #include "blk.h" #include "blk-mq.h" @@ -1011,6 +1012,46 @@ int blk_register_queue(struct gendisk *disk) } EXPORT_SYMBOL_GPL(blk_register_queue); +#ifdef CONFIG_DEBUG_FS +/* + * blk_prepare_release_queue - rename q->debugfs_dir and q->blk_trace->dir + * @q: request_queue of which the dir to be renamed belong to. + * + * Because the final release of request_queue is in a workqueue, the + * cleanup might not been finished yet while the same device start to + * create. It's not correct if q->debugfs_dir still exist while trying + * to create a new one. + */ +static void blk_prepare_release_queue(struct request_queue *q) +{ + struct dentry *new = NULL; + struct dentry **old = NULL; + char name[DNAME_INLINE_LEN]; + int i = 0; + +#ifdef CONFIG_BLK_DEBUG_FS + if (!IS_ERR_OR_NULL(q->debugfs_dir)) + old = &q->debugfs_dir; +#endif +#ifdef CONFIG_BLK_DEV_IO_TRACE + /* q->debugfs_dir and q->blk_trace->dir can't both exist */ + if (q->blk_trace && !IS_ERR_OR_NULL(q->blk_trace->dir)) + old = &q->blk_trace->dir; +#endif + if (old == NULL) + return; + while (new == NULL) { + sprintf(name, "ready_to_remove_%s_%d", + kobject_name(q->kobj.parent), i++); + new = debugfs_rename(blk_debugfs_root, *old, + blk_debugfs_root, name); + } + *old = new; +} +#else +#define blk_prepare_release_queue(q) do { } while (0) +#endif + /** * blk_unregister_queue - counterpart of blk_register_queue() * @disk: Disk of which the request queue should be unregistered from sysfs. @@ -1039,6 +1080,7 @@ void blk_unregister_queue(struct gendisk *disk) mutex_unlock(&q->sysfs_lock); mutex_lock(&q->sysfs_dir_lock); + blk_prepare_release_queue(q); /* * Remove the sysfs attributes before unregistering the queue data * structures that can be modified through sysfs. -- 2.17.2