From patchwork Tue Feb 11 03:51:37 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yu Kuai X-Patchwork-Id: 11374813 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 2FFE0109A for ; Tue, 11 Feb 2020 03:52:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1A6E62082F for ; Tue, 11 Feb 2020 03:52:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727953AbgBKDwo (ORCPT ); Mon, 10 Feb 2020 22:52:44 -0500 Received: from szxga05-in.huawei.com ([45.249.212.191]:9720 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727800AbgBKDwo (ORCPT ); Mon, 10 Feb 2020 22:52:44 -0500 Received: from DGGEMS412-HUB.china.huawei.com (unknown [172.30.72.59]) by Forcepoint Email with ESMTP id 0293FC4337C545197046; Tue, 11 Feb 2020 11:52:42 +0800 (CST) Received: from huawei.com (10.175.124.28) by DGGEMS412-HUB.china.huawei.com (10.3.19.212) with Microsoft SMTP Server id 14.3.439.0; Tue, 11 Feb 2020 11:52:33 +0800 From: yu kuai To: , CC: , , , , , Subject: [PATCH] block: rename 'q->debugfs_dir' in blk_unregister_queue() Date: Tue, 11 Feb 2020 11:51:37 +0800 Message-ID: <20200211035137.19454-1-yukuai3@huawei.com> X-Mailer: git-send-email 2.17.2 MIME-Version: 1.0 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' in blk_unregister_queue(). [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 Reported-by: kbuild test robot Reported-by: kbuild test robot --- block/blk-sysfs.c | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index fca9b158f4a0..69d28b3f52d0 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 +1012,33 @@ int blk_register_queue(struct gendisk *disk) } EXPORT_SYMBOL_GPL(blk_register_queue); +/* + * blk_prepare_release_queue - rename q->debugfs_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 struct dentry *blk_prepare_release_queue(struct request_queue *q) +{ + struct dentry *new = NULL; + char name[DNAME_INLINE_LEN]; + int i = 0; + + if (IS_ERR_OR_NULL(q->debugfs_dir)) + return q->debugfs_dir; + + while (new == NULL) { + sprintf(name, "ready_to_remove_%d", i++); + new = debugfs_rename(blk_debugfs_root, q->debugfs_dir, + blk_debugfs_root, name); + } + + return new; +} + /** * blk_unregister_queue - counterpart of blk_register_queue() * @disk: Disk of which the request queue should be unregistered from sysfs. @@ -1039,6 +1067,7 @@ void blk_unregister_queue(struct gendisk *disk) mutex_unlock(&q->sysfs_lock); mutex_lock(&q->sysfs_dir_lock); + q->debugfs_dir = blk_prepare_release_queue(q); /* * Remove the sysfs attributes before unregistering the queue data * structures that can be modified through sysfs.