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=-8.2 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_SANE_1 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 9EF9BC3F2D1 for ; Fri, 28 Feb 2020 10:14:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 803F6246A8 for ; Fri, 28 Feb 2020 10:14:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726838AbgB1KOw (ORCPT ); Fri, 28 Feb 2020 05:14:52 -0500 Received: from szxga05-in.huawei.com ([45.249.212.191]:10703 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726063AbgB1KOw (ORCPT ); Fri, 28 Feb 2020 05:14:52 -0500 Received: from DGGEMS410-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id 74996682768A73C0462D; Fri, 28 Feb 2020 18:14:48 +0800 (CST) Received: from [127.0.0.1] (10.173.220.66) by DGGEMS410-HUB.china.huawei.com (10.3.19.210) with Microsoft SMTP Server id 14.3.439.0; Fri, 28 Feb 2020 18:14:41 +0800 Subject: Re: [PATCH V2] block: rename 'q->debugfs_dir' and 'q->blk_trace->dir' in blk_unregister_queue() To: , , , , , , , CC: , , , , References: <20200213081252.32395-1-yukuai3@huawei.com> From: "yukuai (C)" Message-ID: <710eb24d-801e-b843-d02e-8a5b16b60265@huawei.com> Date: Fri, 28 Feb 2020 18:14:39 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20200213081252.32395-1-yukuai3@huawei.com> Content-Type: text/plain; charset="gbk"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.173.220.66] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ping... On 2020/2/13 16:12, yu kuai wrote: > 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. >