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=-8.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 EB395C3F2CD for ; Fri, 28 Feb 2020 23:16:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B44F1246B4 for ; Fri, 28 Feb 2020 23:16:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="IE8N0BuN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726418AbgB1XQW (ORCPT ); Fri, 28 Feb 2020 18:16:22 -0500 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:46826 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725957AbgB1XQW (ORCPT ); Fri, 28 Feb 2020 18:16:22 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1582931780; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=FFNtyPEO7ZLHkoemtDDIXS2+6UBUM9dbd+oueyee19E=; b=IE8N0BuN2zLjG1R79ao46VJYi3KhZm8w4VXbg+5PLoFjOndQj+Erm5GFP0F93Bs0jT/3T2 X2LJP9NvWhly9KdKrYnNDj7sj7ijbkGLeSpyONbLSxZBVpElIrhQPZbzlwI076BdzKPeqN qa5nnaDGUnCz0oAkyNLbUR+IABrQHWk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-218-KhxuM6SaPZK063QXXdeFHQ-1; Fri, 28 Feb 2020 18:16:13 -0500 X-MC-Unique: KhxuM6SaPZK063QXXdeFHQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A40698017CC; Fri, 28 Feb 2020 23:16:11 +0000 (UTC) Received: from ming.t460p (ovpn-8-18.pek2.redhat.com [10.72.8.18]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BFE4119756; Fri, 28 Feb 2020 23:16:02 +0000 (UTC) Date: Sat, 29 Feb 2020 07:15:57 +0800 From: Ming Lei To: yu kuai Cc: axboe@kernel.dk, chaitanya.kulkarni@wdc.com, damien.lemoal@wdc.com, bvanassche@acm.org, dhowells@redhat.com, asml.silence@gmail.com, ajay.joshi@wdc.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, yi.zhang@huawei.com, zhangxiaoxu5@huawei.com, luoshijie1@huawei.com Subject: Re: [PATCH V2] block: rename 'q->debugfs_dir' and 'q->blk_trace->dir' in blk_unregister_queue() Message-ID: <20200228231557.GA18123@ming.t460p> References: <20200213081252.32395-1-yukuai3@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200213081252.32395-1-yukuai3@huawei.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Thu, Feb 13, 2020 at 04:12:52PM +0800, 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 blk_trace->dir isn't same with .debugfs_dir, you will just rename blk_trace->dir, this way can't avoid the failure in step3, can it? I understand that we just need to rename .debugfs_dir, meantime making sure blktrace code removes correct debugfs dir, is that enough for fixing this issue? > + 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); > + } The above code can be run concurrently with blktrace shutdown, so race might exit between the two code paths, then bt->dir may has been renamed or being renamed in debugfs_remove(bt->dir), can this function work as expected or correct? And there is dead loop risk, so suggest to not rename this way. Thanks, Ming