Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: KASAN: use-after-free Read in debugfs_remove (2)
To:     Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        syzbot <syzbot+db48ce201b524603190a@syzkaller.appspotmail.com>,
        syzkaller-bugs@googlegroups.com,
        weiping zhang <zhangweiping@didichuxing.com>,
        Jan Kara <jack@suse.cz>
Cc:     gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org
References: <000000000000fbda89056a818f20@google.com>
 <a5b6e0ff-ad8e-18f4-8c24-cdfafe4e3883@I-love.SAKURA.ne.jp>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <7156e8d9-4c4a-1a98-2767-3508b9b3798f@kernel.dk>
Date:   Thu, 3 May 2018 09:36:56 -0600
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.0
MIME-Version: 1.0
In-Reply-To: <a5b6e0ff-ad8e-18f4-8c24-cdfafe4e3883@I-love.SAKURA.ne.jp>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 4/23/18 4:34 AM, Tetsuo Handa wrote:
> From be88e559ec13f49b1c3aec2457c14c70f6b1926a Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Date: Mon, 23 Apr 2018 11:21:03 +0900
> Subject: [PATCH] bdi: Fix use after free bug in debugfs_remove()
> 
> syzbot is reporting use after free bug in debugfs_remove() [1].
> 
> This is because fault injection made memory allocation for
> debugfs_create_file() from bdi_debug_register() from bdi_register_va()
> fail and continued with setting WB_registered. But when debugfs_remove()
> is called from debugfs_remove(bdi->debug_dir) from bdi_debug_unregister()
>  from bdi_unregister() from release_bdi() because WB_registered was set
> by bdi_register_va(), IS_ERR_OR_NULL(bdi->debug_dir) == false despite
> debugfs_remove(bdi->debug_dir) was already called from bdi_register_va().
> 
> Fix this by making IS_ERR_OR_NULL(bdi->debug_dir) == true.
> 
> [1] https://syzkaller.appspot.com/bug?id=5ab4efd91a96dcea9b68104f159adf4af2a6dfc1

Applied for 4.17, thanks.

-- 
Jens Axboe