Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.33 as permitted sender) client-ip=23.128.96.33;
Date:   Fri, 3 Nov 2023 09:12:51 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Li Lingfeng <lilingfeng@huaweicloud.com>
Cc:     josef@toxicpanda.com, linux-kernel@vger.kernel.org, hch@lst.de,
        linux-block@vger.kernel.org, nbd@other.debian.org, axboe@kernel.dk,
        chaitanya.kulkarni@wdc.com, yukuai1@huaweicloud.com,
        houtao1@huawei.com, yi.zhang@huawei.com, yangerkun@huawei.com,
        lilingfeng3@huawei.com
Subject: Re: [PATCH] nbd: fix uaf in nbd_open
Message-ID: <20231103081251.GB16854@lst.de>
References: <20231103101334.1750094-1-lilingfeng@huaweicloud.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20231103101334.1750094-1-lilingfeng@huaweicloud.com>
User-Agent: Mutt/1.5.17 (2007-11-01)
Precedence: bulk

On Fri, Nov 03, 2023 at 06:13:34PM +0800, Li Lingfeng wrote:
> From: Li Lingfeng <lilingfeng3@huawei.com>
> 
> Commit 4af5f2e03013 ("nbd: use blk_mq_alloc_disk and
> blk_cleanup_disk") cleans up disk by blk_cleanup_disk() and it won't set
> disk->private_data as NULL as before. UAF may be triggered in nbd_open()
> if someone tries to open nbd device right after nbd_put() since refcount
> of nbd device is zero and private_data is not NULL.

I don't think this is the right fix.  nbd needs to move to ->free_disk
to free it's private data.