linux-kernel - Re: [PATCH] nbd: fix uaf in nbd

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Date:   Fri, 3 Nov 2023 09:12:51 +0100
From:   Christoph Hellwig <hch@....de>
To:     Li Lingfeng <lilingfeng@...weicloud.com>
Cc:     josef@...icpanda.com, linux-kernel@...r.kernel.org, hch@....de,
        linux-block@...r.kernel.org, nbd@...er.debian.org, axboe@...nel.dk,
        chaitanya.kulkarni@....com, yukuai1@...weicloud.com,
        houtao1@...wei.com, yi.zhang@...wei.com, yangerkun@...wei.com,
        lilingfeng3@...wei.com
Subject: Re: [PATCH] nbd: fix uaf in nbd_open

On Fri, Nov 03, 2023 at 06:13:34PM +0800, Li Lingfeng wrote:
> From: Li Lingfeng <lilingfeng3@...wei.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.