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Date:   Tue, 23 May 2023 22:58:09 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Vincent Whitchurch <vincent.whitchurch@axis.com>
Cc:     Richard Weinberger <richard@nod.at>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org,
        kernel@axis.com
Subject: Re: [PATCH 1/2] ubi: block: Fix use-after-free of gendisk
Message-ID: <ZG2ncaTjxCnRWcUZ@infradead.org>
References: <20230523-ubiblock-remove-v1-0-240bed75849b@axis.com>
 <20230523-ubiblock-remove-v1-1-240bed75849b@axis.com>
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On Tue, May 23, 2023 at 03:12:16PM +0200, Vincent Whitchurch wrote:
>  static void ubiblock_cleanup(struct ubiblock *dev)
>  {
> +	int first_minor = dev->gd->first_minor;
> +
>  	/* Stop new requests to arrive */
>  	del_gendisk(dev->gd);
>  	/* Finally destroy the blk queue */
>  	dev_info(disk_to_dev(dev->gd), "released");
>  	put_disk(dev->gd);
>  	blk_mq_free_tag_set(&dev->tag_set);
> -	idr_remove(&ubiblock_minor_idr, dev->gd->first_minor);
> +	idr_remove(&ubiblock_minor_idr, first_minor);

I think the real fix here is to implement the free_disk method
and free the idr there.  That ensures the ID can't be reused until
the disk is entirely freed as well.