linux-kernel - Re: [PATCH] char: pcmcia: scr24x_cs: Fix use-after-free in scr24x

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Message-Id: <d28d59c1-1ed0-422b-b749-0082de05e7ee@www.fastmail.com>
Date:   Fri, 16 Sep 2022 08:59:44 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Hyunwoo Kim" <imv4bel@...il.com>,
        "Lubomir Rintel" <lkundrak@...sk>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] char: pcmcia: scr24x_cs: Fix use-after-free in scr24x_fops

On Fri, Sep 16, 2022, at 7:00 AM, Hyunwoo Kim wrote:
> @@ -298,9 +300,10 @@ static void scr24x_remove(struct pcmcia_device *link)
>  	cdev_del(&dev->c_dev);
>  	clear_bit(dev->devno, scr24x_minors);
>  	dev->dev = NULL;
> -	mutex_unlock(&dev->lock);
> 
>  	kref_put(&dev->refcnt, scr24x_delete);
> +
> +	mutex_unlock(&dev->lock);
>  }

This appears to introduce a new use-after-free, when the kref_put()
frees the 'dev' structure and you unlock the mutex in that structure
afterwards.

       Arnd