linux-kernel - Re: [PATCH v3] char: pcmcia: synclink_cs: Fix use-after-free in mgslpc

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Date:   Fri, 16 Sep 2022 16:54:11 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Hyunwoo Kim <imv4bel@...il.com>
cc:     arnd@...db.de, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] char: pcmcia: synclink_cs: Fix use-after-free in
 mgslpc_ops

On Fri, 16 Sep 2022, Hyunwoo Kim wrote:

> A race condition may occur if the user physically removes
> the pcmcia device while calling ioctl() for this tty device node.
> 
> This is a race condition between the mgslpc_ioctl() function and
> the mgslpc_detach() function, which may eventually result in UAF.
> 
> So, add a refcount check to mgslpc_detach() to free the structure
> after the tty device node is close()d.
> 
> Signed-off-by: Hyunwoo Kim <imv4bel@...il.com>

> @@ -2517,9 +2548,14 @@ static int mgslpc_open(struct tty_struct *tty, struct file * filp)
>  	if (debug_level >= DEBUG_LEVEL_INFO)
>  		printk("%s(%d):mgslpc_open(%s) success\n",
>  			 __FILE__, __LINE__, info->device_name);
> +
> +	kref_get(&info->refcnt);
>  	retval = 0;
> +	mutex_unlock(&remove_mutex);
>  
> +	return retval;
>  cleanup:
> +	mutex_unlock(&remove_mutex);
>  	return retval;

Just move the cleanup label instead.


-- 
 i.