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

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Date:   Fri, 16 Sep 2022 07:03:53 -0700
From:   Hyunwoo Kim <imv4bel@...il.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     arnd@...db.de, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>, imv4bel@...il.com
Subject: Re: [PATCH v3] char: pcmcia: synclink_cs: Fix use-after-free in
 mgslpc_ops

On Fri, Sep 16, 2022 at 04:54:11PM +0300, Ilpo Järvinen wrote:
> 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'm sorry, but could you please explain a bit more?


Best Regards,
Hyunwoo Kim.