linux-kernel - Re: [PATCH 2/2] device property: fix for a case of use-after-free

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Date:	Mon, 22 Feb 2016 17:04:04 +0000
From:	"Shevchenko, Andriy" <andriy.shevchenko@...el.com>
To:	"heikki.krogerus@...ux.intel.com" <heikki.krogerus@...ux.intel.com>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>
CC:	"mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"John.Youn@...opsys.com" <John.Youn@...opsys.com>
Subject: Re: [PATCH 2/2] device property: fix for a case of use-after-free

On Mon, 2016-02-22 at 17:40 +0200, Andy Shevchenko wrote:
> On Mon, 2016-02-22 at 16:50 +0200, Heikki Krogerus wrote:
> > In device_remove_property_set(), if the primary fwnode is
> > of type "pset", it has to be set pointing to NULL before
> > calling set_secondary_fwnode(). Otherwise
> > set_secondary_fwnode() will attempt to set the
> > fwnode->secondary member after the fwnode has been freed.
> > 
> > Reported-by: John Youn <John.Youn@...opsys.com>
> > Signed-off-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> > ---
> >  drivers/base/property.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/base/property.c b/drivers/base/property.c
> > index a163f2c..ddf2987 100644
> > --- a/drivers/base/property.c
> > +++ b/drivers/base/property.c
> > @@ -820,7 +820,9 @@ void device_remove_property_set(struct device
> > *dev)
> >  	 * the pset. If there is no real firmware node (ACPI/DT)
> > primary
> >  	 * will hold the pset.
> >  	 */
> > -	if (!is_pset_node(fwnode))
> > +	if (is_pset_node(fwnode))
> > +		dev->fwnode = NULL;
> > +	else
> >  		fwnode = fwnode->secondary;
> >  	if (!IS_ERR(fwnode) && is_pset_node(fwnode))
> >  		pset_free_set(to_pset_node(fwnode));
> 
> 
> What if we do the following
> 
> --- a/drivers/base/property.c
> +++ b/drivers/base/property.c
> @@ -818,9 +818,13 @@ void device_remove_property_set(struct device
> *dev)
>          */
>         if (!is_pset_node(fwnode))
>                 fwnode = fwnode->secondary;
> +
> +       /* Set device fwnode to NULL before we free it */
> +       set_secondary_fwnode(dev, NULL);
> +
> +       /* Free property set for the given device */
>         if (!IS_ERR(fwnode) && is_pset_node(fwnode))
>                 pset_free_set(to_pset_node(fwnode));
> -       set_secondary_fwnode(dev, NULL);
>  }
>  EXPORT_SYMBOL_GPL(device_remove_property_set);
>  
> ?
> 

Just noticed that there is another potential bug is hidden, if we call
this function on non-pset fwnode we will silently get fwnode set to
NULL.

Considering this, perhaps better solution is to convert last lines to

if (!IS_ERR(fwnode) && is_pset_node(fwnode)) {
  set_secondary_fwnode(dev, NULL);
  pset_free_set(to_pset_node(fwnode));
}

I didn't check if we do serialize access to fwnode. It might be more
bugs with access to it in racing manner.

-- 
Andy Shevchenko <andriy.shevchenko@...el.com>
Intel Finland Oy
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