linux-kernel - Re: [PATCH] drivers: usb: gadget: udc: Fix NULL dereference

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Date:	Mon, 9 Mar 2015 10:41:56 -0500
From:	Felipe Balbi <balbi@...com>
To:	Peter Chen <peter.chen@...escale.com>
CC:	Tapasweni Pathak <tapaswenipathak@...il.com>, <balbi@...com>,
	<gregkh@...uxfoundation.org>, <jg1.han@...sung.com>,
	<benoit.taine@...6.fr>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <julia.lawall@...6.fr>
Subject: Re: [PATCH] drivers: usb: gadget: udc: Fix NULL dereference

On Wed, Mar 04, 2015 at 09:11:19AM +0800, Peter Chen wrote:
> On Tue, Mar 03, 2015 at 06:28:42PM +0530, Tapasweni Pathak wrote:
> > This patch fixes multiple instances of null pointer dereference in this code.
> > 
> > ep->udc is assigned to udc. ep is just an offset from _ep. _ep is then
> > checked for NULL. udc is dereferenced under the NULL check for _ep, making
> > an invalid pointer reference.
> > 
> > udc is then checked for NULL, if NULL, it is then dereferenced as
> > udc->dev.
> > 
> > To fix these issues, shift assignment of udc by dereferencing ep after
> > null check for _ep, replace both dev_dbg statements with pr_debug.
> > 
> > Found using Coccinelle.
> > 
> > Signed-off-by: Tapasweni Pathak <tapaswenipathak@...il.com>
> > Suggested-by : Julia Lawall <julia.lawall@...6.fr>
> > Reviewed-by : Julia Lawall <julia.lawall@...6.fr>
> > ---
> >  drivers/usb/gadget/udc/lpc32xx_udc.c |    7 +++----
> >  1 file changed, 3 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/usb/gadget/udc/lpc32xx_udc.c b/drivers/usb/gadget/udc/lpc32xx_udc.c
> > index 27fd413..6398539 100644
> > --- a/drivers/usb/gadget/udc/lpc32xx_udc.c
> > +++ b/drivers/usb/gadget/udc/lpc32xx_udc.c
> > @@ -1807,17 +1807,16 @@ static int lpc32xx_ep_queue(struct usb_ep *_ep,
> >  	    !list_empty(&req->queue))
> >  		return -EINVAL;
> > 
> > -	udc = ep->udc;
> > -
> >  	if (!_ep) {
> > -		dev_dbg(udc->dev, "invalid ep\n");
> > +		pr_debug("invalid ep\n");
> >  		return -EINVAL;
> >  	}
> > 
> > +	udc = ep->udc;
> > 
> >  	if ((!udc) || (!udc->driver) ||
> >  	    (udc->gadget.speed == USB_SPEED_UNKNOWN)) {
> > -		dev_dbg(udc->dev, "invalid device\n");
> > +		pr_debug("invalid device\n");
> >  		return -EINVAL;
> >  	}
> > 
> 
> It is driver code, we'd better use dev_dbg. If _ep exists,
> both ep and udc should exist. So, how about just checking
> _ep at the beginning:
> 
> diff --git a/drivers/usb/gadget/udc/lpc32xx_udc.c b/drivers/usb/gadget/udc/lpc32xx_udc.c
> index 27fd413..c65de0e 100644
> --- a/drivers/usb/gadget/udc/lpc32xx_udc.c
> +++ b/drivers/usb/gadget/udc/lpc32xx_udc.c
> @@ -1803,7 +1803,7 @@ static int lpc32xx_ep_queue(struct usb_ep *_ep,
>  	req = container_of(_req, struct lpc32xx_request, req);
>  	ep = container_of(_ep, struct lpc32xx_ep, ep);
>  
> -	if (!_req || !_req->complete || !_req->buf ||
> +	if (!_ep || !_req || !_req->complete || !_req->buf ||
>  	    !list_empty(&req->queue))
>  		return -EINVAL;
>  
> @@ -1815,8 +1815,7 @@ static int lpc32xx_ep_queue(struct usb_ep *_ep,
>  	}
>  
>  
> -	if ((!udc) || (!udc->driver) ||
> -	    (udc->gadget.speed == USB_SPEED_UNKNOWN)) {
> +	if ((!udc->driver) || (udc->gadget.speed == USB_SPEED_UNKNOWN)) {
>  		dev_dbg(udc->dev, "invalid device\n");
>  		return -EINVAL;
>  	}

what's going to happen here ?

-- 
balbi

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