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

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Message-ID: <20150304011118.GB23399@shlinux2>
Date:	Wed, 4 Mar 2015 09:11:19 +0800
From:	Peter Chen <peter.chen@...escale.com>
To:	Tapasweni Pathak <tapaswenipathak@...il.com>
CC:	<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 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;
 	}

-- 

Best Regards,
Peter Chen
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