linux-kernel - Re: [PATCH] usb: gadget: Check for NULL pointer in disconnect

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Message-ID: <20150322074353.GA25278@shlinux2>
Date:	Sun, 22 Mar 2015 15:43:54 +0800
From:	Peter Chen <peter.chen@...escale.com>
To:	Badhri Jagan Sridharan <badhri@...gle.com>
CC:	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: gadget: Check for NULL pointer in disconnect

On Fri, Mar 20, 2015 at 04:40:52PM -0700, Badhri Jagan Sridharan wrote:
> Added a safety net to make sure that
> composite_disconnect does not end up disconneting
> a NULL device. Prevents NULL pointer crash.
> 
> Signed-off-by: Badhri Jagan Sridharan <Badhri@...gle.com>
> ---
>  drivers/usb/gadget/composite.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
> index 13adfd1..90b37bd 100644
> --- a/drivers/usb/gadget/composite.c
> +++ b/drivers/usb/gadget/composite.c
> @@ -1823,6 +1823,11 @@ void composite_disconnect(struct usb_gadget *gadget)
>  	struct usb_composite_dev	*cdev = get_gadget_data(gadget);
>  	unsigned long			flags;
>  
> +	if (!cdev) {
> +		WARN(1, "Trying to disconnect a NULL composite device\n");
> +		return;
> +	}
> +

Do you really see some udc drivers call it after composite_unbind is
called? If it is, you may add dump_stack() to track that error.

Besides this, function suspended_show is needed to add cdev NULL pointer
checking.

>  	/* REVISIT:  should we have config and device level
>  	 * disconnect callbacks?
>  	 */
> -- 
> 2.2.0.rc0.207.ga3a616c
> 
> --
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-- 

Best Regards,
Peter Chen
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