linux-kernel - Re: [PATCH] usb: gadget: net2280: fix memory leak on probe error handling paths

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Message-ID: <20200722141741.GA1310843@rowland.harvard.edu>
Date:   Wed, 22 Jul 2020 10:17:41 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Evgeny Novikov <novikov@...ras.ru>
Cc:     Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Kees Cook <keescook@...omium.org>,
        Arnd Bergmann <arnd@...db.de>,
        Corentin Labbe <clabbe@...libre.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        ldv-project@...uxtesting.org
Subject: Re: [PATCH] usb: gadget: net2280: fix memory leak on probe error
 handling paths

On Tue, Jul 21, 2020 at 11:15:58PM +0300, Evgeny Novikov wrote:
> Driver does not release memory for device on error handling paths in
> net2280_probe() when gadget_release() is not registered yet.
> 
> The patch fixes the bug like in other similar drivers.
> 
> Found by Linux Driver Verification project (linuxtesting.org).
> 
> Signed-off-by: Evgeny Novikov <novikov@...ras.ru>
> ---
>  drivers/usb/gadget/udc/net2280.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/gadget/udc/net2280.c b/drivers/usb/gadget/udc/net2280.c
> index 5eff85eeaa5a..d5fe071b2db2 100644
> --- a/drivers/usb/gadget/udc/net2280.c
> +++ b/drivers/usb/gadget/udc/net2280.c
> @@ -3781,8 +3781,10 @@ static int net2280_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  	return 0;
>  
>  done:
> -	if (dev)
> +	if (dev) {
>  		net2280_remove(pdev);
> +		kfree(dev);
> +	}
>  	return retval;
>  }

This patch seems to be the tip of an iceberg.  Following through its 
implications led to a couple of discoveries.

usb_del_gadget_udc() calls device_unregister(&gadget->dev).  Once this 
call returns, gadget has to be regarded as a stale pointer.  But the 
very next line of code does:

	memset(&gadget->dev, 0x00, sizeof(gadget->dev));

for no apparent reason.  I'm amazed this hasn't caused problems already.  
Is there any justification for keeping this memset?  It's hard to 
imagine that it does any good.

Similarly, net2280_remove() calls usb_del_gadget_udc(&dev->gadget) at 
its start, and so dev must be a stale pointer for the entire remainder 
of the routine.  But it gets used repeatedly.  Surely we ought to have 
a device_get() and device_put() in there.

Alan Stern