linux-kernel - Re: [PATCH] usb: gadget: udc: add null check before pointer dereference

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Message-ID: <Pine.LNX.4.44L0.1705021029290.1758-100000@iolanthe.rowland.org>
Date:   Tue, 2 May 2017 10:31:51 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     "Gustavo A. R. Silva" <garsilva@...eddedor.com>
cc:     Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jussi Kivilinna <jussi.kivilinna@...tian.com>,
        Tim Harvey <tharvey@...eworks.com>,
        Colin Ian King <colin.king@...onical.com>,
        Raz Manor <Raz.Manor@...ens.com>, <linux-usb@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Peter Senna Tschudin <peter.senna@...il.com>
Subject: Re: [PATCH] usb: gadget: udc: add null check before pointer dereference

On Mon, 1 May 2017, Gustavo A. R. Silva wrote:

> Add null check before dereferencing dev->regs pointer inside
> net2280_led_shutdown() function.
> 
> Addresses-Coverity-ID: 101783
> Signed-off-by: Gustavo A. R. Silva <garsilva@...eddedor.com>
> ---
>  drivers/usb/gadget/udc/net2280.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/usb/gadget/udc/net2280.c b/drivers/usb/gadget/udc/net2280.c
> index 3828c2e..1898a4b 100644
> --- a/drivers/usb/gadget/udc/net2280.c
> +++ b/drivers/usb/gadget/udc/net2280.c
> @@ -3573,7 +3573,11 @@ static void net2280_remove(struct pci_dev *pdev)
>  	BUG_ON(dev->driver);
>  
>  	/* then clean up the resources we allocated during probe() */
> -	net2280_led_shutdown(dev);
> +
> +	if (dev->regs) {
> +		net2280_led_shutdown(dev);
> +		iounmap(dev->regs);
> +	}
>  	if (dev->requests) {
>  		int		i;
>  		for (i = 1; i < 5; i++) {
> @@ -3588,8 +3592,6 @@ static void net2280_remove(struct pci_dev *pdev)
>  		free_irq(pdev->irq, dev);
>  	if (dev->quirks & PLX_PCIE)
>  		pci_disable_msi(pdev);
> -	if (dev->regs)
> -		iounmap(dev->regs);
>  	if (dev->region)
>  		release_mem_region(pci_resource_start(pdev, 0),
>  				pci_resource_len(pdev, 0));

No, you must not move the iounmap() call, because an interrupt could
theoretically occur at any time.

Either just live with an extra test of dev->regs, or else move the 
net2280_led_shutdown() call later.

Alan Stern