Re: [PATCH] USB: s2255 & stkwebcam: fix oops with malicious USB descriptors

[Johan Hovold <johan@kernel.org>]

On Thu, Apr 11, 2019 at 12:54:12PM +0800, Young Xiao wrote:
> From: Young Xiao <YangX92@hotmail.com>
> 
> The driver expects at least one valid endpoint. If given
> malicious descriptors that specify 0 for the number of endpoints,
> it will crash in the probe function.  Ensure there is at least
> one endpoint on the interface before using it.

Why do claim it will crash?

> This vulnerability is same as CVE-2016-2188.

Note that the "fix" for this CVE that you're now copying was incomplete.
Here's the proper fix:

	b7321e81fc36 ("USB: iowarrior: fix NULL-deref at probe")

> Signed-off-by: Young Xiao <YangX92@hotmail.com>
> ---
>  drivers/media/usb/s2255/s2255drv.c       | 7 +++++++
>  drivers/media/usb/stkwebcam/stk-webcam.c | 6 ++++++
>  2 files changed, 13 insertions(+)
> 
> diff --git a/drivers/media/usb/s2255/s2255drv.c b/drivers/media/usb/s2255/s2255drv.c
> index 5b3e54b..7fdf159 100644
> --- a/drivers/media/usb/s2255/s2255drv.c
> +++ b/drivers/media/usb/s2255/s2255drv.c
> @@ -2263,6 +2263,13 @@ static int s2255_probe(struct usb_interface *interface,
>  	iface_desc = interface->cur_altsetting;
>  	dev_dbg(&interface->dev, "num EP: %d\n",
>  		iface_desc->desc.bNumEndpoints);
> +
> +	if (iface_desc->desc.bNumEndpoints < 1) {
> +		dev_err(&interface->dev, "Invalid number of endpoints\n");
> +		retval = -EINVAL;
> +		goto error;
> +	}
> +
>  	for (i = 0; i < iface_desc->desc.bNumEndpoints; ++i) {

Besides that you didn't even bother compile-testing this, there is no
bug here to fix to begin with.

If bNumEndpoints is zero this loop will execute and the driver bails out
just after since dev->read_endpoint is NULL.

>  		endpoint = &iface_desc->endpoint[i].desc;
>  		if (!dev->read_endpoint && usb_endpoint_is_bulk_in(endpoint)) {
> diff --git a/drivers/media/usb/stkwebcam/stk-webcam.c b/drivers/media/usb/stkwebcam/stk-webcam.c
> index 8f54586..d2a4785 100644
> --- a/drivers/media/usb/stkwebcam/stk-webcam.c
> +++ b/drivers/media/usb/stkwebcam/stk-webcam.c
> @@ -1350,6 +1350,12 @@ static int stk_camera_probe(struct usb_interface *interface,
>  	 * for the current alternate setting */
>  	iface_desc = interface->cur_altsetting;
>  
> +	if (iface_desc->desc.bNumEndpoints < 1) {
> +		dev_err(&interface->dev, "Invalid number of endpoints\n");
> +		retval = -EINVAL;
> +		goto error;
> +	}
> +
>  	for (i = 0; i < iface_desc->desc.bNumEndpoints; ++i) {

Same here.

>  		endpoint = &iface_desc->endpoint[i].desc;

Johan