[Acked] [PATCH Trusty/Utopic/Vivid] cdc-acm: add sanity checks

[Andy Whitcroft]

On Mon, Mar 02, 2015 at 11:13:23AM +0800, Adam Lee wrote:
> From: Oliver Neukum <oneukum at suse.de>
> 
> BugLink: http://bugs.launchpad.net/bugs/1413992
> 
> Check the special CDC headers for a plausible minimum length.
> Another big operating systems ignores such garbage.
> 
> Signed-off-by: Oliver Neukum <oneukum at suse.de>
> CC: stable at vger.kernel.org
> Reviewed-by: Adam Lee <adam8157 at gmail.com>
> Tested-by: Adam Lee <adam8157 at gmail.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> (cherry picked from commit 7e860a6e7aa62b337a61110430cd633db5b0d2dd)
> Signed-off-by: Adam Lee <adam.lee at canonical.com>
> ---
>  drivers/usb/class/cdc-acm.c | 21 ++++++++++++++++-----
>  1 file changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
> index 6746103..82dea40 100644
> --- a/drivers/usb/class/cdc-acm.c
> +++ b/drivers/usb/class/cdc-acm.c
> @@ -943,6 +943,7 @@ static int acm_probe(struct usb_interface *intf,
>  	unsigned long quirks;
>  	int num_rx_buf;
>  	int i;
> +	unsigned int elength = 0;
>  	int combined_interfaces = 0;
>  	struct device *tty_dev;
>  	int rv = -ENOMEM;
> @@ -988,9 +989,12 @@ static int acm_probe(struct usb_interface *intf,
>  			dev_err(&intf->dev, "skipping garbage\n");
>  			goto next_desc;
>  		}
> +		elength = buffer[0];
>  
>  		switch (buffer[2]) {
>  		case USB_CDC_UNION_TYPE: /* we've found it */
> +			if (elength < sizeof(struct usb_cdc_union_desc))
> +				goto next_desc;
>  			if (union_header) {
>  				dev_err(&intf->dev, "More than one "
>  					"union descriptor, skipping ...\n");
> @@ -999,31 +1003,38 @@ static int acm_probe(struct usb_interface *intf,
>  			union_header = (struct usb_cdc_union_desc *)buffer;
>  			break;
>  		case USB_CDC_COUNTRY_TYPE: /* export through sysfs*/
> +			if (elength < sizeof(struct usb_cdc_country_functional_desc))
> +				goto next_desc;
>  			cfd = (struct usb_cdc_country_functional_desc *)buffer;
>  			break;
>  		case USB_CDC_HEADER_TYPE: /* maybe check version */
>  			break; /* for now we ignore it */
>  		case USB_CDC_ACM_TYPE:
> +			if (elength < 4)
> +				goto next_desc;
>  			ac_management_function = buffer[3];
>  			break;
>  		case USB_CDC_CALL_MANAGEMENT_TYPE:
> +			if (elength < 5)
> +				goto next_desc;
>  			call_management_function = buffer[3];
>  			call_interface_num = buffer[4];
>  			if ((quirks & NOT_A_MODEM) == 0 && (call_management_function & 3) != 3)
>  				dev_err(&intf->dev, "This device cannot do calls on its own. It is not a modem.\n");
>  			break;
>  		default:
> -			/* there are LOTS more CDC descriptors that
> +			/*
> +			 * there are LOTS more CDC descriptors that
>  			 * could legitimately be found here.
>  			 */
>  			dev_dbg(&intf->dev, "Ignoring descriptor: "
> -					"type %02x, length %d\n",
> -					buffer[2], buffer[0]);
> +					"type %02x, length %ud\n",
> +					buffer[2], elength);
>  			break;
>  		}
>  next_desc:
> -		buflen -= buffer[0];
> -		buffer += buffer[0];
> +		buflen -= elength;
> +		buffer += elength;
>  	}
>  
>  	if (!union_header) {

Looks to do what is claimed, and bug parity with the "other
operating systems" is a laudible goal.

Acked-by: Andy Whitcroft <apw at canonical.com>

-apw