Commit message: USB: core: harden cdc_parse_cdc_header

Andrey Konovalov reported a possible out-of-bounds problem for the
cdc_parse_cdc_header function.  He writes:
	It looks like cdc_parse_cdc_header() doesn't validate buflen
	before accessing buffer[1], buffer[2] and so on. The only check
	present is while (buflen > 0).

So fix this issue up by properly validating the buffer length matches
what the descriptor says it is.

Reported-by: Andrey Konovalov <andreyknvl@google.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CVE: CVE-2017-16534
CWE: CWE-119
Vulnerability description: The cdc_parse_cdc_header function in drivers/usb/core/message.c in the Linux kernel before 4.13.6 allows local users to cause a denial of service (out-of-bounds read and system crash) or possibly have unspecified other impact via a crafted USB device.

Project: linux
File: usbnet.c

int cdc_parse_cdc_header(struct usb_cdc_parsed_header *hdr,
				struct usb_interface *intf,
				u8 *buffer,
				int buflen)
{
	/* duplicates are ignored */
	struct usb_cdc_union_desc *union_header = NULL;

	/* duplicates are not tolerated */
	struct usb_cdc_header_desc *header = NULL;
	struct usb_cdc_ether_desc *ether = NULL;
	struct usb_cdc_mdlm_detail_desc *detail = NULL;
	struct usb_cdc_mdlm_desc *desc = NULL;

	unsigned int elength;
	int cnt = 0;

	memset(hdr, 0x00, sizeof(struct usb_cdc_parsed_header));
	hdr->phonet_magic_present = false;
	while (buflen > 0) {
		elength = buffer[0];
		if (!elength) {
			dev_err(&intf->dev, "skipping garbage byte\n");
 			elength = 1;
 			goto next_desc;
 		}
 		if (buffer[1] != USB_DT_CS_INTERFACE) {
 			dev_err(&intf->dev, "skipping garbage\n");
 			goto next_desc;
		}

		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");
				goto next_desc;
			}
			union_header = (struct usb_cdc_union_desc *)buffer;
			break;
		case USB_CDC_COUNTRY_TYPE:
			if (elength < sizeof(struct usb_cdc_country_functional_desc))
				goto next_desc;
			hdr->usb_cdc_country_functional_desc =
				(struct usb_cdc_country_functional_desc *)buffer;
			break;
		case USB_CDC_HEADER_TYPE:
			if (elength != sizeof(struct usb_cdc_header_desc))
				goto next_desc;
			if (header)
				return -EINVAL;
			header = (struct usb_cdc_header_desc *)buffer;
			break;
		case USB_CDC_ACM_TYPE:
			if (elength < sizeof(struct usb_cdc_acm_descriptor))
				goto next_desc;
			hdr->usb_cdc_acm_descriptor =
				(struct usb_cdc_acm_descriptor *)buffer;
			break;
		case USB_CDC_ETHERNET_TYPE:
			if (elength != sizeof(struct usb_cdc_ether_desc))
				goto next_desc;
			if (ether)
				return -EINVAL;
			ether = (struct usb_cdc_ether_desc *)buffer;
			break;
		case USB_CDC_CALL_MANAGEMENT_TYPE:
			if (elength < sizeof(struct usb_cdc_call_mgmt_descriptor))
				goto next_desc;
			hdr->usb_cdc_call_mgmt_descriptor =
				(struct usb_cdc_call_mgmt_descriptor *)buffer;
			break;
		case USB_CDC_DMM_TYPE:
			if (elength < sizeof(struct usb_cdc_dmm_desc))
				goto next_desc;
			hdr->usb_cdc_dmm_desc =
				(struct usb_cdc_dmm_desc *)buffer;
			break;
		case USB_CDC_MDLM_TYPE:
			if (elength < sizeof(struct usb_cdc_mdlm_desc *))
				goto next_desc;
			if (desc)
				return -EINVAL;
			desc = (struct usb_cdc_mdlm_desc *)buffer;
			break;
		case USB_CDC_MDLM_DETAIL_TYPE:
			if (elength < sizeof(struct usb_cdc_mdlm_detail_desc *))
				goto next_desc;
			if (detail)
				return -EINVAL;
			detail = (struct usb_cdc_mdlm_detail_desc *)buffer;
			break;
		case USB_CDC_NCM_TYPE:
			if (elength < sizeof(struct usb_cdc_ncm_desc))
				goto next_desc;
			hdr->usb_cdc_ncm_desc = (struct usb_cdc_ncm_desc *)buffer;
			break;
		case USB_CDC_MBIM_TYPE:
			if (elength < sizeof(struct usb_cdc_mbim_desc))
				goto next_desc;

			hdr->usb_cdc_mbim_desc = (struct usb_cdc_mbim_desc *)buffer;
			break;
		case USB_CDC_MBIM_EXTENDED_TYPE:
			if (elength < sizeof(struct usb_cdc_mbim_extended_desc))
				break;
			hdr->usb_cdc_mbim_extended_desc =
				(struct usb_cdc_mbim_extended_desc *)buffer;
			break;
		case CDC_PHONET_MAGIC_NUMBER:
			hdr->phonet_magic_present = true;
			break;
		default:
			/*
			 * there are LOTS more CDC descriptors that
			 * could legitimately be found here.
			 */
			dev_dbg(&intf->dev, "Ignoring descriptor: type %02x, length %ud\n",
					buffer[2], elength);
			goto next_desc;
		}
		cnt++;
next_desc:
		buflen -= elength;
		buffer += elength;
	}
	hdr->usb_cdc_union_desc = union_header;
	hdr->usb_cdc_header_desc = header;
	hdr->usb_cdc_mdlm_detail_desc = detail;
	hdr->usb_cdc_mdlm_desc = desc;
	hdr->usb_cdc_ether_desc = ether;
	return cnt;
}