usb: Use well-known descriptor sizes when parsing configuration

The existing USB configuration parsing code relies on the descriptors'
own length values when reading through the configuration blob. Since the
size of those descriptors is always well-defined, we should rather use
the known sizes instead of trusting device-provided values to be
correct. Also adds some safety to potential out-of-order descriptors.

Change-Id: I16f69dfdd6793aa0fe930b5148d4521f3e5c3090
Signed-off-by: Julius Werner <jwerner@chromium.org>

1 files changed, 71 insertions, 16 deletions

diff --git a/common/usb.c b/common/usb.c
index f740e5e..c97f522 100644
--- a/common/usb.c
+++ b/common/usb.c
@@ -323,6 +323,7 @@ static int usb_set_maxpacket(struct usb_device *dev)
 /*******************************************************************************
  * Parse the config, located in buffer, and fills the dev->config structure.
  * Note that all little/big endian swapping are done automatically.
+ * (wTotalLength has already been swapped and sanitized when it was read.)
  */
 static int usb_parse_config(struct usb_device *dev,
 			unsigned char *buffer, int cfgno)
@@ -343,24 +344,43 @@ static int usb_parse_config(struct usb_device *dev,
 			head->bDescriptorType);
 		return -1;
 	}
-	memcpy(&dev->config, buffer, buffer[0]);
-	le16_to_cpus(&(dev->config.desc.wTotalLength));
+	if (head->bLength != USB_DT_CONFIG_SIZE) {
+		printf("ERROR: Invalid USB CFG length (%d)\n", head->bLength);
+		return -1;
+	}
+	memcpy(&dev->config, head, USB_DT_CONFIG_SIZE);
 	dev->config.no_of_if = 0;
 
 	index = dev->config.desc.bLength;
 	/* Ok the first entry must be a configuration entry,
 	 * now process the others */
 	head = (struct usb_descriptor_header *) &buffer[index];
-	while (index + 1 < dev->config.desc.wTotalLength) {
+	while (index + 1 < dev->config.desc.wTotalLength && head->bLength) {
 		switch (head->bDescriptorType) {
 		case USB_DT_INTERFACE:
+			if (head->bLength != USB_DT_INTERFACE_SIZE) {
+				printf("ERROR: Invalid USB IF length (%d)\n",
+					head->bLength);
+				break;
+			}
+			if (index + USB_DT_INTERFACE_SIZE >
+			    dev->config.desc.wTotalLength) {
+				puts("USB IF descriptor overflowed buffer!\n");
+				break;
+			}
 			if (((struct usb_interface_descriptor *) \
-			     &buffer[index])->bInterfaceNumber != curr_if_num) {
+			     head)->bInterfaceNumber != curr_if_num) {
 				/* this is a new interface, copy new desc */
 				ifno = dev->config.no_of_if;
+				if (ifno >= USB_MAXINTERFACES) {
+					puts("Too many USB interfaces!\n");
+					/* try to go on with what we have */
+					return 1;
+				}
 				if_desc = &dev->config.if_desc[ifno];
 				dev->config.no_of_if++;
-				memcpy(if_desc,	&buffer[index], buffer[index]);
+				memcpy(if_desc, head,
+					USB_DT_INTERFACE_SIZE);
 				if_desc->no_of_ep = 0;
 				if_desc->num_altsetting = 1;
 				curr_if_num =
@@ -374,12 +394,31 @@ static int usb_parse_config(struct usb_device *dev,
 			}
 			break;
 		case USB_DT_ENDPOINT:
+			if (head->bLength != USB_DT_ENDPOINT_SIZE) {
+				printf("ERROR: Invalid USB EP length (%d)\n",
+					head->bLength);
+				break;
+			}
+			if (index + USB_DT_ENDPOINT_SIZE >
+			    dev->config.desc.wTotalLength) {
+				puts("USB EP descriptor overflowed buffer!\n");
+				break;
+			}
+			if (ifno < 0) {
+				puts("Endpoint descriptor out of order!\n");
+				break;
+			}
 			epno = dev->config.if_desc[ifno].no_of_ep;
 			if_desc = &dev->config.if_desc[ifno];
+			if (epno > USB_MAXENDPOINTS) {
+				printf("Interface %d has too many endpoints!\n",
+					if_desc->desc.bInterfaceNumber);
+				return 1;
+			}
 			/* found an endpoint */
 			if_desc->no_of_ep++;
-			memcpy(&if_desc->ep_desc[epno],
-				&buffer[index], buffer[index]);
+			memcpy(&if_desc->ep_desc[epno], head,
+				USB_DT_ENDPOINT_SIZE);
 			ep_wMaxPacketSize = get_unaligned(&dev->config.\
 							if_desc[ifno].\
 							ep_desc[epno].\
@@ -392,9 +431,23 @@ static int usb_parse_config(struct usb_device *dev,
 			debug("if %d, ep %d\n", ifno, epno);
 			break;
 		case USB_DT_SS_ENDPOINT_COMP:
+			if (head->bLength != USB_DT_SS_EP_COMP_SIZE) {
+				printf("ERROR: Invalid USB EPC length (%d)\n",
+					head->bLength);
+				break;
+			}
+			if (index + USB_DT_SS_EP_COMP_SIZE >
+			    dev->config.desc.wTotalLength) {
+				puts("USB EPC descriptor overflowed buffer!\n");
+				break;
+			}
+			if (ifno < 0 || epno < 0) {
+				puts("EPC descriptor out of order!\n");
+				break;
+			}
 			if_desc = &dev->config.if_desc[ifno];
-			memcpy(&if_desc->ss_ep_comp_desc[epno],
-				&buffer[index], buffer[index]);
+			memcpy(&if_desc->ss_ep_comp_desc[epno], head,
+				USB_DT_SS_EP_COMP_SIZE);
 			break;
 		default:
 			if (head->bLength == 0)
@@ -473,7 +526,7 @@ int usb_get_configuration_no(struct usb_device *dev,
 			     unsigned char *buffer, int cfgno)
 {
 	int result;
-	unsigned int tmp;
+	unsigned int length;
 	struct usb_config_descriptor *config;
 
 	config = (struct usb_config_descriptor *)&buffer[0];
@@ -487,16 +540,18 @@ int usb_get_configuration_no(struct usb_device *dev,
 				"(expected %i, got %i)\n", 9, result);
 		return -1;
 	}
-	tmp = le16_to_cpu(config->wTotalLength);
+	length = le16_to_cpu(config->wTotalLength);
 
-	if (tmp > USB_BUFSIZ) {
-		printf("usb_get_configuration_no: failed to get " \
-		       "descriptor - too long: %d\n", tmp);
+	if (length > USB_BUFSIZ) {
+		printf("%s: failed to get descriptor - too long: %d\n",
+			__func__, length);
 		return -1;
 	}
 
-	result = usb_get_descriptor(dev, USB_DT_CONFIG, cfgno, buffer, tmp);
-	debug("get_conf_no %d Result %d, wLength %d\n", cfgno, result, tmp);
+	result = usb_get_descriptor(dev, USB_DT_CONFIG, cfgno, buffer, length);
+	debug("get_conf_no %d Result %d, wLength %d\n", cfgno, result, length);
+	config->wTotalLength = length; /* validated, with CPU byte order */
+
 	return result;
 }