[PATCH 3.18 14/32] USB: fix out-of-bounds in usb_set_configuration

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

commit bd7a3fe770ebd8391d1c7d072ff88e9e76d063eb upstream.

Andrey Konovalov reported a possible out-of-bounds problem for a USB interface
association descriptor.  He writes:
	It seems there's no proper size check of a USB_DT_INTERFACE_ASSOCIATION
	descriptor. It's only checked that the size is >= 2 in
	usb_parse_configuration(), so find_iad() might do out-of-bounds access
	to intf_assoc->bInterfaceCount.

And he's right, we don't check for crazy descriptors of this type very well, so
resolve this problem.  Yet another issue found by syzkaller...

Reported-by: Andrey Konovalov <andreyknvl@google.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/usb/core/config.c    |   14 +++++++++++---
 include/uapi/linux/usb/ch9.h |    1 +
 2 files changed, 12 insertions(+), 3 deletions(-)

--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -538,15 +538,23 @@ static int usb_parse_configuration(struc
 
 		} else if (header->bDescriptorType ==
 				USB_DT_INTERFACE_ASSOCIATION) {
+			struct usb_interface_assoc_descriptor *d;
+
+			d = (struct usb_interface_assoc_descriptor *)header;
+			if (d->bLength < USB_DT_INTERFACE_ASSOCIATION_SIZE) {
+				dev_warn(ddev,
+					 "config %d has an invalid interface association descriptor of length %d, skipping\n",
+					 cfgno, d->bLength);
+				continue;
+			}
+
 			if (iad_num == USB_MAXIADS) {
 				dev_warn(ddev, "found more Interface "
 					       "Association Descriptors "
 					       "than allocated for in "
 					       "configuration %d\n", cfgno);
 			} else {
-				config->intf_assoc[iad_num] =
-					(struct usb_interface_assoc_descriptor
-					*)header;
+				config->intf_assoc[iad_num] = d;
 				iad_num++;
 			}
 
--- a/include/uapi/linux/usb/ch9.h
+++ b/include/uapi/linux/usb/ch9.h
@@ -705,6 +705,7 @@ struct usb_interface_assoc_descriptor {
 	__u8  iFunction;
 } __attribute__ ((packed));
 
+#define USB_DT_INTERFACE_ASSOCIATION_SIZE	8
 
 /*-------------------------------------------------------------------------*/