Re: usb/core: slab-out-of-bounds in usb_get_bos_descriptor

[Alan Stern]

On Wed, 18 Oct 2017, Andrey Konovalov wrote:

> Hi!
> 
> I've got the following report while fuzzing the kernel with syzkaller.
> 
> On commit 3e0cc09a3a2c40ec1ffb6b4e12da86e98feccb11 (4.14-rc5+).
> 
> Looks like usb_get_bos_descriptor() doesn't check that buffer has
> enough space for usb_dev_cap_header, which causes out-of-bounds
> accesses.

Please try the patch below.

Alan Stern



Index: usb-4.x/drivers/usb/core/config.c
===================================================================
--- usb-4.x.orig/drivers/usb/core/config.c
+++ usb-4.x/drivers/usb/core/config.c
@@ -952,10 +952,12 @@ int usb_get_bos_descriptor(struct usb_de
 	for (i = 0; i < num; i++) {
 		buffer += length;
 		cap = (struct usb_dev_cap_header *)buffer;
-		length = cap->bLength;
 
-		if (total_len < length)
+		if (total_len < sizeof(*cap) || total_len < cap->bLength) {
+			dev->bos->desc->bNumDeviceCaps = i;
 			break;
+		}
+		length = cap->bLength;
 		total_len -= length;
 
 		if (cap->bDescriptorType != USB_DT_DEVICE_CAPABILITY) {