Re: usb/hid: slab-out-of-bounds read in usbhid_parse

From: Alan Stern
Date: Wed Sep 20 2017 - 11:50:54 EST

On Wed, 20 Sep 2017, Kim Jaejoong wrote:

> To. usb & input guys.
> While dig this report, i was wondering about bNumDescriptors in HID descriptor.
> HID document from said, 'this number must be at least one (1)
> as a Report descriptor will always be present.'
> There is no mention of the order of class descriptors. Suppose you
> have a HID device with a report descriptor and a physical descriptor.
> If you have the following hid descriptor in this case,
> HID descriptor
> bLength: 12
> bDescriptor Type: HID
> .. skip
> bNumDescriptors: 2
> bDescriptorType: physical
> bDescriptorLength: any
> bDescriptorType: Report
> bDescriptorLength: any
> If the order of the report descriptor is the second as above,
> usbhid_parse () will fail because my patch is only check the first
> bDescriptor Type.
> But If the order of the report descriptor is always first, there is no
> problem. How do you think this?

The descriptors can appear in any order. You should not assume that
the report descriptor will always come first.

Alan Stern