usb: gadget: composite: fix integer underflow in WebUSB GET_URL handling

The WebUSB GET_URL handler in composite_setup() narrows
landing_page_length to fit the host-supplied wLength using

	landing_page_length = w_length
		- WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH + landing_page_offset;

If wLength is smaller than WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH the
unsigned subtraction wraps, and the subsequent

	memcpy(url_descriptor->URL,
	       cdev->landing_page + landing_page_offset,
	       landing_page_length - landing_page_offset);

ends up copying close to UINT_MAX bytes from cdev->landing_page into
cdev->req->buf.  KASAN reports a slab-out-of-bounds in composite_setup
on the kmalloc-2k gadget_info allocation, and FORTIFY_SOURCE traps the
memcpy as a 4294967293-byte field-spanning write into
url_descriptor->URL (size 252).

A USB host can reach this from a single SETUP packet against any
gadget that has webusb/use=1 and a landingPage configured.

Handle the small-wLength case before the math: when the host requested
fewer bytes than the URL descriptor header, only the header is
meaningful and no URL bytes need to be copied.  Setting
landing_page_length to landing_page_offset makes the existing memcpy a
no-op and leaves the descriptor returned to the host unchanged for all
larger wLength values.

Fixes: 93c473948c58 ("usb: gadget: add WebUSB landing page support")
Cc: stable <stable@kernel.org>
Signed-off-by: Jeremy Erazo <mendozayt13@gmail.com>
Link: https://patch.msgid.link/20260512160530.352318-1-mendozayt13@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

0 files changed, 0 insertions, 0 deletions