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@vger.kernel.org
Signed-off-by: Jeremy Erazo <mendozayt13@gmail.com>
---
Changes in v3:
- Add missing version-change notes below the --- separator.
Changes in v2:
- Drop the self Reported-by tag.
- Add Fixes tag.
- Cc stable.
drivers/usb/gadget/composite.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index a902184bd..dc3664374 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -2172,7 +2172,10 @@ composite_setup(struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
sizeof(url_descriptor->URL)
- WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH + landing_page_offset);
- if (w_length < WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH + landing_page_length)
+ if (w_length < WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH)
+ landing_page_length = landing_page_offset;
+ else if (w_length <
+ WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH + landing_page_length)
landing_page_length = w_length
- WEBUSB_URL_DESCRIPTOR_HEADER_LENGTH + landing_page_offset;
--
2.53.0