CVE-2026-63896usb: gadget: composite: fix integer underflow in WebUSB GET_URL handling

Official description

In the Linux kernel, the following vulnerability has been resolved: 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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/046870ff6b6f7b743c953c061043a9b30700d491
• https://git.kernel.org/stable/c/f5869dfaa89854dcf34121036294d42d6c7acb8f
• https://git.kernel.org/stable/c/f8f5a8f48c7cae3fac85e04b593bd47939f9725f
• https://git.kernel.org/stable/c/a20f0ccf45708af6e063c7234c215d364b00de25
• https://git.kernel.org/stable/c/6c5dbc104dadd79fc2923497c20bae759a18758c