CVE-2026-98764

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

usb: gadget: f fs: Fix NULL pointer dereference in FUNCTIONFS ENDPOINT DESC

When user space sets up FunctionFS with only full-speed descriptors (e.g., flags = FUNCTIONFS HAS FS DESC) and the gadget operates at a higher speed (such as USB SPEED HIGH or USB SPEED SUPER), config ep by speed() detects that the function lacks descriptors for the current speed, logs a warning, and falls back to full-speed descriptors. The endpoint is then successfully enabled via usb ep enable(), and epfile->ep becomes valid.

However, when user space subsequently issues the FUNCTIONFS ENDPOINT DESC ioctl to query the endpoint descriptor, ffs epfile ioctl() selects the descriptor index solely based on gadget->speed:

switch (epfile->ffs->gadget->speed) {
case USB SPEED SUPER:
case USB SPEED SUPER PLUS:
	desc idx = 2;
	break;
case USB SPEED HIGH:
	desc idx = 1;
	break;
default:
	desc idx = 0;
}
desc = epfile->ep->descs[desc idx];
memcpy(&desc1, desc, desc->bLength);

Because user space only supplied full-speed descriptors, epfile->ep->descs[1] is NULL. Dereferencing desc->bLength triggers an immediate kernel NULL pointer dereference panic.

Fix this by falling back through lower speed descriptors if the current speed descriptor was not supplied, matching the fallback logic in config ep by speed() and historical f fs behavior. If still missing, fall back to epfile->ep->ep->desc (the active descriptor), and return -EINVAL safely if no valid descriptor is found. In addition, mark desc as const to match struct usb ep::desc and avoid discarding qualifiers.