CVE-2021-47267

In the Linux kernel, the following vulnerability has been resolved: usb:
fix various gadget panics on 10gbps cabling usb_assign_descriptors() is
called with 5 parameters, the last 4 of which are the usb_descriptor_header
for: full-speed (USB1.1 - 12Mbps [including USB1.0 low-speed @ 1.5Mbps),
high-speed (USB2.0 - 480Mbps), super-speed (USB3.0 - 5Gbps),
super-speed-plus (USB3.1 - 10Gbps). The differences between
full/high/super-speed descriptors are usually substantial (due to changes
in the maximum usb block size from 64 to 512 to 1024 bytes and other
differences in the specs), while the difference between 5 and 10Gbps
descriptors may be as little as nothing (in many cases the same tuning is
simply good enough). However if a gadget driver calls
usb_assign_descriptors() with a NULL descriptor for super-speed-plus and is
then used on a max 10gbps configuration, the kernel will crash with a null
pointer dereference, when a 10gbps capable device port + cable + host port
combination shows up. (This wouldn’t happen if the gadget max-speed was set
to 5gbps, but it of course defaults to the maximum, and there’s no real
reason to artificially limit it) The fix is to simply use the 5gbps
descriptor as the 10gbps descriptor, if a 10gbps descriptor wasn’t
provided. Obviously this won’t fix the problem if the 5gbps descriptor is
also NULL, but such cases can’t be so trivially solved (and any such
gadgets are unlikely to be used with USB3 ports any way).