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

usb: gadget: composite: fix dead empty check in the USB_DT_OTG handler

The OTG branch of composite_setup() falls back to the first
configuration when none is selected:

	if (cdev->config)
		config = cdev->config;
	else
		config = list_first_entry(&cdev->configs,
					  struct usb_configuration, list);
	if (!config)
		goto done;
	...
	memcpy(req->buf, config->descriptors[0], value);

list_first_entry() never returns NULL. On an empty list it returns
container_of() of the list head. So the "if (!config)" check is dead.

When cdev->configs is empty, config points at the head inside struct
usb_composite_dev. config->descriptors[0] reads whatever sits at that
offset. The memcpy copies up to w_length bytes of it into the response
buffer.

cdev->configs can be empty in two cases. One is a teardown race on
gadget unbind with a control transfer in flight. The other is a driver
that sets is_otg before it adds a config. A reproducer that holds
cdev->configs empty triggers a KASAN fault in this branch.

Use list_first_entry_or_null() so the existing check does its job.

https://git.kernel.org/stable/c/01feaf024f29618d5ffa7ab0fd858e0579dcbf7b

https://git.kernel.org/stable/c/2454264b2ab4cf0055c0bfd39e79f830452bd0db

https://git.kernel.org/stable/c/56add2b9b2e89ec61c0761165d758f73004fdfdf

https://git.kernel.org/stable/c/8ac463fe6c0f85bdb1ce8c30e8c9e060802e4483

https://git.kernel.org/stable/c/91b3ecd34b60f950c50c560974945b6596a6f207

https://git.kernel.org/stable/c/d3e72cfef2e38bd588055739a8100d14f9773b17

https://git.kernel.org/stable/c/f8f680609c2b3ab795ffcd6f21585b6dfc46d395

https://git.kernel.org/stable/c/fcb21bf747640c9d6bd1eda9da85420f076d59c1

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