usb: gadget: f_fs: Use local copy of descriptors for userspace copy

The function may be unbound causing the ffs_ep and its descriptors
to be freed while userspace is in the middle of an ioctl requesting
the same descriptors. Avoid dangling pointer reference by first
making a local copy of desctiptors before releasing the spinlock.

Fixes: c559a3534109 ("usb: gadget: f_fs: add ioctl returning ep descriptor")
Reviewed-by: Peter Chen <[e-mail]>
Signed-off-by: Vamsi Krishna Samavedam <[e-mail]>
Signed-off-by: Jack Pham <[e-mail]>
Cc: stable <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/gadget/function/f_fs.c

···
 	case FUNCTIONFS_ENDPOINT_DESC:
 	{
 		int desc_idx;
-		struct usb_endpoint_descriptor *desc;
+		struct usb_endpoint_descriptor desc1, *desc;
 
 		switch (epfile->ffs->gadget->speed) {
 		case USB_SPEED_SUPER:
···
 		default:
 			desc_idx = 0;
 		}
+
 		desc = epfile->ep->descs[desc_idx];
+		memcpy(&desc1, desc, desc->bLength);
 
 		spin_unlock_irq(&epfile->ffs->eps_lock);
-		ret = copy_to_user((void __user *)value, desc, desc->bLength);
+		ret = copy_to_user((void __user *)value, &desc1, desc1.bLength);
 		if (ret)
 			ret = -EFAULT;
 		return ret;