In the Linux kernel, the following vulnerability has been resolved:
usb: gadget: f_printer: take kref only for successful open
printer_open() returns -EBUSY when the character device is already
open, but it increments dev->kref regardless of the return value. VFS
does not call ->release() for a failed open, so every rejected second
open permanently leaks one reference.
Move kref_get() into the successful-open branch.