In the Linux kernel, the following vulnerability has been resolved:
xhci: dbgtty: Fix unregister on tty_register_driver() failure
If tty_register_driver() fails, it drops the reference, but fails to set
the global dbc_tty_driver to NULL, causing the unregister to be called
again when module exits.
On module unload dbc_tty_exit() only gates its cleanup on the driver
pointer being non-NULL, so it operates on the already-freed driver:
module_init(xhci_hcd_init)
xhci_hcd_init()
xhci_dbc_init() [return value ignored]
dbc_tty_init()
tty_register_driver() fails
tty_driver_kref_put() -> driver freed
(dbc_tty_driver left dangling)
…
module_exit(xhci_hcd_fini)
xhci_hcd_fini()
xhci_dbc_exit()
dbc_tty_exit()
if (dbc_tty_driver) -> true (dangling)
tty_unregister_driver() -> use-after-free
