atomic_t variables are currently used to implement reference
counters with the following properties:
- counter is initialized to 1 using atomic_set()
- a resource is freed upon counter reaching zero
- once counter reaches zero, its further
increments aren't allowed
- counter schema uses basic atomic operations
(set, inc, inc_not_zero, dec_and_test, etc.)
Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.
The variable cn_callback_entry.refcnt is used as pure reference counter.
Convert it to refcount_t and fix up the operations.
Suggested-by: Kees Cook <firstname.lastname@example.org>
Reviewed-by: David Windsor <email@example.com>
Reviewed-by: Hans Liljestrand <firstname.lastname@example.org>
Signed-off-by: Elena Reshetova <email@example.com>
Signed-off-by: David S. Miller <firstname.lastname@example.org>