From: Elena Reshetova <[email protected]> Date: Fri, 20 Oct 2017 10:57:57 +0300
> 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 mdesc_handle.refcnt is used as pure reference counter. > Convert it to refcount_t and fix up the operations. > > Suggested-by: Kees Cook <[email protected]> > Reviewed-by: David Windsor <[email protected]> > Reviewed-by: Hans Liljestrand <[email protected]> > Signed-off-by: Elena Reshetova <[email protected]> Applied.
