On 10/20/2017 12:37 AM, Elena Reshetova wrote:

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 cached_dev.count is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <redacted>
Reviewed-by: David Windsor <redacted>
Reviewed-by: Hans Liljestrand <redacted>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>

Reviewed-by: Michael Lyle <redacted>

Thanks for this-- I'm including it in my tree for possible inclusion in
4.15 (I've already sent my main chunk of changes upwards).

Mike