vmur: convert urdev.ref_count from atomic_t to refcount_t
authorElena Reshetova <elena.reshetova@intel.com>
Fri, 20 Oct 2017 07:47:48 +0000 (10:47 +0300)
committerMartin Schwidefsky <schwidefsky@de.ibm.com>
Thu, 26 Oct 2017 06:36:38 +0000 (08:36 +0200)
commit0462d9921e3dfcb022600e4db2d67e6ceab57769
treec0574b57bb643f0f21145e1fb9113aeadf6f1b73
parent3593eb944c65c7a0adfd679949e67f96d97d1768
vmur: convert urdev.ref_count from atomic_t to refcount_t

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

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
drivers/s390/char/vmur.c
drivers/s390/char/vmur.h