drivers, net, mlx5: convert mlx5_cq.refcount 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 mlx5_cq.refcount 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: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 2 deletions

diff --git a/include/linux/mlx5/cq.h b/include/linux/mlx5/cq.h
index 95898847c7d4..6a57ec2f1ef7 100644
--- a/include/linux/mlx5/cq.h
+++ b/include/linux/mlx5/cq.h
@@ -35,7 +35,7 @@
 
 #include <rdma/ib_verbs.h>
 #include <linux/mlx5/driver.h>
-
+#include <linux/refcount.h>
 
 struct mlx5_core_cq {
 	u32			cqn;
@@ -43,7 +43,7 @@ struct mlx5_core_cq {
 	__be32		       *set_ci_db;
 	__be32		       *arm_db;
 	struct mlx5_uars_page  *uar;
-	atomic_t		refcount;
+	refcount_t		refcount;
 	struct completion	free;
 	unsigned		vector;
 	unsigned int		irqn;