drivers, net, mlx5: convert fs_node.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 fs_node.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, 1 deletions

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/fs_core.h b/drivers/net/ethernet/mellanox/mlx5/core/fs_core.h
index 80f6f3c714c8..397d24a621a4 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/fs_core.h
+++ b/drivers/net/ethernet/mellanox/mlx5/core/fs_core.h
@@ -33,6 +33,7 @@
 #ifndef _MLX5_FS_CORE_
 #define _MLX5_FS_CORE_
 
+#include <linux/refcount.h>
 #include <linux/mlx5/fs.h>
 #include <linux/rhashtable.h>
 
@@ -84,7 +85,7 @@ struct fs_node {
 	struct fs_node		*root;
 	/* lock the node for writing and traversing */
 	struct rw_semaphore	lock;
-	atomic_t		refcount;
+	refcount_t		refcount;
 	bool			active;
 	void			(*del_hw_func)(struct fs_node *);
 	void			(*del_sw_func)(struct fs_node *);