From: Elena Reshetova <elena.reshetova@intel.com>
Date: Fri, 20 Oct 2017 10:23:38 +0300
Subject: drivers, net, mlx4: convert mlx4_qp.refcount from atomic_t to
 refcount_t
Patch-mainline: v4.15-rc1
Git-commit: 0068895ff845c38e9e2b65c002c53c623379e436
References: bsc#1103989 FATE#326004

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 mlx4_qp.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>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 drivers/net/ethernet/mellanox/mlx4/qp.c |    8 ++++----
 include/linux/mlx4/device.h             |    2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

--- a/drivers/net/ethernet/mellanox/mlx4/qp.c
+++ b/drivers/net/ethernet/mellanox/mlx4/qp.c
@@ -55,7 +55,7 @@ void mlx4_qp_event(struct mlx4_dev *dev,
 
 	qp = __mlx4_qp_lookup(dev, qpn);
 	if (qp)
-		atomic_inc(&qp->refcount);
+		refcount_inc(&qp->refcount);
 
 	spin_unlock(&qp_table->lock);
 
@@ -66,7 +66,7 @@ void mlx4_qp_event(struct mlx4_dev *dev,
 
 	qp->event(qp, event_type);
 
-	if (atomic_dec_and_test(&qp->refcount))
+	if (refcount_dec_and_test(&qp->refcount))
 		complete(&qp->free);
 }
 
@@ -420,7 +420,7 @@ int mlx4_qp_alloc(struct mlx4_dev *dev,
 	if (err)
 		goto err_icm;
 
-	atomic_set(&qp->refcount, 1);
+	refcount_set(&qp->refcount, 1);
 	init_completion(&qp->free);
 
 	return 0;
@@ -520,7 +520,7 @@ EXPORT_SYMBOL_GPL(mlx4_qp_remove);
 
 void mlx4_qp_free(struct mlx4_dev *dev, struct mlx4_qp *qp)
 {
-	if (atomic_dec_and_test(&qp->refcount))
+	if (refcount_dec_and_test(&qp->refcount))
 		complete(&qp->free);
 	wait_for_completion(&qp->free);
 
--- a/include/linux/mlx4/device.h
+++ b/include/linux/mlx4/device.h
@@ -768,7 +768,7 @@ struct mlx4_qp {
 
 	int			qpn;
 
-	atomic_t		refcount;
+	refcount_t		refcount;
 	struct completion	free;
 	u8			usage;
 };